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.

MRC-5 cells, a model for Junín virus persistent infection.

Persistent infection of MRC-5 cells was established following inoculation with attenuated Junín virus (JV). In the acute phase of the infection both the pathogenic XJ and the attenuated XJ0 and XJC13 strains showed severe c.p.e. and free viral titres reached 10(5) p.f.u./ml. Recovery and establishment of persistently infected MRC-5 sublines (MRC-5PI) proved a very common event and seemed to be independent of viral strain, m.o.i. employed or virus passage history. These MRC-5PI sublines released virus throughout their life span and infectious centre assays performed at different passage levels with two sublines showed that 5 to 9% of the cells were producing virus. Heterotypic but not heterologous resistance to superinfection developed, as observed in persistent JV-heteroploid cell systems. Analysis of released JV showed that attenuation had not been markedly altered, but alteration in plaque morphology under methyl cellulose, appearance of temperature-sensitive mutants and alterations in mouse pathology imply that some properties of JV have been altered. Results presented here stress once again the ability of JV to establish persistent infections. The source and diploid characteristics of MRC-5 cells make them a satisfactory model for JV persistence studies.

Pathogenesis of attenuated Junin virus in the guinea pig model.

The purpose of this work was to elucidate the pathogenesis of attenuated Junin virus (JV) strains in the guinea pig model. Three groups of guinea pigs were infected by the IM route with 10(3) PFU of the XJC13 and XJO-attenuated strains or with the XJ pathogenic strain of JV, respectively. Viremia was studied at 3, 5, 7, 9, 12, and 14 days postinfection (pi) (a) in serum samples of all animals and in washed cells from XJC13-infected guinea pigs by conventional techniques and (b) in whole blood samples from XJC13 and XJO animals by coculture with Vero cells. Virus spread was studied at 14 days pi in brain, spleen, lymph nodes, and bone marrow by parallel suckling mouse inoculation or organ homogenates and coculture of cell suspensions with Vero cells. By coculture techniques of whole blood, an otherwise undetectable viremia was demonstrated for both attenuated strains throughout the observation period. In contrast, XJ viremia was easily detected by direct techniques, as has already been shown. Attenuated virus was also shown to reach brain and bone marrow when coculture methods were employed. But titers were always markedly lower than those of the pathogenic strain. The sustained viremia demonstrated in guinea pigs infected with either attenuated strain explains the mode of viral dissemination and accounts for viral rescue and antigen detection from some organs. These results suggest that attenuated strains do not differ greatly in their invasive capacity in guinea pigs, but later on viral replication is impaired. Therefore, these findings reveal potential risks and should be noted when developing human vaccines.

Congenital guinea pig infection with attenuated Junin virus strains.

Guinea pigs born from mothers infected before or during pregnancy with 10(3) PFU of the attenuated XJC13 or XJ0 strains of Junin virus (JV) by the intramuscular route showed 31.5% mortality that was not attributable to the mothers' clinical condition or to lack of care. There was a slight drop in mortality rate when the mothers were infected at the beginning or end of their gestation period. JV isolation from the 9 offspring killed from 1 to 125 days of age proved that virus transmitted transplacentally or soon after birth was able to persist, although titers were not higher than 10(2.7) PFU/g of tissue in various organs, including brain. Cell-associated viremia could thus account for viral spread after birth. Since an active humoral response was detected in the same animals, although Nt antibody titers were below 1:16, a state of tolerance did not exist in these congenitally infected animals. The carrier state appeared to modify guinea pig susceptibility to JV; after challenge with the pathogenic XJ strain of JV, 2 animals survived and developed normal humoral responses, while half of the remaining animals did not show typical signs of Argentine hemorrhagic fever. Although JV persistence appeared to cause no deleterious effects in surviving guinea pigs, its long-term risk remains to be determined.

Attenuated Junin virus infection in Callithrix jacchus.

Twenty marmosets, male Callithrix jacchus, were used during this study. Fifteen of the marmosets were inoculated with 5,000 TCID50 of the attenuated XJC13 strain of Junin virus by intramuscular route and five were left as uninoculated controls. Animals were observed for a 420-day period. In order to carry out virologic, hematologic, serologic, and histologic studies the animals were bled and/or killed at different days post infection(pi). Results obtained showed that the attenuated strain produced an infection with no mortality or signs of illness. There was only a slight loss of weight at 18-40 days pi, which was soon recovered. Viremia was present from day 6 to 22, titers peaking at 4.0 log. Viral spread was limited to the lungs, spleen, lymph nodes, and bone marrow in the animal killed on day 14. No virus was found in the organs of the animal killed on day 23, and neither hematologic alterations nor pathologic lesions were seen in these monkeys except for ganglionar hypertrophy with immunoblast proliferation. Antigen was detected by immunofluorescence (IF) in lymph nodes, spleen, adrenals, lungs and brain. Neutralizing antibodies were detected from the third week onward. Protection conferred by the XJC13 strain proved effective when XJC13-inoculated monkeys were challenged with 1,000 TCID50 of the pathogenic XJ strain at days 60 or 380 pi, while normal controls died. When viral persistence was searched for on days 370, 390, and 420 pi, no infectious virus was detected, but viral antigen was seen in certain organs, which, however, lacked tissue damage.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

[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)

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

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)

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

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)