Tanapox is a zoonotic poxvirus infection. It begins with 2 to 4 days of fever, headache and tiredness, followed by the appearance of a small dark mark at the site of an itch. It may initially have a slight raised central part before developing into a small bump with a dip. Most affected people have one bump, but there may be as many as 10, typically on the legs. It subsequently becomes a larger bump with surrounding redness and swollen near-by glands, and tends to become firm and ulcerate, growing to as wide as 2cm over 2-weeks before resolving usually within 6-weeks.
Tanapox is caused by Yatapoxvirus. Its natural reservoir is not known for certain, but likely simian. It is also unclear as to how it is transmitted to humans, but possibly involves an intermediate insect.
One infection of tanapox appears to protect a person from further infections of tanopox.
It occurs chiefly in Kenya and the Democratic Republic of Congo.
Signs and symptoms
It begins with a fever. The incubation period in human cases remains unknown, but in a person who underwent voluntary inoculation, erythema and central thickening appear by the fourth day. Most people present a mild pre-eruptive fever that lasts 3–4 days, severe headaches and backaches, and often itching at the site where the skin lesion develops.
There is initially a small nodule, without any central abrasion. This small nodule soon becomes papular and gradually enlarges to reach a maximum diameter of about 15 mm by the end of the second week of infection. The draining lymph nodes are also enlarged and tender from about the fifth day following the appearance of the skin lesion. The lesion remains mostly nodular but, ulcerates during the third week and then gradually heals within five to six weeks, leaving a scar.
In Kenya, the lesions were almost always solitary and were found on the upper arm, face, neck, and truck. Conversely, in Zaire, 22% of patients had multiple lesions, usually two or three. The maximum number of lesions seen in one patient was ten. In the case of Zairian patients, the lesions were mostly found on the lower limbs, with a couple of patients reporting lesions on the upper limbs, trunk, and head.
Tanapox virus in humans produces increased thickening of the epidermis with extensive degeneration of the prickle cell layer. The cytoplasm of the swollen epidermal cells is filled with large, pleomorphic, eosinophilic B-type inclusion bodies. Nuclei of infected cells are also swollen, with chromatin being concentrated at the nuclear periphery.
Human tanapox has been mostly documented in Kenya and Zaire, but it is believed to occur much more widely throughout tropical Africa. All age groups and both sexes appear to be affected by this virus. During the Kenyan epidemics of 1957 and 1962, cases of tanapox were reported more frequently among persons who worked or played close to the river. As a result of this, researchers concluded that tanapox is most likely a zoonosis. However, neither the reservoir host nor the mode of transmission from wild animal to human is known. It is hypothesized that tanapox virus may be transferred from monkeys or another reservoir host to humans by infected arthropods that act as mechanical vectors. Only one case of human to human transmission has been reported.
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- Definition of Tanapox Archived 2022-05-13 at the Wayback Machine from MedicineNet.com Archived 2021-09-21 at the Wayback Machine