Visceral leishmaniasis
Visceral leishmaniasis
Visceral leishmanisasis (VL), also known as kala-azar, is the most severe form of leishmaniasis and involves infection of the liver, spleen and bone marrow. It is a chronic infection and the disease is fatal if left untreated. It is caused by the protozoan parasite Leishmania donovani or Leishmania infantum in parts of Asia, Africa and Latin America.
Typical symptoms include fatigue, irregular bouts of fever lasting for 14 days or more, serious loss of appetite and weight, swelling of the spleen and liver and potentially chronic anaemia. If untreated, the case fatality rate can be as high as 100% within 2 years.
There are two types of VL, which differ in their transmission characteristics: Zoonotic VL is transmitted from animal to vector to human and anthroponotic VL is transmitted from human to vector to human. In the former, humans are occasional hosts and animals, mainly dogs, are the reservoir of the parasite. Zoonotic VL is found in areas of L. infantum transmission whereas anthroponotic VL is found in areas of L. donovani transmission.
Canine leishmaniasis (CanL) is caused by infection through sand fly bites infected with L. infantum. It is a zoonotic infection in humans and is found in more than 70 countries worldwide, including regions of southern Europe, Africa, Asia, South and Central America. It has also been reported in the USA although the transmission route is not necessary the sand fly.
Post-kala-azar dermal leishmaniaisis
Where L. donovani is endemic, post-kala-azar dermal leishmaniasis (PKDL) can occur as a sequelae of VL, producing a hypopigmented macular, maculopapular, nodular rash in clinically recovered patients usually within 6 months to a year or more after the apparent cure of the disease.
It may also occur earlier or even concurrently with VL. PKDL heals spontaneously in most cases in Africa, but rarely in patients in India, and is thought to play an important role in the continued transmission of the disease, especially in inter-epidemic periods of VL, acting as a reservoir for parasites.
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Climate change influencing vector biology and hence transmission as well as population migration could see the disease brought to other parts of the world not currently endemic for leishmaniasis.