Investigation of tick-borne viruses as pathogens of humans in South Africa and evidence of Dugbe virus infection in a patient with prolonged thrombocytopenia

In the course of investigating suspected cases of viral haemorrhagic fever in South Africa patients were encountered who had been bitten by ticks, but who lacked evidence of infection with Crimean-Congo haemorrhagic fever (CCHF) virus or non-viral tick-borne agents. Cattle sera were tested by enzyme-linked immunoassay to determine whether tick-borne viruses other than CCHF occur in the country. The prevalence of antibody in cattle sera was 905/2116 (42.8%) for CCHF virus, 70/1358 (5.2%) for Dugbe, 21/1358 (1.5%) for louping ill, 6/450 (1.3%) for West Nile, 7/1358 (0.5%) for Nairobi sheep disease, 3/625 (0.5%) for Kadam and 2/450 (0.4%) for Chenuda. No reactions were recorded with Hazara, Bahig, Bhanja, Thogoto and Dhori viruses. The CCHF findings confirmed previous observations that the virus is widely prevalent within the distribution range of ticks of the genus Hyalomma, while antibody activity to Dugbe antigen was detected only within the distribution range of the tick Amblyomma hebraeum. Cross-reactivity for the nairoviruses, Hazara, Nairobi sheer disease and Dugbe, was detected in serum samples from 3/72 human patients with confirmed CCHF infection, and serum from 1/162 other patients reacted monospecifically with Dugbe antigen. The latter patient suffered from febrile illness with prolonged thrombocytopenia.