Sero-epidemiological investigation of Crimean-Congo hemorrhagic fever virus infection in humans and livestock in West Africa

Abstract

Crimean-Congo hemorrhagic fever virus (CCHFV), the causative agent of Crimean-Congo hemorrhagic fever (CCHF), is a zoonotic, tick-borne pathogen endemic in parts of Africa, Asia, Middle East, and Europe. CCHF outbreaks pose a significant threat to public health with a high case fatality ratio of up to 40%. Treatment is primarily supportive and there is no vaccine available. Human infections are often subclinical and in severe cases can lead to hemorrhaging and death as the risk of being misdiagnosed is common. Animals are asymptomatic hosts of CCHFV and are vital in the transmission cycle involving the primary vector, Hyalomma ticks. Ruminants have been shown to play a major role in the natural transmission cycle of CCHF, suggesting these are suitable indicator animals for serological studies to assess risks of human infections. This study, therefore, aimed to investigate the seroprevalence and seroepidemiology of CCHFV in at-risk populations (humans and livestock) in endemic settings of West Africa – Nigeria and The Gambia. For studies at both locations, serum samples were tested for the presence of CCHFV antibodies against the viral nucleocapsid protein using a validated dual antigen enzyme linked immunosorbent assay kit. A convenience sampling of 486 serum samples were collected from apparently healthy and febrile participants between August 2010 and March 2018 from three major regions in Nigeria to identify risk factors and potential endemicity. To investigate the risk of zoonotic transmission of CCHF, serum samples were collected from indigenous goats (n = 544), sheep (n = 474), and cattle (n = 399) including recording georeferenced coordinates in environmental settings of close human-livestock interactions from selected villages at various locations in The Gambia. The sampled livestock in The Gambia had no relationship to the humans sampled in Nigeria. In Nigeria, results revealed an overall seroprevalence of 1.65% (8/486) in at-risk human populations. CCHF seroprevalence in The Gambia was observed at 13.6% (138/1,018) in small ruminants and 59.9% (239/399) in cattle; with the seroprevalence of sheep 18.8% (89/474) being almost twice that of goats 9.0% (49/544). Primary risk factors for CCHF infection in humans included age, gender, and febrile illness; and data suggests that manifestation of febrile symptoms among patients may be associated with CCHFV infection in endemic settings. The results support previous epidemiological studies conducted in Nigeria and Senegal that borders Gambia indicating serological evidence and possible endemicity of CCHFV infection within these countries, as CCHF has been consistently observed within these regions. Further confirmatory testing is needed to state CCHF is endemic within the area. To our knowledge, this is the first CCHFV serological study of cattle and small ruminants in The Gambia and results were compared to previous studies conducted throughout West Africa including Senegal. Seroprevalence in small ruminants and cattle are within the range detected elsewhere in endemic settings in sub-Saharan Africa. These results suggest that CCHFV has potential endemicity in The Gambia and West Africa generally.