Antemortem diagnosis and prevention of human rabies

Human rabies still continues to be a significant health problem in India and other developing countries where dogs are the major vectors of transmission. Rabies in humans can present in two clinical forms, i.e., furious and paralytic. While diagnosis of furious rabies can be made based on the typical symptoms and signs, paralytic rabies poses a diagnostic dilemma to the neurologists who may encounter these cases in their practice. Although there are certain clinical features that distinguish this disease from other forms of Guillain-Barre syndromes, confirmation of diagnosis may require laboratory assistance. Conventional techniques such as antigen detection, antibody assays and virus isolation have limited success. The recently introduced molecular techniques show more promise in confirming the cases of paralytic rabies. There has not been much success in the treatment of confirmed rabies cases and recovery from rabies is extremely rare. Therefore, preventive measures of this dreaded disease after an exposure become extremely important. The present article reviews the current status of human rabies with regard to antemortem diagnosis, disease management and post-exposure prophylaxis.     

Furious and paralytic rabies of canine origin: Neuroimaging with virological and cytokine studies

Furious and paralytic rabies differ in clinical manifestations and survival periods. The authors studied magnetic resonance imaging (MRI) and cytokine and virus distribution in rabies-infected dogs of both clinical types. MRI examination of the brain and upper spinal cord was performed in two furious and two paralytic dogs during the early clinical stage. Rabies viral nucleoprotein RNA and 18 cytokine mRNAs at 12 different brain regions were studied. Rabies viral RNA was examined in four furious and four paralytic dogs during the early stage, and in one each during the late stage. Cytokine mRNAs were examined in two furious and two paralytic dogs during the early stage and in one each during the late stage. Larger quantities of rabies viral RNA were found in the brains of furious than in paralytic dogs. Interleukin-1beta and interferon-gamma mRNAs were found exclusively in the brains of paralytic dogs during the early stage. Abnormal hypersignal T2 changes were found at hippocampus, hypothalamus, brainstem, and spinal cord of paralytic dogs. More widespread changes of less intensity were seen in furious dog brains. During the late stage of infection, brains from furious and paralytic rabid dogs were similarly infected and there were less detectable cytokine mRNAs. These results suggest that the early stage of furious dog rabies is characterized by a moderate inflammation (as indicated by MRI lesions and brain cytokine detection) and a severe virus neuroinvasiveness. Paralytic rabies is characterized by delayed viral neuroinvasion and a more intense inflammation than furious rabies. Dogs may be a good model for study of the host inflammatory responses that may modulate rabies virus neuroinvasiveness.     

Rabies encephalitis following fox bite--histological and immunohistochemical evaluation of lesions caused by virus

Rabies caused by fox bite is uncommon, most cases being caused by bite of rabid dogs (95%). We report a 45-year-old lady with rabies encephalomyelitis caused by bite of a rabid wild fox (Vulpes vulpes), a species prevalent in the Deccan plateaus of Central India. Though foxes are known to be susceptible to rabies, literature on the pathological changes caused by fox bite rabies in humans is scarce. Unlike the mild histological alterations described in canine rabies, a florid encephalitic process evolved in fox bite rabies, in our case, with intense microglial reaction, neuronophagia and perivascular inflammatory infiltrates despite clinical manifestation as a paralytic rabies. Immunostaining using polyclonal antibodies to the rabies viral nucleocapsid antigen and to the whole virion demonstrated high viral load within neurons with extensive spread along dendritic arborization and axonal tracts. Genomic sequence analysis demonstrated close homology with canine virus strain with only minor variations.     

Diabolical effects of rabies encephalitis

Rabies is an acute encephalomyelitis in humans and animals caused by rabies virus (RABV) infection. Because the neuropathological changes are very mild in rabies, it has been assumed that neuronal dysfunction likely explains the severe clinical disease. Recently, degenerative changes have been observed in neuronal processes (dendrites and axons) in experimental rabies. In vitro studies have shown evidence of oxidative stress that is caused by mitochondrial dysfunction. Recent work has shown that the RABV phosphoprotein (P) interacts with mitochondrial Complex I leading to overproduction of reactive oxygen species, which results in injury to axons. Amino acids at positions 139 to 172 of the P are critical in this process. Rabies vectors frequently show behavioral changes. Aggressive behavior with biting is important for transmission of the virus to new hosts at a time when virus is secreted in the saliva. Aggression is associated with low serotonergic activity in the brain. Charlton and coworkers performed studies in experimentally infected striped skunks with skunk rabies virus and observed aggressive behavioral responses. Heavy accumulation of RABV antigen was found in the midbrain raphe nuclei, indicating that impaired serotonin neurotransmission from the brainstem may account for the aggressive behavior. We now have an improved understanding of how RABV causes neuronal injury and how the infection results in behavioral changes that promote viral transmission to new hosts.     

Difference in neuropathogenetic mechanisms in human furious and paralytic rabies

Whereas paralysis is the hallmark for paralytic rabies, the precise pathological basis of paralysis is not known. It is unclear whether weakness results from involvement of anterior horn cells or of motor nerve fibers. There is also no conclusive data on the cause of the neuropathic pain which occurs at the bitten region, although it has been presumed to be related to sensory ganglionopathy. In this study, six laboratory-proven rabies patients (three paralytic and three furious) were assessed clinically and electrophysiologically. Our data suggests that peripheral nerve dysfunction, most likely demyelination, contributes to the weakness in paralytic rabies. In furious rabies, progressive focal denervation, starting at the bitten segment, was evident even in the absence of demonstrable weakness and the electrophysiologic study suggested anterior horn cell dysfunction. In two paralytic and one furious rabies patients who had severe paresthesias as a prodrome, electrophysiologic studies suggested dorsal root ganglionopathy. Postmortem studies in two paralytic and one furious rabies patients, who had local neuropathic pain, showed severe dorsal root ganglionitis. Intense inflammation of the spinal nerve roots was observed more in paralytic rabies patients. Inflammation was mainly noted in the spinal cord segment corresponding to the bite in all cases; however, central chromatolysis of the anterior horn cells could be demonstrated only in furious rabies patient. We conclude that differential sites of neural involvement and possibly different neuropathogenetic mechanisms may explain the clinical diversity in human rabies.     

Correlation of clinical and neuroimaging findings in a case of rabies encephalitis

BACKGROUND: Rabies encephalitis is a feared, virtually uniformly fatal form of central nervous system infection. The incidence of rabies encephalitis in the United States is almost certainly underestimated because of the predominance of bat-borne rabies, which can be spread without traumatic exposure. Because of its rarity in developed countries, rabies encephalitis has been seldom studied with modern imaging techniques. SETTING: University-based teaching hospital. PATIENT: A case of pathologically confirmed rabies encephalitis is presented. Diagnosis of rabies was made by seroconversion testing while the patient was alive and was confirmed postmortem by the presence of rabies antigens and Negri bodies in the brain. The patient had 2 magnetic resonance studies done that showed dramatic abnormalities in the medulla and pons that correlated with features of the neurologic examination and hypothalamic-pituitary abnormalities. RESULT: The patient had a fulminant encephalitic course that ended in death. CONCLUSION: Rabies is an uncommon cause of fatal encephalitis. Anatomic imaging studies such as computed tomographic and magnetic resonance scans have generally been negative in confirmed cases of rabies. We report a case of confirmed rabies with extensive brainstem and hypothalamic-pituitary abnormalities on magnetic resonance imaging. Although these findings are nonspecific, they should raise the clinical suspicion of rabies in the setting of aggressive encephalitis of unclear cause, and appropriate diagnostic tests should be performed.     

Immunohistochemical study of human rabies

Rabies is a communicable disease that is almost always fatal. In its classic form, rabies is well recognized, but cases presenting with a paralytic illness mimic Landre's Guillain–Barre syndrome and in such cases the diagnosis remains in doubt. This problem is further compounded when the history of dogbite is not forthcoming. At autopsy rabies can be diagnosed by subjecting fresh tissue to virologic investigations or examining formalin‐fixed paraffin‐embedded tissue sections for the presence of characteristic inclusions; that is, the Negri bodies. However, these inclusions are not present in all cases. Hence, the need arises for a better method for diagnosis. The present study utilized immunohistochemistry as a diagnostic tool using both monoclonal and polyclonal antirabies antibodies in 20 cases of rabies encephalomyelitis. The diagnosis of rabies could be confirmed in 17 cases (85%) based on neuropathologic findings alone. In contrast, immunohistochemistry yielded positive results in all cases. Moreover, the amount of rabies viral antigen was much more abundant than could be expected from the histopathologic findings. Thus immunohistochemistry is a rapid, safe, sensitive and specific technique for the diagnosis of rabies.     

Rabies

Rabies is an important disease in wildlife in the United States and Canada, and dog rabies is still a major public health problem in many developing countries of the world. Rabies virus is transmitted in saliva by animal bites. Bats transmitted most recent cases of human rabies in the United States, often without known exposures. There have been recent developments in our understanding of rabies pathogenesis. Characteristic clinical features should raise the possibility of a diagnosis of rabies and initiation of appropriate diagnostic tests. Therapy of human rabies has been futile except in four patients who were immunized with rabies vaccine prior to the onset of their disease. Rabies can be prevented after an exposure in unimmunized patients with local wound cleansing and administration of rabies vaccine and human rabies immune globulin.     

SPONTANEOUS RECOVERY FROM THE ENCEPHALOMYELITIS IN MICE CAUSED BY STREET RABIES VIRUS

Recovery from rabies was studied in an experimental model. Young adult mice were inoculated in a hindlimb footpad with street rabies virus (fox salivary gland isolate). In a group of 62 mice, 97% developed clinical rabies with paresis of the extremities and spasticity, and 37% recovered with neurological sequelae. There was an acute inflammatory reaction in the brainstem and grey matter of the spinal cord, and degeneration of myelinated axons in the white matter of the cord and in the dorsal roots. Rabies virus antigen was found in the central nervous system of all mice examined between day 5 and 13, and also in trigeminal and dorsal root ganglia. Surviving mice had neutralizing antibodies in serum and brain tissue, and 90% survived an intracerebral challenge with the CVS strain of fixed rabies virus. Spontaneous recovery from rabies encephalomyelitis was demonstrated with evidence of viral replication and pathological changes in the central nervous system.     

Regional distribution of rabies viral antigen in central nervous system of human encephalitic and paralytic rabies

We studied the distribution of rabies viral antigen in the brain and spinal cord of 7 patients with rabies by immunohistochemical techniques. Four patients presented with encephalitis, the remaining 3 had paralysis. Neither the rabies viral antigen distribution nor inflammation paralleled clinical presentations. Patients who had survival times of 7 days or less (4/7) had a greater amount of antigen-positive neurons in brainstem and spinal cord regardless of the clinical type. Neuroglial cells were also found to contain rabies antigen. Our findings suggest that virus localization may not account for the difference in clinical manifestations.     

Overlap of pathology in paralytic rabies and axonal Guillain-Barre syndrome

We describe clinical and pathological features of a case of paralytic rabies with acute axonal neuropathy that closely resembled axonal Guillain-Barre syndrome. This case emphasizes that there is overlap of both clinical and pathological features in paralytic rabies and axonal Guillain-Barre syndrome. These findings raise the possibility that infectious and autoimmune etiologies can lead to similar morphological changes in the nerves.     

Rabies

Rabies remains an important public health problem in developing countries, and the indigenous threat of rabies continues in developed countries because of wildlife reservoirs. A diagnosis of rabies is often not considered by physicians until late in the clinical course or after death in North America and Europe, even with typical clinical presentations. Transmission of rabies virus has occurred in association with transplantation of tissues and also recently with organs. In 2004 a young patient survived rabies in Wisconsin, but the reasons for this favorable outcome remain elusive. This article reviews current information and developments on a variety of neurologic aspects of rabies.     

Neuronal dysfunction and death in rabies virus infection

Because morphologic changes in natural rabies are usually relatively mild, it is thought that the severe clinical disease with a fatal outcome must be due to neuronal dysfunction of rabies virus-infected neurons. The precise bases of this functional impairment are unknown, and current knowledge on electro-physiological alterations, effects on ion channels and neurotransmission, and neurotoxicity are reviewed. Rabies virus may induce neuronal death, possibly through apoptotic mechanisms. Neuronal apoptosis has been observed in vitro and also in vivo under particular experimental conditions. The relevance of neuronal apoptosis in these situations to natural rabies has not yet been fully elucidated.     

The application of reverse genetics technology in the study of rabies virus (RV) pathogenesis and for the development of novel RV vaccines

Rabies is a central nervous system (CNS) disease that is almost invariably fatal. Neurotropism, neuroinvasiveness, and transsynaptic spread are the main features that determine the pathogenesis of rabies. Recent advances in rabies virus (RV) research, which made direct genetic manipulations of the RV genome possible, greatly improved the understanding of the role of different viral and host cell factors in the pathogenesis of rabies. Here the authors discuss molecular mechanisms associated with rabies RV infection and its spread to the CNS.     

Update on rabies

Rabies remains an important public health problem worldwide due to endemic dog rabies in developing countries. Rabies was a re-emerging disease in the United States during the 1990s due to bat rabies virus variants. Australian bat lyssavirus also emerged in Australian bat populations and caused two human deaths. There have been important recent advances in our knowledge of the pathogenesis of rabies and in our ability to diagnose and prevent it.     

Rabies

Despite increases in our understanding of rabies pathogenesis, it remains an inevitably fatal disease. Lack of awareness, low level of political commitment to rabies control, and failure to recognize and correlate clinical, laboratory, and neuroimaging features contribute to continuing deaths. Clinical symptomatology, once believed to be unique, may be variable, even in patients associated with lyssaviruses of the same genotype. This article discusses virus transport, the role of virus and host response mechanisms in relation to protean clinical manifestations, and mechanisms responsible for relative intactness of consciousness in human rabies. Differential involvement of the anterior horn cell in furious rabies and the peripheral nerve in paralytic rabies is summarized. Escape mechanisms from host defenses explain why a fatal outcome is unavoidable regardless of therapy. Neuroprotective treatment, using a coma-induction regimen, proves not to be beneficial. Survival of patients with excellent recovery relies on early innate and adaptive immunity plus adequate intensive care support.     

Survival of rabid rabbits after intrathecal immunization

Rabies is a fatal zoonotic disease for which no effective treatment measures are currently available. Rabies virus (RABV) has anti‐apoptotic and anti‐inflammatory properties that suppress nerve cell damage and inflammation in the CNS. These features imply that the elimination of RABV from the CNS by appropriate treatment could lead to complete recovery from rabies. Ten rabbits showing neuromuscular symptoms of rabies after subcutaneous (SC) immunization using commercially available vaccine containing inactivated whole RABV particles and subsequent fixed RABV (CVS strain) inoculation into hind limb muscles were allocated into three groups. Three rabbits received no further treatment (the SC group), three rabbits received three additional SC immunizations using the same vaccine, and four rabbits received three intrathecal (IT) immunizations, in which the vaccine was inoculated directly into the cerebrospinal fluid (the SC/IT group). An additional three naïve rabbits were inoculated intramuscularly with RABV and not vaccinated. The rabbits exhibited neuromuscular symptoms of rabies within 4–8 days post‐inoculation (dpi) of RABV. All of the rabbits died within 8–12 dpi with the exception of one rabbit in the SC group and all four rabbits in SC/IT group, which recovered and started to respond to external stimuli at 11–18 dpi and survived until the end of the experimental period. RABV was eliminated from the CNS of the surviving rabbits. We report here a possible, although still incomplete, therapy for rabies using IT immunization. Our protocol may rescue the life of rabid patients and prompt the future development of novel therapies against rabies.     

Calbindin distribution in cortical and subcortical brain structures of normal and rabies-infected mice

Rabies has been an enigmatic disease of the nervous system because microscopic findings in the brain tissue are not paralleled by the severity of the clinical illness. The calcium binding protein calbindin (CB) is a neuronal marker of great interest in neuroanatomy and neuropathology. CB-ir neurons in the striatum and cerebral cortex are gabaergic cells. In the present work CB-immunoreactivity was evaluated in brains of normal and rabies-infected mice. Rabies infection caused loss of CB-immunostaining in the cortical supragranular layers as well as in the striatum. Loss of CB in the brains of mice infected with rabies virus can produce impairment in Ca++ homeostasis and in the gabaergic neurotransmission.     

CALBINDIN DISTRIBUTION IN CORTICAL AND SUBCORTICAL BRAIN STRUCTURES OF NORMAL AND RABIES-INFECTED MICE

Rabies has been an enigmatic disease of the nervous system because microscopic findings in the brain tissue are not paralleled by the severity of the clinical illness. The calcium binding protein calbindin (CB) is a neuronal marker of great interest in neuroanatomy and neuropathology. CB-ir neurons in the striatum and cerebral cortex are gabaergic cells. In the present work CB-immunoreactivity was evaluated in brains of normal and rabies-infected mice. Rabies infection caused loss of CB-immunostaining in the cortical supragranular layers as well as in the striatum. Loss of CB in the brains of mice infected with rabies virus can produce impairment in Ca⁺⁺ homeostasis and in the gabaergic neurotransmission.