A filarial worm infection called Loiasis that affects over 10 million people in Africa and has been assumed to be a relatively harmless disease could possibly contribute to increased risk of death, according to a study recently published in Lancet Infectious Diseases.
Transmitted by horseflies breeding in the forest areas of West and Central Africa, Loiasis is known as ‘African Eye Worm’, and gets its name from its most infamous tell-tale sign: the visible passing of the Loa loa worm through the eye. Yet, to date, the disease has received little attention by public health officials. It is only considered as a barrier to other disease control efforts because individuals with a large amount of Loa loa larvae (microfilariae) in the blood are at risk of life-threatening complications if they receive ivermectin, a drug for onchocerciasis (river blindness) and lymphatic filariasis (elephantiasis).
Researchers from the Institut de Recherche pour le Développement (IRD) in Montpellier, France, the University of Yaoundé and the Ministry of Health in Cameroon have shown that this assumption is fatally wrong. Their study, funded by the Drugs for Neglected Diseases initiative (DNDi), is the first ever to assess if infection with Loa loa leads to excess mortality.
Researchers followed up on an initial 2001 study of over 3600 people living in a Loa loa endemic region in Eastern Cameroon. The individuals were re-surveyed for survival in 2016 and researchers found those who in 2001 had high levels of Loa loa (more than 30,000 per mL of blood) died significantly earlier than those without infection. For every 1% increase in the proportion of subjects harbouring such high densities of microfilariae in a community, the mortality rate increased by 4%.
Overall, 14.5% of the mortality in the group could be attributed to Loa loa.
“Our findings strongly suggest that Loa loa reduces the life expectancy of those infected, due to a direct or indirect effect of the infection,” said Dr Cédric B Chesnais, the lead author of the study. “With more than 40% of the population harbouring Loa loa blood-borne microfilariae in some villages, this study is a clear call for more attention to the disease.”
Yet at this point, there are no safe treatments for patients presenting very high Loa loa densities in the blood. And because of the threat of potentially fatal side effects, known as Loa loa encephalopathy, some river blindness endemic areas with Loa loa coinfection do not achieve the needed coverage from regular “mass drug administration” with ivermectin. In some areas, ivermectin cannot be distributed at all meaning that people who live in those areas remain at risk of river blindness.
“This study highlights the ongoing neglect that patients at risk of filarial diseases face and shows that Loa loa is too serious to be ignored anymore,” said Rob Don, Head of the Filarial Programme at DNDi.
The authors of the study encourage further clinical studies to assess the long-term morbidity associated with the infection. They also call for the inclusion of Loa loa in the WHO’s list of neglected tropical diseases in order to encourage research and development (R&D) into safe and effective treatments for the disease.
The study will be presented on November 14th at the American Society of Tropical Medicine and Hygiene (ASTMH) 65th Annual Meeting in Atlanta.
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