Abstract
In their article “Characterization of spinal cord lesions in cattle and horses with rabies: the importance of correct sampling” (J Vet Diagn Invest 2016;28:455–460), DM Bassuino, et al., describe their sampling to detect Rabies virus (RABV) by direct fluorescent antibody test (DFAT) as follows: “Fragments of cerebral cortex, thalamus, cerebellum, medulla oblongata, and spinal cord collected at cervical, thoracic, lumbar, and sacral levels, were refrigerated and submitted for RABV detection by DFAT.” This resulted in a false-negative rate of 71.5% for 7 horses, and 23.1% for 22 cattle. However, this method constitutes improper sampling for rabies DFAT; also, the polyclonal conjugate used by the authors does not follow the Standard Protocol for Rabies Diagnosis (https://goo.gl/m7iASW). An entire cross-section of brain stem and cerebellum, rather than “fragments,” must be submitted, and approved reagents, mostly monoclonal, should be used. Diagnosis of rabies in livestock can be challenging, but it is misleading to state that immunohistochemistry is more sensitive than DFAT without first following the Standard Protocol. Please see Figure 1 for an example of unilateral distribution of RABV, which could lead to a false-negative result if sampled improperly.
Cross-section of brain stem from naturally infected donkey with rabies. Positive staining on left side of brain stem shows unilateral virus spread. Direct fluorescent antibody test. 200× magnification, frozen section.