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Contrary to what was previously thought, Loiasis is not a harmless tropical disease. The worm infection impairs the quality of life and performance of those affected more than previously assumed. A team at the Bernhard Nocht Institute for Tropical Medicine (BNITM) in cooperation with the Centre de Recherches Médicales de Lambaréné (CERMEL) has investigated this and has now published the results in the journal The Lancet Infectious Diseases.
Loiasis is a worm disease that occurs exclusively in central and parts of West Africa. It is transmitted by bloodsucking insects of the genus Chrysops. The adult worms migrate under the skin and in the tissue and can occasionally pass through the eye. They produce microscopically small so-called microfilariae that can be detected in the blood. Loiasis not only causes typical symptoms such as tissue swelling (so-called calabar swelling) and the eponymous phenomena when passing through the eye. It can also lead to late effects, such as damage to the central nervous system and to the heart and kidneys. For the first time in 2016, a study showed an increased mortality in loiasis patients. In addition, general non-specific symptoms such as fatigue, joint pain and headaches are associated with the disease. These symptoms significantly affect people in the affected areas.
The Clinical Research team led by Prof. Michael Ramharter has for the first time ever investigated the exact extent of the disease burden. The researchers carried out studies in Gabon, one of the countries in which the worm disease is most common. In order to be able to measure the impairment of the people, the researchers collected the so-called "DALYs" (=disability adjusted life years) for Loiasis in a field study. DALYs are a unit that scientists use in health research. They make it possible to quantify and compare the burden of disease from different causes in a population. The DALYs are used, among other things, in "Global Burden of Disease Studies".
Ramharter's group carried out the cross-sectional study in 2017 and 2018, in collaboration with the Gabonese research institutions Centre de Recherches Médicales de Lambaréné and the Centre de Recherches Médicales de la Ngounié. They investigated the effects of the Loiasis on the population and calculated the corresponding DALYs. 1,232 people took part in the surveys and medical examinations. The result: Loiasis is significantly associated with a variety of symptoms, including temporary painful oedema, joint pain, headache, but also sensory disturbances and temporary paralysis of arms and legs. 42 per cent of all participants reported having noticed at least once a migration of the worm through the eye, 94 per cent associated with pain and 79 per cent with concurrent visual disturbances.
Luzia Veletzky, researcher and physician in the Clinical Research Department of the BNITM, coordinated the study: "The symptoms of loiasis cannot be trivialized. They severely restrict the quality of life and work of those affected. The worm disease is associated with a significant disease burden, comparable to other neglected tropical parasitic diseases such as schistosomiasis".
So far, the World Health Organization has not listed Loiasis as a neglected tropical disease. Research funds for this disease are scarce, and today we do not even understand the exact disease mechanisms of the infection and how organ damage occurs. The study is an important step in raising awareness of this disease and raising interest in research and development of better therapeutic options for loiasis, said Veletzky.
Luzia Veletzky et al., Burden of disease in Gabon caused by loiasis: a cross-sectional survey. The Lancet Infectious Deseases (June 22, 2020). doi.org/10.1016/S1473-3099(20)30256-5