Morbidity due to Loiasis:
Population-wide evaluation and identification of pathogenic mechanisms
This project has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement No 949963).
Loiasis, an infectious disease caused by the parasitic worm Loa loa, affects more than 20 million individuals in central Africa, and more than 100 million people are potentially exposed to infection. Since its first description in 1770, the international scientific community has considered this filarial disease as benign. As a result, loiasis is not considered a Neglected Tropical Disease (NTD), according to the list edited by the WHO; with the impact of the absence of programs to fight this disease.
The main clinical features associated with loiasis are chronic hypereosinophilia, joint pain, temporary joint edema (named “Calabar’s swelling”), pruritus, and occasional passage of the worm under the skin as well as under the conjunctiva of the eye (also known as "eye worm" disease). However, loiasis is known to be one of the main reasons for consultations in endemic areas. And recently, we demonstrated that loiasis significantly reduces the life expectancy of infected people, which should lead to further studies to understand this result.
While some more severe complications are suspected, no studies to date have demonstrated the reality of loiasis-related complications. Serious clinical conditions result of several interacting mechanisms. The main hypothesis is that loiasis induces a chronic pathology possibly related to the very stable microfilarial levels. Most clinical sequelae may be indirect and unspecific, and this might explain why direct links have not been demonstrated so far.
Last, more generally, representative data on the prevailing morbidity in rural communities of Central Africa is dramatically lacking. This is particularly true for loiasis, but also for cardiac and kidney diseases in general. Thus, beyond its main objectives focusing on loiasis, the present project will contribute to the collection of invaluable information on the prevalence of complications of various infectious and non-infectious diseases.
The MorLo project aims at generating for the first time accurate estimates of cardiovascular and renal morbidity in Central Africa, at assessing the real frequency of severe complications of loiasis.
The results of this project might lead (i) to a radical shift in the current dogma that loiasis is a benign disease, and (ii) to the development of specific community-wide and individual-based strategies to combat loiasis and reduce its direct and indirect effects. Indeed, should loiasis induce a functional asplenia, large-scale control of loiasis would advert high numbers of malaria and Streptococcus pneumoniae infections. Strategies will have to be developed to identify on a large scale highly infected individuals who are probably the most at risk of complication, and to treat them safely. These strategies would have to be articulated with, and integrated to the current onchocerciasis elimination programmes which are ongoing for many years.
To goal our objectives, we will conduct the first population-wide evaluation of morbidity in rural areas of Cameroon by performing systematic examinations on ~4,500 selected individuals. This sample size will enable accurate estimation of prevalences of cardiovascular and renal diseases, among other things. Standardized questionnaires, clinical examinations, biological and ultrasounds examinations (cardiac, renal, and splenic) will be performed. In addition, pilot biological studies will be conducted on haemostatic system and inflammatory biological markers. Last, we will perform for the first time a prospective cohort in the general population living in the Lekoumou Department in the Republic of the Congo.
This ERC-Starting Grant project is a collaborative research project including the French Institut de Recherche pour le Développement, TransVIHMI, the Centre for Research on Filariasis and other Tropical Diseases (CRFilMT) – based in Yaoundé, Cameroon, the Haematological Department of the University Hospital of Yaoundé, and the Programme National de Lutte contre l’Onchocercose (PNLO) – based in Brazzaville, Republic of the Congo.