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Vector ControlModule 2B

Mosquito borne diseases

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Behaviour of mosquitoes

Genus Breeding site Disease and distribution

Anopeline mosquito

Biting period : NIGHT

Non polluted water: Edges of rivers, swamps, tanks,

rice fields, saltwater without wave action,

Malaria : Tropical and sub-tropical

Filariasis : Asia and Africa

Aedes mosquito

Biting period : DAY

Small water containers:

Cans, jars, gutters

Yellow fever : Africa and Americas

Dengue : Africa and Americas, Asia

Filariasis : Pacific

Culex mosquito

Biting period : NIGHT

Any dirty water: Waste water ditches, latrines, septic pits,

Filariasis : Most tropical areas

Encephalitis virus: worldwide

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Mosquito Life Cycle

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• Transmission by mosquitoes– Anophelenes and

Culicines

• Filarial worms, Mainly Wuchereria bancrofti, – Also Brugia malayi or B. timori

Lymphatic Filariasis

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Lymphatic Filariasis Endemic Areas

Endemic in 83 Endemic in 83 countriescountries Guerrant et al 2006,

Tropical Infectious Diseases 2nd Ed.

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Clinical Disease

• Hydrocoele

• Elephantiasis

• Tropical Pulmonary Eosinophilia

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Chichungunya

• 'Chikungunya' 'that which bends up' Swahili

• 1st documented in 1952 to 1953 in Africa• Alphavirus of family Togaviridae• Primary vectors : Aedes albopictus or aegypti. • 2005 to 2006 - 266,000 cases = 35.0% of the

population in Reunion, Madagascar, Mauritius and Seychelles.

• 2006 –2007 Outbreaks in India, Sri Lanka & Italy

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Chikungunya Global Distribution

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Outbreaks have increased in scale and frequency in recent years.

Distribution follows dengue as it can be transmitted same vectors.

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Insecticide Treated Nets (ITN)

Also help to reduce fleas and mites in the bed clothing and mattress

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Environmental Control

• The elimination of mosquito breeding sites. The elimination of mosquito breeding sites. • In most circumstances, difficult because of lack In most circumstances, difficult because of lack

of staff, the extent of the breeding sites and of staff, the extent of the breeding sites and cost. cost.

• Some breeding sites may also be the only Some breeding sites may also be the only available water.available water.

• Malaria mosquitoes can fly several km.Malaria mosquitoes can fly several km.• Localised (household) grass cutting and bush Localised (household) grass cutting and bush

cleaning not useful for malaria control.cleaning not useful for malaria control.

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Time of biting:Number caught (no.) and Number positive for sporozoites (+)

1800-2200h 2200-0200h 0200-0600hSpecies Source

An. gambiae no. 248 743 606 Tanganyika (Gilles, 1957)

+ 9 20 8

An. gambiae/An. funestus no. 5900 13000 10850 Burkina Faso (Robert 1991)

+ 295 1040 2061

An. gambiae no. 91 1269 1831 Sierra Leone (Bockarie1996)

An . gambiae no. 23 189 211 Tanzania (Maxwell 1997)

+ 2 14 9

An. funestus no. 31 232 86 “

+ 0 7 2

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Mosquito prefer pregnant women

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Issue for Control #1

• Different insect vectors may peak in different seasons. The malaria vector may be present during the dry season when other mosquito populations are low.

It is important to use LLITN throughout the year if you want to control malaria.

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Longevity (daily survivorship)

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Issue for Control #2• Mosquitoes don’t live very long – most will die

before they can transmit malaria. A mosquito will rest on the wall after it feeds.

Therefore Indoor residual spraying (IRS) works It kills the mosquito sometime within the incubation period

Spraying your own house, but not the others in the community will not protect your family from malaria.

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Issue for Control #3

• At 25º it takes 12 days before a mosquito can transmit malaria – most will die before then. Below 19º malaria can not be transmitted.

• Malaria falls off in winter because of the cooler temperature, but can happen before the rains as long as there is ground water

• IRS works by killing the mosquito sometime within the incubation period

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VBD Control Myths

1. All mosquitoes are the same

2. Cutting grass and maize is useful

3. Filling in puddles around house is useful

4. Clearing garbage is useful for malaria control

5. Wearing long sleeve shirts and pants protects

6. Spraying individual houses protects the family

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VBD Control Facts

• Sleeping under an LL ITN every night provides good protection against malaria, some filariasis and Lieshmaniasis

• IRS also protects equally well against malaria if >85% of houses in a community are sprayed. It may also be effective against mosquito borne Rift valley fever

• Larval control works well for dengue fever and to a lesser extend also malaria (i.e. temporary floods etc) but all breeding sites within the flight range of the vector need to be eliminated