efffects of climate change on epidemiology of vector borne zoonotic diseases

7/30/2019 efffects of climate change on epidemiology of vector borne zoonotic diseases

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EFFECTS OF CLIMATE CHANGE ON THE EPIDEMIOLOGY OF VECTOR BORNE

ZOONOSES IN DEVELOPING COUNTRIES

(A case study of Rift Valley Fever in Kenya)

1. INTRODUCTION

1.1 Preamble.

Volatility of infectious diseases may be one of the earliest biological expressions of

climate instability (Epstein P, 2008).

Changes in climatic patterns and in seasonal conditions may affect disease behaviour in

terms of spread pattern, diffusion range, amplification and persistence in novel habitats

(Martin et al, 2008). Vector-borne and zoonotic diseases, such as, Lyme disease, West

Nile virus, Malaria, Rift Valley Fever (RVF), Plague, Hantavirus pulmonary syndrome,

and Dengue fever have been shown to have a distinct seasonal pattern, and in some

instances their frequency has been shown to be weather sensitive. Because of the

sensitivities of the vectors and animal hosts of these diseases to climatic factors, climate

change-driven ecological changes, such as variations in rainfall and temperature, could

significantly alter the range, seasonality, and human incidence of many zoonotic and

vector-borne diseases (FAO/IAEA, 2010).

Rift Valley Fever is a vector borne zoonotic disease of importance in Kenya. It is a

peracute or acute disease of domestic ruminants caused by a mosquito borne virus and

characterized by necrotic hepatitis and a hemorrhagic state. Humans become infected

from contact with tissues of infected animals or mosquito bite. Infection in humans is

usually associated with mild to moderately severe influenza-like illness, but severe


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complications such as ocular sequelae, encephalitis and hemorrhagic disease, occur in

some patients. Outbreaks of the disease occur when particularly heavy rains favour the

breeding of mosquito vectors (Swanepoel and Coetzer, 2003).

Climate change is likely to affect the epidemiology of RVF owing to its effect on the

frequency of extreme weather patterns like droughts and floods hence the effect on the

population of the mosquitoes and other biting insects which are the main vectors.

Ironically, the countries that have contributed least to global warming mainly the

developing countries are the most vulnerable to its impact especially from diseases that

higher temperatures can bring (FAO/IAEA, 2010). This is because they lack not only the

technology, but also the financial resources and the public-health infrastructure. (Barnhill

H, 2008).

Rift Valley fever (RVF) disease was first reported in Kenyan livestock in 1912 and the

country has reported the most frequent epidemics of the disease involving both humans

and livestock (Murithi et al, 2010).Although low-level RVF virus transmission likely

occurs within enzootic regions each year, the emergence of virus activity in large

epizootic-epidemic cycles is periodic and associated with abnormally high rainfall events

that allow for the abundant emergence ofAedes species floodwater mosquitoes

transovarially infected with RVF virus and secondary vectors ( Bird et al, 2008).

This project seeks to analyze the change in weather patterns (specifically temperature and

rainfall) and its relationship with RVF outbreaks in Kenya in the last 15 years. This will

help to give a general understanding on how the epidemiology of vector borne zoonotic

diseases is likely to change as a result of climate change and suggest ways in which


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Kenya and other developing countries can constitute public health modalities by which to

deal with the resulting health challenges.

1.2.Problem statement.

Climate change is emerging as one of the main challenges that humankind will have to

face for many years to come. Human and animal health issues are only two of many

concerns, albeit quite crucial. Climate change could also become a major threat to world

food security, as it has a strong impact on food production, access and distribution.

Abnormal changes in air temperature and rainfall and the increasing frequency and

intensity of drought and floods have long-term implications for the viability and

productivity of world agro-ecosystems (Martin et al, 2008).

While the implications of future climate change are complex and difficult to assess, it is

certain that infectious zoonotic diseases will have an increased impact on global health

issues and their control will be a major factor in social wellbeing. If vulnerable

communities can be helped by significant investments in health services and improved

management of climate-sensitive diseases in the immediate future, then humans will at

least face the potential impacts of climate change with a lower baseline of infections

(Martin et al, 2008).

Based on the problem stated, this study seeks to analyze the periodic prevalence of RVF

in the last 15 years versus the climatic trend(rainfall and temperature) in this period and

in this way show how climate change is likely to affect the epidemiology and the

resultant socioeconomic impacts of RVF and the steps that should be taken in terms of

early prediction, prevention and control, in order to minimize or eradicate the negative

impacts of this disease as well as other vector borne zoonoses.


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1.3. Objectives

1. To determine how many outbreaks of Rift Valley Fever have occurred in Kenya between

1995 and 2009.

2. To assess the climatic trend between 1995 and 2009 using rainfall, temperature and

humidity.

3. To assess the relationship between Rift Valley Fever outbreaks and climate (rainfall and

temperature) between 1995 and 2009.

4. To study the trend of average annual temperatures in a representative district of each

province between 1995 and2009 to ascertain if temperatures have generally been

increasing or decreasing.

1.4. Justification

Climate change has far reaching consequences that go beyond health and touch on all

life-support systems. It is therefore a factor that should be rated high among those that

affect human health and survival (Githeko et al, 2000).

Studying how climate change impacts the epidemiology of RVF in Kenya helps us use

this as a model to project the expected changes in epidemiology of vector borne zoonotic

diseases in developing countries in general. Greenhouse gas emissions which are the

major culprits of global warming are bound to be on the increase as the country aims to

transform itself into a newly industrializing, Middle-income country providing a high

quality life to all its citizens by the year 2030. To combat poverty, Kenya is expected to

raise income in agriculture, livestock and fisheries even as the industrial production and

the service sector expand. The country plans to implement 4-5 disease free zones and

livestock processing factories to enable Kenyan meat, hides and skins to meet


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international standards (Government of the Republic of Kenya, 2007). It also aims at

having a sustainable environment and reducing losses attributed to environment related

disasters. To do this, Kenya seeks to enhance disaster preparedness in all disaster prone

areas and improve capacity for adaptation to global climate change. Incorporating or

integrating adaptation to climate change into planning processes is a necessary strategy

for sustainable development over the long term (Government of the Republic of Kenya,

2007).

This study will help come up with solutions that will bring the country one step closer to

realizing its vision 2030 goals as well as implementing changes that will benefit the

developing countries in general to be in line with the Millennium Development Goals


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2. LITERATURE REVIEW: CLIMATE CHANGE AND VECTOR BORNE ZOONOSES.

2.1 CLIMATE CHANGE

2.1.1 What is climate change?

As defined by the Encyclopedia of Climate Change and Global Warming complied by Prof. S.

George Philander, climate change is commonly used to describe any systematic alteration or

statistically significant variation in either the average state of climate elements such as

precipitation, temperature, winds, or pressure; or in its variability, sustained over a finite time

period (decades or longer). (Nsikak Benson, 2008).

2.1.2 Causes of climate change

The earths main source of energy is the sun, but this planet would be far too cold for

most of its inhabitants were it not for its atmosphere, the thin veil of transparent gases

that covers the globe. The atmosphere serves as a parasol that reflects sunlight, thus

keeping the planet cool, and as a blanket that traps heat from the Earths surface, thus

keeping us warm. The blanket is the greenhouse effect, which depends not on the two

gases nitrogen and oxygen that are most abundant, but on trace gases that account for

only a tiny part of the atmosphere. These gases warm the air in their interior mainly by

blocking convective mixing with the outside (Philander ,2008) .They include carbon

dioxide, methane and nitrous oxide, along with water vapor and are known as the Green

House Gases (GHGs) as the working principle is the same as that of a greenhouse. Just as

the glass of the greenhouse prevents the radiation of excess energy, this gas blanket


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absorbs some of the energy emitted by the earth and keeps temperature levels intact

(Shrivastava, 2001).

The earths temperature is controlled by the balance between input energy from the sun

and its loss back into space. Green house gases are critical to this temperature balance in

that the energy received from the sun is in the form of short-wave radiation that warms

the earths surface and as a result emits long-wave infrared radiation. The greenhouse

gases trap and re-emit some of this long-wave radiation, and warm the atmosphere. On

average, one-third is reflected back into space and two-thirds warms the planet and drives

its weather engine.

This warming takes place through a shield known as the ozone layer that limits the loss of

heat from the Earths surface and increases the average global temperature by 33 oC,

without which the Earth would be frozen and life on the planet would cease.

It is a well established fact that the emission of greenhouse gases that produce greenhouse

effect; most notably carbon dioxide (CO2), nitrous oxide (N2O), chlorofluorocarbons

(CFCs), methane (CH4), and ozone (O3), are increasing in the atmosphere and thereby

deflecting more long-wave infra-red solar radiation back to Earth, hence global warming

and the ongoing climate changes. This is threatening the survival of many plants and

animals as well as the well being of people around the world. The industrial revolution in

the19th century saw the large use of fossil fuels for industrial activities (Shrivastava,

2001). These industries created jobs and over the years there has been urban migration, a

trend that continues to date. More and more land that was covered with vegetation has

been cleared to make way for houses. Natural resources are being used extensively for

construction, industries, transport and consumption. In its 2007 report, the


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Intergovernmental Panel on Climate Change (IPCC,2007), a large International panel of

scientists, all experts on the Earths climate, concluded that human activities, specifically

those that cause an increase in the atmospheric concentration of carbon dioxide, have

started affecting the Earths climate. The panel further predicted that far more significant

climate changes are imminent (Shrivastava, 2001).

2.1.3 Effects of climate change

According to Wikipedia, the following are some of the effects of climate change.

Glacier retreat and disappearance

This widespread decrease in glaciers and ice caps has contributed to observed sea level rise. With

very high confidence, IPCC (IPCC, 2007) made the following projections relating to future

changes in glaciers:

In Polar Regions, there will be reductions in glacier extent and thickness.

More than one-sixth of the world's population is supplied by meltwater from major

mountain ranges. Changes in glaciers and snow cover are expected to reduce water

availability for these populations.

a) Oceans

Global warming is projected to have a number of effects on the oceans. Ongoing effects

include rising sea levels due to thermal expansion and melting of glaciers and ice sheets,

and warming of the ocean surface, leading to increased temperature stratification. Other

possible effects include large-scale changes in ocean circulation. The oceans serve as a
http://wiki/Polar_regionhttp://wiki/Polar_region


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sink for carbon dioxide, taking up much that would otherwise remain in the atmosphere,

but increased levels of CO2 have led to ocean acidification (Wikipedia).

b) Extreme weather

Climate change is likely to change the frequency of extreme weather events, such as tropical

cyclones, floods, droughts, heatwaves and hurricanes, and may destabilize and weaken the

ecosystem services upon which human society depends.

c) Health

Climate change is also expected to affect animal, human and plant health via indirect pathways.

It is likely that the geography of infectious diseases and pests will be altered, including the

distribution of vector borne zoonotic diseases such as RVF, which are highly sensitive to

climatic conditions.

2.1.4 Adaptation to effects of climate change

Africa is the most vulnerable region to climate change, due to the extreme poverty of many

africans, frequent natural disasters such as droughts and floods, and agricultural systems heavily

dependent on rainfall(IPCC, 2001).

It is, therefore, essential for these countries to prepare themselves for coping with or, one can

say, adapting to such adverse impacts and to ensure that such adaptation measures and policies

are built-in to their existing national and sectoral development activities (Chowdhury, 2003).

Climate change has the potential to undermine sustainable development, increase poverty and

delay or prevent the realization of the MDGs. An effective way to address the impacts of climate

change is by integrating adaptation measures into sustainable development strategies so as to
http://wiki/Ocean_acidificationhttp://wiki/Ocean_acidification


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reduce the pressure on natural resources, improve environmental risk management, and increase

the social well-being of the poor (United Nations Framework Convention on Climate

Change,2006).

The public health and medical community have made enormous strides in control of infectious

diseases during the past half-century. Widespread availability of antimicrobial drugs, vector-

control systems, diagnostics, vaccines, and increasingly sophisticated predictive models

represent a powerful set of tools to protect public health from emerging diseases (Rosenthal,

2010).

2.2 VECTOR BORNE ZOONOSES

According to the World Health Organization, zoonoses are diseases naturally transmitted to

people from non-human vertebrates e.g. dogs, raccoons, etc as well as invertebrates e.g.

arthropods.

From the perspective of infectious diseases, vectors are the transmitters of disease-causing

organisms that carry the pathogens from one host to another. By common usage, vectors are

considered to be invertebrate animals, usually arthropods. Technically, however, vertebrates can

also act as vectors, including foxes, raccoons, and skunks, which can all transmit the rabies virus

to humans via a bite.

Arthropods account for over 85 percent of all known animal species, and they are the most

important disease vectors. Arthropods may affect human health either directly by bites, stings, or

infestation of tissues, or indirectly through disease transmission.. The most significant mode of

vector-borne disease transmission is by biological transmission by blood-feeding arthropods. The

pathogen multiplies within the arthropod vector, and the pathogen is transmitted when the


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arthropod takes a blood meal. Mechanical transmission of disease agents may also occur when

arthropods physically carry pathogens from one place or host to another, usually on body parts.

The transmission of vector-borne diseases to humans depends on three different factors: the

pathologic agent; the arthropod vector; and the human host.

A majority of vector-borne diseases survive in nature by utilizing animals as their vertebrate

hosts, and are therefore zoonoses.There are different patterns of vector-borne disease occurrence;

parasitic and bacterial diseases, such as malaria and Lyme disease, tend to produce a high disease

incidence but do not cause major epidemics. In contrast, many vector viral diseases, such as

Yellow Fever, Rift Valley Fever, dengue, and Japanese encephalitis, commonly cause major

epidemics. (enotes.www.enotes.com)

Globalization and climate change have had an unprecedented worldwide impact on emerging and

re-emerging animal diseases and zoonoses. Climate change is disrupting natural ecosystems by

providing more suitable environments for infectious diseases allowing disease-causing bacteria,

viruses, and fungi to move into new areas where they may harm wild life and domestic species,

as well as humans. Diseases that were previously limited only to tropical areas are now spreading

to other previously cooler areas e.g. malaria. Pathogens that were restricted by seasonal weather

patterns can invade new areas and find new susceptible species as the climate warms and/or the

winters get milder. There is evidence that the increasing occurrence of tropical infectious

diseases in the mid latitudes is linked to global warming. (FAO/IAEA, 2010).


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2.3 RIFT VALLEY FEVER

2.3.1 Introduction

Rift Valley Fever (RVF) is a peracute or acute disease of domestic ruminants caused by a

mosquito-borne virus and characterized by necrotic hepatitis and a hemorrhagic state, but

infections are frequently inapparent or mild. The aetiologic agent is a mosquito-borne, RNA

virus of the family Bunyaviridae, genus Phlebovirus (Swanepoel and Coetzer, 2003). The

disease is most severe in sheep, cattle and goats, producing high mortality in newborn animals

and abortion in pregnant animals. It is a zoonosis and humans get infected from contact with

tissues of infected animals or mosquito bites. Outbreaks of the disease occur when particularly

heavy rains favour the breeding of the mosquito vectors (Swanepoel and Coetzer, 2003).

2.3.2 Clinical Findings

a) The disease in animals

Signs of the disease in domestic ruminants tend to be non-specific, rendering it difficult to

recognize individual cases of RVF. During epidemics however, the simultaneous occurrence of

numerous cases of abortion and disease in ruminants, together with disease of humans, tends to

be characteristic of RVF (Swanepoel and Coetzer, 2003).

In the peracute disease animals die suddenly without exhibiting noteworthy signs of illness.

Under field conditions, most animals develop the acute disease. Following an incubation period

of 24-72 hours, there is fever of up to 42oC that lasts for 24-96 hours, anorexia, weakness,

listlessness and an increased respiratory rate. Some animals may regurgitate ingesta, and develop

melaena or foetid diarrhea and a blood tinged, mucopurulent nasal discharge. A few animals may

be icteric (Swanepoel and Coetzer, 2003).


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Pregnant animals may abort at any stage as a result of the febrile reaction and/ or infection of the

fetus. Aborted fetuses are usually autolysed. Although there is no evidence that infertility is

impaired after abortion, this is possible in instances where retained placenta and purulent metritis

occur as complications to abortion, particularly if there is also salpingitis (Swanepoel and

Coetzer, 2003).

b) The disease in humans

Humans acquire RVF through bites from infected mosquitoes and through exposure to blood,

body fluids, or tissues of infected animals. Direct exposure to infected animals can occur during

handling and slaughter or through veterinary and obstetric procedures. Laboratory technicians

are at risk of acquiring disease by inhalation of infectious aerosols generated from specimens.

(Anyangu et al, 2010).

Human RVF outbreaks are primarily characterized by mild, acute febrile illness with

spontaneous recovery, although in a few cases (< 8%) the disease can be associated with severe

jaundice, rhinitis, encephalitis and hemorrhagic manifestations, hence fatal (Mohammed et al,

2010).

2.3.3Mosquitoes as RVF vectors

Laboratory studies indicate that numerous species of mosquitoes and sand flies are susceptible to

oral infection, some of which are able to transmit RVF virus by bite to domestic animals

including sheep, goats, cattle and camels, as well as human beings (Sang et al, 2010).

The Aedine mosquitoes are the main vectors of the virus though other species, as explained in

the later in this section, are involved in the spread of the disease. The virus is also present in

milk, feces and aborted fetuses (Turell et al, 1984).


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Following the ingestion of an infective blood meal by a susceptible mosquito, there is an

extrinsic incubation period of approximately one to two weeks before transmission can occur.

During this time RVF virus replicates in the cells of the midgut, escapes to the haemocoel and is

disseminated via the haemolymph to replicate in the salivary glands and other organs, but in a

proportion of some mosquitoes infection is confined to the midgut, implying that there is a

mesenteroneal barrier to spread of infection (Swanepoel and Coetzer, 2003).

In Aedine mosquitoes, transovarial transmission of virions occurs from the female mosquito to

her progeny, and females of the next generation can transmit the virus orally without having

become infected by a prior blood meal. It is obligatory for Aedine eggs to be subjected to a

period of drying as the water recedes before being wetted again next time the dambo floods.

Dambos are topographic depressions which suddenly flood during heavy rains causing the eggs

of dormant RVF virus-infected floodwater Aedes spp. mosquitoes to hatch. Aedine eggs can

survive for long periods in dried mud, possibly for several seasons if the dambo remains dry.

Moreover, only a proportion of eggs hatch at each successive flooding, which clearly represents

a survival mechanism to prevent the mosquito population from being lost when precipitation has

been inadequate to sustain breeding. Dams with shallows that are subject to periodic drying and

flooding also provide suitable habitat for floodwater breeding Aedines (Swanepoel and Coetzer,

2003).

These mosquitoes maintain RVF virus through transovarial transmission and transmit it to

domestic and wild ungulates that come to the dambos for water, functioning as enzootic vectors.

As amplification ensues, epizootic vectors such as Culex theileri become important in

transmission to domestic livestock. A variety of mosquitoes have been associated with RVF

virus, including Culex pipens in the Egyptian outbreak. Rift Valley Fever virus has also been


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isolated from Culex zombaensis and Mansonia africana in Kenya (Swanepoel and Coetzer,

2003).

In the proportion of mosquitoes in which theres infection, internal dissemination of infection

and transmission of the virus occur, and the duration of the extrinsic incubation period tends to

be characteristic for each vector species and does not appear to be influenced by the strain of

RVF virus, but by increased doses of virus, and higher ambient temperatures during extrinsic

incubation which produce disseminated infection in a greater proportion of mosquitoes and

shorter extrinsic periods (Turell et al, 1985).

Thus, apart from favoring the breeding of vectors, warm weather may be an accessory factor in

precipitating outbreaks of RVF through increasing vector efficiency (Swanepoel and Coetzer,

1994).

2.3.4 Epidemiology of Rift Valley Fever.

According to the American Journal of Tropical Medicine and Hygiene, vol. 83(2), outbreaks are

associated with unusually heavy rainfall, leading to flooding and a synchronous generation of a

large number of infected mosquitoes (Anyangu et al, 2010). These are thought to occur when

topographic depressions called dambos suddenly flood, causing the eggs of dormant RVF

virus-infected floodwaterAedes spp. mosquitoes to hatch.

In the interepidemic period the virus is maintained within the eggs ofAedes mosquitoes

embedded in soils where previous RVF outbreaks have occurred. Other findings suggest that the

virus may also be maintained by cryptic cycling between domestic livestock or wild herbivores

and mosquitoes. During the epizootics, heavy rainfall and flooding provide an environment for

Aedes mosquitoes to rapidly multiply and become the predominant mosquito population, which

results in extensive livestock transmission and amplification of the virus. After an initial burst of


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transmission, other mosquito species (e.g. Culex, Anopheles, Mansonia, etc) and biting insects

can become infected and transmit the virus among animals and from animals to human beings

(Mohamed et al, 2010).

The flooding of dambos and the humid weather conditions prevailing in epidemics favour the

breeding not only of the Aedine maintenance vectors, and the non-aedine mosquitoes which

serve as epidemic vectors, but also of other biting insects which are potential mechanical

transmitters of RVFV (Swanepoel and Coetzer, 2003).

Eggs of species which breed in water, other than aedine mosquitoes, cannot survive dry

conditions and these insects re-colonize flooded dambos from suitably close rivers and dams, so

that a succession of vector species occurs once flooding takes place. Infected livestock circulate

high levels of virus and mechanical transmission of infection by mosquitoes, midges,

phlebotomids, stomoxids, simulids and other biting flies is thought to play a significant role in

epidemics (Logan et al, 1991).

Infected animals appear to be more attractive to mosquitoes, and by implication other biting flies,

than non-infected animals and it has been shown that probing for blood and feeding proceed

more rapidly and efficiently on viraemic hosts. (Bailey, 1981)

Factors which determine the morbidity and mortality associated with outbreaks of RVF include

the virulence of the strain of virus and the susceptibility of the vertebrates involved (Anderson &

Peters, 1988).

The RVF epizootics and epidemics are closely linked to the occurrence of the warm phase of the

El Nino / Southern Oscillation phenomenon and elevated Indian Ocean temperatures that lead to

heavy rainfall and flooding of habitats suitable for the production ofAedes and Culex mosquitoes

that serve as the primary RVF virus vectors in East Africa. El Nino-Southern Oscillation events


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are a combined ocean atmosphere phenomenon, involving changes in the temperatures of surface

waters in the tropical Pacific and in its closely linked atmospheric counterpart, the Southern

Oscillation. El Nino-Southern Oscillation events involve a large exchange of heat between the

ocean and the atmosphere, and affect:

Global mean temperature

Trade winds

Tropical circulation

Precipitation.

Such events occur about once every three to seven years (Martin et al, 2008).

2.3.5. Rift Valley Fever in Kenya.

An acute and highly fatal disease to lambs associated with heavy rains and accompanied by

reports of illness in humans was first recognized in the Rift Valley in Kenya at the turn of the

century, but the causative agent was not isolated until 1930. Major outbreaks of the disease

affecting sheep and cattle were recorded in Kenya in 1930-31, 1968, 1978-79, 1997-98, 2006-07

and lesser outbreaks at irregular intervals during intervening years (Davies et al, 1985).

The 1997-98 epidemic which started in Garissa district, North Eastern Kenya and adjacent parts

of Somalia in October 1997, occurred in an essentially arid area following exceptionally heavy

rains (Woods et al, 2002).

In mid-December 2006, the Ministry of Health in Kenya received reports of fatal cases of a

febrile haemorrhagic illness of unknown aetiology among people living in Garissa district in the

North eastern province, after unusually heavy rains and flooding in the area as shown in figure 2.

The RVF virus was isolated and Immunoglobulin M (IgM) antibodies to RVFV were detected in


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clinical specimens from affected patients and animals. During the next 4 months, approximately

700 suspected cases of RVF with 272 confirmed and 120 probable cases were reported in 18

districts within six of eight provinces in Kenya. During this period, RVF outbreaks were also

reported in Somalia and Tanzania (Amwayi et al, 2007).

2.3.6 Impact of climate change on RVF

At present, the world climate is in a warming phase. In 1996, The Intergovernmental Panel on

Climate Change (IPCC) concluded that, the balance of evidence suggests a discernible human

influence on global climate (IPCC, 1996). Indeed, evidence suggests that human activities

contribute to warming the planet and climate models predict an increase in global mean

temperatures of between 1 C and 3.5 C during the 21st century, with large differences in trends

between locations.

Temperature changes are one of the most obvious and easily measured changes in climate, but

atmospheric moisture, precipitation and atmospheric circulation also change as the whole system

is affected. These effects alter the hydrological cycle, especially the characteristics of

precipitation/rainfall (amount, frequency, intensity, duration, type) (Trenberth et al. (2007).

Finally, it is anticipated that global climate change will induce changes in the magnitude and

frequency of extreme events and have significant effects on the geographical range and seasonal

activity of many vector species (McMichael et al, 1996).

It is therefore expected that global climate change will alter the distribution and increase the risk

of some vector-borne zoonoses, including Rift Valley fever (RVF), leading to significant

changes in the geographical distribution and frequency of RVF epidemics.


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As mentioned in the IPCC report ( IPCC, 1996), heavy rainfall events are likely to become much

more frequent in years to come and extremes of the hydrological cycle, such as floods and

drought will invariably be enhanced with global warming. In fact, the increase in rainfall in East

Africa, extending into the Horn of Africa, is robust across the entirety of the models surveyed in

the IPCC report. Thus, it may be assumed that the frequency and severity of RVF outbreaks on

this part of the continent will increase. This could also affect other countries that import animals

from Africa, such as some islands in the Indian Ocean.

Climate changes may also affect the three fundamental components of the epidemiological cycle

of RVF, namely: vectors, hosts and virus. The consequences of global warming on vectors, in

particular, may be many. The greenhouse effect, through changes to temperatures and the pattern

of seasonal and geographical variation in rainfall, will alter the prevalence of mosquito vector

populations. Temperature has a direct effect on mosquitoes. It leads to increased activity,

increased reproduction and therefore increased frequency of blood meals and faster digestion of

blood (Martin et al, 2008).

Pathogens harboured by mosquitoes also mature faster. Increased water temperature cause

mosquito larvae to develop faster also increasing overall vector capacity (Reiter, 2008).

The effect of precipitation on vectors is indirect. Increased precipitation creates more potential

breeding sites for mosquitoes. The vegetation is dense after rainfalls and this provides shelter and

resting grounds for vectors (Githeko et al, 2000).

Heavy rainfalls are predicted for East Africa and therefore more RVF outbreaks. In turn, this

may affect the potential for transmission of Rift Valley Fever.

As far as hosts are concerned, climate changes may induce modifications in their distribution and

density, as well as their migratory pathways. Historically, the dissemination of RVF has been


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attributed in part to nomadic herds: the modification of migratory pathways could introduce the

virus into previously virus-free areas. Climate modification may also result in the selection of a

strain that is either more or less virulent (Martin et al, 2008).

2.3.7. Prevention and control.

a) Vectors

The viability of mosquito eggs in dambo soil can be reduced by burning of the grass cover, and

strategically timed application of larvicides can be used to suppress mosquito breeding (Logan et

al, 1990). Other measures such as chemical control of adult vectors, movement of stock from

low-lying areas to well-drained and wind-swept pastures at higher altitudes, or confining of

animals to mosquito proof stables, are usually impractical, instituted too late and at best

palliative in the face of a RVF epidemic (Swanepoel and Coetzer, 2003).

b) Immunization

Immunization remains the only effective way of protecting livestock. Two vaccines are

currently available for vaccination of animals against RVF. The first being, formalin inactivated

vaccine available in South Africa and Egypt. This vaccine safe in pregnant ewes, but is poorly

immunogenic, thus requiring a booster dose to achieve immunity and regular revaccination to

maintain immunity. The second is a live vaccine based on the attenuated Smithburn strain. This

vaccine is widely used in Africa and the Middle East. It is more immunogenic than the formalin

inactivated alternative, but may cause abortion and foetal teratogenicity when ewes are

vaccinated during pregnancy. A live Clone 13 RVF vaccine has recently been registered for use

in cattle, sheep and goats in South Africa. The vaccine is based on a natural RVF virus mutant


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with a large deletion in the NSs gene. Evidence so far indicates that the vaccine is highly

immunogenic, and does not cause abortion or foetal teratogenicity in ewes vaccinated during

pregnancy. The risk of reversion to virulence is believed to be negligible given the substantial

genetic deletion present in the vaccine virus. The Clone 13 RVF vaccine therefore seems to be a

safer and more effective alternative to RVF vaccines currently being used to protect livestock in

Kenya. (GALV Med, 2010)

Epidemics of RVF tend to occur at irregular intervals of many years and it is usually difficult to

persuade farmers to vaccinate livestock during the long inter-epidemic periods. The occurrence

of epidemics is usually difficult to predict as they usually have a very sudden onset. Hence it is

advisable in African countries with large sheep and goat populations to immunize the offspring

of vaccinated ewes and nannies on a regular basis (at six months of age), when colostral

immunity has waned, with a single dose of the modified live Smithburn vaccine. This should

offer life-long protection (Assad et al, 1983). Lambs and kids of susceptible dams can be

immunized at any age.

On the other hand, veterinarians and others engaged in the livestock industry should be made

aware of the potential dangers of exposure to zoonotic agents in handling tissues of diseased

animals, and precautions should be increased during RVF epidemics. A formalin-inactivated cell

culture vaccine produced in the USA is used on an experimental basis to immunize persons such

as laboratory and field workers who are regularly exposed to RVF infection (Eddy, et al 1981).

c) Technology use

Advancing technologies are creating exciting possibilities for prevention and control of emerging

diseases. They include: far-reaching and constantly improving communication tools, including

use of mobile text messaging resulting in improved surveillance approaches, and state-of-the-art


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satellite imagery and mapping capacity to forecast and detect ecologic changes and climate

anomalies relevant to disease prevalence (Ford, et al, 2009).

In addition, monitoring of animal and insect vector motility and geographic distributions and,

development of highly sensitive diagnostic tools for use in human, animal and vector

surveillance are enhancing the ability to detect new` pathogens or changes in reservoir patterns

for known pathogens. These new capacities will dramatically improve the ability to detect early

and, ultimately to forecast in advance, the emergence of disease threats so that effective

measures can be taken to avert or minimize the public health impact (Breiman et al, 2010).


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3. METHODOLOGY

3.1 Research Design

This will be a retrospective cross-sectional study that will utilize quantitative

techniques of data collection, on the prevalence of RVF versus the weather

patterns; specifically temperature and rainfall between the years 1995 and 2010.

This will meet the outlined objectives in chapter 1 in a bid to show the

relationship between climate and RVF outbreaks in order to project the likely

effects of climate change on its epidemiology in terms of increased frequency of

outbreaks.

3.2 Study areas and data collected

By the year 2007, six of the eight provinces in Kenya had reported outbreaks of

RVF i.e. Rift Valley, Eastern, Central, North Eastern, Coast and Nairobi

provinces.

In each of these provinces data will be obtained on the year when outbreaks

occurred within the years 1995-2010.

Because heavy rains and flooding have been associated with RVF epizootics,

rainfall data as well as the prevailing temperatures between the years 1995-2010

available will be examined.

Annual rainfall data and prevailing temperatures from one representative station

will be reported in each of the six provinces between 1995 and 2010.

In the six provinces where RVF outbreaks have been reported, the representative

stations will be those closest to the districts reporting RVF; i.e. Nakuru station


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(Rift Valley province), Garissa station (Northeastern province), Meru station

(Eastern province), Malindi station (Coast province), Thika station (Central

province), and Wilson airport station (Nairobi province). Though Western and

Nyanza provinces have never reported RVF, they will be part of this study and the

representative stations will be Kakamega and Kisumu respectively.

3.3 Data collection procedures

This will entail:

a) Collection of recorded cases of RVF in Kenya from The Central Veterinary Research

Laboratories, the Kenya Medical Research Institute, Nairobi, Kenya and the Department

of Disease Surveillance, Ministry of Health, for the period between 1995 and 2010.

b) Collection of recorded weather patterns i.e., temperature and rainfall from the Kenya

Meteorological Department for the period between 1995 and 2010.

c) Study of published and unpublished material as well as relevant case studies sourced

from the internet, including all support documentation and articles unavailable locally,

graphic representations in form of photographs and drawings of relevance to climate

change and its effect on RVF epidemiology.

d) Data collected will be entered in data collection sheets.

3.4 Data analysis.

This will be analyzed as follows:

i. Tabulation of data and calculation of averages for annual temperature and rainfall in

1995-2009 for the representative districts in the 8 provinces using Microsoft Excel.


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ii. Tabulation of administrative districts that reported cases of rift valley fever during the

1997-98 and 2006-07 outbreaks showing percentages and bar graphs to show proportion

of the country involved in the two outbreaks.

iii. Graphical representation of annual temperature, and rainfall in 1995-2009for the

representative districts in the 8 provinces as well as the magnitude of both outbreaks

(1997/1998 & 2006/2007) in terms of the number of districts involved in the province

expressed as a percentage of total administrative districts in the same province. For the

purpose of uniformity the administrative districts used are based on the geographic

boundaries of the eight provinces and 69 administrative districts in place in 1999 as the

number and size of districts have recently been restructured.

iv. Graphical representation of average annual temperatures per province between 1995 and

2009 using Microsoft Excel and using the trend line to study the trend of average annual

temperatures in each representative district.


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DATA ANALYSIS

INTRODUCTION

A total of 38/69 (55%) administrative districts in the country had reported RVF epizootics by the

end of 2007. The Western and Nyanza provinces, located on the southwestern region of the

country, had never reported RVF infections by 2007 (Murithi et al, 2010). As shown below, the

2006/2007 outbreak involved 36/69 administrative districts (52.2%) compared to the 1997/1998

outbreak which involved 22/69 administrative districts (31.8%).

DISTRICTS PER PROVINCETHAT REPORTED RVF IN 1997/1998 OUTBREAK AND

THE 2006/2007 OUTBREAK

1997/1998 0UTBREAK (22/69 DISTRICTS- 31.8%)

1. Rift Valley Province: West Pokot, Uasin Gishu, Trans Nzoia, Narok, Nakuru, Laikipia,

Kajiado.

2. Eastern Province: Isiolo, Makueni, Marsabit, Machakos.

3. North Eastern Province: Garissa, Mandera, Wajir.

4. Coast: Kilifi, Kwale, Tana River.

5. Central: Kiambu, Maragua, Nyeri, Thika.

6. Nairobi

7. Western Province: None.

8. Nyanza Province: None.

2006/2007 OUTBREAK (36 DISTRICTS- 52.2%)


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1. Rift Valley Province: West Pokot, Uasin Gishu, Nakuru, Laikipia, Kajiado,

Baringo, Samburu, Marakwet, Kericho.

2. Eastern Province: Isiolo, Makueni, Machakos, Mbeere, Embu, Moyale, Meru

Central, Meru North, Meru South, Mwingi, Kitui.

3. North Eastern Province: Garissa, Mandera, Wajir, Ijara.

4. Coast: Kilifi, Kwale, Tana River, Taita Taveta, Lamu, Malindi.

5. Central: Kiambu, Maragua, Thika, Muranga, Kirinyaga.

6. Nairobi.

7. Western Province: None.

8. Nyanza Province: None.


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PROVINCE TOTAL NUMBER

OF

ADMINISTRATIVE

DISTRICTS

DISTRICTS

INVOLVED IN

1997/1998

0UTBREAK (%)

DISTRICTS

INVOLVED IN

2006/2007

OUTBREAK (%)

Rift Valley 18 7 (39%) 9 (50%)

Eastern 12 4 (33%) 11 (92%)

North Eastern 4 3 (75%) 4 (100%)

Coast 7 3 (43%) 7(100%)

Central 7 4 (57%) 5 (71%)

Nairobi 8 - -

Nyanza 12 0 (0%) 0 (0%)

Western 8 0 (0%) 0 (0%)

1. RIFT VALLEY PROVINCE

Nakuru

R 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005

FALL 59.5 72.7 93.7 95.8 55.79 50.83 101.85 83.24 94.67 80.9777.1

6

PERATURE 18.57 18.14 18.56 18.72 18.85 19.32 18.69 18.87 18.77 18.7418.7

7

BREAKS 0 0 39% 39% 0 0 0 0 0 0 0


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2. NORH EASTERN PROVINCE

Garissa

R 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004

NFALL 34.21 11.76 79.2 53.25 25.09 13.44 21.68 46.71 33.2 15.4

PERATU

28.92 28.99 28.62 28.71 28.57 28.84 29.05 28.91

TBREAKS 0 0 75% 75% 0 0 0 0 0 0


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3. EASTERN PROVINCE

Meru

1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2

NFALL

126.9

8 81.15

184.9

9

127.5

2 84.67 49.85

101.4

4 152.1

127.5

5

118.1

4 68

PERATU

18.42 18.54 18.55 18.31 18.24 18.58 18.47 18.34 18.93 19

TBREAKS 0 33 33 0 0 0 0 0 0 0

4. COAST PROVINCE

Malindi

1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2

NFALL 65.21 87.47

177.9

2

117.9

2

103.8

2 85.05 81.55 89.5 89.35 75.1 72

PERATU

26.28 27.45 26.45 27.01 26.5 26.43 26.66 26.84 27.2 26.97

TBREAKS 0 0 48 48 0 0 0 0 0 0


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5. CENTRAL PROVINCE

Thika

1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2

NFALL 63.33 66.7

116.6

7 115 75 29.1 66.7 108.3 58.3 63

PERATU

14.09 14.03 15.29 14.63 13.97 14.31 15.27 15.04 14.07 14.93 15

TBREAKS 0 0 57 57 0 0 0 0 0 0


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6. NAIROBI PROVINCE

RS 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2

NFALL 73.56 56.61 81.94 117.5 62.75 44.1 120.1 79.35 78 70.56 60

PERATU

18.98 18.35 20.39 19.38 19.45 19.71 19.56 19.89 19.8 19.73 19

7. WESTERN PROVINCE


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Kakamega

1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2

NFALL

167.2

5

174.6

3 134.9

159.2

5 145.8

117.8

5

185.5

6

178.7

8

175.8

5 129.5

13

PERATU

20.56 20.61 21.1 20.81 20.45 20.91 20.76 21.05 21.34 21.24 21

TBREAKS O 0 0 0 0 0 0 0 0 0

8. NYANZA PROVINCE

Kisumu

1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2

NFALL

120.9

8

128.3

5 134.2

104.7

3

128.6

6

101.2

4

124.2

9

134.8

7

104.3

6

115.9

9 9

PERATU

23.5 23.28 23.85 23.87 23.25 23.6 23.31 23.66 23.67 24

TBREAKS 0 0 0 0 0 0 0 0 0 0


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GRAPHICAL REPRESENTATION OF AVERAGE ANNUAL

TEMPERATURES PER PROVINCE BETWEEN 1995 AND 2009

1. RIFT VALLEY PROVINCE

Nakuru


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2. NORTH EASTERN PROVINCE

Garissa

3. EASTERN PROVINCE

Meru


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4. COAST PROVINCE

Malindi


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5. CENTRAL PROVINCE

Thika

6. NAIROBI PROVINCE

Nairobi


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7. NYANZA PROVINCE

Kisumu

8. WESTERN PROVINCE

Kakamega


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SUMMARY

The purpose of this project was to study the climatic trends in terms of rainfall and temperature

between 1995 and 2009 and how the epidemiology of RVF has changed over the same period.

Findings of the study are summarized below;

1. There have been two major outbreaks between 1995 and 2009, i.e. 1997/1998.

2. These outbreaks occur when the affected regions record extremely high rainfall having

been preceded by a relatively dry period. E.g. as seen in the 1997/98 outbreak, Garissa

went from 11.7mm in 1996 to 79.2mm in 1997 and Thika from 66.7mm in 1996 to

116.67mm in 1997.

3. Comparison of the two outbreaks shows that the 2006/2007 one was more extensive,

involving 52.2% of the country as compared to that of 1997/1998 that only involved

38.1% of the country.

4. From the graphical analysis of average annual temperatures per province it is clear from

the trend line in the graphs that the temperatures have been gradually increasing during

this period.

DISCUSSION


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The challenges of climate change and development in Africa are closely linked. But we

urgently need to improve our understanding of how climate change will affect Africa

Beckett (2004).

This study reveals that temperatures have been gradually increasing and that the

magnitude in terms of number of regions involved in the outbreak has increased. This

may partly be explained by what is in chapter 2 of this report under the subtopic on

effects of climate change on RVF (2.3.7) which states that it is therefore expected that

global climate change will alter the distribution and increase the risk of some vector-

borne zoonoses, including Rift Valley fever (RVF), leading to significant changes in the

geographical distribution and frequency of RVF epidemics. This is further explained by

the fact that temperature has a direct effect on mosquitoes, the principal vectors of RVF

virus. It leads to increased activity, increased reproduction and therefore increased

frequency of blood meals and faster digestion of blood (Martin et al, 2008). Pathogens

harboured by mosquitoes also mature faster. Increased water temperature cause mosquito

larvae to develop faster also increasing overall vector capacity (Reiter, 2008).

If this trend goes unchecked, RVF may further extend to involve more regions and this

will be detrimental to Kenya as a developing country. By 2100 it is estimated that

average global temperatures will have risen by 1.03.5 oC, increasing the likelihood of

many vector-borne diseases in new areas. Human settlement patterns in the different

regions will influence disease trends in that this will lead to introduction of pathogens to

new areas and due to global warming which accompanies climate change, these

pathogens and their vectors thrive and cause disease since the climatic conditions are now

conducive (Githeko et al, 2000).


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RVF has negative socioeconomic impacts which retard development. Outbreaks result in

substantial hardship, directly through illness and through direct economic impact (as a

result of animal deaths and abortions, and because of a variety of commercial bans.).

Specifically hard hit by the latest outbreak were the pastoral communities of the north

eastern (NE) part of Kenya. In this region, livestock serve an important livelihood

function for pastoralists, with livestock trade representing over 90% of pastoral incomes

(Mutunga, 2010). Moreover, NE Kenya has the highest incidence of poverty within

Kenya, with poverty rates of approximately 70% in 2004 (Society for International

Development, 2010).

It is important to note that RVF does not just affect producers, but also impacts a host of

other service providers within the livestock supply chain and other parts of the larger

economy. Beyond livestock producers in the affected areas, traders, slaughter-house

workers, butchers, transporters, and a range of small-scale businesses, such as operators

of food kiosks who served these workers, all incurred losses. It was reported that

significant numbers of livestock traders and butchers were unable to resume their

business activities after the bans on livestock movement and slaughter were lifted

because of depletion of capital. Cumulatively, these downstream impacts can often dwarf

the impacts of the disease at the farm level (Rich et al, 2010). This shows that there is

increasing need for us as a country to adapt ways in which we can mitigate climate

change and to adapt to its impacts especially when it comes to health.

RECOMMENDATIONS


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1. As the world embraces the one health initiative, there should be better

coordination between veterinary epidemiologists, medical epidemiologists and

environmentalists and through the combination of their different areas of expertise

study the new trend of diseases, especially vector borne diseases as a result of

climate change and therefore come up with better methods of surveillance,

prevention and control of such diseases.

2. Veterinary and medical experts, through extension services should educate and

create awareness to the public, especially in marginalized areas where poverty and

illiteracy is at its highest, on what climate change is and the effects we are likely

to experience. We should enlighten them on coping strategies which might

include educating people in areas solely dependent on livestock for their

livelihood on alternative sources of income.

3. It is our responsibility as veterinary extension officers to educate people on the

importance of livestock insurance as most insurance companies nowadays insure

animals against losses due to epidemics.

4. We cannot ignore the fact that we have started experiencing effects of climate

change on epidemiology of most diseases, among many others. It would be

advisable to introduce studies on global warming and climate change into the

curriculum in both veterinary and medical schools so that we are well equipped to

deal with some of the unexpected changes seen in terms of disease epidemiology

e.g. whereby a while ago wed disregard the likelihood of a certain disease

occurring in a certain area based on the fact that the environment wasnt


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conducive for the causative agent to thrive and cause disease. This is bound to

change and it would be quite costly to be ignorant on such issues.

5. REFERENCES

1. Paul Epstein (2008) Climate change and infectious disease: stormy weather ahead?

Epidemiology13(4), pg 373-375.

2. Joint FAO/IAEA Program (2010) Climate change & the Expansion of Animal &

Zoonotic Diseases.

3. V. Martin, V. Chevalier, and others (2008) Impact of Climate Change on the

epidemiology and control of RVF,Revue Scientifique technique Office international

Epizooties, 27 (2):413-426.

4. GithekoA K, Lindsay S W, Confalonieri U E and Patz J A (2000) Climate change and

vector-borne diseases: a regional analysis.Bulletin of the World Health Organization,

78 (9): 1143.

5. Anthony Nyong (2005); Key Vulnerabilities to Climate Change in Africa


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6. United Nations Framework Convention on Climate Change, (2007) Climate

change: Impacts, vulnerabilities and adaptations in developing countries, pg 29-52

7. Mohammed M, Fausta Mosha, Janeth Mghamba, Sherif Zaki and others (2010).

Epidemiologic and clinical aspects of Rift Valley Fever Outbreak in Humans in

Tanzania, 2007.AmericanJournal of Tropical Medicine and Hygiene, 83(2): 22

8. Rosemary Sang, Elizabeth Kioko, Joel Lutomiah and others (2010). RVF Epidemic in

Kenya, 2006/2007: The Entomologic Investigations. AmericanJournal of Tropical

Medicine and Hygiene, 83(2):28

9.Bailey, C.L, (1981). U.S. Army Medical Research Institute for infectious diseases, Fort

Detrick, Maryland. Personal communication

10.Anderson, G.W. & Peters, C.J. (1988) Viral determinants of virulence for RVF in rats.

Microbial Pathogenesis2: 283-293

11.Davies, F.G. (1985) Rainfall and epizootic Rift Valley Fever, Bulletin of the World

Health Organization, 63:941-943.

12.Woods, C.W, Karpati A.M and others (2002).An outbreak of Rift Valley Fever in

northeastern Kenya, 1997-98.Emerging Infectious Diseases, 8:138-144.

13.Amwayi S and others (2007). Risk factors for severe Rift Valley Fever Infection in

Kenya. The American journal of tropical medicine and hygiene, 83; 14-21.

14.Reiter P (2008) Climate change and mosquito-borne disease: knowing the horse before

hitching the cart. Revue Scientifique technique Office international Epizooties

27(2):383-398.


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15.Assad, F., Davies F.G. & Eddy G.A. (1983). The use of veterinary vaccines for

prevention and control of Rift Valley Fever. Bulletin of the World Health Organization,

61:261-268).

16.Robert F Breiman, Bruno Minajauw and others (2010).Rift Valley fever: Scientific

Pathways toward Public Health Prevention and Response. The American Journal of

Tropical Medicine and Hygiene, 83:1-4.

17.Government of the Republic of Kenya (2007). Vision 2030.

18.Logan T.M and others (1991). Mosquito species collected from a marsh in western

Kenya during the long rains. Journal of the American Mosquito Control Association,

7:395-399.

19.R. M. Murithi , P. Munyua, P.M. Ithondeka, J.M. Macharia, A. Hightower, E. T.

Luman, R. F. Breiman & M. Kariuki Njenga (2010) Rift Valley fever in Kenya: history

of epizootics and identification of vulnerable districts. Epidemiology, pg 1-9.

20.Swanepoel Rand Jaw Coetzer, (2004) Infectious Diseases of Livestock volume two

(2nd Edition).

21.Prof. S. George Philander, (2008) Encyclopaedia of climate change and global

warming.

22.Shrivastava, A.K, (2001) Global warming.

23.Anthony E Castro (1992) Veterinary Diagnostic virology.

24.Global Alliance Livestock Vet Medicine (GALVmed) (2010), Safety and efficacy of

OBP clone 13 Rift Valley fever vaccine in sheep, goats and cattle under Kenyan field

conditions, Study protocol.

Documents

efffects of climate change on epidemiology of vector borne zoonotic diseases