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Presentation by Dr Peter Ithondeka, Director of Veterinary Services,Kenya, at the Enhancing Safe Inter-regional Livestock Trade workshop held at Dubai, UAE, 13-16 June 2011.
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Practical Considerations in the Control of a Rift Valley Fever Epizootic
Presented at OIE Regional Conference NairobiSAMAYA HOTEL UNITED ARAB EMIRATE
byDr Peter Maina Ithondeka PhD, MBS
Director of Veterinary Services, Kenya14th June 2011
Introduction Rift Valley Fever (RVF) is a viral haemorrhagic disease
primarily of cattle, sheep, goats, camels, wildlife and humans
Spread: - Aedes mosquitoes, other blood-sucking insects and through skin abrasions
Maintenance of virus between outbreaks remains unclear
One of the most significant zoonotic disease problems in Africa
The haemorrhagic human disease syndrome generates a high degree of panic among the human populations at risk
RVF occurrence in Kenya• A disease fitting RVF description was first described in
Kenya in 1912 by Montgomery.
• It is believed that the disease might have occurred in 1913 because an outbreak fitting the description of RVF was associated with heavy mortalities of sheep in the Rift Valley (Bres, 1981).
• Described as a specific viral entity in 1931
• Since then the disease has occurred in 5-15 year cycles
– 1926, 1931, 1936, 1944, 1951, 1960/63, 1967/68, 1978/79, 1997/98 and 2006/07
• Refer to MS Word tabulation of outbreaks
RVF antibody to virus studies in camels
• Study carried out in 1979 after the 1978/79 RVF epizootic in Kenya (Davis, Koros and Mbugua, 1984)
• 571 camel sera samples were collected and analysed
• 22% of these had high titers of the RVFV neutralizing antibodies
RVF antibody to virus studies in birds
–Carried out in 1979 using 171 bird sera (Davies, 1979)
–Study was to check if RVF produced viraemia or neutralizing antibodies in birds
–Only 3 of Ploceus weavers tested contained specific antibodies to RVF
Role of primates in spread of RVF
• To find the natural reservoir to RVF has been the subject of several studies
• Smithburn et al.,(1948) failed to detect antibodies in sera from 72 wild monkeys trapped in Uganda in an area where RVFV was isolated in mosquitoes
• Pellisier&Rousselet (1954) reported the presence of antibodies in 12 out of 122 monkeys kept in captivity in Brazzaville
Role of primates in spread of RVF(2)
• Davies et al.,(1972) failed to detect antibodies from baboon (Papio anubis) in Kenya most of which were from an area where an epizootic of RVF had recently occurred
• Davies et al.,(1975) failed to detect antibodies in 1304 velvet monkeys) in Kenya most of which were again from an area where an epizootic of RVF had recently occurred
RVF antibody to virus studies in wildlife
Study carried out in 2007 on 896 sera collected from 16 Kenyan wildlife species (Evans et al., 2007)
Specimen from 7 species had detectable neutralizing antibodies against RVFV i.e. African buffalo, black rhino, lesser kudu, impala, African elephant, Kongoniand waterbuck.
Flooded Dambo North Eastern Province, Kenya
Number of RVF outbreaks in Kenya from 1912-2002 (5-15 year cycles)
0
5
10
15
20
25
30
35
40
45
1912
1931
1951
1960
1962
1964
1967
1969
1971
1978
1983
1989
1991
1993
1998
2002
Year
No
.of
ou
tbreaks
contingency plans
• Preparedness planning, including the development and approval of contingency plans
• Prior approval of plans will allow decisions to be made at a political level more rapidly
Response to the 2006/07 RVF outbreak
Veterinary department formed a technical committee to advice on control strategy
The committee composed of experts from other institutions, development partners, ministry of health and Meteorological department.
Departmental management committee for coordination of activities for prevention and control of RVF
Zoonotic committee composed of CDC, MOH, FAO, Veterinary Department and WHO
1. Quarantines and slaughter bans
Quarantines were imposed in infected districts (livestock movement controls)
Livestock slaughterhouses were closed and home slaughters banned
Enforcement of quarantine/slaughter bans was through education, use of imams and other law enforcers
The quarantine and slaughter bans were lifted based on absence of clinical disease
preventive action by moving livestock to high altitude areas to avoid Aedes infested areas
2006/2007 Outbreak: Intervention activities
1. Quarantines and slaughter bans
2. Surveillance 3. Vaccination4. Vector control (insect
repellants, sythetic pyrethroids)
5. Public education and awareness
2. RVF Surveillance in livestock• Immediately carried out in districts adjacent to
the outbreak area to determine the spread
• Later extended to areas with known endemic foci - based on
–Previous infections
–Areas ecologically conducive for vector habitation e.g. thick vegetation cover, swampy and flooded grounds
• Veterinary field personnel continuously searched for the disease and collected samples
RVF Surveillance in livestock (2)
• In cattle, sheep, goats and camels assessment of titers of anti–RVF virus IgM antibody relative to anti–RVF virus IgG antibody can be used to differentiate recent from historical RVF virus infection.
• This is because the duration of detectable anti-RVF IgM antibody in these animals is transient, approximately 60 to 90 days (Bird et al.,2009)
2006/2007 Outbreak: RVF surveillance sites
0 300 Kilometers N
EW
S
2006/2007 RVF wildlife surveillance
• Serum samples collected from buffaloes, Giraffes, warthogs, Elands, Gerenuks
• Surveillance done in areas where outbreaks had occurred
• Opportunistically during Rinderpest surveillance
• In all areas where unusual wildlife deaths were reported
Distribution of sentinel herds to monitor disease
##
##
#
#
#
#
#
Japata
Ngambo Salabani
Shantabak
Sangailu
Marey
Kotile
Naivasha
Bachuma
200 0 200 400 Kilometers
N
EW
S
3. Vaccination against RVF• Vaccinations were carried out in goats, sheep, cattle and
camels
• Started in January 2007 in the North Eastern Province
• Later focus shifted to known endemic districts
• A total of 2,550,300 doses of RVF vaccine were used in control efforts
• Type of vaccine: Smithburn live attenuated vaccine
2006/2007 Outbreak: Vaccinated areas
200 0 200 Kilometers
N
EW
S
4. Vector control• Reduction of vector population using
insecticides (pyrethroids) on livestock –- pour-on preparations and spray wash
• All herds visited were treated
• A total of 5,890 liters of insecticide Pour-on preparation and 632 liters of insecticide spray were used in 14 districts as part of integrated RVF vector control activities.
5. Public awareness and training Press conferences Ministers for Livestock and Fisheries Development and
Health DVS on the updates of the disease
Radio interviews to educate , inform the public and increase compliance with legal requirements
Newspaper advertisements, brochures, radio announcements and television infomercials
Training of department field staff on RVF recognition, surveillance and bio- security measures
Impacts of RVF outbreak
• Financial losses due to:
– Livestock deaths
–Abortions
– Trade restrictions
– Slaughter restrictions
• Food insecurity
• Decreased demand and prices of meat
• Loss of stock
Decision Making Tool for Kenya The department of veterinary services has come
up with a contingency plan for RVF outbreaks in Kenya.
This plan covers issues such as:
RVF preparedness protocols
Surveillance protocol (including sentinel herd)
Personal protection protocol
SOPs for sample collection and storage
SOPs for RVF laboratory bio-safety
Contingency plan in RVF control Pre-outbreak protocols Monitoring of weather patterns Passive surveillance Rumor and outbreak investigation Management, maintenance and monitoring of sentinel
herds Risk analysis Maintenance of RVF database
Outbreak protocols Risk assessment Active surveillance Collection of samples Wildlife surveillance Investigating of disease reports
Decision Making in RVF control (2)
RVF simulation protocol
Vaccination protocol
Vector control protocol
Protocol on imposition and management of RVF quarantine measures
Protocol for RVF outbreak communication
Phased out decision making
• based on using key events as triggers or decisionpoints for partial responses reduce the risk ofinappropriate decisions and assure betterpreparation.
• decision-making process involves balancing the lackof perfect information with the need to take adecision to avert losses due to failure to take action.
• If the decision is taken too early with scantinformation, the likelihood of taking a wrong decisionis increased and costs will result from inappropriateor unnecessary activities.
Phased out decision making (2)
• if a decision is taken too late, the opportunity to intervene effectively may be lost.
• Thus, the decision-maker has to balance the risks of over-reacting against those of under-reacting.
• effectiveness of phased decision making rests heavily on the trust of its predictive value.
RVF hot spots vaccination strategy
• Kenya currently adopts vaccinations in the known RVF hot spots when never the flooding is predicted.
• However, it is difficult to gauge the ideal point, in terms of information availability, where a decision should be taken.
Cumulative RVF Vaccination
Year Doses
• 2007 2,077,000
• 2008 1,500,000
• 2009 1,199,600
• 2010 600,000
• Vaccinations have been carried out in RVF outbreak hotspots.
Time lines based on DVS/ILRI 2007 study
Risk Factors Cases Response
Rains Vectors Livestock Human Human Vet
33.1 days 19.2 days 21 days 35.6 days 12.3 days 68.9 days
Thank you for Listening
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