| Diagnostics A positive serological test
result, evidence of viral antigen in tissue by immunohistochemistry, or the presence of
amplifiable viral RNA sequences in blood or tissue, with compatible history of HPS, is
considered diagnostic for HPS.
Serologic assays
At the time of the 1993 outbreak in the Four Corners area, cross-reactive antibodies to
the previously known hantaviruses (e.g., Hantaan, Seoul, Puumala, and Prospect Hill
viruses) were found in the acute- and convalescent-phase sera of some of the initial HPS
patients. Tests based on specific viral antigens from SNV have since been developed and
are now widely used for the routine diagnosis of HPS. CDC uses an enzyme-linked
immunosorbent assay (ELISA) to detect IgM antibodies to SNV and to diagnose acute
infections with other hantaviruses. This assay is also available in some state health
laboratories.
An IgG test is used in conjunction with the IgM-capture test. Acute- and
convalescent-phase sera should reflect a four-fold rise in IgG antibody titer or the
presence of IgM in acute-phase sera to be diagnostic for hantaviral disease. Note that
acute-phase serum sent as an initial diagnostic specimen may not yet have IgG. IgG
antibody is long lasting, and sera of patients retrospectively identified appear to have
retained antibody for many years. The SNV IgG ELISA has therefore been used in serologic
investigations of the epidemiology of the disease and appears to be appropriate for this
purpose. Investigations of selected populations using this assay have confirmed that
infections with the virus are not common and that mild or inapparent infections are rare.
A Western blot assay using recombinant antigens and isotype-specific conjugates for
IgM-IgG differentiation has also been developed and its results are generally in agreement
with those of the IgM-capture format.
Also in use is a rapid immunoblot strip assay (RIBA), an investigational prototype
assay to identify serum antibody to recombinant proteins and peptides specific for SNV and
other hantaviruses.
Serologic confirmation of hantaviral infections has traditionally been done with
neutralizing plaque assays, which have been recently described for SNV. However, these
specific assays are also not commercially available.
Isolation
Isolation of hantaviruses (see below) from human sources is difficult, and the viruses
causing HPS seem to be no exception to this rule. To date, no isolates of SNV-like viruses
have been recovered from humans, and therefore virus isolation is not a consideration for
diagnostic purposes.
Immunohistochemistry (IHC)
IHC testing of formalin-fixed tissues with specific monoclonal and polyclonal
antibodies can be used to detect hantavirus antigens and has proven to be a sensitive
method for laboratory confirmation of hantaviral infections. IHC has an important role in
the diagnosis of HPS in patients from whom serum samples and frozen tissues are
unavailable for diagnostic testing and in the retrospective assessment of disease
prevalence in a defined geographic region.
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Caption:
A. High power magnification showing immunostaining of renal
interstitial capillaries using Peromyscus serum. Images courtesy Sherif R. Zaki,
MD, Ph.D. To view large-size versions of images, click
directly on the image buttons. |
Polymerase Chain Reaction (PCR)
Reverse transcriptase-PCR (RT-PCR) can be used to detect hantaviral RNA in fresh frozen
lung tissue, blood clots, or nucleated blood cells. However, RT-PCR is very prone to
cross-contamination and should be considered an experimental technique. Differences in
viruses in the United States complicate the use and sensitivity of RT-PCR for the routine
diagnosis of hantaviral infections.
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National
Center for Infectious Diseases
