Helminth Ecology Research Group
Head of Group: Dr Maria-Gloria Basáñez (Reader in Parasite Epidemiology)
Research Interests:
Research in Dr. Basáñez' group focuses on the population biology, transmission dynamics, and mathematical modelling of helminth infections of humans. The primary objective of the research is to understand the population ecology of the parasites and their intermediate hosts / vectors, with the knowledge that the research will underpin the rational design, implementation, monitoring and evaluation of intervention strategies for the control / elimination of such infections. The mathematical models necessary for the study of helminth infections are based on intensity frameworks, which take into account not only whether hosts are infected or not, but also the worm burden (the number of parasites per host). Such frameworks are being used for the study of malaria within the mosquito where there are detailed data of parasite density for each developmental transition within the sporogonic cycle.
Location and People:
The research group is currently located in the Department of Infectious Disease Epidemiology, St Mary's Campus, and includes Dr Thomas S Churcher (presently working on malaria) and Dr Poppy Lamberton (presently working on onchocerciasis) as post-doctoral researchers, and Emma Dawes (malaria in the mosquito) and Martin Walker (ascariasis) as PhD students. The interests of the group overlap with those of the Disease Ecology Research Group (Dr Nicholas C. Grassly), the Schistosomiasis Reseach Group (Prof Joanne P. Webster), and the Schistosomiasis Control Initiative (Prof Alan Fenwick), with whom we have a number of shared PhD students that include Isobel Blake (trachoma modelling), James Rudge (schistosomiasis japonica), and Mr Michael D French (schistosomiasis modelling). Mr Simon J O'Hanlon is at present working on the Global Burden of Disease Study (http://www.globalburden.org/) for onchocerciasis, of which Dr Basáñez is a co-disease leader together with Dr Wilma Stolk at the Erasmus Medical Centre in Rotterdam.
Seminar Series: We hold regular and informal meetings under the wider umbrella of the Helminth Research Groups currently at DIDE. For further information contact Anna Phillips.
Current research asks the following questions:
1) How is population abundance in definitive hosts and vectors regulated? This leads to investigation into the role of density-dependent processes and at which point of the life-cycles such processes operate. We have highlighted that both negative (constraining) and positive (facilitating) density dependence occurs in the life-cycle of parasites such as Onchocerca volvulus (the causal agent of River Blindness) in the human and the Simulium host; Ascaris lumbricoides (the intestinal roundworm), and Plasmodium berghei (a rodent model for Malaria) in Anopheles stephensi (the latter in collaboration with Professor Robert E Sinden's group at South Kensington). A focus of this research is to explore how these nonlinear processes impact on the transmission biology and response by the parasites to control interventions.
2) Is anthelmintic resistance an emerging problem that could threaten the success of mass drug administration programmes for human helminthiases? The key ssue here is to promptly detect and identify sub-optimal drug responses and distinguish between natural inter-host variation and true reduction of drug efficacy due to chemotherapeutic pressure. We have started this research with ivermectin and onchocerciasis, both in Ghana (with Mike Osei-Atweneboana) and Cameroon (with Michel Boussinesq and Sébastien Pion), requiring the development of genetically structured mathematical models, and the use of statistical methodologies to identify true atypical responses by the parasite to the drug. Genetically structured models of lymphatic filariasis for the investigation of albendazole and ivermectin resistance have also been developed (in collaboration with Prof Roger Prichard).
3) Is the contact rate in vector-borne disease models dependent on the abundance of hosts and vectors? The biting rate per vector on humans consists of the product of the human blood index and the reciprocal of the duration between two consecutive bloodmeals. The biting rate enters as a square term in mathematical expressions for the basic reproduction ratio (R0) and vectorial capacity (C) of vector-borne diseases. If the human blood index depends on vector density, host abundance, the vector to host ratio, or the ratio between human and non-human blood hosts, this will introduce nonlinear processes in the contact rate between hosts and vectors with important repercussions for the epidemiology and control of such infections. We are investigating this question with the Onchocerca-Simulium combinations prevailing in southern Ghana (in collaboration with Prof Robert Cheke, Prof Rory Post, and Prof Michael Wilson).
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ADDITIONAL COLLABORATORS: Dr Christian Bottomley (London School of Hygiene and Tropical Medicine, UK) Dr Michel Boussinesq (IRD, Montpellier, France) Prof Robert A Cheke (University of Greenwich, UK) Dr María Eugenia Grillet (Institute of Tropical Zoology, Universidad Central de Venezuela) Dr Andrew Hall (University of Westminster, London, UK) Prof Valerie Isham (Department of Statistical Science, University College London) Dr Sébastien Pion (IRD, Montpellier, France) Prof Rory J Post (Natural History Museum and LSHTM, London, UK) Prof Roger K Prichard (Institute for Parasitology, McGill University) Prof Michael D Wilson (Noguchi Memorial Institute for Medical Research, Legon, Ghana) |
Selected Recent Publications
Basáñez M-G, Churcher TS & Grillet M-E (2009). Onchocerca-Simulium interactions and the population and evolutionary biology of Onchocerca volvulus. Advances in Parasitology 68, 263-313.
Basáñez M-G, Pion SDS, Boakes E, Filipe JAN, Churcher TS & Boussinesq M (2008). Effect of single dose ivermectin on Onchocerca volvulus: a systematic review and meta-analysis. Lancet Infectious Diseases 8, 310-322.
Basáñez M-G, Razali K, Renz A & Kelly, D. (2007). Density-dependent host choice by disease vectors: Epidemiological implications of the Ideal Free Distribution. Transactions of the Royal Society of Tropical Medicine and Hygiene 101, 256-269.
Basáñez M-G, Pion SDS, Churcher TS, Breitling L, Little MP & Boussinesq M (2006). River Blindness: A success story under threat? PLoS Medicine 3, e371.
Bottomley C, Isham V, Collins RC & Basáñez M-G (2008). Rates of microfilarial production by Onchocerca volvulus are not cumulatively reduced by multiple ivermectin treatment. Parasitology (Special Modelling Issue, editors: Basáñez M-G & Chappell L) 135, 1571-1581.
Bottomley C, Isham V & Basáñez M-G (2007). Population biology of multispecies helminth infection: competition and coexistence. Journal of Theoretical Biology 244, 81-95.
Churcher TS & Basáñez M-G (2009). Sampling strategies to detect anthelmintic resistance: the perspective of human onchocerciasis. Trends in Parasitology 25, 11-17.
Churcher TS & Basáñez M-G (2008). Density dependence and the spread of anthelmintic resistance. Evolution 62, 528-537.
Churcher TS, Schwab AE, Prichard RK & Basáñez M-G (2008). Genetic diversity and inbreeding in Wuchereria bancrofti: implications for the spread and detection of drug resistance. PLoS Neglected Tropical Diseases 2, e211.
Churcher TS, Filipe JAN, Basáñez M-G (2006). Density dependence and the control of helminth parasites. Journal of Animal Ecology 75, 1313-1320.
Filipe JAN, Boussinesq M, Renz A, Collins RC, Vivas-Martinez S, Grillet ME, Little MP & Basáñez M-G (2005). Human infection patterns and heterogeneous exposure in river blindness. Proceedings of the National Academy of Sciences of the USA 102, 15265-15270.
Grillet M-E, Villamizar NJ, Frontado HL, Cortez J, Escalona M, Botto C & Basáñez M-G (2008). Vector competence of Simulium oyapockense s.l. and S. incrustatum for Onchocerca volvulus: implications for ivermectin-based control in the Amazonian focus of human onchocerciasis, a multi-vector-host system. Acta Tropica 107, 80-89.
Pion SDS, Clarke P, Filipe JAN, Kamgno J, Gardon J, Basáñez M-G & Boussinesq M. (2006). Co-infection with Onchocerca volvulus and Loa loa microfilariae in central Cameroon: are these two species interacting? Parasitology 132, 843-854.
Rudge JW, Carabin H, Balolong E, Tallo V, Shrivastava J, Lu DB, Basáñez M-G, Olveda R, McGarvey ST & Webster JP (2008). Population genetics of Schistosoma japonicum within the Philippines suggest high levels of transmission between humans and dogs. PLoS Neglected Tropical Diseases 2, e340.
Sinden RE, Dawes EJ, Alavi Y, Waldock J, Finney O, Mendoza J, Butcher GA, Andrews L, Hill AV, Gilbert SC & Basáñez M-G (2007). Progression of Plasmodium berghei through Anopheles stephensi is density-dependent. PLoS Pathogens 3, e195.
Walker M, Hall A, Anderson RM & Basáñez M-G (2009). Density-dependent constraints on the weight of female Ascaris lumbricoides infections of humans and its impact on patterns of egg production. Parasites and Vectors 2, 11.
Publications in Spanish
Basáñez M-G & Rodríguez D (2004). [Transmission dynamics and mathematical models of vector-borne diseases]. Entomotropica 19, 113-134 (In Spanish).
Basáñez M-G (2005). [Epidemiology, control, and evolution of helminthic disease: River Blindness as a case study]. Acta Biologica Venezuelica 25 (1−2), 19-42 (In Spanish).
Vivas-Martínez S, Grillet M-E, Botto C & Basáñez M-G (2007). [Human onchocerciasis in the Amazonian focus]. Boletín de Malariología y Salud Ambiental 47, 15-46 (In Spanish).
