Dermatology MCQ - Viral Infections - Tanapox

A missionary returns from a humanitarian trip to the Democratic Republic of the Congo with a sudden onset of fever, headache, and profound malaise. Two days later, one or two large, deep-seated, ulcerated nodules with a central eschar develop on their exposed limbs. The patient reports seeing many mosquitoes and recalls being bitten frequently. Which of the following is the most likely causative agent?

A) Plasmodium falciparum
B) Leishmania donovani
C) Tanapox virus
D)Francisella tularensis
E) Bartonella quintana

Correct Answer: C) Tanapox virus

Explanation

This presentation is highly suggestive of tanapox, a rare zoonotic infection endemic to equatorial Africa.

Key Clinical Features of Tanapox:

• Geographic Exposure: Travel to or residence in equatorial Africa (especially regions of Kenya and the Democratic Republic of the Congo) is a key epidemiologic clue.

• Transmission: Believed to be transmitted by arthropod vectors (likely mosquitoes) or through direct contact with infected animals (primates).

• Clinical Course:

  1. Prodrome: A brief but severe febrile illness with headache, backache, and prostration.

  2. Skin Lesions: Following the prodrome, 1-10 skin lesions appear. They begin as macules, rapidly progress through papular and vesicular stages, and become large (1-2 cm), firm, ulcerated nodules with a central eschar (necrosis). They are often painful and are typically located on exposed skin (limbs, face).

• Resolution: Lesions heal slowly over 4-6 weeks, often leaving a scar.

Virologic Features:

• Causative Agent: Tanapox virus.

• Virus Family: A double-stranded DNA virus belonging to the Poxviridae family, genus Yatapoxvirus.

• Distinction from Smallpox/Monkeypox: Unlike smallpox (variola) or mpox (monkeypox), the rash is localized (not generalized) and the number of lesions is very small.

Why Not the Other Options?

• (A) Plasmodium falciparum: Causes malaria, which presents with cyclic high fevers, chills, and sweats, but not characteristic skin nodules with eschars.

• (B) Leishmania donovani: Causes visceral leishmaniasis (kala-azar), which presents with fever, hepatosplenomegaly, and pancytopenia. Cutaneous leishmaniasis causes ulcers but typically has a longer incubation period and a different geographic distribution (e.g., South America, Middle East).

• (D) Francisella tularensis: Causes tularemia, which can present with ulceroglandular disease (a skin ulcer with regional lymphadenopathy). However, the ulcer is typically smaller and the prodrome is less severe. Tularemia is not primarily associated with equatorial Africa.

• (E) Bartonella quintana: Causes trench fever (and bacillary angiomatosis in immunocompromised hosts), which is characterized by relapsing fevers and body aches, but not typically large, escharated nodules. It is associated with body lice, not mosquitoes.

Diagnosis:

• PCR or electron microscopy of lesion material can confirm the diagnosis by identifying the poxvirus.

• Viral culture is possible but requires specialized biosafety facilities.

Management:

• Supportive care is the mainstay, as the infection is self-limiting.

• Wound care to prevent secondary bacterial infection.

• There is no specific antiviral treatment, though tecovirimat may be considered in severe cases due to its activity against other poxviruses.

Prognosis: Excellent in immunocompetent individuals, with full recovery.