Discrimination between epidemiological cycles of rabies in Mexico

The design of efficient rabies control programs within a geographic area requires an appropriate knowledge of the local epidemiological cycles. In Latin America, there is a geographical overlap of the two main epidemiological cycles: (a) the terrestrial cycle, where the dog is the main terrestrial vector and the principal cause of human transmission; and (b) the aerial cycle, in which the vampire bat Desmodus rotundus is representative in Mexico. This bat is the major sylvatic rabies vector transmitting rabies to cattle. The purpose of this study was to distinguish between the epidemiological cycles of rabies virus (aerial and terrestrial) circulating in Mexico, using restriction fragment length polymorphism (RFLP).

Thirty positive rabies isolates were obtained from different species (including humans, domestic, and wildlife animals) and geographical regions. The methodology included the extraction of RNA, and synthesis of cDNA, PCR, and RFLP using four restriction endonucleases. To determine the aerial cycle, BsaW I and BsrG I were utilized, and for terrestrial cycle, BamH I and Stu I. Most of the samples belonged to the aerial and terrestrial cycles, except for two skunk isolates from Northwestern Mexico, which were not cut by any of the enzymes.

Three different migration patterns were detected: (a) the first was observed in six amplicons, which were cut by BsaW I and BsrG I (aerial cycle); (b) 19 amplified samples were digested with BamH I and Stu I enzymes (terrestrial cycle); and (c) two skunk isolates from Northwest Mexico, were not cut by any of the enzymes utilized in the experiments (hypervariable cycle).

This concludes that RFLP can be used for the classification of rabies field samples in epidemiological studies. Moreover, it has demonstrated its usefulness, not only for differentiating between the main epidemiological rabies cycles present in Mexico, but also to detect new cycles in wildlife species.