**3. Laboratory diagnosis of rabies in livestock**

During the eclipse phase after infection, the rabies virus replicates in non-nervous tissue such as muscle. After several days or months, the virus enters the peripheral nerves and is transported to the central nervous system and then disseminated within the CNS and the highly innervated tissues, resulting in clinical signs. Most of the virus is found in nervous tissue, salivary glands, saliva, and cerebrospinal fluid (CSF), which should all be handled with extreme caution. As there are neither gross pathognomonic lesions nor specific and constant clinical signs for rabies, confirmatory laboratory diagnosis must be performed [41]. Laboratory diagnosis of rabies is based on the direct detection of rabies viral antigen using different histopathological and serological techniques with the dominance of fluorescent antibody test (FAT) (**Figure 4**). RABV infection induces the formation of cytosolic protein aggregates called Negri Bodies (NBs) detected by histopathology. However, this test is no longer recommended for diagnosis [41]. Brain samples are tested using the rapid immuno-chromatographic and direct Fluorescent Antibody assay in Nigeria [28, 29]. In China, FAT and RT/PCR are used for diagnosing rabies [8]. Real-time PCR is used as well in different laboratories [30]. Diagnosis of rabies is performed in Ethiopia by animal inoculation, cell cultures, serological tests, histological examination, molecular methods, and immunohistochemistry [42].

In Iran, laboratory diagnosis of rabies is practiced using different techniques, antigen in saliva using mouse inoculation test (MIT), fluorescence antibody test (FAT) and rapid tissue cell inoculation test (RTCIT). Antibodies against rabies in serum and cerebrospinal fluid (CSF) using mouse neutralization test (MNT) [10].

#### **Figure 4.**

*Direct fluorescent antibody test (dFA), brain impression smears (source: Centers for Disease Control and Prevention (CDC)).*
