Ribavirin therapy for Hantaan virus infection in suckling mice.

We recently reported that ribavirin inhibited Hantaan virus (HV) replication in vitro. In the present study, we used the HV suckling mouse model to evaluate the efficacy of treatment with various doses of ribavirin. Beginning on day 10, untreated animals, infected with ten times the amount of HV (strain 76/118) required to kill 50% of the animals, lost weight; by days 15 to 18, they developed paralysis of both hind limbs, and they died between days 20 and 21. Treatment with 50 mg of ribavirin/kg per day begun on day 10-following onset of early clinical signs and demonstrable virus in serum and organs--saved 11 of 20 animals compared with 0 of 70 controls. Treated animals did not develop further signs of infection, and by day 22, survivors resumed normal weight gain. After ribavirin treatment, titers of virus decreased in serum, liver, and spleen by two days; in lung within six days; and in the kidney by eight days. By day 18, titers in organs of treated animals were 100-fold lower than in sham-treated animals, with the exception of the brain. Titers of virus in brain fell by day 20, when virus in untreated animals reached greater than 10(7) pfu/g. Treated survivors continued to have decreasing titers of virus in organs and were followed for 75 days with no sign of disease recurrence.

Retention of fluorescent antigenicity of virus-infected cells on spotslides under various conditions of storage.

Ten well, epoxy-coated spotslides containing arbo- and arenavirus-infected cells were tested as determined by fluorescent methods for the retention of antigenicity after storage in a nitrogen atmosphere at various temperatures and times. In most cases antigen stability was maintained at -70 or -20 degrees C for periods exceeding 1-3 years. Antigen deterioration was greatest at ambient temperature, and less so at 4 degrees C.

Hantaan virus, aetiological agent of Korean haemorrhagic fever, has Bunyaviridae-like morphology.

Spherical to oval particles with a unit membrane and subunit surface structure were demonstrated by negative-contrast staining of supernatant fluids of A-549 cell cultures infected with strain 76-118 of Hantaan virus. The particles had an average diameter of about 95 nm, with a range of 80 to 110 nm. Similar particles were isolated by buoyant density fractionation in sucrose gradients. In four separate experiments, infectivity cosedimented with 95 nm particles at buoyant densities from 1.15 to 1.18 g/ml. Immunoaggregation of the virions was specifically produced by antisera obtained after Hantaan virus infection of man and rabbit. The known physicochemical and morphological properties of these particles are compatible with those generally reported for the Bunyaviridae family of viruses.

The African green monkey as an alternate primate host for studying Machupo virus infection.

African green monkeys (Cercopithecus aethiops) are highly susceptible to Bolivian hemorrhagic fever (BHF). Six monkeys were inoculated with 1,000 plague-forming units of Machupo virus, the etiologic agent of BHF. They were observed and monitored for clinical signs, body temperature, viremia, hematologic changes, and virus neutralizing antibody. Onset of fever, anorexia, and depression was noted on days 3 to 6 postinoculation. These and other signs increased in severity and all monkeys died: 5 of 6 died by day 13 and one survived until day 24. The median time to death for the group was 12.5 days. The mean value for hematocrit determinations gradually decreased to 30 on day 10 but subsequently increased. Mean neutrophil and lymphocyte values increased slightly until day 3, and then decreased to minimal values of 3,000 and 2,000, respectively, on day 10. Four monkeys were viremic by day 7 and all were viremic on day 10. The monkey that survived until day 24 had a neutralizing antibody titer of 1:32 on day 14 and appeared to recover from the initial acute illness by day 16. It died following onset of severe neurologic signs on day 23. BHF in the African green monkey is similar to the disease described in two species of macaques.

Pathogenesis of Machupo virus infection in primates.

Experimental Machupo virus infection of rhesus and cynomolgus monkeys produced a severe illness consisting of an initial clinical phase and a later neurological phase. Cumulative mortality during the two phases was 80% and 95% respectively. Attempts to alter the pathogenesis with decomplementation or immunosuppression resulted in earlier deaths of the monkeys.

Preparation of noninfectious arbovirus antigens.

Noninfectious arbovirus antigens were prepared from borate-saline suspensions of infected suckling mouse brain buffered with tris(hydroxmethyl)aminomethane and treated with beta-propiolactone (BPL). The activity and stability of these antigens were enhanced by altering the buffering system, by passing the virus seed through a series of four or more continuous passages in the brains of suckling mice, or by a combination of these procedures. The titers of group A and B arbovirus antigens were comparable to titers of antigens extracted by the conventional sucroseacetone-BPL (SA-BPL) method. Antigens prepared from some ungrouped and Bunyamwera arboviruses by either the borate-saline-BPL or SA-BPL method produced inconsistent results and will require the development of more unique procedures to obtain suitable hemagglutinating antigens.