Abstract
Ivermectin (IVM) is a broad spectrum endectocide whose initial indication was onchocerciasis. Although loiasis is not among its indications, IVM also exhibits antiparasitic activity against Loa loa. IVM-based preventive chemotherapies (PCs), so-called community-directed treatment with ivermectin (CDTI), have led to the interruption of transmission of onchocerciasis in some foci. A cross-sectional study was conducted in the Yabassi Health District where CDTI have been implemented since 20 years to fight onchocerciasis. All volunteers aged ≥ 5 years underwent daytime calibrated thick blood smears to search for L. loa microfilariae (mf). The prevalence of loiasis was 3.7% (95% CI: 2.2–6.2), significantly lower than its baseline prevalence (12.4%; 95% CI: 10.1–15.2; Chi-Square = 21.4; df = 1; p < 0.0001). Similarly, the microfilarial density was significantly low (mean = 1.8 mf/mL; SD = 13.6; max = 73,600) compared to baseline microfilarial density (mean = 839.3 mf/mL; SD = 6447.1; max = 130,840; Wilcoxon W = 179,904.5; p < 0.0001). This study revealed that the endemicity level of loiasis was significantly low compared to its baseline value, indicating a significant impact of IVM-based PC on this filarial disease. However, transmission is still ongoing, and heavily infected individuals are still found in communities, supporting why some individuals are still experiencing severe adverse events despite > 2 decades of CDTI in this Health District.
Highlights
IntroductionInfection with L. loa manifests itself in human populations by pruritus and two main clinical signs, the migration of adult worms under the bulbar conjunctiva, and migratory edema commonly known as Calabar swelling
Loiasis or African eye worm is a vector-borne disease caused by a parasitic nematode, Loa loa, transmitted by a tabanid belonging to the genus Chrysops that colonizes forested areas of West and Pathogens 2020, 9, 1043; doi:10.3390/pathogens9121043 www.mdpi.com/journal/pathogensCentral Africa, considered as high-risk for loiasis, where over 14 million people currently reside [1,2].Infection with L. loa manifests itself in human populations by pruritus and two main clinical signs, the migration of adult worms under the bulbar conjunctiva, and migratory edema commonly known as Calabar swelling
The prevalence of L. loa infection was 3.7% in the six communities of the Yabassi Health District, varying from 0.0% to 8.6% across communities (Table 1)
Summary
Infection with L. loa manifests itself in human populations by pruritus and two main clinical signs, the migration of adult worms under the bulbar conjunctiva, and migratory edema commonly known as Calabar swelling. Apart from these clinical signs, which are considered benign though representing only nuisance for infected individuals, several studies have reported an association of L. loa infection with renal, cardiac, ocular and neurological complications [3], and excess mortality [4], giving a broader picture to the burden of loiasis [5]. These control efforts have led to substantial reductions in the prevalence of infection, and the transmission of river blindness has been successfully interrupted by long-term mass
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