MOLECULAR EPIDEMIOLOGY OF RABIES EPIZOOTICS IN TEXAS

Background: Texas is in the midst of two independent epizootics of rab ies, involving coyotes (Canis latrans) and domestic dogs (Canis famili aris) in southern Texas and grey foxes (Urocyon cinereoargenteus) in w est central Texas. The domestic dog/coyote (DDC) and grey fox (TF) rab ies virus variants cannot be differentiated by antigenic typing with c urrently available monoclonal antibodies. These two variants also cann ot be distinguished from a third variant, Sonora dog (SD) rabies, that is not enzootic in Texas, but occasionally occurs in animals along th e western border with Mexico. Objectives: To determine a method for th e differentiation of the DDC, TF and SD variants, which is essential f or epidemiologic monitoring of the Oral Rabies Vaccination Program (OR VP), a program instituted to control rabies in coyotes and grey foxes in Texas. Study Design: Primers complementary to nucleoprotein sequenc e of either the DDC or TF rabies virus permit specific reverse transcr iption and amplification by polymerase chain reaction. In addition, ge neral primers, which recognize a broad range of rabies variants, used in conjunction with a restriction digest for the differentiation of DD C, TF or SD rabies virus were investigated. Results and Conclusions: O f 122 specimens tested with specific primers, 111 (91%) were specifica lly identified as either DDC (33 samples) or TF (78 samples). Overly s tringent conditions, enzyme inhibitors, or limiting RNA may account fo r the 11 non-amplifications. Amplification of RNA under less stringent conditions, with primers recognizing a broad range of rabies variants followed by digestion with either restriction enzyme Desulfovibrio de sulfuricans I(DdeI) or Haemophilus influenzae Rf. (HinfI), was used to identify the 11 isolates that did not amplify with specific primers ( 6 DDC, 4 TF and 1 SD). In addition to these 11 isolates, the less stri ngent method of amplification, followed by enzyme digestion has identi fied a total of 125 additional specimens (26 DDC, 94 TF and 5 SD) that were not tested by variant-specific amplification. These data provide a means to track the spread of the different rabies virus variants an d allow the ORVP to plan its vaccine disbursement by defining the two epizootic boundaries. (C) 1997 Elsevier Science B.V.