The genetic and antigenic variability of the G glycoproteins from 76 human respiratory syncytial (RS) viruses (subgroup A) isolated during six consecutive epidemics in either Montevideo, Uruguay, or Madrid, Spain, have been analyzed. Genetic diversity was evaluated for all viruses by the RNase A mismatch cleavage method and for selected strains by dideoxy sequencing. The sequences reported here were added to those published for six isolates from Birmingham, United Kingdom, and for two reference strains (A2 and Long), to derive a phylogenetic tree of subgroup A viruses that contained two main branches and several subbranches. During the same epidemic, viruses from different branches were isolated. In addition, closely related viruses were isolated in distant places and in different years. These results illustrate the capacity of the virus to spread worldwide, influencing its mode of evolution. The antigenic analysis of all isolates was carried out with a panel of anti-G monoclonal antibodies that recognized strain-specific (or variable) epitopes. A close correlation between genetic relatedness and antigenic relatedness in the G protein was observed. These results, together with an accumulation of amino acid changes in a major antigenic area of the G glycoprotein, suggest that immune selection may be a factor influencing the generation of RS virus diversity. The pattern of RS virus evolution is thus similar to that described for influenza type B viruses, expect that the level of genetic divergence among the G glycoproteins of RS virus isolates is the highest reported for an RNA virus gene product.

Partial sequences of the G protein gene of 33 isolates from antigenic group B of human respiratory syncytial virus were determined. Phylogenetic analysis indicated that the evolutionary pattern of group B viruses is similar to that previously described for isolates of antigenic group A, including worldwide distribution of related viruses and co-circulation of viruses from different lineages during the same epidemic. Dominance of AGM GA over UCM CU transitions was observed when G sequences of group B viruses were compared, as previously found in viruses from antigenic group A. Interestingly, differences in protein length, determined by the usage of alternative termination codons, were more pronounced in group B than in group A viruses. Changes in protein length correlated with the classification of viruses in different lineages. Thus, mutations that determined termination codon usage seem to have played an important role in the diversification of group B viruses.Human respiratory syncytial virus (HRSV) is the leading cause of severe lower respiratory tract infections in infants and very young children (Collins et al., 1996). The virus is distributed worldwide and in temperate climates outbreaks of HRSV infections occur yearly as sharp peaks of activity in winter months. This epidemiological pattern differs in tropical countries where HRSV infections are distributed throughout extended periods of time, mainly during the rainy seasons (Heirholzer et al., 1994). Although severe HRSV infections occur most frequently during infancy, there is growing evidence that HRSV is an important pathogen for the elderly

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.

Surveillance for HIV infection among people at increased risk was conducted in five countries in South America. Seroprevalence studies were conducted in more than 36,000 people in Ecuador, Peru, Boliva, Uruguay, and Argentina, along with genetic analysis of the HIV-1 strains. In all countries, the prevalence of HIV-1 among men who have sex with men (MSM) was high (3-30%), whereas the prevalence among female commercial sex workers (FCSMs) was low (0.3-6%). By envelope heteroduplex mobility assay, subtype B predominated in MSM communities and in FCSWs in Ecuador, Bolivia, and Peru. A new genetic screening assay, the multiregion hybridization assay for subtypes B and F (MHA-bf), was developed to improve large-scale genetic screening in South America. MHA-bf can screen four regions of the genome for subtype B or subtype F, and thus can detect most recombinants. The sensitivity of MHA-bf when applied to a panel of pure subtypes and CRF12_BF was 100%, and 88% of unique recombinants were also detected as recombinant. Using MHA-bf, more than 80% of samples from Ecuador, Peru, and Bolivia were classified as pure subtype B, whereas in Uruguay and Argentina this proportion was only 30 to 40%. BF recombinants were the most prevalent form of HIV-1 in Uruguay and Argentina. Subtype B is the most common subtype in countries lacking injecting drug use (IDU) epidemics, whereas BF recombinants are more common in countries where extensive IDU epidemics have been documented, suggesting the ontogeny of recombinant strains in particular risk groups in South America.