O’nyong-nyong Virus Infection: Virology, Transmission Dynamics, Pathogenesis, and Public Health Implications

O’nyong-nyong virus (ONNV) is a mosquito-borne alphavirus of the Togaviridae family, known for causing febrile illness and severe polyarthralgia in humans. The virus has drawn scientific and public health attention due to its potential for widespread outbreaks in sub-Saharan Africa. ONNV is an enveloped, spherical virus measuring about 65–70 nm in diameter. Its genome is a single-stranded, positive-sense RNA of approximately 11.8 kilobases, encoding two major open reading frames (ORFs) responsible for structural (Capsid, E1, E2, E3, and 6K) and non-structural (nsP1–nsP4) polyproteins, which play vital roles in replication and assembly. Transmission occurs primarily through the bites of Anopheles funestus and Anopheles gambiae mosquitoes, with an incubation period of 7–10 days. Infection begins when ONNV enters host cells via receptor-mediated endocytosis, followed by uncoating and replication of viral RNA. Newly formed virions are released through budding, leading to systemic dissemination. The virus initially infects skin-resident immune cells before spreading to joints and muscles, inducing inflammatory responses responsible for fever, joint pain, and lymphadenopathy—its hallmark symptoms. ONNV infections are largely confined to East and Central Africa, notably in Uganda, Kenya, and Tanzania, particularly in rural communities where vector density is high. All age groups are susceptible, though adults experience more pronounced arthralgia, and those with outdoor occupations are at increased risk. Diagnosis involves viral isolation, serological assays, molecular detection, and immunofluorescence tests. Currently, no specific antiviral therapy or vaccine exists for ONNV. Prevention relies on mosquito control measures, personal protection, and surveillance in endemic regions to mitigate transmission and disease burden.