Lab notes: The spread of kala azar is linked not just to infected blood but to skin as well

Even as India has set a target to eliminate kala azar, also known as visceral leishmaniasis, by the end of 2017, there has been a stubborn resurgence of the disease in Bihar. But new research on transmission of the disease could hold clues as to why previous attempts at eliminating it in India and other developing countries have not been entirely successful.

Kala azar is a parasitic infection that kills between 20,000 to 40,000 people in the world every year. It is a classified as a Neglected Tropical Disease and affects mostly poor populations. The disease has been present in India since the last 1800s and is now endemic to four states in the country – Bihar, Jharkhand west Bengal and Uttar Pradesh. The disease is characterised by bouts of fever, weight loss, anaemia, and an enlargement of the spleen and liver.

Kala azar is caused by the parasite Leishmania donovani. It has been assumed so far that the parasite, which is is transmitted through the bite of female sand flies, is picked up directly from a host’s blood when a fly bites an infected person before spreading the disease to uninfected people in subsequent bites. But researchers from the University of York have now discovered that an infected person’s skin may also play a role in transmitting the disease.

While investgating the surprisingly low number of parasites found in infected blood the research team comprising mathematicians, experimental biologists and immunologists found “patchy landscapes of parasites” found on disease carriers’ skin. This, they say, determines how many parasites are picked up by sand flies. Some areas of skin can contain very high numbers of the parasite while other do not, which implies that whether a sand fly becomes infected or not depends on where they bite a person.

The findings published in the journal Nature Communications, suggests that we may need to look for new methods of treating kala azar that focus on treatments that affect parasites in the skin to interrupt the cycle of transmission. The researchers say that clinical studies and elimination campaigns need to take this new finding into account to effectively control leishmaniasis.