Investigations
1st investigations to order
serology
Test
Serological analysis aimed at the detection of anti-B virus antibodies, usually using ELISA, is the standard first-line test for diagnosing B virus infections. It is the most clinically feasible way to assess infection. However, due to the time required to develop detectable virus-specific antibodies, it will not inform immediate treatment decisions, which must be made based on clinical judgement.
Neither serological testing nor virus detection are used to guide a decision on whether to offer antiviral prophylaxis. Again, this decision must be made on clinical grounds.
An acute serum sample for serological analysis should be obtained immediately after exposure to serve as a baseline. A second convalescent sample should be obtained 3 to 6 weeks following exposure to document seroconversion to B virus. If the patient is receiving prophylaxis with an antiviral drug, a third serum sample should be obtained 3 months after the initial exposure as seroconversion may be delayed.
Acute and convalescent serum samples should be tested at the same time using paired samples when feasible. Testing of single specimens might be considered if clinical signs or symptoms of B virus infection are present.
For patients for whom initial baseline serum is not negative, a substantial rise in B virus antibody titre (>4-fold) in temporal association with potential B virus exposure is highly suggestive of infection.
Serological testing for B virus is complicated by the cross reactivity of serological results with those from other herpes viruses (e.g., herpes simplex virus [HSV]), which can result in false-positive reactions. PCR or viral culture should be undertaken alongside serological testing and is used to confirm B virus infection suggested by serological testing. PCR is preferred to viral culture as it is quicker, more sensitive, and more cost-effective. People with a history of possible exposure should not be diagnosed as infected on the basis of serological reactivity alone in the absence of symptomatic disease or laboratory confirmation of virus shedding by PCR or culture. Expert assistance with diagnostic testing and interpretation is essential.
Result
positive for B virus-specific serum antibodies IgM and subsequently IgG
polymerase chain reaction (PCR)
Test
If the patient is symptomatic, a rapid diagnosis is paramount to ensure appropriate management. PCR should be the first investigation to order in this situation. In an asymptomatic patient, a positive PCR from the exposure site does not confirm infection. However, a positive PCR from the exposure site at a time distant from exposure in association with symptoms concordant with B virus infection, or a positive PCR from a site not exposed to the virus (e.g., lesions, conjunctivae, oropharynx, cerebrospinal fluid [CSF]) at any time with symptoms concordant with B virus disease indicates infection.[4]
Serological results suggestive of B virus infection must be confirmed if possible using an agent-specific test, such as PCR or viral culture. PCR is the most expedient and reliable approach to confirming the DNA present is that of B virus and not another herpes virus that can cross react serologically with B virus (e.g., HSV). It is also preferred over virus culture due to the potential hazards associated with growing the virus in the laboratory as well as the time required for viral culture. Virus culture is also less sensitive than PCR. Thus, serological analysis with confirmation by PCR is the most feasible clinical approach.
Specimens for PCR should be collected from symptomatic patients potentially infected with B virus regardless of the risk assessment of the exposure and regardless of whether or not the patient is receiving post-exposure prophylaxis (PEP). Collection of wound specimens for PCR testing should only be done after the site has been thoroughly cleansed to reduce the risk of forcing the virus more deeply into the wound; however, collection of wound specimens at the time of exposure is not recommended.
It should also be recognised that specimens collected for PCR from the exposure site at the time of exposure are often negative due to removal of free viral particles during cleansing. Even if positive, presence of virus at the exposure site does not confirm infection in the absence of symptoms. Thus, specimens collected from the exposure site at the time of exposure may lack diagnostic or clinical significance for infection.
For symptomatic patients with positive PCR, serial PCR tests of the shedding sites should be followed to inform management decisions and infection control practices. Follow-up PCR testing should be repeated weekly until two consecutive negative PCR or culture results are obtained. Crusted lesions can be used to provide samples for PCR.
B virus is a biosafety level-4 (BSL-4) pathogen; therefore, specimens must be sent to a specialist diagnostic laboratory with BSL-4 capabilities as well as established capacity to perform diagnostics for B virus.[1]
Result
positive for B virus DNA
Investigations to consider
viral culture
Test
Serological results suggestive of B virus infection must be confirmed if possible using an agent-specific test, such as PCR or viral culture. Viral culture remains an option to confirm B virus infection. However, the utility of viral culture to guide clinical management is limited as it is slower, less sensitive, and more costly than PCR.
There are potential hazards associated with growing the virus in the laboratory. Thus, serological analysis with confirmation by PCR is the most feasible clinical approach. Collection of wound specimens at the time of exposure is not recommended.
Collection of specimens for culture can be considered for symptomatic patients potentially infected with B virus regardless of the risk assessment of the exposure, and regardless of whether or not the patient is receiving PEP. Collection of wound specimens for culture should only be done after it has been thoroughly cleansed to reduce the risk of forcing the virus more deeply into the wound.
It should also be recognised that specimens collected for culture from the exposure site at the time of exposure are often negative due to removal of free viral particles during cleansing. The presence of virus at the time of exposure indicates exposure, not infection. Thus, specimens collected at the time of exposure lack diagnostic or clinical significance for infection.
In an asymptomatic patient, a positive culture at the site of exposure does not confirm infection. However, a positive culture from the exposure site at a time distant from exposure in association with symptoms concordant with B virus infection, or a positive culture from a site not exposed to the virus (e.g., lesions, conjunctivae, oropharynx, CSF) at any time with symptoms concordant with B virus disease indicates infection.[4]
Positive cultures from symptomatic patients should be repeated weekly (or PCR testing from the same site repeated instead) until there are two consecutive negatives to monitor response to treatment, inform infection control practices, and confirm cessation of virus shedding. During follow-up visits on symptomatic patients, samples for culture can be obtained from any lesions that have not yet crusted.
Positive growth of B virus must be confirmed using an agent-specific test (e.g., PCR, DNA sequencing, restriction endonuclease analysis, or sodium dodecyl sulfate-polyacrylamide gel electrophoresis [SDS-PAGE] analysis of viral proteins).
Culture is not required for clinical confirmation of B virus infection, but it may be helpful in confirming the presence of viable virus and for assessment of drug sensitivity.[47]
B virus is a biosafety level-4 (BSL-4) pathogen; therefore, specimens must be sent to a specialist diagnostic laboratory with BSL-4 capabilities as well as established capacity to perform diagnostics for B virus.[1]
Result
positive growth of B virus
brain MRI
Test
Carried out to assess for encephalomyelitis or other central nervous system infection if neurological symptoms develop.
Result
brainstem encephalomyelitis
brain CT
Test
If MRI is unavailable, a brain CT with contrast can be carried out to assess for brainstem encephalomyelitis if neurological symptoms develop. However, CT findings are less sensitive than MRI for brainstem encephalitis.
Result
brainstem encephalomyelitis
CSF tests
EEG
Test
Guided by a neurology consultant.
EEG can be considered if help is needed to differentiate B virus encephalitis (a brainstem encephalitis that becomes diffuse over time) from HSV encephalitis (a unilateral temporal lobe encephalitis).
Result
brainstem encephalitis becoming diffuse over time
brainstem auditory evoked responses
Test
Guided by a neurology consultant.
In conscious patients, additional useful information about brainstem or upper spinal cord function may be obtained with brainstem auditory evoked responses. Should be done under neurological consultation.
Result
abnormal results suggesting B virus infection
somatosensory evoked potentials
Test
Guided by a neurology consultant.
In unconscious patients, additional useful information about brainstem or upper spinal cord function may be obtained with somatosensory evoked potentials. Should be done under neurological consultation.
Result
abnormal results suggesting B virus infection
laboratory testing of animal specimen
Test
Guided by a veterinary consultant.
Laboratory testing (e.g., serological analysis, PCR, culture) of the animal responsible for exposure can be considered to identify B virus infection.
Samples for testing should only be collected from the animal if possible and safe to do so, and under veterinary consultation.
Decisions to test animals associated with possible B virus exposures may inform management of that animal or the larger troop from which it comes; they are unlikely to substantially inform patient management. Decisions on evaluation and management of the patient must be initiated before these results will be available and continued based on the evidence of the patient, not the exposure source.
Result
positive for B virus infection
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