Immunological Profiling of Untreated and Ivermectin-Treated Onchocerca-Infected Patients in the Oti Region, Ghana

Abstract

Onchocerciasis also referred to as river blindness is a neglected tropical disease that affects the skin and eyes. It is caused by the nematode Onchocerca volvulus. Disease pathology is largely attributed to host immune responses to microfilariae. The efficacy of ivermectin (IVM) is defined by its microfilaricidal effects (clearing > 60% of microfilariae within 24 hours, ~ 100% within 7 days) and its ability to temporarily retard adult parasite embryogenesis at least within 90 days. This study sought to determine the immune profile of untreated microfilariae positive (microfilaremic) and ivermectin treated microfilariae negative (amicrofilaremic) onchocerciasis patients in order to contribute to understanding the pathophysiology (skin lesions, itching, visual impairment, etc.) of the disease. White blood cell differentials were measured for 124 adults; 53 microfilaremic (Mf) and 71 ivermectin treated (1-5 rounds) seropositive amicrofilaremic (Amf) individuals 3 months following last treatment at the Nkwanta North District of Ghana. Subgroups (16 ≤ n ≤20) of both Mf and first-time IVM-treated Amf were assayed for plasma cytokines, total IgE and urine histamine. The geometric mean microfilariae density/milligram skin snip was 22.5 (range 5.8-56.3). Basophil count was lower (p<0.0001) while eosinophil counts were higher (p=0.02) for Mf compared to Amf. Out of 14 cytokines, Interleukin (IL)-13 (p=0.002), IL-8 (p=0.03) and Interferon-gamma (p=0.003) were higher among Mf compared to first time treated Amf. Histamine and IgE were not different between the two groups. IL-13, IL-8 and interferon-gamma and eosinophils were elevated while basophils were significantly lower in microfilaremic onchocerciasis and these parameters may contribute to disease pathophysiology. These indices would be helpful in complementing diagnosis and monitoring treatment efficacy.