Onchocerciasis in Three Decades: Through the Lens of Prof. Samuel Wanji

By Pamela Bongkiyung

Prof. Samuel Wanji is Head of Department for Microbiology and Parasitology at the University of Buea, Cameroon. He is also Executive Director of the Research Foundation in Tropical Diseases and Environment, Buea. He heads the COUNTDOWN programme’s partnership with the University of Buea. He has worked extensively on Onchocerciasis control and been instrumental in its control. We caught up with him while he was on a visit to the Liverpool School of Tropical Medicine.

Pamela: Hello Prof. Wanji. Thank you for taking the time to talk to us. How long have you worked on Onchocerciasis?

Prof. Wanji:  My journey with onchocerciasis started as far back as 1988. We could be talking of almost 30 years of research in onchocerciasis. Everything started with an experimental model when I was doing my postgraduate studies in Paris, France. And later on, I remained within Filariasis/Onchocerciasis for my research and university career. So actually, it has been a very faithful relationship with research and onchocerciasis throughout my life as a student and a worker both for teaching and research.

P: In the almost three decades that you have worked on various projects in relation to onchocerciasis, what changes have you observed?

PW: Yes, there have been changes. I started almost when Ivermectin was introduced as a new tool for the control of Onchocerciasis. And we witnessed the huge impact Ivermectin has made in the control of Onchocerciasis through the African Programme for Onchocerciasis Control – APOC. We were among the researchers involved in mapping the disease across Africa for the implementation of the control. We also witnessed the decline of the disease in many of foci where the endemicity was really high.

But what has been my major contribution for the control of onchocerciasis came from another filarial parasite Loa Loa. Originally, nobody knew that Loa Loa could cause a problem for the onchocerciasis control. So, when it was established that some people taking Ivermectin could develop severe adverse events and could even die, the link was established with Loa Loa and it became a priority to know those places where the endemicity of Loa Loa that is dangerous for the intake of Ivermectin was.

We participated in those early days around 2000 to develop the rapid assessment procedure for Loa Loa which was later on extended to 15 African countries, where we coordinated the mapping exercises in those countries, to generate the first map for Loa Loa in Africa. This map was operationally very useful in saying this place is very dangerous, this place is safe. And that is how we contributed heavily to the control of onchocerciasis in those areas where there was co-endemicity with Loa Loa.

Besides that, at the level of the laboratory we developed an experimental model in baboons to understand the mechanisms of encephalopathy due to Loa Loa with the treatment we have with Ivermectin. Today we know that the microfilaria are massively killed and they block the micro capillary of the brain and that is how people almost get killed. People become withdrawn and they go into coma because of such. We know that mechanism and we even have an idea of how such things could be prevented with ivermectin and aspirin. We have worked a lot through Loa Loa to see how the control of onchocerciasis could be safe in the forested areas of Africa.

P: What are the major impediments to controlling Onchocerciasis not just in Cameroon as you seem to have worked extensively across Africa, but also how does Loa Loa add to these impediments that you might have encountered in your work?

PW: As we know Onchocerciasis is a Neglected Tropical Disease. So just by that fact, it is already an impediment in controlling such disease. Less attention was paid to it. Fortunately for the past ten years there has been a lot of momentum around Neglected Tropical Diseases and Onchocerciasis has also benefitted from that.

As you can imagine that for almost 30years, the only drug that has been used for the control of Onchocerciasis has been Ivermectin. Ivermectin does not kill adult Onchocerciasis besides of the fact that it creates problems with Loa Loa in areas where the two diseases co-exist, Ivermectin kills only Microfilaria, the children of filarial of Onchocerca Volvulus (O. Volvulus).

So you need to take the drug for longer than 15years, to expect getting rid of the disease. And that is a very long time because people can easily go into fatigue. If the resources are not properly mobilised people may not have resources to sustain such long term control.

One probable consequence of such impediment has been the suspicion (and I will call it suspicion because there has been a lot of controversy around it) of sub-optimal response of the worms to Ivermectin. That means when you have a long term pressure of the same one medication on a parasite, the parasite may develop a strategy to not be sensitive to that drug anymore. And that has been a very shortcoming of onchocerciasis control to know that instead of having two or three drugs to play with, only one drug exists.

It is only of recent that there is a lot of work going on to develop microfilaria drug that will kill the adult worm. That is why in many areas we are really doubting how the elimination will be feasible. Those areas where the transmission was very high or is very high, we are almost sure that Ivermectin alone cannot do the job. We need alternative strategies. That is why you have been hearing about Doxycycline which was developed recently. Doxycycline can kill adult Onchocerca Volvulus but it needs at least 4weeks to do that job. The four weeks treatment is far better than 15years yearly treatments because with 15yrs yearly treatment you may have fatigue effect more than 4wks continuous treatment. At the level of the public health people think it is not suitable to have a regimen of 4wks, they insist on shorter regimens.

Here at the Liverpool School of Tropical Medicine, we have the AWOL consortium which is developing a shorter regimen of Anti-Wolbachia. Doxycycline is an anti-wolbachia. It is a drug that kills the bacteria that lives in a worm. Because that bacteria is starkly associated to the worm, they exchange some functions. So if you kill the bacteria, the worm also dies. It is an indirect effect. So the AWOL consortium is developing a shorter regimen of antibiotics that can do the same job like doxycycline. We hope that doxycycline will play its own role in the elimination of onchocerciasis or anti-wolbachia drugs globally. But we are expecting contributions from other drugs like Flubendazole which is in the pipeline.

Globally to answer your question, the impediment has come from the fact that we are dealing with only one tool, for the control of onchocerciasis.

To be continued…

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