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In South America Andes hantavirus (ANDV) is hosted by the rodent Oligoryzomys longicaudatus (also known as pygmy rice rat). In humans, ANDV causes Hantavirus Pulmonary Syndrome (HPS), with a fatality rate of about 40%. Epidemiologic and molecular evidence has shown that ANDV can be transmitted from person to person. Sin Nombre hantavirus, occurring in North America, and ANDV are genetically related, and both cause HPS with similar clinical evolution and mortality rate. However, only ANDV is transmitted from person to person. A recent hantavirus outbreak in a small village in Southern Argentine, with 29 HPS cases and 11 deaths has brought to mind that person-to-person transmission continues to be a public health emergency. The present investigation was aimed to understand how does ANDV actually spread between persons. Tissue samples of lung and salivary glands from infected Oligoryzomys longicaudatus and lethal cases of human HPS were investigated by bright field immunocytochemistry, multichannel immunofluorescence, and transmission electron microscopy. The findings are consistent with ANDV infection and replication in the lung alveolar epithelium and macrophages, and in the secretory cells of the submandibular salivary glands. In the lung of infected Oligoryzomys longicaudatus and human cases HPS, the bulk of immunoreactive hantavirus antigens was localized in epithelial cells of the alveolar walls and macrophages. The ultrastructural study supports that in the lung of HPS patients the virus replicates in the alveolar epithelial cells with virus particles being discharged into the alveolar lumen. Virus-like particles were seen within vacuoles of the lung macrophages. Considering that these macrophages can reach the conductive segments of the airways, their expectoration becomes a deadly bullet for ANDV transmission. In the submandibular glands of infected rodents and HPS cases, ANDV antigens were in capillary endothelium, the secretory cells and filling the lumen of the excretory pathway. It is proposed that in patients with HPS caused by ANDV the alveolar epithelium and macrophages would be the gate for the airway spreading of the virus, while the salivary glands are a target for virus replication and an exit pathway through saliva.

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Borrelia burgdorferi sensu lato (s.l.), transmitted by Ixodes spp. ticks, is the causative agent of Lyme disease. Although Ixodes spp. ticks are distributed in both Northern and Southern Hemispheres, evidence for the presence of B. burgdorferi s.l. in South America apart from Uruguay is lacking. We now report the presence of culturable spirochetes with flat-wave morphology and borrelial DNA in endemic Ixodes stilesi ticks collected in Chile from environmental vegetation and long-tailed rice rats (Oligoryzomys longicaudatus). Cultured spirochetes and borrelial DNA in ticks were characterized by multilocus sequence typing and by sequencing five other loci (16S and 23S ribosomal genes, 5S-23S intergenic spacer, flaB, ospC). Phylogenetic analysis placed this spirochete as a new genospecies within the Lyme borreliosis group. Its plasmid profile determined by polymerase chain reaction and pulsed-field gel electrophoresis differed from that of B. burgdorferi B31A3. We propose naming this new South American member of the Lyme borreliosis group B. chilensis VA1 in honor of its country of origin.

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BACKGROUND: In Chile, three Hantavirus seropositive rodent species (O longicaudatus, A olivaceus and A longipilis) are distributed from the Pacific coast to the Andes mountains and represent nearly 90% of the rodents captured in the Xth Region. AIM: To study the seroprevalence of Hantavirus among captured rodent species and its relationship with the appearance of human cases of pulmonary syndrome. MATERIAL AND METHODS: From May 1998 to September 2001, 675 rodents were captured in the region. Serum samples were tested by ELISA for the presence of IgG antibodies against Andes and Sin Nombre virus. Sera from human cases with a suspected Hantavirus infection were analyzed for IgM antibodies against Black Lagoon virus and for IgG antibodies against Andes and Sin Nombre virus. RESULTS: Twenty two of the 675 rodents were seropositive for the virus, 18 O longicaudatus and 4 A longipilis. Regional seroprevalence changed from 2.2% in 1998, 0.0% in 1999, 1.0% in 2000 and up to 7.1% in 2001. A total of 77 positive human cases were studied from 1998 to March 2002. Although there were positive cases in all seasons, data showed a spring-summer seasonal preponderance. A relationship between the flowering of "colihue" bushes and the increased values of rodent abundance, seroprevalence and positive animals was established. CONCLUSIONS: A dispersal movement of O longicaudatus to open habitats close to human outdoor activities during the dry season was confirmed.

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A discriminant analysis on vegetational variables was performed in order to determine differences in habitat utilization by two sympatric Chilean rodents. Akodon olivaceus brachiotis is associated with vegetational variables that provide greater cover from above. Oryzomys longicaudatus philippii, on the other hand, is related with structural variables such as foliage density, which provide dense areas with thick understory that offer protection from a horizontal viewing. A clear relationship was found between shrub and herbaceous cover and length of species hindfoot.

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Ecological divergences in two congeneric sympatric woodland rodents, Akodon olivaceus brachiotis and Akodon longipilis apta (Family Cricetidae) was demonstrated from determination of energetic bud gets and food preferences. It was found that each species posseses a different bioenergetic strategy. The heavier (A. longipilis) species has a larger daily energetic budget as compared to the lighter one (A. olivaceus). This phenomenon can be partially explained by their differential selection of seeds.Finally, it is hypothesized that these ecological differences could be important in enabling the coexistence for these species.