Detection of hantaviruses with RNA probes generated from recombinant DNA

Hantavirus pulmonary syndrome: the Four Corners disease

OBJECTIVE

To review the epidemiology, pathogenesis, clinical features, diagnosis, and treatment of hantavirus infections, focusing on the recent outbreak of hantavirus pulmonary syndrome in the US.

DATA SOURCES

A MEDLINE search (1966 to present) of English language literature pertaining to hantaviruses was performed. Additional literature was obtained from reference lists of pertinent articles identified through the search.

STUDY SELECTION AND DATA EXTRACTION

All articles were considered for possible inclusion in the review. Pertinent information, as judged by the authors, was selected for discussion.

DATA SYNTHESIS

Hemorrhagic fever with renal syndrome (HFRS) has long been recognized in Eurasia and is the predominant disease manifestation of hantavirus infection worldwide. Hantavirus pulmonary syndrome (HPS) recently has been described in the US and exhibits greater pulmonary involvement and mortality than HFRS. Historically, 4 hantavirus serotypes (Hantaan, Seoul, Puumala, Prospect Hill) are recognized; however, additional serotypes have been proposed as distinct serogroups, including the serotype responsible for HPS in the Four Corners area: the Four Corners virus (FCV). Phylogenetic analysis shows that FCV is most closely related to Prospect Hill virus, another hantavirus previously isolated in the US that has not yet been identified with human disease. Additional hantavirus serotypes isolated in the US may provide insight into the prevalence of hantavirus infection and disease in this country. Inhalation of aerosolized virus is the predominant mechanism of hantavirus infection. Diagnosis is based primarily on clinical findings and serologic evidence of hantavirus antibody or direct evidence in clinical tissue specimens. Limited clinical studies evaluating ribavirin as a therapeutic modality demonstrated that the agent improves clinical outcome in HFRS. However, the role of ribavirin in the treatment of HPS remains to be determined.

CONCLUSIONS

Hantavirus infections are becoming increasingly recognized as a cause of disease worldwide. Recognition of hantavirus disease in the US suggests enzoonosis of pathogenic hantaviruses. In the absence of a well-established cure, early diagnosis is imperative so that aggressive supportive care can be initiated.

Detection of hantavirus RNA in tissues of experimentally infected mice using reverse transcriptase-directed polymerase chain reaction

Detection of hantaviruses, the etiological agents of hemorrhagic fever with renal syndrome (HFRS), by virus isolation using experimental animals or cell culture is time-consuming. A more rapid but equally specific method is needed. We used a reverse transcriptase-directed polymerase chain reaction (RT-PCR) to detect hantavirus genomic sequences and compared its sensitivity with conventional virus isolation. RNA, extracted by the guanidinium isothiocyanate-cesium chloride method from hantavirus-infected Vero E6 cells and from tissues of infant mice inoculated intracerebrally with 100 LD50 of hantavirus, was initially reverse transcribed using avian myeloblastosis virus reverse transcriptase. The resulting complementary DNA (cDNA) was used as template to amplify the glycoprotein 2-encoding region of the hantavirus M segment. With this method, Vero E6 cell cultures infected with Hantaan virus strains 76-118 (prototype) and HV114 (an isolate from the urine of an HFRS patient in China) were positive, while control cultures were negative. Brain, lung, and heart tissues from hantavirus-infected mice were positive by RT-PCR at 5, 8, and 11 days after intracerebral inoculation. The specificity of the positive results was confirmed by restriction endonuclease digestion of the amplified fragments with AluI and HpaI. The sensitivity of the RT-PCR was equal to cell culture amplification but required less time. This method is being adapted for detection of hantavirus genomic sequences in clinical specimens and postmortem tissues from patients with HFRS.

Determination of the coding capacity of the M genome segment of nephropathia epidemica virus strain Hällnäs B1 by molecular cloning and nucleotide sequence analysis

The M genome RNA segment of nephropathia epidemica virus (NEV) strain Hällnäs B1 was characterized by molecular cloning and DNA nucleotide sequencing of the corresponding cDNA clones. The size of the M RNA segment is 3682 nucleotides. The 3' and 5' terminal sequences are complementary for 21 bases and their predicted secondary structure is very stable. The viral complementary messenger RNA possesses a single long open reading frame with a coding capacity of 1148 amino acids (polypeptide of 126 kDa). A comparison of the NEV M segment to that of Hantaan virus strain 76-118 reveals 61% sequence homology at the nucleotide level and 53% at the deduced amino acid level. Four out of five potential asparagine-linked glycosylation sites of the encoded glycoproteins have been conserved between NEV and Hantaan M. The isoelectric points (IEP) are nearly identical. Furthermore it was found that 90% of all cysteine residues have been conserved. Putative NEV G1 and G2 are preceded by a short hydrophobic sequence as shown for G1 and G2 of Hantaan virus. Hydrophilicity profiles of the two segments are of striking similarity. These data indicate that NEV- and Hantaan virus M-encoded polypeptides seem to be very similar in structure and function despite the relatively low amino acid sequence homology.

Immunoblot analysis of the serological response in Hantavirus infections

Sera from patients with nephropathia epidemica (NE) or Korean hemorrhagic fever (KHF) were tested for specific antibody response to antigens of Hällnäs virus and Hantaan virus strain 76-118. A Vero E6 derived cell line persistently infected with Hällnäs virus strain B1, and Vero E6 cells freshly infected with Hantaan virus type strain 76-118 were used as antigens in the immunofluorescence assay (IFA) and the immunoblot. Blots were prepared from whole cell lysates. The convalescent-phase sera of NE patients tested in this study regularly revealed a marked reaction with a 52 kilodalton (Kd) protein of Hällnäs virus and a 50 Kd protein of Hantaan virus. A convalescent serum from a patient with Korean hemorrhagic fever and a rat antiserum against Hantaan virus could recognize the 50 Kd band of Hantaan virus but showed no apparent reactivity with the 52 Kd component of Hällnäs virus in the standard dilutions. Some sera could additionally identify minor bands in the 55 Kd and/or 67 Kd region of the blots. A one-way cross reactivity between Hantaan and Hällnäs viruses was also evident from the results of the immunofluorescence assays in that NE convalescent sera reacted with both viruses, whereas KHF convalescent or anti-Hantaan sera gave strongly positive results with Hantaan virus but only faint reaction with Hällnäs virus.