Development and evaluation of a solid-phase enzyme immunoassay based on Andes hantavirus recombinant nucleoprotein.

Hantavirus pulmonary syndrome (HPS) with high mortality rate has been reported in five countries in South America. Rapid accurate methods are important both for monitoring acute infections and for epidemiological studies. The Andes virus nucleoprotein amino acid sequence has a high identity percentage compared with other sequences of this region and has been chosen for the development of diagnostic reagents. Andes nucleoprotein expressed in Escherichia coli was applied as antigen in IgG, IgA and mu-capture IgM enzyme-linked inmunosorbent assays (ELISAs). An evaluation of this reagent was conducted to establish its usefulness for differential diagnosis of HPS and seroprevalence studies. Samples from 135 reverse transcription (RT)-PCR-confirmed HPS cases, 77 individuals with other respiratory infections and 957 healthy inhabitants from endemic and non-endemic areas were analysed. The hantavirus-infected patients had an early and strong IgM, IgG and IgA serum antibody response, in most of the cases as early as 1, 7 and 1 days following onset of symptoms, respectively. IgM and IgG detection showed a specificity and sensitivity of 100%. Andes-specific IgM antibodies were found in all patients in the first available sample, which remained detectable for at least 43 days. Specific IgA antibodies were also detected in saliva of patients with acute HPS. The short duration of the disease and the risk for contacts due to person-to-person transmission of Andes virus necessitate the use of highly sensitive tests which might lead to earlier detection of infected people and improve the treatment and management of patients with HPS.

Junín virus persistence in mice.

Newborn mice surviving intracerebral infection with Junín virus (JV) strain XJ showed viral persistence in brain up to 140 days post-infection (p.i.). Mild meningoencephalitis or encephalitis, but not the neutralizing antibody titres (NtAb) correlated with virus presence.

[Association of the infection of the thymus and bone marrow with the establishment of persistent infection with Junin virus in 2 genera of rodents]. / Asociación de la infección del timo y médula ósea con el establecimiento de la infección persistente con virus Junín en dos géneros de roedores.

Junin virus infection of immune system organs was correlated with persistence establishment in the mouse and rat. Rockland mice under 24 or at 72 and 120 h of age received 10(4) pfu of Junin virus XJ strain by ic route. Separately, two groups of mice under 24 h old were infected with the same dose of XJ or XJCl3 strain by the same route respectively. Results showed that higher thymus virus titer correlated with greater survival. In turn, the former also seemed to correlate with decreasing age at inoculation time, although there was considerable strain dependence. In order to correlate replication levels in thymus with clinical progress in mice, animals under 24 h of age were inoculated with XJ. At 14 days pi apparently healthy mice from this batch were separated from those presenting severe neurologic sings. In the asymptomatic mice, thymus titers ranged from 1.7 to 3.2 log, while no virus was found in thymus harvested from obviously ill animals. However brain virus titers in the two groups proved similar. To confirm these findings, 72 h old Wistar rats were inoculated in with 10(4) pfu of either Junin virus strain: with XJ strain (90% survival) virus could be readily isolated from thymus and bone marrow at day 7 pi, whereas with XJCl3 (5% survival) no virus could be rescued from any organ tested. Therefore, our results strongly suggest a close correlation between productive thymic infection and Junin virus persistence establishment in these rodents, depending on immune response regulation rather than on viral variation.

[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)

Viral reactivation and pseudotype production in an in vitro superinfection system with two different strains of HIV-1.

Viral production and variability of HIV-1 is normally high in vivo causing the necessary conditions for cellular superinfection. In order to evaluate the superinfection dynamics in vitro, H9HTLVIIIB cell line was superinfected with HIVMN. Superinfected cells showed nearly 50% cell mortality at day 1 post-superinfection (ps), which increased significantly up to day 4 ps. Superinfecting genome was detectable until day 10 ps. The superinfecting strain was found in the supernatant only on day 1 ps, but was recovered up to day 4 ps by coculture with non-infected cells. The existing strain (HIVHXB2) was recovered throughout the studied period. Pseudotype formation by the HIVHXB2 genome and envelope proteins of the superinfecting strain (HIVMN) was observed from day 1 to 6 ps. Viral production was increased by 1.7 LOG in superinfected cells from day 1 ps. Both viral production increase and pseudotype formation could be relevant for HIV pathogenesis in vivo.

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.

Oxytocin and prostaglandins F2alpha and E2 do not enhance HIV antigen production in vitro.

Oxytocin and prostaglandins (PGs) are hormones involved in labor and are used clinically for its induction. In this study the effect of oxytocin, PGF(2alpha), and PGE(2) on Humour immunodeficiency virus-1 production in acutely and persistently infected cells was measured. No significant effect on p24 antigen production was found with oxytocin or PGs, except for a transient decrease in persistently infected cells treated with 1 micro M PGF(2alpha). These results showed that oxytocin and PGs could be used clinically for labor induction without any direct enhancement in viral production. Besides, the results with PGF(2alpha) at the highest concentration studied may indicate a pharmacological effect.

Identification of human immunodeficiency virus type 1 subtypes B and F B/F recombinant and dual infection with these subtypes in Argentina.

DNA sequences encoding the third variable region (V3) of human immunodeficiency virus type-1 (HIV-1) envelope glycoprotein gp120 were obtained from 18 infected individuals residing in different regions of Argentina. Proviral DNA representing the env V3 region was obtained by PCR from uncultured peripheral blood mononuclear cells (PBMC) and genetic heterogeneity was examined by phylogenetic analysis. Sequences representing the gag p17 region were also obtained for a subset of these samples. Moreover, 1 sample that it was not possible to classify according to initial phylogenetic analysis was further analysed by molecular cloning of both V3 and p17 regions. Phylogenetic analysis according to different methodologies were performed comparing obtained sequences with a set of reference sequences representing previously characterized HIV-1 subtypes. The recombinant identification program (RIP) was used to study the presence of possible recombinant sequences. Phylogenetic analysis demonstrated that viruses representing both subtypes B and F are circulating among HIV-1 infected individuals in Argentina. In addition, RIP analysis showed that an initially unclassified sequence exhibited similarities to subtypes B and F in different fragments of the V3 region. Separate phylogenetic analysis of each of these fragments revealed divergent clustering, suggesting that this sequence harbours a point of recombination within the V3 loop. Interestingly, we also identified a dually infected individual with viruses belonging to subtypes B and F, as demonstrated by molecular cloning analysis of the env V3 and the gag p17 regions. Taken together, our study shows that both subtypes B and F are circulating in different regions of Argentina. Moreover, the data presented here show that dual infections with subtypes B and F can occur, and consequently B/F recombinant sequences are arising in the region.

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.

Hantavirus pulmonary syndrome outbreak in Argentina: molecular evidence for person-to-person transmission of Andes virus.

An increase of Hantavirus Pulmonary Syndrome (HPS) cases around a southwestern Argentina town and in persons living 1400 km away but in contact with those cases was detected during the spring of 1996. In order to evaluate person-to-person transmission we compared the homology of PCR-amplified viral sequences of 26 Argentine and Chilean cases. Sixteen of them were epidemiologically linked cases and had the same sequence (Epilink/96) in the S segment 3' noncoding region and in the M segment partial G1 and G2 region (a total of 1075 nucleotides). Contrarily, two geographical and contemporary but nonepidemiologically related cases differed from Epilink/96 in the compared regions. No significant differences, such as glycosylation or hydrophilic pattern, were found between Epilink/96 and the other sequences. Nucleotide and deduced amino acid sequence homologies between samples from southern Argentina and Chile ranged from 90.9 to 100% and 96.4 to 100%, respectively. Phylogenetic analysis revealed that all the analyzed southwestern viruses belong to the Andes lineage. Although human infection principally occurs via inhalation of contaminated rodent excreta, our results with Andes virus show the first direct genetic evidence of person-to-person transmission of a hantavirus.

Different integrated and unintegrated HIV-1 DNA after superinfection and cell to cell transmission.

Efficient superinfection of H9HTLVIIIB cell line (persistently infected with HIVHXB2 strain) with HIVMN strain is reported. The superinfecting viral DNA was found in the chromosomic and extrachromosomic fractions at early stages, but at 48 hours post superinfection, it remained mainly unintegrated. Interestingly, superinfected cells only produced HIVHXB2 in the supernatant and no increase of viral yield of this persistent virus was observed. Remarkably, virions of both strains. HIVHXB2 and HIVMN, were recovered after cocultivating superinfected cells with MT2 cell line. In the extrachromosomic fractions of seven different superinfected subclons of H9HTLVIIIB, viral DNA of the superinfecting HIVMN strain predominated while in the chromosomic fraction, the proportion of superinfecting viral DNA differed. The study of the presence of different integrated and unintegrated genomes in a single cell could be crucial in the understanding of HIV biology.

Genetic diversity, distribution, and serological features of hantavirus infection in five countries in South America.

Since 1995 when the first case of hantavirus pulmonary syndrome (HPS) was reported in Patagonia, there have been more than 400 cases of HPS reported in five countries in South America. The first case of HPS was associated with Andes (AND) virus. In this study, we report on the genetic diversity, geographical distribution, and serological features of hantavirus infection in six countries in South America based on 87 HPS cases from Argentina, Bolivia, Chile, Paraguay, and Uruguay. An early immunoglobulin M (IgM), IgA, and IgG humoral response was observed in almost all HPS cases. The IgM response appears to peak 1 or 2 days after the onset of symptoms. Peak IgG antibody titers occur mostly after the first week. Low IgG titers or the absence of IgG was associated with higher mortality rates. The IgA response peaks around day 15 and then rapidly decreases. The results of phylogenetic analysis based on partial M-fragment G1- and G2-encoding sequences showed that HPS cases from the five countries were infected with viruses related to AND or Laguna Negra (LN) virus. Within AND virus-infected persons, at least five major genetic lineages were found; one lineage was detected in Uruguayan and Argentinean cases from both sides of the Rio de la Plata river. Two Paraguayan patients were infected with a virus different from LN virus. According to the results of phylogenetic analyses, this virus probably belongs to a distinct lineage related more closely to the AND virus than to the LN virus, suggesting that there is probably an Oligoryzomys-borne viral variant circulating in Paraguay. These studies may contribute to a better understanding of hantavirus human infection in South America.