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Transmission Pathways: Vectors and the Environment February 4th, 2010 Vectors of disease • Vectors are arthropods – – – – Mosquitoes Flies Ticks Fleas • Organisms can multiply inside the vector • Vector is not harmed • Sometimes animals are involved in vector transmission cycles Transmission cycles • Sylvatic cycle – Takes place in environment without humans present – Vector-animal-vector – Humans interrupt this cycle, get infected – Sometimes we are a dead-end host – Plague Transmission cycles • Urban cycle – – – – – Takes place in populated human settlements Vectors live in urban areas Standing water Transmission is vector-human-vector Yellow fever • The urban and sylvatic cycles can exist side by side • The existence of the sylvatic cycle can make the urban cycle difficult to control • The organisms involved in each cycle can be genetically distinct from each other Vector borne bacteria • Lyme disease – Borrelia burgdorferi – Ticks • Plague – – – – Yersinia pestis Rodent fleas Is an endemic, zoonotic disease People intrude on the natural transmission cycle Vector borne bacteria • Rocky Mountain spotted fever – Rickettsia rickettsii – Ticks • Tularemia – Francisella tularensis – Ticks Vector borne parasites • Filariasis – Parasitic worm – Wucheria Bancrofti – Mosquitos: Aedes, Culex, Anopheles • Leishmaniasis – Protozoan parasite – Genus Leishmania – Sandflies Vector borne parasites • Malaria – Protozoan – Plasmodium – Mosquitos: Anopheles • Sleeping sickness and Chaga’s Disease – hemoflagellates – Trypanosoma – Tsetse fly Vector-borne viruses • Dengue fever – – – – Mosquitoes: Aedes agypti Two transmission cycles Urban (human-mosquito-human) Sylvatic (monkey-mosquito-monkey) • Yellow fever – Yellow fever virus (flavivirus) – Mosquitoes: Aedes – Also transmits via urban and sylvatic cycles Control of vector-borne disease • Control of vectors – Getting rid of vector habitats and breeding grounds – Urban dengue • Eliminating sources of infection – Getting rid of infection in individuals so they are no longer sources – Mass drug treatment: filariasis – Vaccination: yellow fever Control of vector-borne disease • Prevention of biting on individual level – Insecticide treated bednets – Skin application of repellents – Malaria • Prevention of biting on community level – Insecticide treated bednets – Indoor residual spraying – Malaria
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