O'nyong'nyong Virus

O’nyong’nyong virus (ONNV) is a single stranded, positive sense RNA virus that belongs to the genus Alphavirus, a member of the Togaviridae family of viruses. It is closely related to members of the Semliki Forest antigenic sero-complex, a serological group within the Alphavirus genus, including Chikungunya virus (CHIKV), Mayaro virus and Ross River virus. Initially, O’nyong’nyong virus was thought to be a strain of CHIKV but phylogenetic studies have shown that the two viruses are distinct (Powers, AM). Two major clades of ONNV have been identified (Rezza, G).

ONNV is a mosquito-borne virus that is transmitted, to humans, by infected anopheline mosquitoes Anopheles funestus and Anopheles gambiae. The disappearance of the virus between epidemics suggests that the virus is maintained in an enzootic cycle, but no vertebrate reservoir has been reliably identified. Serological studies suggest that domestic livestock and some rodent species may be likely candidates.

Unlike the closely related CHIKV, ONNV is restricted to the African continent. Since the virus was first isolated in Uganda in 1959, two major epidemics of the virus have occurred. The first epidemic occurred in Eastern and Western Africa between 1959 – 1962, affecting over two million people, and the second between 1996 – 1997. Sporadic cases have since been reported in travellers returning from African countries, raising concerns that ONNV may represent an emerging virus with the potential to spread to areas outside the African continent (CDC) .

In humans, the virus causes O’nyong’nyong fever which is a self-limiting disease characterised by clinical symptoms of low grade fever, severe join pain, headache, maculopapular rash, lymphadenopathy and conjunctivitis. The incubation period for ONNV infection is approximately 8 weeks. Symptoms may last from 1 week to several months, which has an economic impact in regions affected due to loss of working days.

Currently, there is no antiviral therapy for the treatment of symptomatic cases of ONNV, and no licensed prophylactic vaccine to prevent ONNV infection. Diagnosis of ONNV in humans is achieved using clinical criteria and serological methods to measure O’nyong’nyong specific IgM levels of infected patients.

References
Powers AM, Brault AC, Tesh RB, Weaver SC.2000. Re-emergence of Chikungunya and O’nyong-nyong virus: evidence for distinct geographical lineages and distant evolutionary relationships. J Gen Virol. 2000 Feb;81(Pt 2):471-9.

Rezza G, Chen R, Weaver SC.2017. O’nyong-nyong fever: a neglected mosquito-borne viral disease. Pathog Glob Health. Sep;111(6):271-275.

Centers for Disease Control and Prevention. Letters: O’nyong-nyong Virus Infection Imported to Europe from Kenya by a Traveler. Volume 20, Number 10—October 2014

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