It has been isolated from goats, sheep, cattle, hares, hedgehogs and a number of species of ticks associated with these mammals. The infected mammals develop high viraemias, which last for approximately one week, but clinical illness is rare. Humans may become infected by tick bites, by contamination with body contents from disrupted ticks, or by contact with the blood, tissues or body fluids of infected animals. Clinical disease in infected humans is common and often severe. There is a high viraemia early in the illness.
Early diagnosis is possible using antigen detection by immunolluorescence techniques.
Some laboratories use reverse transcriptase PCR methods. IgM antibodies are often detectable after the first five to seven days of fever, but their concentration diminishes significantly after about 10 days, and is replaced by rising IgG levels. The incubation period is about two to seven days, and has not been recorded as longer than 12 days. Illness begins abruptly with high fever, myalgia, headache, vomiting and pain in the epigastrium, lower back and thighs. Loose stools, dry cough and relative bradycardia may be present.