Light-microscopical diagnosis of rabies. A reappraisal

A comparative study of the fluorescent antibody test for rabies diagnosis in fresh and formalin-fixed brain tissue specimens

Many diagnostic methods have been used to detect rabies virus antigen. The preferred method for routine diagnosis of rabies in fresh or frozen brain tissues is the fluorescent antibody test (FAT). In this study, the FAT was used to evaluate the rabies status of fresh/frozen brain specimens from more than 800 rabies-suspected cases, in more than 14 different species of animals. A comparable brain specimen from each case was fixed in 10% buffered formalin and examined by the FAT. The evaluation of rabies status between fresh and formalin-fixed tissues was in agreement in more than 99.8% of the cases. When fresh tissue is not available for testing, these results validate the use of this procedure for routine diagnosis of rabies in formalin-fixed brain tissues.

Detection of infection or infectious agents by use of cytologic and histologic stains

A wide variety of stains are useful for detection of different organisms or, for viruses, the cytopathologic changes they induce, in smears prepared directly from clinical specimens and in tissue sections. Other types of stains, such as hematoxylin and eosin, are used routinely to stain tissue sections and are most valuable for assessing the immunologic response of the host to the invading pathogen. In many cases, the pattern of inflammation provides important clues to diagnosis and helps to guide the selection of additional "special" stains used predominantly for diagnosis of infectious diseases. A stain may be nonspecific, allowing detection of a spectrum of organisms, as do the Papanicolaou stain and silver impregnation methods, or detection of only a limited group of organisms, as do the different acid-fast techniques. Some nonspecific stains, such as the Gram stain, are differential and provide valuable preliminary information concerning identification. Immunohistochemical stains, on the other hand, are specific for a particular organism, although in some cases cross-reactions with other organisms occur. Despite the wealth of information that can be gleaned from a stained smear or section of tissue, however, the specific etiology of an infection often cannot be determined on the basis of only the morphology of the organisms seen; culture data are essential and must be considered in the final diagnosis.

A dipstick dot enzyme immunoassay for detection of rabies antigen

A dipstick Dot enzyme immuno diagnosis test was standardized to detect rabies viral antigens from brain, of rabies-suspected dogs, cattle, horses, cats and goats. This test was compared with the direct fluorescent antibody test (FAT). When compared to the direct FAT, the dipstick dot ELISA test did not produce non-specific false-positive results and was therefore specific and reliable. The advantages of the dipstick Dot-ELISA are discussed.

Evaluation of five different methods for routine diagnosis of rabies

Brain tissue from 187 animals of different species was investigated by means of fluorescent antibody test, peroxidase anti-peroxidase technique, mouse inoculation test and cell culture technique for a diagnosis of rabies. With peroxidase anti-peroxidase technique the rabies specific reaction comprised inclusion bodies and a granular staining of the cytoplasm of affected cells. A specific positive reaction was found only in neurons, in which perikaryon as well as cell processes were affected. Fluorescent antibody test and peroxidase anti-peroxidase technique detected 98% each, mouse inoculation test 95% and cell culture technique 81% of the rabies positive animals. In conclusion, peroxidase anti-peroxidase technique allows a highly reliable diagnosis of rabies when only formalin-fixed and paraffin-embedded material is available. Histopathological alterations comprising Negri bodies, inflammatory and degenerative lesions were encountered in 53% of the rabies positive brains.

Comparison of enzyme immunodiagnosis with immunofluorescence for rapid diagnosis of rabies in dogs

A comparison between Direct Immunofluorescence Test (FAT) and Rapid Rabies Enzyme Immunodiagnosis test (RREID) was made to detect rabies viral antigens from the brain and salivary gland tissues of experimentally infected and in rabies suspected dogs. Both the tests presented an efficiency level of 100 per cent and both are equally sensitive.

Morphological characteristics of a unique intracytoplasmic neuronal inclusion body

Unique intracytoplasmic inclusion bodies unaccompanied by a clinically apparent neurologic disease were found in the neurons of the hippocampus, subiculum, and mammillary body of a man who died suddenly, presumably of cardiac disease. The eosinophilic inclusions were round and often targetoid , with a central core that had the staining characteristics of RNA. Ultrastructurally, the inclusions were mainly composed of osmiophilic granular material. Rabies viral antigen was not detected by immunofluorescence, and heavy metals were not detected by energy dispersive spectrometry. These neuronal inclusions should be distinguished from Negri bodies.