[Susceptibility of 11-day-old mice to infection with the Junin virus grown in different hosts].

Twelve clones derived from a stock of Junin virus grown in baby mouse brain were isolated in Vero cells. Some properties of those viral clones were determined and compared with parental virus in order to ascertain the degree of heterogenicity of the original population. No differences were observed among clones and parental virus when the degree of thermolability was measured by heating them at 50 degrees C for 30 min. (Table 1). Similarly no ts phenotype character was present among all viral isolates tested since ratios 40 degrees C/37 degrees C, alike parental virus, oscillated around 0.48 (Table 1). Also virulence for 2 days old mice, expressed as the ratio of PFU/LD50 varied between 5.27 to 25 while parental virus ratio was 4.56. A completely different picture was observed when virulence ratio was determined in 11 days old mice. The values found for viral clones were all above 47 being the maximum 210 (Table 1) whereas the ratio of parental virus was 2.65. Considering that the difference observed could be due to the last host where the virus multiplied, parental virus stock was passed once or two times in Vero or BHK21 cells before assaying virulence. Results quoted in Table 2 show that after one or two passages in cells, the ratio of virulence decreased, at least, 60 times independently of the virus stock or the type of cells used. Furthermore, the appearance of a viral population with an intermediate virulence index was detected by a passage through mouse embryo cells (Table 2).(ABSTRACT TRUNCATED AT 250 WORDS)