Biological characteristics of an enzootic subtype of western equine encephalomyelitis virus from Argentina.

In order to expand our knowledge on the biological characteristics of an enzootic South American subtype of western equine encephalomyelitis (WEE) virus, strain AG80-646, we inoculated guinea pigs, rabbits, newborn chickens and Vero and chick embryo cell cultures with this and other WEE and Wee-related viruses. AG80-646 was found apathogenic for guinea pigs even when inoculated intracranially (i.e.) or intraperitoneally (i.p.), and the animals did not develop viraemia. AG80-646 killed rabbits and the animals developed high viraemia (peak titer was 7.0 log PFU/0.1 ml). These data and previous serological evidence led us to look for a mammal as a natural host. AG80-646 was found lethal for newborn chickens inoculated subcutaneously (s.c.) (peak viraemia titer was 6.6 log PFU/0.1 ml). AG80-646 produced plaques (diameter 0.8-1.0 mm) in Vero and chick embryo cells 3-4 days post infection (p.i.) A comparison of AG80-646 with other WEE complex virus strains led to the following observations: (1) The lethality for guinea pigs was high for the two epizootic Argentinian strains, Cba 87 and Cba CIV 180, zero for the two enzootic strains, AG80-646 and BeAr 10315 (virus Aura), and intermediate for the Russian strain Y62-33 (low by i.c. route and zero by i.p. route); (2) AG80-646 was more virulent for rabbits inoculated i.p. than the three epizootic strains Cba 87, Cba CIV 180 and McMillan; (3) AG80-646 was less virulent for new-born chickens than the Argentinian epizootic strain Cba CIV 180; (4) The viraemia level correlated always with the strain virulence in each animal host. This study provides tools for the differentiation of WEE complex viruses and strains in the future ecological work on WEE in South America.