Progress in the Development of Hantavirus Diagnostic Assays --
United States
Through September 29, 1993, a total of 39 persons in 11
states, including one recently identified in Montana, with
confirmed acute hantavirus respiratory illness have been reported
to CDC (1,2); 25 (64%) of these cases have been fatal. The
diagnosis of confirmed hantavirus infection has been based on the
presence in serum of immunoglobulin M (IgM) antibodies or rising
titers of immunoglobulin G (IgG) antibodies that cross-react to
four previously identified hantaviruses (Hantaan, Seoul, Puumala,
and Prospect Hill), immunohistochemical staining of tissues, or a
positive polymerase chain reaction (PCR) test in tissues.
Genetic recombinant-derived proteins have been produced in
vitro from viral genomic sequences amplified from tissues obtained
from patients who died with confirmed hantavirus illness. These
proteins have been adapted to assays for homologous antiviral
antibodies in patients with suspected hantavirus infection and in
rodent hosts. At the University of New Mexico (UNM), Western blot
assays with N and G1 proteins have been developed that successfully
detected antibodies in serum from all 16 patients with confirmed
disease who were tested; in nine of nine persons tested, antibodies
were detected on the first day of hospital admission. The serum
specimens did not react with the G1 proteins of Prospect Hill or
Puumala viruses, the two hantaviruses that are most cross-reactive
with the new hantavirus. No false-positive reactions occurred in 20
control serum specimens.
At CDC, purified recombinant N protein has been used as an
antigen for IgG enzyme-linked immunosorbent assays (ELISAs) that
demonstrated higher specific optical density values compared to
Prospect Hill virus, the viral antigen previously identified as
most reactive with serum specimens obtained from patients and
rodents in the southwestern United States. Preliminary results with
these ELISAs suggest that the use of homologous antigen may
moderately increase the estimates of prevalence among infected
rodents; no additional cases in humans have been recognized through
the use of these assays. Negative tests on 232 serum specimens
obtained from patients with adult respiratory distress syndrome not
associated with hantavirus infections confirmed the specificity of
the recombinant N protein antigen. Initial application of this same
purified recombinant protein in IgM assays indicates that the
protein is reactive in this format.
Reverse transcription and PCR amplification of genomic
sequences from human blood obtained during the early phases of
disease also has been attempted in collaborative studies between
UNM and CDC. Stored peripheral blood mononuclear cells obtained
early in the course of disease from seven patients with confirmed
disease were PCR positive; four of the seven corresponding plasma
specimens from these patients also were positive. All four stored
blood clots available from these patients were positive as well.
Cases of acute hantavirus disease continue to be confirmed in
the United States. The diagnostic findings of the prototypic tests
described in this report suggest that it may be possible to rapidly
diagnose infection in patients with suspected hantavirus disease.
Use of recombinant-derived homologous antigens, which has preceded
the isolation of the virus in cell culture, should improve the
sensitivity and specificity of results obtained with available
heterologous antigens. However, these hantavirus assays are for
experimental use only and none have been approved by the Food and
Drug Administration for use in the United States. These newer
assays will require standardization and systematic evaluation with
larger numbers of specimens before approval for marketing and
broader usage are considered. Until assays are approved, health
providers caring for patients with suspected hantavirus illness
should forward specimens for testing to CDC through their
respective state health departments.
Reported by: B Hjelle, MD, S Jenison, MD, N Torrez-Martinez, Univ
of New Mexico School of Medicine, Albuquerque. TA Damrow, PhD,
State Epidemiologist, Montana State Dept of Health and
Environmental Sciences. Div of Viral and Rickettsial Diseases,
National Center for Infectious Diseases, CDC.
References
CDC. Update: hantavirus disease -- United States, 1993. MMWR
1993;42:612-4.
CDC. Update: hantavirus-associated illness -- North Dakota,
1993.
MMWR 1993;42:707.
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