Martha C. Boxaca

Overt and latent HIV 1 and HTLV-I infection in cohorts of at high risk individuals in Argentina.

We conducted a survey using serology and polymerase chain reaction assays to detect HIV 1 and/or HTLV-I antibodies and viral DNA, respectively, in 113 intravenous drug abusers and in 62 sexually active high risk individuals attending two Drug Addict Centres and a Centre for Venereal Diseases in Buenos Aires, Argentina. At the time of the survey 137 of these subjects were known to be HIV 1 seropositive but none of them was symptomatic. Serological tests for HTLV-I were found to be positive in 38 (21.7%) of the HIV 1 positive individuals, whereas all of the 38 HIV 1 seronegative subjects were also seronegative for HTLV-I antibodies. Gene amplification assays carried out in blood sample DNA from the 38 HIV 1/HTLV-I seronegative individuals, revealed HIV 1 DNA in six out of 28 intravenous drug abusers (21.5%). One subject (2.6%) was positive for both HIV 1 and HTLV-I DNA sequences, whereas four (10.5%) showed HTLV-I DNA only. To determine whether these individuals were infected with HTLV-I and/or HTLV-II, DNA samples were also amplified with HTLV-II specific primers and no evidence of HTLV-II infection was observed. None of the subjects seroconverted according to conventional serological tests during the 2 year follow-up period. The 10 seronegative subjects belonging to the sexual risk group were negative for both HIV 1 and HTLV-I in polymerase chain reaction assays. We conclude that not only HIV 1, but also HTLV-I is a widely spread infection in intravenous drug abusers and sexually active high risk individuals in Argentina.(ABSTRACT TRUNCATED AT 250 WORDS)

The occurrence of virus, interferon, and circulating antibodies in mice after experimental infection with Junin virus

Groups of white mice 3 to 30 days old were inoculated intracerebrally or intraperitoneally with Junin virus, the etiological agent of argentine hemorrhagic fever. Samples of brain and blood were taken at different intervals after inoculation to study the presence of virus, interferon and neutralizing antibodies. Mice increased its resistance to Junin virus with age, regardless the route of inoculation. When inoculated by intracerebral route, mortality reached 100% in 5 to 10 days old mice, decreasing to 7% by the age of 30 days. Virus was detected in the brain of 5–10 days old mice from the 3rd day on until death (11th day) occurred; in older groups of mice virus was no longer detectable by the 10th day after infection. Generally interferon (IF) in brain roughly paralleled the virus curve. Viremia was only detected in 5 days old animals on the 4th day after infection. Circulating IF was found from the 2nd day on in approximately similar levels in all cases. Neutralizing antibodies appeared late, not before the 20th day p. i. and therefore could be only detected in surviving 15 to 30 days old mice. When inoculated by intraperitoneal route mortality was 100% in 24 hours old mice, decreasing to 5% by the age of 6 days. Only in the 3 days old group, virus was briefly detected in brain on the 5th day; but neither in this group nor in the olders an interfering activity in this organ could be demonstrated. No viremia or circulating antibodies were detected in any animal during the period of observation. However circulating IF persisted from 20 hours on in all age groups, suggesting that virus multiplication did occur.

Transplacental infection in guinea pigs inoculated with an attenuated strain of Junin virus.

Transplacental infection by the attenuated XJC13 strain of Junin virus (JV) in the guinea pig model was evaluated. 5 pregnant guinea pigs were infected intramuscularly at 45 +/- 3 days of pregnancy. 4 animals were killed at 14 days postinfection (p.i.), and 1 was sacrificed at 137 days p.i. at the end of its second pregnancy. Evidence of JV was obtained by Vero cell cocultivation in all 14 fetuses harvested (brain and/or spleen) and in 10 of 11 placentas. The results strongly suggest that the attenuated JV strain infected the fetus by the transplacental route, as previously demonstrated for the pathogenic XJ strain. Despite limited sampling, the acute as well as the chronic stage proved viable.

Epidemic Hemorrhagic Fever in Argentina.

A DISEASE of unknown etiology appeared a few years ago in the northwestern part of the Province of Buenos Aires. The clinical aspects were first described by Arribalzaga (1) and later by Duva (2), who suggested that it may be of leptospiral origin. The disease appeared again in 1958, and in May of that year we went to the city of Junin to study its clinical and etiological features. This study was the first to provide evidence of the virological nature of the causative agent (3). Later, Margni and co-workers, on the basis of little evidence, presented the opinion that poisoning by dieldrin, aldrin, or other products, might be an auxiliary factor (4). At a special meeting held in the University of Buenos Aires on December 19, 1958, we presented a full report of our work with the disease, defining it as new in Argentina and giving additional evidence of its virus etiology (5,6). This work has since been confirmed by other investigators (7). The clinical descriptions, which we had previously published, were recently confirmed by studies of the disease produced by inoculation of human volunteers. This research was conducted by two groups, working independently, and their reports appeared at about the same time (7,8).

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.

Mouse Splenocyte Transfer Effect Depends on Donor’s Junin Virus Infection Stage

Splenocytes from Junin-virus-persistently-infected euthymic mice taken at 45 days postinfection seemed unable to induce overt signs of disease, to cause death, or to modify brain viral levels when transferred to athymic Junin-virus-infected mice. Findings differed sharply when the same recipients were transferred with splenocytes taken at 6 or 30 days postinfection from immunocompetent mice infected in adult life, since mortality reached 80 or 50%, respectively, and brain viral titers were significantly lowered. Furthermore, splenocytes taken at 6 days postinfection from whole adult mice proved harmless to persistently infected euthymic mice. These findings strongly suggest the existence of an immune system alteration in the immunocompetent mouse, attributable to Junin virus persistence. This premise is based on the fact that splenocytes from persistently infected mice were unable to recognize viral antigen expressed on recipient-infected cells. The absence or impairment of a specific cytotoxic T cell population is hereby postulated.

Infection of Pregnant Guinea Pigs with Attenuated Junin Virus Strains

The effect of the attenuated XJC13 and XJ0 strains of Junin virus (JV) was studied in guinea pigs infected before and during pregnancy. The 58% mortality rate in animals infected during gestation and the 16.7% mortality rate in chronically infected animals were attributed to a viral effect. An abortion rate of 33% occurred in animals infected before the 7th week of gestation. Regardless of the time of infection, JV was isolated from central nervous system tissue, placentas, and fetuses of animals killed just before parturition, even when circulating neutralizing antibodies were present. Results confirmed that transplacental infection is a regular event and showed that guinea pigs are more susceptible to attenuated JV strains during pregnancy, most probably due to immunosuppression, hormonal changes, or both.

Modification of Junin Virus Neurotropism in Mice by Selective Brain or Spinal Cord Passaging

The percentage of suckling mice that developed paralysis after intracerebral Junin virus (XJ-JV pathogenic strain) inoculation (13.8%) consistently increased after 5 serial passages of virus-infected brain or spinal cord obtained from paralytic animals, reaching 37.9 and 45.7%, respectively. As expected, all paralytic mice exhibited an identical spinal cord histologic picture, with widespread JV antigen in spinal cord astrocytes and neurons, particularly the large motor neurons of the anterior horn. These findings strongly support the existence of a motor neurotropic viral particle subpopulation in parental XJ-JV stock.