Laboratory Testing and Diagnosis

Specimen Collection

Obtain specimens for virus culture and serologic testing from the exposed person and, when feasible, from the associated monkey.

From exposed person: Collection of acute (as soon as feasible after exposure, and after the appropriate cleansing protocol has been completed) and convalescent (3 weeks post-exposure) serum is advisable, and should be submitted for serologic testing. Samples for Polymerase chain reaction (PCR) testing should not be obtained at the time of exposure, as the act of collection could push infectious virus more deeply into the wound. Samples for PCR should be collected only if symptoms consistent with B virus disease appear, for example, appearance of blisters at or near the exposure site).

From associated monkey: A sample of saliva should be collected for B virus PCR testing to determine whether the monkey is actively shedding B virus. A sample of serum should also be collected and tested to determine whether the monkey is seropositive for B virus.

The National B virus Resource CenterExternal at Georgia State University’s Viral Immunology Center provides diagnostic testing, educational resources, and emergency information 24 hours a day, year round.

Virus Detection and Diagnosis

Immediately following exposure, and prior to the onset of symptoms, it is important to collect sera approximately 3 weeks apart to determine whether seroconversion to B virus infection has occurred. If symptoms consistent with B virus disease develop, collection of saliva or material from blisters (if present) can be tested by B virus PCR to determine whether the virus is present.

  • Using B virus serology, determine whether a patient who was B virus seronegative has begun making antibodies to B virus.
  • Samples for PCR should not be obtained at the time of exposure due to the possibility of forcing the virus more deeply into the wound.
  • Samples for PCR are also not recommended immediately following cleansing, because the sample is unlikely to contain detectable levels of virus and could lead to false negative results.
  • If symptoms develop, saliva and/or material from local blisters should be collected and tested by PCR for B virus.

Diagnoses of B virus infections have been hampered because herpes simplex virus (HSV) and B virus are closely related (both are members of the Alphaherpesviridae). As such, antibodies produced in response to either virus have substantial levels of cross-reactivity, which can increase the potential for both false-positive and false-negative results. The development of diagnostic methods that can reliably differentiate between HSV and B virus infection was an essential first step in advancing B virus detection for the National B virus Resource Center.

Direct culture of B virus has been the standard for diagnosis of infection, but requires a biosafety level 4 (BSL-4) containment facility to reduce the risk of exposure for laboratory workers, and the collection of samples must be delayed until symptoms appear. The specificity of B virus serologic methods has improved substantially; however, the assays rely on specimens obtained weeks after the possible exposure and, thus, are not useful for making decisions about treatment, which must be made soon after a person is exposed.

The availability of PCR protocols that reliably discriminate B virus from HSV should permit the direct detection of B virus infection without needing to resort to the more hazardous procedure of culturing virus. PCR has the additional advantage of being more rapid, potentially providing results in a matter of hours rather than days. However, the process shares the limitation with B virus culture that sample collection must be delayed until symptoms appear.

A quantitative, real-time PCR method has been developed by the National B virus Resource Center and is being evaluated for use as a clinical diagnostic. While a PCR diagnostic assay would substantially reduce the risk to diagnostic laboratory workers, the samples tested could contain viable B virus and need to be handled with appropriate caution.

 

Page last reviewed: January 31, 2019