Visceral leishmaniasis: global understanding of a complex disease

Visceral leishmaniasis (VL) is the most severe form of leishmaniasis and, without proper treatment, it is most often deadly. After malaria, this disease is the second-largest parasitic killer in the world, and it is responsible for an estimated 200,000 to 400,000 infections each year. The Tropical Medicine Research Centre (TMRC), a multi-country project which aims to  add to the global understanding of this complex disease and to generate new data to inform and guide current and future policies and practices on the Indian subcontinent, held its annual meeting in February in Varanasi, where ITM epidemiologist Kristien Cloots represented our Institute. 

This project has provided the context for establishing, among others, the first and only Health and Demographic Surveillance System (HDSS) within a VL-endemic area (Muzaffarpur, India), in which a community of 66 villages are monitored on VL and demographic events through time, providing a unique platform for research on VL, as well as other neglected tropical diseases.

As the second phase of the project is coming to an end, the Varanasi meeting gave an overview of the progress made in the recent years. ITM and its Unit of Epidemiology and Control of Tropical Diseases has mainly been involved in the epidemiological part of the project, currently focusing on two major topics. The first is the role of latent infection in the transmission dynamics. With the progressively declining caseload, the question of whether people who produce antibodies - and hence have been exposed to the parasite – but do not develop any symptoms of disease are also contributing to transmission, is becoming more and more key. However, finding the best (combination of) tests to correctly identify these asymptomatically infected people remains a challenge until today. The second topic is defining the determinants of disease progression, with one of the key findings in recent years in this domain being described by ITM epidemiologists, namely that there is a strongly increased risk of progressing to disease among individuals with high levels of antibodies against leishmania in their blood.

The initially 5-year-long project TMRC 1 was launched in 2007, two years after the memorandum of understanding was signed by the Ministers of Health of India, Nepal and Bangladesh together with WHO to reach the elimination target by the year 2015, which was later postponed to 2017. Funded by the National Institute of Health of the USA,  TMRC involves, among others, universities in the USA, India, Australia, UK, and ITM.