Epidemiology of loiasis and its impact on human health
Loiasis affects more than 20 million individuals residing mainly in forest and savannah regions of the following countries: Angola, Benin, Cameroon, Central African Republic, Chad, Equatorial Guinea, Gabon, Nigeria, South Sudan, Sudan, the Republic of Congo, the Democratic Republic of Congo, and Uganda. Around 42 million persons are exposed to the risk of a L. loa infection, with 20 million and 22 million living in high transmission and intermediate transmission regions, respectively (2024). The prevalence of loiasis may vary importantly within countries and may exceed 70% in adult residents of high transmission regions.
Burden of disease
Loiasis has long been considered a benign condition causing only minor discomfort. This concept has been refuted based on recent studies demonstrating the morbidity and mortality associated with loiasis.
Our team demonstrated in a large cross-sectional survey that morbidity as measured by “disability adjusted life years” is at 413 per 100,000 in high transmission regions. This morbidity measure is comparable or exceeding other infectious diseases that are listed on WHO’s list of NTDs. Mortality associated with loiasis was investigated in Cameroon and Republic of Congo indicating an up to 15% excess mortality in highly microfilaraemic individuals. These measures clearly indicate the individual and public health importance of loiasis.
Until recently, little was known about the knowledge and perception of loiasis by residents of endemic areas. A recent qualitative study in a rural community in Gabon demonstrated good overall knowledge of the disease by the community. However, L. loa’s mode of transmission by the blood-sucking Chrysops fly was known to only a minority of the population indicating an important gap in the understanding of the disease.
References:
Ramharter M, Butler J, Mombo-Ngoma G, Nordmann T, Davi SD, Zoleko Manego R. Lancet Infect Dis. 2024 Mar;24(3):e165-e178. doi: 10.1016/S1473-3099(23)00438-3.
Burden of disease in Gabon caused by loiasis: a cross-sectional survey.
Veletzky L, Hergeth J, Stelzl DR, Mischlinger J, Manego RZ, Mombo-Ngoma G, McCall MBB, Adegnika AA, Agnandji ST, Metzger WG, Matsiegui PB, Lagler H, Mordmüller B, Budke C, Ramharter M. Lancet Infect Dis. 2020 Nov;20(11):1339-1346. doi: 10.1016/S1473-3099(20)30256-5.
Excess mortality associated with loiasis: a retrospective population-based cohort study.
Chesnais CB, Takougang I, Paguélé M, Pion SD, Boussinesq M. Lancet Infect Dis. 2017 Jan;17(1):108-116. doi: 10.1016/S1473-3099(16)30405-4.
