Skip to 0 minutes and 9 secondsPaul Ready: Now, we're going to consider how visceral leishmaniasis is spread by its natural sand fly vectors and mammalian hosts.

Skip to 0 minutes and 22 secondsSome definitions-- Anthroponotic transmission means the sand fly vector spreads the parasite from human to human. In comparison, zoonotic transmission involves the parasite being transmitted from a mammal-- a reservoir host-- to a human. Visceral leishmaniasis caused by Leishmania donovani, is anthroponotic on the Indian subcontinent, with the sand fly species, Phlebotomus argentipes, transmitting the parasite from one human to another.

Skip to 1 minute and 1 secondParasites have been detected in water buffalo and other domesticated mammals, but these have not been demonstrated to be reservoir hosts, meaning they are not proven to be a source of infection to humans.

Skip to 1 minute and 16 secondsConsequently, some of the more important risk factors for contracting anthroponotic visceral leishmaniasis

Skip to 1 minute and 22 secondson the subcontinent are A: proximity to human cases, including those with PKDL.

Skip to 1 minute and 32 secondsB: proximity to high densities of adult females of Phlebotomus argentipes and the mammals providing these vectors with blood meals, such as cattle and water buffalo.

Skip to 1 minute and 45 secondsAnd C: proximity to larval breeding sites in soil or dung, before they become flooded towards the end of the monsoon season.

Skip to 1 minute and 57 secondsIn contrast, visceral leishmaniasis caused by Leishmania donovani could be zoonotic as well as anthroponotic in Sub-Saharan Africa, although the wild mammals found infected, such as mongoose or other rodents, have not yet been proven to be reservoir hosts.

Skip to 2 minutes and 20 secondsThe more important risk factors include the time spent in the Acacia-Balanites savannah environment of the sand fly, Phlebotomus orientalis-- mostly in Sudan and Ethiopia, or near the termite mounds in the alternative savannah environments of Phlebotomus martini and related sand flies-- mostly in Sudan, Ethiopia, and Kenya. Many visceral leishmaniasis cases result from migration into these environments because of drought and warfare, or the movements of pastoralists and their livestock herds following seasonal rains.

Skip to 3 minutes and 1 secondVisceral leishmaniasis caused by Leishmania infantum is usually zoonotic, with the domestic dog being the main reservoir host, both in the Mediterranean region and in Latin America. The Mediterranean region has many different sand fly vectors, mostly in the subgenus Phlebotomus larroussius. Whereas the predominant vector in Latin America is Lutzomyia longipalpis. This reflects the fact that visceral leishmaniasis was introduced to Latin America in dogs transported from the Mediterranean region, starting about 500 years ago. However, the vectors in both continents-- Europe and Latin America-- are usually most abundant in the yards of rural houses and farms, although Lutzomyia longipalpis and visceral leishmaniasis are reported to be increasing in suburban areas. The more important risk factors in such environments

Skip to 4 minutes and 1 secondare A: proximity to infected dogs, and B: proximity to high densities of the vectors. Leishmania infantum was named because many infections in the early 20th century were found in children. Adults are at high risk of infections, causing death in areas where transmission to children was interrupted by control measures. Many adults in such areas have not acquired immunity as children, and this can lead to more rapid disease progression if transmission resumes after control measures are terminated.

How is VL spread by its natural sand fly vectors and mammalian hosts?

Professor Paul Ready follows on from step 1.6 by looking at how the sand fly spreads infection amongst its mammalian host or hosts. The terms anthroponotic and zoonotic transmission will be explained. There will also be a discussion on how diverse environments can have an impact on transmission cycles and risk of transmission.

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This video is from the free online course:

Control and Elimination of Visceral Leishmaniasis

London School of Hygiene & Tropical Medicine