Al-Khurma Haemorrhagic Fever

Abstract

Al-Khurma haemorrhagic fever (AHF) is an emerging infectious disease described initially in Saudi Arabia and considered among major health risks to the pilgrims during Hajj and Umrah. The first case was diagnosed in a butcher who became sick after he slaughtered a sheep originated from al-Khurma, a small settlement near Taif. The causative agent, al-Khurma haemorrhagic fever virus (AHFV), is a variant of Kyasanur Forest disease virus, a member of the mammalian tick-borne virus subgroup of the genus Flavivirus, family Flaviviridae. It has been isolated from adult soft and hard ticks collected in both western and southern Saudi Arabia. Clinical cases have been linked to handling sheep, goats and camels and to drinking raw camel milk. Seroprevalence in Saudi Arabia seems as 1%. Confirmation of AHFV infection in tourists visiting southeastern Egypt near the Sudanese border extended its geographical spread. Incubation period is 2-4 days after tick exposure. Most patients present with a nonspecific clinical picture difficult to distinguish from other similar febrile illnesses. Haemorrhagic manifestations together with gastrointestinal, hepatic and neurologic involvement are clinical hallmarks in severe forms in common with other viral haemorrhagic fevers. Major laboratory abnormalities in hospitalized patients are thrombocytopenia, leukopenia, elevated levels of liver enzymes, creatine kinase and lactate dehydrogenase. Rapid laboratory confirmation depends principally on real-time RT-PCR to detect viral RNA in the plasma and serum during viremic phase of illness. Virus isolation in cell culture or suckling mice is not routinely performed since AHFV is classified as biosafety level 3 or 4 agent. Caution is required in interpretation of serological tests because of antigenic cross-reactivity between related viruses. An overall case fatality rate appears to be 1-2% according to recent observations in contrast to much higher initial data. Although no person-to-person transmission are reported, standard precautions should be taken by healthcare workers involved in the management of AHF cases. People processing meat from freshly slaughtered animals are advised to wear gloves. There is no immunoprophylactic measure and no specific treatment for AHF at present.