Mr Simon J O'Hanlon

PhD Student

I am studying for my PhD under the supervision of Dr Maria-Gloria Basáñez (Reader in Parasite Epidemiology) within the Helminth Ecology Research Group in the Department of Infectious Disease Epidemiology. We are examining the transmission dynamics and feasibility of elimination of onchocerciasis using current tools. My project is paying particular attention to Ghana, West Africa, as a public health control program against onchocerciasis has been in operation since 1974, yet ongoing transmission is still a cause of morbidity in rural populations there. In fact the Ghanaian Health Service (GHS) estimates that there are  3.4 million persons at risk living in 3,204 communities in 9 out of a total of 10 regions in Ghana. Despite over 30 years of disease control efforts, onchocerciasis persists as a problem of public health importance.

 

The Helminth Ecology Research Group at Imperial has strong ties with research partners based in Ghana, through on-going collaborations and joint grants. We are actively involved in research in conjunction with groups and persons from the Ghanaian Ministry of Health, the Council for Scientific and Industrial Research, and the University of Ghana. In addition to gathering quantitative data, this project will also integrate empirical qualitative data and sociological factors into a better understanding of river blindness transmission and control.

 

My PhD research is supported through a stipend from the Economic and Social Research Council, and through funding in grants awarded to Dr Basáñez from the Wellcome Trust, a Royal Society-Leverhulme Africa Award, with some additional funding/travel for a specific sub-component provided by the Sabin Vaccine Institute and Institute for Health Metrics and Evaluation.

Objectives of my PhD:

1) Re-estimate the global burden of disease due to onchocerciasis in 1990 and 2005 with particular reference to the area previously covered by the Onchocerciasis Control Program (OCP) in West Africa (which includes Ghana).

2) To map spatio-temporal variation of infection prevalence in Ghanaian villages and vector species distribution in order to ascertain areas of persisting endemicity and simuliid species responsible for ongoing transmission.

3) Investigate coverage of and compliance to ivermectin in a selection of villages identified in (2) by means of cluster surveys and interviews with community distributors. Parasitological surveys may be conducted to identify mf-positive persons, recording geospatial data. Data on connectivity between villages (by human movement) may also be recorded by interview

4) In a selection of villages and for a range of simuliid species, conduct fly-feeding experiments (or help analyse data already available) to characterise microfilarial uptake curves which will be used to develop and parameterise mathematical models of disease transmission and control based on the data collected in (1)-(4) above

5) Calibrate onchocerciasis mathematical models with coverage- and vector-specific parameters from (3) and (4) to explore ongoing transmission in Ghana. Time permitting, stochastic versions of these models may need to be developed to assess the possibility of onchocerciasis elimination

6) Conduct economic analysis of annual vs. biannual ivermectin distribution in terms of morbidity reduction, onchocerciasis control, and the possibility of parasite elimination 

 

 Helminth Ecology Research Group

Research in Dr. Basáñez's 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). 

 

The Epidemiological Significance of Onchocerciasis

Human onchocerciasis (River Blindness) is a neglected tropical disease (NTD) of the eyes and skin, caused by the filarial nematode Onchocerca volvulus (Filarioidea: Onchocercidae). It is transmitted by the bites of blackflies of the Simulium genus (Diptera: Simuliidae), which breed in fast flowing streams and rivers, hence the term ‘river blindness’. It is endemic in large tropical regions across Africa; from Senegal in the West, to Ethiopia in the East. Of the total number of persons at risk of onchocerciasis, 95% live in Africa. The disease is also endemic in Latin America in small, circumscribed foci, the largest of which is found in the Amazonas region bordering Venezuela and Brazil. It is also endemic in the Yemen where a rare hyper-reactive clinical manifestation of the disease called ‘Sowda’ is found. With at least 37 million people infected and a further 120 million people at risk, it is the second largest cause of infectious blindness in humans (after trachoma), thought to be responsible for at least 270,000 cases of blindness with another 500,000 people suffering from severe visual impairment. The other main pathologies caused by onchocerciasis are disfiguring skin lesions and severe dermal itching that can drastically impair individuals’ quality of life and lead to stigmatisation and social isolation. Blindness and severe skin pathology strongly limit both individual, and population-wide socio-economic development, and are estimated to be responsible for the annual loss of one million disability-adjusted life years. Prior to the implementation of the Onchocerciasis Control Programme in West Africa (OCP) in 1974 by the World Health Organization (WHO), entire villages and fertile valleys were left deserted due to onchocercal disease.