Visceral Leishmaniasis
Visceral Leishmaniasis (VL) is the second most deadly parasitic disease in the world following malaria, and is responsible for an estimated 20,000-40,000 deaths worldwide each year. Its distribution is highly localised, with over 90% of the 200,000-400,000 estimated annual cases occurring in just 6 countries: Bangladesh and India in the Indian sub-continent (ISC); Ethiopia, Sudan and South Sudan in Africa; and Brazil.
Map of global VL distribution (WHO, 2015)
The disease is vector-borne and is caused by chronic infection with protozoan parasites of the Leishmania genus. The parasites are transmitted between humans via the biting of female phlebotomine sandflies. Once inside the body the parasites pass through different stages of their life cycle, reproduce inside macrophages, and migrate to internal organs such as the liver, spleen and bone marrow. Symptoms of the disease include fever, weight loss, anaemia, and substantial swelling of the liver and spleen. If left untreated, the disease is almost always fatal.
Top left: flagellate Leishmania parasite, top right: phlebotomine sandfly, bottom left: swelling of the liver and spleen seen in visceral leishmaniasis, bottom right: life cycle of the Leishmania parasite
Our research focuses on modelling visceral leishmaniasis in the Indian sub-continent, which accounts for the majority of the global burden of the disease. VL in the ISC is caused by Leishmania donovani, and is believed to be anthroponotic (i.e. have no animal reservoir) and spread by a single sandfly species, Phlebotomus argentipes. Consequently, it has been targeted by the WHO for elimination as a public health problem (less than one new case of KA per 10 000 people per year) by 2017. In the rest of the world, VL is zoonotic, limiting the possibility of elimination, and therefore the goal is 100% detection and treatment of all human cases by 2020.
Approximately 80% of VL cases in the ISC occur in the state of Bihar, in north east India, predominantly amongst those who are very poor. Current control strategies are based on sandfly control by indoor residual spraying of insecticide, active case detection and early diagnosis and treatment, but it is not clear whether additional measures are required to achieve elimination.
The majority of individuals infected with the parasite are asymptomatic, i.e. recover from infection without developing clinical symptoms, but are still infectious to sandflies. Determining the role that these individuals play in transmission of VL is of particular concern to the elimination effort and is a focus of our resarch.
Publications
Buckingham-Jeffery, E., Hill, E. M., Datta, S., Dilger, E., & Courtenay, O. (2019). . Parasites & Vectors, 12(1), 215.
Chapman, L. A., Jewell, C. P., Spencer, S. E., Pellis, L., Datta, S., Chowdhury, R., ... & Hollingsworth, T. D. (2018). . PLoS Neglected Tropical Diseases, 12(10), e0006453.
E.A. Le Rutte L.A.C. Chapman L.E. Coffeng, J.A. Ruiz-Postigo, P.L. Olliaro, E.R. Adams, E.C. Hasker, M.C. Boelaert, T.D. Hollingsworth, G.F. Medley, S.J. de Vlas (2018). . Clinical Infectious Diseases, 66 (suppl_4):S301–S308.
S. Jervis, L.A.C. Chapman, S. Dwivedi, M. Karthick, A. Das, E.A. Le Rutte, O. Courtenay, G.F. Medley, I. Banerjee, T. Mahapatra, I. Chaudhuri, S. Srikantiah and T.D. Hollingsworth (2017). . Parasites and Vectors, 10:601.
E.A. Le Rutte, L.A.C. Chapman, L.E. Coffeng, S. Jervis, E.C. Hasker, S. Dwivedi, M. Karthick, A. Das, T. Mahapatra, I. Chaudhuri, M.C. Boelaert, G.F. Medley, S. Srikantiah, T.D. Hollingsworth, S.J. de Vlas (2017). . Epidemics, 18:67-80.
L.A.C. Chapman, L. Dyson, O. Courtenay, R. Chowdhury, C. Bern, G.F. Medley and T.D. Hollingsworth (2015). . Parasites and Vectors, 8:521.
M.M. Cameron, A. Acosta-Serrano, C. Bern, M. Boelaert, M. den Boer, S. Burza, L.A.C. Chapman, A. Chaskopoulou, M. Coleman, O. Courtenay, S. Croft, P. Das, E. Dilger, G. Foster, R. Garlapati, L. Haines, A. Harris, J. Hemingway, T. D茅irdre Hollingsworth, S. Jervis, G. Medley, M. Miles, M. Paine, A. Picado, R. Poch茅, P. Ready, M. Rogers, M. Rowland, S. Sundar, S.J. de Vlas and D. Weetman (2016). Parasites and Vectors, 9:25.
K.S. Rock, G. Medley, R. Quinnell, O. Courtenay (2016). Advances in Parasitology, 94:49-131.
G.F. Medley, T.D. Hollingsworth, P.L. Olliaro, E.R. Adams (2015). Nature Supplement, 528:S102–S108.
K.S. Rock, E.A. le Rutte, S.J. de Vlas, E.R. Adams, G. Medley, and T.D. Hollingsworth (2015). Trends in Parasitology, 31 (6):251-259.
Funded by: Bill and Melinda Gates Foundation
People involved:
Collaborators:
Emily Adams (LSTM)
Caryn Bern (UCSF)
Lloyd Chapman
Deirdre Hollingsworth
Graham Medley
Piero Olliaro (WHO TDR)