Neglected Tropical Diseases
CMMID interests in neglected tropical diseases include work modelling cholera, dengue fever, lymphatic filariasis, Rift Valley fever, schistosomiasis and trypanosomiasis.
Dengue is a mosquito-borne viral infection, with the severe forms of the clinical disease also known as dengue haemorrhagic fever and break-bone fever. There is no anti-viral treatment and no licensed vaccine. Air travel and the international trade in used tires, in which pools of water provide breeding ground for the mosquito, are thought to have contributed to the spread of dengue, which affects most parts of SE and south Asia and the Pacific. There are four main strains with some cross immunity providing short-term protection and potential immune over-reaction to different strains. With local and regional partners, we are involved in modelling both multi-strain circulation in SE Asia and real-time outbreak modelling following introductions to Pacific islands.
Lymphatic filariasis, commonly known as elephantiasis, is a painful and disfiguring disease. Infection is usually acquired in childhood but visible manifestations usually occur later in life. In endemic countries, lymphatic filariasis has a major social and economic impact. We are currently supporting the development of predictive maps linking the prevalence of lymphatic filariasis across Africa to mathematical models of transmission dynamics, which can be used to predict the potential impact of interventions.
Rift Valley fever
Rift Valley fever (RVF) is a zoonotic and vector-borne disease, affecting human and animal health, and livestock production. To date, it is not fully known why and how the virus suddenly re-emerges and spreads in previously affected areas (mainly Africa), and causes epidemics. Answering those questions is essential to reduce the impact of RVF on local populations, and to mitigate the risk of disease spread to currently disease-free areas. The research that has been conducted at the CMMID focused on disease spread in South Africa, using spatio-temporal statistical modelling in combination with epidemic data and remote-sensing images (work conducted by Raphaelle Metras and Richard White) The current and future research aims at quantifying those factors underlying RVF virus re-emergence in Mayotte island, as a case-study for RVF in general. This research is done using dynamic modeling, in combination with existing RVF datasets, which will be supplemented by additional field data collection. This work is conducted by Raphaelle Metras, in collaboration with Prof. John Edmunds, Dr Eric Cardinale (CRVOI-CIRAD, La Reunion, France) and Prof Matt Keeling (University of Warwick, UK), and is funded by the Wellcome Trust.
Métras, R., Baguelin, M., Edmunds, W.J., Thompson, P.N., Kemp, A., Pfeiffer, D.U., et al. Transmission potential of Rift Valley fever virus over the course of the 2010 epidemic in South Africa. Emerg Infect Dis. 2013; Jun;19(6):916-24. doi: 10.3201/eid1906.121641.
Métras, R., Porphyre, T, Pfeiffer, D.U., Kemp, A., Thompson, P.N., Collins L.M. and White R.G. Exploratory space-time analyses of Rift Valley fever in South Africa in 2008-2011. PLoS Negl Trop Dis. 2012; Aug;6(8):e1808. Epub Aug 28
Métras, R., Collins, L.M., White, R.G., Alonso, S., Chevalier, V., Thuranira-McKeever, C. and Pfeiffer, D.U. Rift Valley Fever Epidemiology, Surveillance, and Control: What Have Models Contributed? Vector-Borne and Zoonotic Diseases. 2011; Vol. 11, No. 6: 761-771
Human African trypanosomiasis (sleeping sickness)
African sleeping sickness, or HAT, is a vector-borne disease that affects remote, mostly conflict-affected, communities of Sub-Saharan Africa, and is almost always fatal unless treated. While its burden has decreased from alarming levels during the 1980s and 1990s, it remains a serious epidemic threat, particularly where vertical control programmes are interrupted. We are working on models to explore different aspects of this poorly understood disease, including: (i) estimation of the fraction of cases detected during active and passive screening; (ii) transmission reduction potential of passive case detection; (iii) the role of chronic carriers of infection and of putative animal reservoirs in maintaining transmission of the West African form of HAT, which accounts for >95% of human cases. These studies shed light on potential obstacles for the elimination of HAT and help to optimise control programmes based on case detection.
Funk, S., Nishiura, H., Heesterbeeck, J.A.P, Edmunds, W.J. and Checchi, F. Identifying transmission cycles at the human-animal interface: The role of animal reservoirs in maintaining Gambiense Human African Trypanosomiasis. PLoS Computational Biology 2013; 9(1):e1002850
Checchi, F., Cox, A.P, Chappuis, F., Priotto, G., Chandramohan, D. and Haydon, D.T. Prevalence and under-detection of gambiense human African trypanosomiasis during mass screening sessions in Uganda and Sudan. Parasites & Vectors 2012; 5:157
Typhoid fever is a systemic bacterial infection which enters the body through the gut, potentially on food or in water. The highest burden of disease is in Asia-Pacific. It affects humans only, and increasing antibiotic resistance means that death rates risk returning to those of the pre-antibiotic era.
We are working with the Coalition against Typhoid on vaccination strategies for new conjugate vaccines. We are also doing field investigations the Pacific, using immunity data from recovering patients and a cross-sectional serological survey as a basis for transmission modelling.This is done in collaboration with local partners, the World Health Organization, the Oxford University Clinical Research Unit in Vietnam and other academic partners.