Immunoperoxidase test for rabies: utility as a diagnostic test

Diagnostic sensitivity and specificity of immunohistochemistry for the detection of rabies virus in domestic and wild animals in South Africa

We estimated the diagnostic sensitivity (DSe) and specificity (DSp) of an immunohistochemistry (IHC) protocol compared to the direct fluorescent antibody test (DFAT), which is the gold standard test for rabies diagnosis. We obtained brain samples from 199 domestic and wild animal cases (100 DFAT-negative, 99 DFAT-positive), by convenience sampling from 2 government-accredited rabies virus (RABV) testing laboratories in South Africa, between February 2015 and August 2017. Tissues that had been stored at 4-8°C for several days to weeks at the 2 accredited laboratories were formalin-fixed and paraffin-embedded. Nighty-eight cases tested IHC-positive using a polyclonal anti-RABV nucleoprotein antibody and a polymer detection system. The overall DSe and DSp for the RABV IHC test were 98% (95% CI: 93-100%) and 99% (95% CI: 95-100%), respectively. Domestic dogs accounted for 41 of 98 RABV IHC-positive cases, with the remainder in 4 domestic cats, 25 livestock, and 28 wildlife. Herpestidae species, including 7 meerkats and 9 other mongoose species, were the most frequently infected wild carnivores, followed by 11 jackals. Three cases in domestic dogs had discordant test results; 2 cases were IHC-/DFAT+ and 1 case was IHC+/DFAT-. Considering the implications of a false-negative rabies diagnosis, participating in regular inter-laboratory comparisons is vital, and a secondary or confirmatory method, such as IHC, should be performed on all submitted specimens, particularly negative cases with human contact history.

Application and Comparative Evaluation of Fluorescent Antibody, Immunohistochemistry and Reverse Transcription Polymerase Chain Reaction Tests for the Detection of Rabies Virus Antigen or Nucleic Acid in Brain Samples of Animals Suspected of Rabies in India

Accurate and early diagnosis of animal rabies is critical for undertaking public health measures. Whereas the direct fluorescent antibody (DFA) technique is the recommended test, the more convenient, direct rapid immunochemistry test (dRIT), as well as the more sensitive, reverse transcription polymerase chain reaction (RT-PCR), have recently been employed for the laboratory diagnosis of rabies. We compared the three methods on brain samples from domestic (dog, cat, cattle, buffalo, horse, pig and goat) and wild (leopard, wolf and jackal) animals from various parts of India. Of the 257 samples tested, 167 were positive by all the three tests; in addition, 35 of the 36 decomposed samples were positive by RT-PCR. This is the first study in which such large number of animal samples have been subjected to the three tests simultaneously. The results confirm 100% corroboration between DFA and dRIT, buttress the applicability of dRIT in the simple and rapid diagnosis of rabies in animals, and reaffirm the suitability of RT-PCR for samples unfit for testing either by DFA or dRIT.

Rabies - epidemiology, pathogenesis, public health concerns and advances in diagnosis and control: a comprehensive review

Rabies is a zoonotic, fatal and progressive neurological infection caused by rabies virus of the genus Lyssavirus and family Rhabdoviridae. It affects all warm-blooded animals and the disease is prevalent throughout the world and endemic in many countries except in Islands like Australia and Antarctica. Over 60,000 peoples die every year due to rabies, while approximately 15 million people receive rabies post-exposure prophylaxis (PEP) annually. Bite of rabid animals and saliva of infected host are mainly responsible for transmission and wildlife like raccoons, skunks, bats and foxes are main reservoirs for rabies. The incubation period is highly variable from 2 weeks to 6 years (avg. 2-3 months). Though severe neurologic signs and fatal outcome, neuropathological lesions are relatively mild. Rabies virus exploits various mechanisms to evade the host immune responses. Being a major zoonosis, precise and rapid diagnosis is important for early treatment and effective prevention and control measures. Traditional rapid Seller's staining and histopathological methods are still in use for diagnosis of rabies. Direct immunofluoroscent test (dFAT) is gold standard test and most commonly recommended for diagnosis of rabies in fresh brain tissues of dogs by both OIE and WHO. Mouse inoculation test (MIT) and polymerase chain reaction (PCR) are superior and used for routine diagnosis. Vaccination with live attenuated or inactivated viruses, DNA and recombinant vaccines can be done in endemic areas. This review describes in detail about epidemiology, transmission, pathogenesis, advances in diagnosis, vaccination and therapeutic approaches along with appropriate prevention and control strategies.

Identification and genetic characterization of rabies virus from Egyptian water buffaloes (Bubalus bubalis) bitten by a fox

Rabies is caused by negative strand RNA-virus classified in the genus Lyssavirus, family Rhabdoviridae of the order Mononegavirales. The aim of the present study was to identify and analyze nucleotides sequence of nucleoprotein (N) gene of rabies virus (RABV) from two cases of water buffaloes (Bubalus bubalis) bitten by a fox in Egypt, 2013. The diseased buffaloes showed nervous manifestations with fever. Specimens from brains of the buffaloes with suspected rabies were collected. RABV in collected samples was identified using direct fluorescent antibody (dFA) technique, histopathological examination and reverse transcription-polymerase chain reaction (RT-PCR). Also, nucleotides sequence of partially amplified nucleoprotein (N) gene was compared with the other street strains of RABV available on GenBank. The results revealed that RABV antigen was identified in the brains of diseased buffaloes by dFA technique and the characteristic intracytoplasmic inclusions (Negri bodies) and RABV nucleic acid were detected by histopathology and RT-PCR, respectively. The identified virus showed close genetic relationship with street strains identified previously from dogs in different Governorates in Egypt and with strains identified in Israel and Jordan indicating transmission of the virus between Egyptian Governorates with a potential transmission from and/or to our neighboring countries.

Enfermedad neurológica bovina con diagnóstico no conclusivo en la región norte de Colombia. Análisis histológico e inmunohistoquímico

<p>La enfermedad neurológica bovina genera altas pérdidas económicas en las ganaderías y algunos de sus agentes etiológicos son zoonóticos, hechos que hacen prioritario su estudio. El objetivo del trabajo fue identificar antígenos del virus de la rabia y del herpes virus bovino-5 (BoHV-5) en muestras de encéfalos de bovinos archivados como casos de enfermedad neurológica con diagnóstico no conclusivo. Se seleccionaron 10 muestras del laboratorio del Instituto Colombiano Agropecuario -ICA- de Montería. Los tejidos fueron analizados mediante histopatología e inmunohistoquímica; para esta última técnica fueron utilizados tres anticuerpos: dos contra antígenos del virus de la rabia a una dilución de 1:200 y uno contra BoHV-5 a una dilución de 1:100. Histológicamente en nueve casos se observaron lesiones que variaron de tipo y severidad; la identificación de antígenos del virus de la rabia se demostró en 20% (2/10) de los casos y en ningún caso se demostró la presencia BoHV-5. Se discute sobre los resultados histopatológicos e inmunohistoquímicos y se concluye la importancia de asociar los hallazgos de las dos técnicas para establecer la etiología de la enfermedad neurológica, especialmente en casos con diagnóstico inconcluso.</p>

Sequence analysis of attachment gene of lumpy skin disease and sheep poxviruses

In Egypt, protection of cattle against lumpy skin disease (LSD) was carried out using a sheep poxvirus (Kenyan strain) vaccination strategy. In the present study 15 skin nodules from LSD suspected cows and 5 scab samples from sheep pox (SP) suspected sheep were collected. Hyperimmune rabbit sera to Lumpy skin disease virus (LSDV)/Ismailyia88 strain and sheep pox virus (SPV)/ Kenyan vaccinal strain were prepared. The causative agent in the collected samples was identified using immunoflourescence (IF) and immunoperoxidase techniques. Of the 15 skin nodules suspected of LSD, 10 showed a positive reaction and 3 out of 5 skin scabs suspected of sheeppox were found to be positive. An antigenic correlation between field skin isolate of LSDV, tissue culture adapted LSDV/Ismailyia88 strain, field skin isolate of SPV and SPV/Kenyan vaccinal strain was studied using prepared hyperimmune sera. Also, nucleotide sequence of the PCR amplified attachment gene fragments of field skin isolate of LSDV, tissue culture adapted LSDV/Ismailyia88 strain, field skin isolate of SPV and SPV /Kenyan vaccinal strain were compared. The results revealed that the four used viruses were antigenically identical. Sequence analysis indicated that field skin LSDV isolate is more related to tissue culture adapted LSDV/Ismailyia88 strain than to vaccinal SPV/ Kenyan strain and the skin isolate of SPV is more closely related to field skin isolate of LSDV than to SPV/Kenyan vaccinal strain. Thus, further study should be applied on the advantage of a LSD vaccine prepared from LSDV in protection of cattle against LSD compared to the commonly used sheep pox vaccine.

Padronização da técnica de imuno-histoquímica para raiva em amostras de tecido do sistema nervoso central de bovinos fixadas em formol e emblocadas em parafina

Para a padronização da técnica de imuno-histoquímica para raiva foram utilizadas cinco amostras de SNC de bovinos infectados naturalmente com o vírus da raiva usando-se um anticorpo policlonal e dois monoclonais. Para a recuperação antigênica foram avaliados os seguintes reagentes: protease XIV, proteinase K e tampão citrato pH 6,0 mantido a 100ºC por 15 minutos. A detecção de antígeno rábico nas amostras foi possível com os três anticorpos utilizados. O anticorpo policlonal foi superior aos anticorpos monoclonais, demonstrando bons resultados com os três protocolos de recuperação antigênica, obtendo uma maior intensidade de marcação quando utilizado o tampão citrato e calor. A técnica de imuno-histoquímica demonstrou a presença do antígeno viral no citoplasma de neurônios na forma de agregados de grânulos ou de forma redonda ou oval, mostrando cor púsculo de inclusão viral único a múltiplos nos neurônios. A imuno-histoquímica é um método rápido, podendo ser usada na rotina em casos onde inicialmente há suspeita de raiva, especialmente em casos onde fragmentos de cérebro submetidos ao laboratório foram fixados em formol, onde as amostras não podem ser enviadas ao laboratório imediatamente e para a realização de estudos retrospectivos.

Detection of rabies viral antigens in non-autolysed and autolysed tissues by using an immunoperoxidase technique

The objectives of this study were to determine the potential of an immunoperoxidase technique involving the avidin-biotin complex (ABC) stain for the diagnosis of rabies in fresh tissues and compare it with other standard methods, including the fluorescent antibody test (FAT), haematoxylin and eosin and Seller's stain, and to investigate its capacity to detect rabies antigen in autolysed tissues. Samples of non-autolysed brain from 81 domestic and wild animals suspected of having rabies were examined. Rabies antigen was detected by FAT in 41 of these samples and Negri bodies were detected in 40 (97.6 per cent) of them by the immunoperoxidase technique, in 25 by haematoxylin and eosin and in 22 by Seller's stain. The sensitivity of the immunoperoxidase technique decreased as the tissues were left to autolyse; after two days it was 91.2 per cent, after four days 70.6 per cent, and after seven days 11.8 per cent.

Cross-reactive antigenicity of nucleoproteins of lyssaviruses recognized by a monospecific antirabies virus nucleoprotein antiserum on paraffin sections of formalin-fixed tissues

Diagnosis of rabies is routinely confirmed by detection of rabies virus antigens in acetone-fixed frozen brain tissues or imprint smears using an immunofluorescence method with commercial antirabies virus antibodies. Since recent molecular analyses disclosed wide heterogeneity in the genome sequences of rabies virus strains and related lyssaviruses, it is necessary to confirm the presence of common epitopes in these lyssaviruses. In this study we confirmed the presence of cross-reactive antigens of various lyssaviruses in paraffin sections of formalin-fixed tissue using a monospecific rabbit antiserum prepared by immunization with a recombinant nucleoprotein of rabies virus. By immunohistochemical application, the antigen was detected predominantly in the cytoplasm of neurons in the brains of mice infected with rabies virus, Duvenhage virus, Mokola virus and European bat lyssavirus-1, while no cross-reaction was observed in uninfected humans and animals including dogs, bats, and raccoons. In addition, we examined one autopsy case that was infected in a rabies-endemic nation and developed the clinical manifestation of rabies after returning to Japan in 1970, and found that the antigen was well preserved in paraffin sections of formalin-fixed tissues. Thus, this suggests that the lyssavirus-specific antigen is recognized by the monospecific antibody against rabies virus nucleoprotein, and that this cross-reactive antigen is detectable on formalin-fixed paraffin-embedded tissues by immunohistochemical analysis.

Preliminary report on a single-tube, non-interrupted reverse transcription-polymerase chain reaction for the detection of rabies virus in brain tissue

A simple method for the rapid detection of rabies virus was developed employing a single-tube reverse transcription polymerase chain reaction (RT-PCR). The method utilized a single buffer system for both RT and PCR and was performed without interruption as a single thermal cycling programme. Two primer sets within the genes coding for rabies nucleoprotein and glycoprotein were used to amplify a 533 bp and a 406 bp amplicon, respectively. The amplified products were detected with a challenge virus strain (CVS) of rabies. There was no amplified product with uninfected mouse or dog brain. The method was applied to detect rabies virus in 10 mouse inoculation test (MIT)-positive and three MIT-negative brain tissue samples. The amplified product was found only in the MIT-positive samples. The amplified product was confirmed by restriction endonuclease analysis using Hinf1. The results from RT-PCR correlated well with the results from MIT. This indicates that the single-tube RT-PCR may be a useful method for detecting rabies virus in brain tissue samples from suspected cases of rabies.

Neuronal vacuolation in raccoons (Procyon lotor)

Microscopic vacuolar changes in neuronal perikaryon are described in two free-ranging raccoons (Procyon lotor) from different geographic locations in the United States. Both animals were negative for rabies and scrapie-associated antigens. Microscopically, lesions were not seen in the neuropil. Neuronal vacuolations have previously been documented in brains of normal animals and in diseases such as rabies and prion-associated encephalopathies. Although experimental transmission of a spongiform mink encephalopathy has been documented in raccoons, a naturally occurring spongiform encephalopathy has not been described in this species. The presence of neuronal vacuolations in the raccoons is novel and requires further investigation to elucidate the mechanism of this phenomenon.

Clinicopathologic variation in raccoons infected with different street rabies virus isolates

Ten raccoons were divided into two random groups (groups 1 and 2) of five animals each. Group 1 raccoons were inoculated intramuscularly in the masseter muscle with a raccoon rabies virus isolate obtained from a natural case of raccoon rabies from the northeastern USA. Group 2 raccoons were infected by a similar route with a Latin American canine isolate of rabies virus. Raccoons either died suddenly or developed neurologic signs compatible with rabies. Clinical signs of rabies in group 1 raccoons were more severe than in group 2. Raccoons in group 1 either died acutely or were euthanized within 25 days (mean +/- SD = 20.6 +/- 2.7 days) postinfection, whereas all group 2 raccoons showed neurologic signs and were euthanized within 17 days (14.2 +/- 2.2 days) postinfection. Light microscopic findings revealed extensive nonsuppurative encephalitis predominantly located in the cerebrum and brain stem of raccoons in group 1, whereas in group 2 raccoons the lesions were confined to the brain stem regions. In group 1 raccoons, Negri bodies were commonly seen on hematoxylin and eosin (HE)-stained sections of brain and in ganglion cells of 5 other tissues (trigeminal nerve, salivary glands, duodenum, pancreas, adrenal gland). Negri bodies, however, were either absent or were only occasionally observed in corresponding tissues of raccoons infected with the canine strain (group 2). Paraffin-embedded tissue sections were also examined for Negri bodies by an immunoperoxidase test, which revealed results similar to the HE findings. Results of this study are compared with histopathologic and immunohistochemical findings in raccoons naturally infected with rabies.