Risk factors associated with exposure to Crimean-Congo haemorrhagic fever virus in animal workers and cattle, and molecular detection in ticks, South Africa

Abstract

Crimean-Congo haemorrhagic fever (CCHF) is a severe tick-borne viral zoonosis endemic to parts of Africa, Europe, the Middle East and Central Asia. Human cases are reported annually in South Africa, with a 25% case fatality rate since the first case was recognized in 1981. We investigated CCHF virus (CCHFV) seroprevalence and risk factors associated with infection in cattle and humans, and the presence of CCHFV in Hyalomma spp. ticks in central South Africa in 2017-18. CCHFV IgG seroprevalence was 74.2% (95%CI: 64.2-82.1%) in 700 cattle and 3.9% (95%CI: 2.6-5.8%) in 541 farm and wildlife workers. No veterinary personnel (117) or abattoir workers (382) were seropositive. The prevalence of CCHFV RNA was significantly higher in Hyalomma truncatum (1.6%) than in H. rufipes (0.2%) (P = 0.002). Seroprevalence in cattle increased with age and was greater in animals on which ticks were found. Seroprevalence in cattle also showed significant geographic variation. Seroprevalence in humans increased with age and was greater in workers who handled livestock for injection and collection of samples. Our findings support previous evidence of widespread high CCHFV seroprevalence in cattle and show significant occupational exposure amongst farm and wildlife workers. Our seroprevalence estimate suggests that CCHFV infections are five times more frequent than the 215 confirmed CCHF cases diagnosed in South Africa in the last four decades (1981-2019). With many cases undiagnosed, the potential seriousness of CCHF in people, and the lack of an effective vaccine or treatment, there is a need to improve public health awareness, prevention and disease control.

Fig 1. Study area showing human and animal sampling sites for Crimean-Congo haemorrhagic fever virus antibodies or RNA in central South Africa, 2017–18.

The map was constructed for the manuscript in Esri ARCGIS 10.2 using country and provincial boundaries from Municipal Demarcation Board [23] and National Geo-Spatial Information [24], coordinates of sampling sites and towns collected during the survey data available under a Creative Commons Attribution (CC BY 4.0) license.

Fig 2. Sampling and testing of humans, cattle and ticks for Crimean-Congo haemorrhagic fever virus antibodies or RNA, central South Africa, 2017–18.

Fig 3. Distribution of individuals seropositive to Crimean-Congo haemorrhagic fever virus among farm workers, veterinary and wildlife personnel in central South Africa, 2017–2018.

Yellow circles indicate number of people sampled and red dots show seropositive individuals. The map was constructed for the manuscript in Esri ARCGIS 10.2 using country and provincial boundaries from Municipal Demarcation Board [23] and National Geo-Spatial Information [24], coordinates of sampling sites and towns collected during the survey data available under a Creative Commons Attribution (CC BY 4.0) license.

Fig 4. Seroprevalence of Crimean-Congo haemorrhagic fever virus antibodies amongst cattle on farms in Free State and Northern Cape provinces.

Size of circle indicates the number of cattle on the farm and colour indicates farm-level seroprevalence. The map was constructed for the manuscript in Esri ARCGIS 10.2 using country and provincial boundaries from Municipal Demarcation Board [23] and National Geo-Spatial Information [24], coordinates of sampling sites and towns collected during the survey data available under a Creative Commons Attribution (CC BY 4.0) license.

Fig 5. Crimean-Congo haemorrhagic fever virus status amongst cattle Hyalomma spp. ticks on farms in Free State and Northern Cape Provinces.

The map was constructed for the manuscript in Esri ARCGIS 10.2 using country and provincial boundaries from Municipal Demarcation Board [23] and National Geo-Spatial Information [24], coordinates of sampling sites and towns collected during the survey data available under a Creative Commons Attribution (CC BY 4.0) license.