Discrimination between epidemiological cycles of rabies in Mexico

Background. The design of efficient rabies control programs within a geogra phic area requires an appropriate knowledge of the local epidemiological cy cles. In Latin America, there is a geographical overlap of the two main epi demiological cycles: (a) the terrestrial cycle, where the dog is the main t errestrial vector and the principal cause of human transmission; and (b) th e aerial cycle, in which the vampire bat Desmodus rotundus is representativ e in Mexico. This bat is the major sylvatic rabies vector transmitting rabi es to cattle. The purpose of this study was to distinguish between the epid emiological cycles of rabies virus (aerial and terrestrial) circulating in Mexico, using restriction fragment length polymorphism (RFLP). Methods. Thirty positive rabies isolates were obtained from different speci es (including humans, domestic, and wildlife animals) and geographical regi ons. The methodology included the extraction of RNA, and synthesis of cDNA, PCR, and RFLP using four restriction endonucleases. To determine the aeria l 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 cycl es, except for two skunk isolates from Northwestern Mexico, which were not cut by any of the enzymes. Results. Three different migration patterns were detected: (a) the first wa s observed in six amplicons, which were cut by BsaW I and BsrG I (aerial cy cle); (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 c ycle). Conclusions. This concludes that RFLP can be used for the classification of rabies field samples in epidemiological studies. Moreover, it has demonstr ated its usefulness, not only for differentiating between the main epidemio logical rabies cycles present in Mexico, but also to detect new cycles in w ildlife species. (C) 1999 IMSS. Published by Elsevier Science Inc.