A more harmful illness than originally believed


Loiasis, the parasitic infection predominantly found in central Africa, is not as benign as first thought. Highly infected people may in fact have reduced life expectancy. This is the finding of a new study, conducted by IRD and its partners in Cameroon with support from the Drugs for Neglected Diseases initiative (DNDi), covering more than 3,000 people. Monitoring, over a period of 15 years, of these people showed that the mortality rate was higher in infected individuals than in the rest of the population and that it increased with the concentration of parasites in the blood.

According to those behind the research, published in The Lancet Infectious Diseases, the disease should be considered for inclusion in the WHO's list of « neglected tropical diseases » to pave the way for control programmes.

A little-known disease

Considered to be a benign condition, loiasis – from the name of the small filarial worm that causes it, the Loa loa – received limited attention up to now. This infection, endemic in the forested areas of central Africa, was mainly feared and studied due to the acute neurological reactions that it can sometimes induce during treatment for another more common filarial infection: onchocerciasis (also known as "river blindness"). A new study conducted by IRD and its partners in Cameroon reveals that high levels of infection with Loa loa may itself have serious consequences. This research, published in The Lancet Infectious Diseases, shows that loiasis is associated with excess mortality. This retrospective cohort study, based on monitoring a population over a period of 15 years, was carried out with the support of the Drugs for Neglected Diseases initiative (DNDi).

More than one in ten deaths due to Loa loa

The research team first of all measured the infection rate in thirty or so villages in Cameroon in 2001, before then conducting a second survey in 2016 in order to count the number of deaths that had occurred in the meantime. At community level, the study revealed a directly proportionate relationship between the mortality rate and the prevalence of loiasis. More than one in ten deaths was therefore found to be related to the infection.

At individual level, mortality was higher among infected people: 25.5% compared with 19% in the rest of the population. It also increased in line with the concentration of parasite larvae in the blood. However, excess mortality was not related to the previous appearance of Calabar swellings or eyeworm, in other words, manifestations caused by adult parasites.

Will loiasis now be acknowledged as a neglected tropical disease?

Loiasis, which until now has not had any control programme, would appear therefore not to be as benign as previously thought. A high level of Loa loa infection appears in fact to have a significant effect on life expectancy.

These findings are likely to have major impact on how the disease is perceived by the international community and should lead to it becoming considered by the WHO as a neglected tropical disease.

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