Dermatology MCQ - Viral Infections - Herpes B virus infection

A primatologist presents to the emergency department with a 2-day history of fever, headache, and vesicular lesions at the site of a bite on her hand received from a macaque monkey 5 days ago. She now reports ascending numbness and tingling in the affected arm. Which of the following is the most appropriate immediate management and the causative agent of this infection?

A) Administer valacyclovir; causative agent is Macacine alphaherpesvirus 1 (Herpes B virus)
B) Administer penicillin G; causative agent is Pasteurella multocida
C) Administer ribavirin; causative agent is monkeypox virus
D) Administer acyclovir; causative agent is herpes simplex virus type 1
E) Administer doxycycline; causative agent is Bartonella henselae

Correct Answer: A) Administer valacyclovir; causative agent is Macacine alphaherpesvirus 1 (Herpes B virus)

Explanation

This scenario describes a potential Herpes B virus infection, a rare but often fatal zoonotic disease.

Key Clinical Features of Herpes B Virus Infection:

• Exposure: Bite, scratch, or mucosal exposure to macaque monkeys (e.g., rhesus, cynomolgus). The virus is endemic in these species.

• Incubation Period: Typically 3 days to 3 weeks.

• Initial Symptoms: Fever, headache, and vesicular lesions at the exposure site.

• Neurologic Symptoms: Ascending numbness, tingling, or paralysis indicates neurologic spread, which can progress rapidly to encephalomyelitis with high mortality (~70% without treatment).

Virologic Features:

• Causative Agent: Macacine alphaherpesvirus 1 (formerly Cercopithecine herpesvirus 1), also known as Herpes B virus.

• Pathogenesis: The virus is latent in macaques (similar to HSV-1 in humans). In humans, it causes severe neurologic disease due to neurotropism.

Immediate Management:

• Post-exposure prophylaxis: Valacyclovir or acyclovir should be started immediately after exposure, even before symptoms appear, to reduce viral replication and neurologic complications.

• Symptomatic disease: Intravenous acyclovir or ganciclovir is required for established infection, especially with neurologic symptoms.

• Wound care: Thorough irrigation and cleaning of the wound.

Why Not the Other Options?

• (B) Penicillin G for Pasteurella multocida: Pasteurella is a common cause of infected animal bites (e.g., cats/dogs) but does not cause vesicular lesions or neurologic symptoms.

• (C) Ribavirin for monkeypox: Monkeypox causes a generalized vesiculopustular rash, not ascending paralysis. Ribavirin is not first-line for orthopoxviruses (tecovirimat is).

• (D) Acyclovir for HSV-1: HSV-1 can cause herpetic whitlow but is not acquired from monkey bites and does not cause ascending paralysis as rapidly.

• (E) Doxycycline for Bartonella henselae: Causes cat-scratch disease with regional lymphadenopathy, not vesicular lesions or neurologic symptoms.

Diagnosis:

• PCR of vesicular fluid, blood, or CSF for Herpes B virus DNA.

• Viral culture (requires BSL-4 facilities due to high lethality).

Prognosis:

• High mortality if untreated; early antiviral therapy reduces risk.

• Survivors may have residual neurologic deficits.

Prevention:

• Use of personal protective equipment (PPE) when handling macaques.

• Immediate wound cleaning and post-exposure antiviral prophylaxis.