Modification of Junin virus neutropism in the guinea pig model.

Virulent and attenuated Junin virus (JV) strains have been employed to study the influence of virus passage history on the neurotropism for guinea pigs. Five i.p. successive passages (P1-P5) of the pathogenic JV-XJ strain and of the attenuated XJO variant were performed in guinea pig spleen. Viral titrations of organ suspensions were made through P1-P5 passages. The XJ strain produced a widespread infection in P1 guinea pigs with viral dissemination to all organs except brain, in P5 animals the brain has been involved as well. XJO-infected P1 guinea pigs showed lower viral titres than XJ-infected P1 animals, and again, the virus reached the CNS in P5 only. The passaging by i.p. route was shown to enhance CNS invasivity of the XJ strain as well as to maintain the XJO neurotropism for guinea pigs. Neurotropism of both strains seemed somewhat affected by the passage history of the virus and the inoculation route appeared critical for its expression. In addition, the neurotropic potential of the attenuated strains has apparently remained unaltered.

Early protection to Junín virus of guinea pig with an attenuated Junín virus strain.

Inoculation of guinea pigs with attenuated XJO Junín virus (JV) strain confers protection against challenge with pathogenic XJ-JV strain starting as early as 3 days post infection (p.i.). The protection increased continuously up to 100% by 30 days p.i. Neither stimulation of non-specific cell mediated mechanisms by previous BCG sensitization nor circulating interferon (IFN) seemed essential for such protection. The early detection of the virus in guinea pig organs considered the site of primary JV multiplication suggests that early resistance phenomenon was attributed mainly to direct viral interference.

[Development of the infection in guinea pigs infected with the attenuated variant XJO of Junín virus]. / Evolución de la infección en cobayos infectados con la variante atenuada XJO del virus Junín.

As previously shown, the XJO variant of Junin virus (JV) is attenuated and elicits in guinea pigs a lasting humoral response and resistance to the challenge with XJ pathogenic strain, during at least three months. In this paper the long term evolution of guinea pigs inoculated with XJO by im route was studied. Ten animals were infected with 10(3) PFU of XJO at day 0 (group I) and an other 10, at days 0 and 77 (group II). Another 30 guinea pigs were inoculated with 10(2) PFU at day 0 (group III) and 30 at days 0 and 12 (group IV). The animals were observed during 12 months. Circulating complement fixing (CF) and neutralizing (Nt) antibodies were measured at different periods pi in all groups, and lots of four guinea pigs from groups III and IV were challenged with 10(2) PFU of XJ strain at 120, 180, 240 and 360 days pi. Independently of the number of inoculations, the humoral response was similar in the four groups. CF antibodies appeared in all animals around 30 days pi in low values (1:4-1:8) and after a peak, which in a few animals reached 1:32-1:64, returned to previous levels by 12 months pi. Nt antibodies, first detected 15-20 days pi, reached maximum titers by 75-80 days pi, decreasing afterwards to a plateau which persisted throughout the 12 month period (Fig. 1A-B). Probably the continuous presence of antibodies could account for the 100% resistance to the challenge with XJ pathogenic strain shown by these animals (table I).(ABSTRACT TRUNCATED AT 250 WORDS)