Pathobiological investigation of naturally infected canine rabies cases from Sri Lanka

Abstract

BackgroundThe recommended screening of rabies in ‘suspect’ animal cases involves testing fresh brain tissue. The preservation of fresh tissue however can be difficult under field conditions and formalin fixation provides a simple alternative that may allow a confirmatory diagnosis. The occurrence and location of histopathological changes and immunohistochemical (IHC) labelling for rabies in formalin fixed paraffin embedded (FFPE) canine brain is described in samples from 57 rabies suspect cases from Sri-Lanka. The presence of Negri bodies and immunohistochemical detection of rabies virus antigen were evaluated in the cortex, hippocampus, cerebellum and brainstem. The effect of autolysis and artefactual degeneration of the tissue was also assessed.ResultsRabies was confirmed in 53 of 57 (93%) cases by IHC. IHC labelling was statistically more abundant in the brainstem. Negri bodies were observed in 32 of 53 (60.4%) of the positive cases. Although tissue degradation had no effect on IHC diagnosis, it was associated with an inability to detect Negri bodies. In 13 cases, a confirmatory Polymerase chain reaction (PCR) testing for rabies virus RNA was undertaken by extracting RNA from fresh frozen tissue, and also attempted using FFPE samples. PCR detection using fresh frozen samples was in agreement with the IHC results. The PCR method from FFPE tissues was suitable for control material but unsuccessful in our field cases.ConclusionsHistopathological examination of the brain is essential to define the differential diagnoses of behaviour modifying conditions in rabies virus negative cases, but it is unreliable as the sole method for rabies diagnosis, particularly where artefactual change has occurred. Formalin fixation and paraffin embedding does not prevent detection of rabies virus via IHC labelling even where artefactual degeneration has occurred. This could represent a pragmatic secondary assay for rabies diagnosis in the field because formalin fixation can prevent sample degeneration. The brain stem was shown to be the site with most viral immunoreactivity; supporting recommended sampling protocols in favour of improved necropsy safety in the field. PCR testing of formalin fixed tissue may be successful in certain circumstances as an alternative test.

Cattle rabies: the effect of clinical evolution, viral genetic lineage, and viral load on the severity of histological lesions

“…According to Maxie & Youssef (2006), NBs tend to be scarcer win sites where the inflammation is more severe. In this study, no relationship was established between NBs the intensity of the inflammatory infiltrate, as was previously observed (Langohr et al 2003, Beck et al 2017, since the region with the more severe inflammatory lesions, the medulla, was also the second most likely region to find NBs. The strain or type of virus is another factor that has been shown to influence the histological changes of rabies (Fernandes & Riet-Correa 2007).…”

“…Nervous lesions are characterized by lymphocytic and monocytic infiltration in the perivascular spaces an meninges, gliosis, and neuronal degeneration and necrosis (Beck et al 2017, Rupprecht et al 2018. Characteristic eosinophilic inclusion bodies, the Negri bodies (NBs) may be present in the neuronal cytoplasm (Beck et al 2017). It is estimated that in up to 30% of cases of rabies in cattle, NBs are not visible in routine histological staining (Barros et al 2006).…”

Rabia: 99,9% mortal, 100% prevenible

“…En Asia, se estiman 30.000 las muertes anuales por esta causa y más de 3 mil millones de personas están expuestas cada año a la rabia canina. India, Nepal, Sri Lanka, Bangladés y Pakistán son las áreas más afectadas (8)(9)(10) . En África se estiman en 24.000 las muertes anuales, la mayoría en comunidades rurales empobrecidas con un gran porcentaje de niños.…”

“…La fiebre es un elemento constante. La fase dura hasta una semana y puede manifestarse como rabia encefalítica o paralítica (9,6,(27)(28)(29)(30) .…”

Rabies-induced behavioural changes are key to rabies persistence in dog populations: investigation using a network-based model

“…Rabies virus is neurotropic and clinical manifestations of canine-rabies can be broadly classified as the dumb form (characterised by progressive paralysis) and the furious form (characterised by agitated and aggressive behaviour; (2, 3). Although the mechanisms of rabies-induced behavioural signs are poorly understood (4) pathogen-influenced changes in host behaviour can optimise pathogen survival or transmission (5).…”