Rare human tanapox case in Johannesburg, South Africa

Acknowledgement
This report is published on behalf of the GeoSentinel Office of the Principal Investigator. GeoSentinel is a cooperative agreement U01CK000632-01-00 between the US Centers for Disease Control and Prevention (US CDC) and the International Society of Travel Medicine (ISTM).

Authors
Prof. Lucille Blumberg, MB BCH MMed (Micro) ID (SA) FFTM (RCPS,Glasgow) DTM&H DOH DCH. National Institute for Communicable Diseases, Johannesburg, South Africa

Dr. Evan Shoul, MBChB(UCT) FCP(SA) DTM&H Cert Infectious Dis(SA), Infectious Disease Specialist, Johannesburg, South Africa

Dr. Albie De Frey, Travel Doctor Corporate, Johannesburg, South Africa

Dr. Jacqueline Weyer, Centre for Emerging Zoonotic and Parasitic Diseases, National Institute for Communicable Diseases, National Health Laboratory Service, Johannesburg South Africa

Dr. Monica Birkhead, Centre for Emerging Zoonotic and Parasitic Diseases, National Institute for Communicable Diseases, National Health Laboratory Service, Johannesburg, South Africa

Key findings

• A worker based in a protected area on Lake Tanganyika in northern Zambia was diagnosed with tanapox at a hospital in Johannesburg, South Africa, after developing two skin lesions that progressed from small papules to painful pox-like lesions, accompanied by a brief acute febrile illness. The patient had a history of numerous mosquito bites.
• Tanapox diagnosis was confirmed through comprehensive laboratory testing, including polymerase chain reaction (PCR), sequencing, histology, and electron microscopy of skin samples, following unsuccessful treatment with extended courses of oral and intravenous antibiotics.
• The patient made an uneventful recovery after antibiotics were discontinued and supportive care was provided.
• A second probable case of tanapox was identified in a worker in the same region, suggesting localized transmission.
• The attending infectious diseases physician in Johannesburg consulted a colleague, the co-director of the Johannesburg GeoSentinel site, who had previously managed cases of tanapox, facilitating accurate diagnosis of this rare zoonotic disease.

Epidemiological analysis and public health impact

• The detection of two human tanapox cases in close geographic proximity is unusual for this rare zoonotic disease, particularly given the lack of documented human cases in Zambia in recent years. The presumed vector-borne transmission via mosquitoes, combined with the patients’ exposure in wildlife habitats near Lake Tanganyika, highlights the intersection of environmental conditions, vector presence, and human-wildlife interface as key drivers of infection risk.
• This case highlights the substantial diagnostic challenges posed by this rare disease, which requires specialized laboratory testing and is diagnosed after consultation with an experienced clinician.

Comparative analysis and future outlook

• Since 1957, human tanapox has been reported only sporadically in equatorial and tropical African regions. The first case in South Africa was detected in 2022 in a traveler to the Kruger National Park, followed by 11 additional cases identified in 2024 among individuals in a subtropical area of the park.
• The current detection of two cases (one confirmed, one probable) in Zambia cannot be compared with historical baselines because there are no publicly available reports of prior human tanapox cases or outbreaks in the country. These infections may therefore represent the first documented cases in Zambia, or they may instead indicate historical underreporting related to limited clinical suspicion and diagnostic capacity for this rare zoonotic disease.

Pathogen characteristics and clinical management
Tanapox is a rare zoonotic poxvirus infection, endemic to equatorial Africa. Natural tanapox virus (TANV) circulation occurs among wild non-human primates, and culicine mosquitoes are thought to act as vectors by mechanically transferring the virus from infected non-human primates to humans via contaminated mouthparts. Human infection typically causes a self‑limited febrile illness with one to three painful, nodular or ulcerative skin lesions at exposed sites, which evolve over several weeks and usually heal without specific therapy. There is no vaccine or specific antiviral treatment, and prevention focuses on mosquito avoidance measures. Diagnosis relies on clinical suspicion plus specialized laboratory testing (PCR and, in some cases, histology or electron microscopy). Much of the disease’s natural ecology and epidemiology remains poorly understood.

References

1. South Africa National Institute for Communicable Diseases (NICD). Tanapox
2. Birkhead M, et al. Tanapox, South Africa, 2022. Emerg Infect Dis. 2023;29(6):1206-1209
3. Obermeier PE, Buder SC, Hillen U. Poxvirus infections in dermatology – the neglected, the notable, and the notorious. J Dtsch Dermatol Ges. 2024 Jan;22(1):56-93