Rabies in southeast Brazil: a change in the epidemiological pattern.

This epidemiological study was conducted using antigenic and genetic characterisation of rabies virus isolates obtained from different animal species in the southeast of Brazil from 1993 to 2007. An alteration in the epidemiological profile was observed. One hundred two samples were tested using a panel of eight monoclonal antibodies, and 94 were genetically characterised by sequencing the nucleoprotein gene. From 1993 to 1997, antigenic variant 2 (AgV-2), related to a rabies virus maintained in dog populations, was responsible for rabies cases in dogs, cats, cattle and horses. Antigenic variant 3 (AgV-3), associated with Desmodus rotundus, was detected in a few cattle samples from rural areas. From 1998 to 2007, rabies virus was detected in bats and urban pets, and four distinct variants were identified. A nucleotide similarity analysis resulted in two primary groups comprising the dog and bat antigenic variants and showing the distinct endemic cycles maintained in the different animal species in this region.

Comparison between RT-PCR and the mouse inoculation test for detection of rabies virus in samples kept for long periods under different conditions.

Antigenic and genetic analyses are important tools for retrospective studies of rabies epidemiology in specific geographical areas. Virus recovery and re-isolation from archival samples conserved for long periods at freezing temperature are essential for these studies. Prolonged preservation, associated with temperature variations, causes significant loss of virus viability. However, molecular tools, such as RT-PCR, can overcome this problem. For this purpose, 95 positive samples stored for 4-13 years at -20 and -80 degrees C were evaluated by mouse inoculation test and RT-PCR. Only 32 (33.6%) of the samples were positive with the mouse inoculation test, while RT-PCR detected the viral genome in 62 (65.3%) samples. When the samples were analyzed in relation to storage period, there was a significant difference in those stored for >10 years, with 59.7% positivity for RT-PCR and 22.1% for mouse inoculation test. The present study confirms the significance of RT-PCR for detection of viral genomes in archival samples, including those in an apparent state of decomposition.