Elinor Whitney

California group arboviruses: Electron microscopic studies

Abstract Electron microscopic examination of mouse brains infected with five California group arboviruses revealed similar changes consisting of perineuronal edema formation, minimal inflammatory cell infiltration and neuronal degeneration. Virus particles were observed in the cytoplasm of neurons in association with organelle membranes; particles were round or oval, with a moderately electron dense core surrounded by a ragged halo. Mean virus diameter was 98 mμ. Virus particles also accumulated in extracellular spaces. Similar virus morphology and cellular degeneration were observed in cell cultures infected with one of the viruses.

Two Viruses Isolated from Rodents (Clethrionomys gapperi and Microtus pennsylvanicus) Trapped in St. Lawrence County, New York*

Four strains of C. gapperi virus were isolated from 3 Clethrionomys gapperi and 47 strains of Microtus virus from 15 Microtus pennsylvanicus and 1 Mus musculus. One of the Microtus strains was isolated from a pool of 20 mites while the others were from rodent tissues. These agents were insensitive to ether and sodium desoxycholate, withstood freezing at —70 C for 3 years and lyophilization without loss of titer, and were not killed when heated at 60 C for 1 hour. Their size as determined by filtration was less than 50 mμ and greater than 20–35 mμ. The strains within each group appear to be similar. The illness induced in suckling mice by the C. gapperi agents had a 5-day incubation period followed by prostration and death with a histologic picture of extensive encephalomalacia. The incubation period in mice for the Microtus agents was 9 to 11 days followed by convulsions and death. Histopathology showed meningeal infiltration and necrosis of the molecular layer. No antigenic similarity was detected between the C. gapperi and Microtus viruses by cross complement-fixation test.

Serologic Survey for Arbovirus Activity in Deer Sera from Nine Counties in New York State

Sera from 352 deer from nine New York State counties were tested for neutralizing and hemagglutination-inhibiting antibodies to six arboviruses representing four groups. Antibody titers to California encephalitis and Cache Valley viruses were detected in varying frequency in the 9 counties with foci for the Bunyamwera group in Seneca, Dutchess, and Erie counties. Neutralizing antibodies to western equine encephalomyelitis were noted in sera collected in 1959–61 from Albany and Seneca counties while a focus of group B arbovirus activity, most probably due to Powassan virus, was found in Shelter Island, Suffolk County. Our experience indicates the usefulness of deer as natural indicators of activity of certain arboviruses.

The First Isolations of Powassan Virus in New York State.

Summary Powassan virus was isolated from 2 pools of ticks (1 unidentified, the other Ixodes cookei) removed from 2 Marmota monax live-trapped in northern St. Lawrence County. Powassan virus was also isolated from tissues taken from the same 2 animals. Another strain of POW virus was recovered from the brain of a sick gray fox found in Broome County 200 miles to the south in New York State. The 2 tick strains were compared antigenically with the proto-type POW strain and were found to be antigenically similar.

Response of infant and adult mice to lymphocytic choriomeningitis virus infection.

Summary and Conclusions Freshly isolated strains of lymphocytic choriomeningitis virus induced inapparent infection and immunity in infant mice. A mouse-adapted strain, however, caused obvious signs of infection and a high mortality rate among infant mice. Adult mice were fully susceptible to both freshly isolated and mouse-adapted virus. These findings are in keeping with the epizoology of the disease in naturally infected mouse colonies.

Growth Studies of California Encephalitis Virus in Two Aedes Mosquito Cell Line Cultures

The mouse-adapted New York strain of California encephalitis (CE) (Whitney et al., 1969) virus grew readily on initial passage in cultures of Singh’S (1967) Aedes aegypti and A. albopictus cell lines. The infection persisted over the observation period of 6 weeks. Subsequent experiments with another CE strain have shown that cells on passage still produce virus and are persistently infected. Cytopathic effects were not observed during the first and subsequent 8 passages after which the experiments were discontinued. Fig. 84 shows a comparison of the growth of CE virus on initial passage in two Aedes cell lines. A slight and gradual drop in titer of extracellular virus was demonstrated. The virus titer in A. albopictus cells was 5.9 LD50/ml and generally 1 log10 higher than that observed in A. aegypti cells. In the absence of cells, no virus was detected by the fifth post-inoculation day in the original inoculum incubated at the same temperature.

Immunologic Relationships pf MM, Lansing Poliomyelitis and Mouse Encephalomyelitis Viruses

Conclusion Neutralization and cross immunity tests indicate a relationship between MM and Lansing poliomyelitis but no relationship between MM and TO (Theiler original or low virulence strains) mouse encephalomyelitis. Complement-fixation tests relate MM virus and the GDVII strain of Theilers virus. The results support he view that a group of poliomyelitis viruses exists which may be related by serologic tests.