Rabies laboratory diagnosis: Peculiar features of samples from equine origin

Rabies laboratory diagnosis is performed by using microscopic examination for Negri bodies (MEN), fluorescent-antibody test (FAT) and mouse inoculation test (MIT). In the majority of cases, when specimens are properly collected and conserved and the laboratory worker has good experience, agreement among employed techniques is verified. Comparing the sensitivity of these three diagnosis techniques in 3,713 samples (hippocampus and brain stem) received during 1981-1994 period, being 3,010 from bovine (983 positives) and 703 from equine (Ill positives) species, it was observed that in equine rabid samples, this agreement was not maintained. For the latter specie, only in few opportunities the Negri bodies could be observed. With respect to FAT, the test detected a lower percentage of positive equine samples compared to bovine species. Statistical analysis demonstrated that the difference was significative. Mouse inoculation test proved to be more sensitive. However, a significant difference in mice incubation period was observed for samples from both species. The absence of inclusion bodies and the longer incubation period for equine samples suggest that rabies pathogenesis studies for equine species have to be intensified.