River Blindness transmission with ivermectin treatment: How long is mass drug administration needed?

The main focus of Dr Lamberton’s research is utilising field epidemiological data, laboratory experiments and population genetics to understand population structure, transmission dynamics and effects of long term mass drug administration (MDA) programmes on neglected tropical diseases (NTDs) such as river blindness.

Onchocerciasis, commonly known as river blindnessis, is a parasitic disease that is transmitted by the bite of an infected blackfly (genus Simulium), which breed in fast flowing rivers and streams. The disease may result in skin or eye lesions, which can have a severely disabling effect. The socioeconomic consequences of river blindness are profound and extend beyond the individual, affecting families, communities, and countries as a whole. It is estimated that 26 million people are infected with river blindness and 99% of cases are found in Africa. While the initial infection can be treated, the blindness, once occurred, is irreversible.

Dr Lamberton’s research activities currently involve extensive epidemiological field data and sample collection from five regions of Ghana. She applies morphological and novel molecular techniques for the identification of the vector species, parasite infection and previous host bloodmeal species.

In this presentation Dr Lamberton briefly reviewed the history of river blindness control programmes over the past 35 years, including the introduction of the Mectizan Donation Programme (MDP), established by Merck in 1987 to provide the drug Mectizan (Ivermectin) free of charge to help eliminate river blindness as a public health problem. The MDP has now donated over 1 billion treatments across 28 countries. The formation of the Onchocerciasis Control Programme (OCP) coordinated drug treatment activity and the use of synthetic larvicides  in rivers, resulted in the decision, by 2002, to claim that river blindness had been eliminated as a public health problem in many countries. However, some countries were outside the area of the OCP and still required further assistance. A second initiative, the African Programme for Onchocerciasis Control, would take a more community-based approach and lead to a slowing spread of the disease.

Distributing Ivermectin on a mass scale in areas of high infection has proven a successful method of treatment. However, the drug must be taken annually for many years until the worms inside peoples bodies have died naturally. There are also potential signs of resistance to Ivermectin within the parasite in a few limited areas.

Dr Lamberton’s research, in conjunction with Prof. Maria-Gloria Basáñez (Imperial College London), has involved the monitoring and collection of blackfly populations, using human and cattle bait, and host independent traps, to catch thousands of blackflies. The flies were dissected for parity and Onchocerca prevalence and intensity and the abdomens were sent for molecular bloodmeal analysis, vector species identification and Onchocera microfilariae prevalence databy Eurofins in Germany.

Molecular and morphological tests indicate that there is active onchocerciasis transmission in all of her seven study villages.  Infective flies (with L3 larvae in the head and/or thoraces) were found in three of these villages, with >72% of these identified as O. volvulus by molecular tests.  Bloodmeal analysis has shown that blackflies feed on a range of different hosts, and indicated animals such as cattle, pigs, sheep and goats as important bloodmeal sources, in addition to humans.  Ivermectin, used in community-directed MDA programmes, has helped to eliminate river blindness as a public health problem in some countries, although there is still much more to be done in, particularly in West African countries.

In Asubende, a village in Ghana, for example active transmission of O. volvulus is still very much on-going, despite predictions  that river blindness should have been eliminated by now. At least two people out of a population of only 88 living in Asubende are known to be blind from this disease. The people living in these villages have told Dr Lamberton that they would encourage participation in drug trials to treat river blindness as well as further methods of controlling blackfly populations.

Her experiences at a community-level have shown Dr Lamberton that despite ambitious targets of elimination by 2020, river blindness is still a significant disease in rural communities in countries such as Ghana and continued efforts are necessary to control transmission and treat this disease.

The presentation was well attended by LSTM staff and students, with Professor Moses Bockarie, Director of LSTM’s Centre for Neglected Tropical Diseases, thanking Dr Lamberton for a very interesting presentation.