Signs and Symptoms

Monkeys infected with B virus usually have no or only mild symptoms. In humans, however, B virus infection can result in acute ascending encephalomyelitis (inflammation of the brain and spinal cord), resulting in death or severe neurologic impairment.

Disease onset in B virus–infected humans typically occurs within 1 month of exposure, although the actual incubation period can be a little as 3 to 7 days. Symptoms associated with B virus infection include

• Vesicular skin lesions (small blisters) at or near the site of exposure
• Localized neurologic symptoms (pain, numbness, itching) near the wound site
• Flu-like aches and pains
• Fever and chills
• Headaches lasting more than 24 hours
• Fatigue
• Muscular incoordination
• Shortness of breath

Initial symptoms include fever, headache, and vesicular skin lesions at the site of exposure. Neurologic symptoms vary. Respiratory involvement and death can occur 1 day to 3 weeks after symptom onset.

Disease progression depends on the location of the exposure (usually a bite or scratch) and on the number of infectious virus particles spread during exposure. Although vesicular lesions have sometimes been observed at the exposure site, they do not always occur. The first signs of disease typically are flu-like symptoms such as fever, muscle ache, fatigue, and headache. Other symptoms that have been observed include lymphadenitis (inflamed lymph nodes), lymphangities (infection of lymph vessels), nausea and vomiting, abdominal pain, and hiccups. Once the virus spreads to the central nervous system (CNS), a variety of neurologic signs develop, including hyperesthesias (increase in sensitivity to stimuli), ataxia (lack of voluntary control of muscle movements), diplopia (double vision), agitation, and ascending flaccid paralysis (extreme weakness due to reduced muscle tone). CNS involvement is a sign of serious illness. Most patients with CNS complications will die even with antiviral therapy and supportive care, and those who survive usually suffer serious long-term neurologic problems. Respiratory failure associated with ascending paralysis is the most common cause of death.

Given the number of potential exposures for animal care workers, asymptomatic or mild human B virus infection are thought to occur, but no evidence for asymptomatic B virus infection or for latent infection has been observed in humans. Antibodies produced in response to the human herpesviruses HSV-1 and HSV-2 (present in >80% of adults) are capable of neutralizing B virus in vitro but are not protective against B virus infection. Moreover, such antibodies complicate diagnostic testing for B virus due to their high level of cross-reactivity (i.e., they increase the potential for both false-positive and false-negative results).