Immunovirological correlates in human rabies treated with therapeutic coma

Immunological impact of tetrahydrobiopterin on the central nervous system in a murine model of rabies virus infection

Currently, the Milwaukee protocol presents healing results in human beings affected by the rabies virus. However, there are many points to clarify on the action of drugs and the immune mechanism involved in the evolution of the disease. One of the drugs used is biopterin, which is an important cofactor for nitric oxide, important for preventing vasospasm. Thus, we describe the effect of biopterin on some inflammatory factors in a rabies virus infection developed in an animal model. The immunological mediators studied in animals infected with rabies virus submitted to doses of sapropterin were Anti-RABV, IL-6, IL-2, IL-17a, INF-gamma and Anti-iNOS. It is suggested that the medication in the context of a RABV infection already installed, had the effect of modulating the inflammatory mechanisms mainly linked to the permeability of the blood-brain barrier and the migration of cytotoxic cells.

A combination of two human monoclonal antibodies cures symptomatic rabies

Rabies is a neglected disease caused by a neurotropic Lyssavirus, transmitted to humans predominantly by the bite of infected dogs. Rabies is preventable with vaccines or proper post-exposure prophylaxis (PEP), but it still causes about 60,000 deaths every year. No cure exists after the onset of clinical signs, and the case-fatality rate approaches 100% even with advanced supportive care. Here, we report that a combination of two potent neutralizing human monoclonal antibodies directed against the viral envelope glycoprotein cures symptomatic rabid mice. Treatment efficacy requires the concomitant administration of antibodies in the periphery and in the central nervous system through intracerebroventricular infusion. After such treatment, recovered mice presented good clinical condition, viral loads were undetectable, and the brain inflammatory profile was almost normal. Our findings provide the unprecedented proof of concept of an antibody-based therapeutic approach for symptomatic rabies.

Comparing clinical protocols for the treatment of human rabies: the Milwaukee protocol and the Brazilian protocol (Recife)

INTRODUCTION

Rabies is a major and seriously neglected public health problem worldwide. A treatment consisting of supportive therapy with the use of drugs that show antiviral activity is called the Milwaukee Protocol. In Brazil, this protocol was adapted to the national reality and called the Recife Protocol. In this study, we compared the Milwaukee Protocol with the Recife Protocol, assessing the differences and how these differences may change the course of clinical management.

METHODS

We searched electronic databases for the use of anti-rabies treatments. A total of 65 articles were published between 2004 and 2019.

RESULTS

The protocols have similarities in care related to rabies patients and are important for the treatment of patients in intensive care units. Both protocols indicate deep sedation, antiviral use, constant concern with electrolyte balance, and vasoconstriction related to the condition. Many differences were observed in this study. For the Milwaukee Protocol, sedation should be gradually removed after the eighth day, and on the twelfth day, the patient should be without sedation. In the Recife Protocol, in order to avoid immunomodulation, it is recommended to remove sedation according to the titers of neutralizing antibodies to the rabies virus in the cerebral spinal fluid.

CONCLUSIONS

In addition to the differences and similarities raised, our findings indicate that these protocols require a large center for rabies treatment, but the disease most often occurs in places where resources and hospital infrastructure are scarce.

Prevention of human rabies: a challenge for the European Union and the European Economic Area

Rabies is enzootic in over one hundred countries worldwide. In the European Union/European Economic Area (EU/EEA), the vast majority of human rabies cases are travellers bitten by dogs in rabies-enzootic countries, mostly in Asia and Africa. Thus, EU/EEA travellers visiting rabies enzootic countries should be aware of the risk of being infected with the rabies virus when having physical contact with mammals. They should consider pre-exposure vaccination following criteria recommended by the World Health Organization and if unvaccinated, immediately seek medical attention in case of bites or scratches from mammals. As the majority of the EU/EEA countries are free from rabies in mammals, elimination of the disease (no enzootic circulation of the virus and low number of imported cases) has been achieved by 2020. However, illegal import of potentially infected animals, mainly dogs, poses a risk to public health and might threaten the elimination goal. Additionally, newly recognised bat lyssaviruses represent a potential emerging threat as the rabies vaccine may not confer protective immunity. To support preparedness activities in EU/EEA countries, guidance for the assessment and the management of the public health risk related to rabies but also other lyssaviruses, should be developed.

Bufotenine, a tryptophan-derived alkaloid, suppresses the symptoms and increases the survival rate of rabies-infected mice: the development of a pharmacological approach for rabies treatment

Background:

Between 40,000-70,000 people die yearly of rabies, an incurable disease. Besides post-bite vaccination, no treatment is available for it.

Methods:

First, virus dilution for antiviral effects in mice was determined. Then, animals were treated as follows: control (NaCl 250 µL/animal/day); bufotenine (0.63, 1.05 and 2.1 mg in 250 µL of NaCl/animal/day); rabies (10^-6,82CVS dilution); and test (10^-6,82 CVS dilution and bufotenine, in the above-mentioned doses). Animals were observed daily for 21 days or until the 3^rd stage of rabies infection. Twitch-tension and liposome studies were applied to understand the possible interaction of bufotenine with receptors, particularly acetylcholine.

Results:

Bufotenine was able to increase the survival rate of intracerebrally virus-infected mice from 15 to 40%. Bufotenine did not seem to interfere with the acetylcholine response in the skeletal muscle, indicating that its mechanism of action is not blocking the virus entrance due to nAChR antagonism. By analyzing liposomes, we could observe that bufotenine did not passively penetrates cell membranes, indicating the necessity of complementary structures to cell penetration.

Conclusions:

Bufotenine is a promising candidate for drug development. After further chemical modification, it might be possible to dissociate minor side effects, increase efficiency, efficacy and pharmacokinetics, yielding a true anti-rabies drug.

Trying to treat the untreatable: experimental approaches to clear rabies virus infection from the CNS

Rabies virus causes an invariably fatal encephalitis following the onset of clinical disease. Despite the availability of safe and effective vaccines, the clinical stages of rabies encephalitis remain untreatable, with few survivors being documented. A principal obstacle to the treatment of rabies is the neurotropic nature of the virus, with the blood-brain barrier size exclusion limit rendering the delivery of antiviral drugs and molecules to the central nervous system inherently problematic. This review focuses on efforts to try and overcome barriers to molecule delivery to treat clinical rabies and overviews current progress in the development of experimental live rabies virus vaccines that may have future applications in the treatment of clinical rabies, including the attenuation of rabies virus vectors through either the duplication or mutation of existing genes or the incorporation of non-viral elements within the genome. Rabies post-infection treatment (PIT) remains the holy grail of rabies research.

[Сases of human convalescence from rabies and lifetime diagnostics of lyssavirus encephalitis.]

Notwithstanding the availability of effective vaccines, 40 - 60 thousand rabies cases in humans are reported every year. Almost always the disease is fatal because therapeutic treatment of lyssavirus encephalitis has not been developed. Since 1970 the number of reports on rare cases of convalescence including those using experimental treatment protocols has been gradually increasing 20 cases of convalescence, "partial" convalescence or long-term survival of humans (1970-2015) were selected as they were complaint with laboratory criteria of active lyssavirus infection. Children and teenagers were predominant in the analyzed group (85%). The cases were irregularly spread between the continents: Asia - 6 cases, North America - 6 cases, Africa - 2 cases and Europe - 1 case. India and the USA were on the top of the list of countries by the number of described cases. More than 60% humans were infected from dogs, three cases got infection from bats and 2 cases were allegedly associated with an unknown lyssavirus and an unidentified infection source. 70% cases were vaccinated and 10% cases were treated with gamma globulin before the disease onset. Serological tests for detection of antibodies to lyssaviruses in cerebrospinal fluid of infected humans were typically used for diagnostic laboratory verification. Less than 30% IFA and PCR positives were obtained. Lyssaviruses were never detected. Only 4 convalescent patients were treated using experimental protocols. 80% cases demonstrated severe neurological consequences, four (may be more) patients died afterwards within the period from two months to four years. Different perspectives on prospects of Milwaukee protocol use and other therapeutic techniques are given.

Utility of rabies neutralizing antibody detection in cerebrospinal fluid and serum for ante-mortem diagnosis of human rabies

Background

Early ante-mortem laboratory confirmation of human rabies is essential to aid patient management and institute public health measures. Few studies have highlighted the diagnostic value of antibody detection in CSF/serum in rabies, and its utility is usually undermined owing to the late seroconversion and short survival in infected patients. This study was undertaken to examine the ante-mortem diagnostic utility and prognostic value of antibody detection by rapid fluorescent focus inhibition test (RFFIT) in cerebrospinal fluid (CSF)/serum samples received from clinically suspected human rabies cases from January 2015 to December 2017.

Methodology/Principal findings

Samples collected ante-mortem and post-mortem from 130 and 6 patients with clinically suspected rabies respectively, were received in the laboratory during the study period. Ante-mortem laboratory confirmation was achieved in 55/130 (42.3%) cases. Real time PCR for detection of viral nucleic acid performed on saliva, nuchal skin, brain tissue and CSF samples could confirm the diagnosis in 15 (27.2%) of the 55 laboratory confirmed cases. Ante-mortem diagnosis could be achieved by RFFIT (in CSF and/or serum) in 45 (34.6%) of the 130 clinically suspected cases, accounting for 81.8% of the total 55 laboratory confirmed cases. The sensitivity of CSF RFFIT increased with the day of sample collection (post-onset of symptoms) and was found to be 100% after 12 days of illness. Patients who had received prior vaccination had an increased probability of a positive RFFIT and negative PCR result. Patients who were positive by RFFIT alone at initial diagnosis had longer survival (albeit with neurological sequelae) than patients who were positive by PCR alone or both RFFIT and PCR.

Conclusions/Significance

Detection of antibodies in the CSF/serum is a valuable ante-mortem diagnostic tool in human rabies, especially in patients who survive beyond a week. It was also found to have a limited role as a prognostic marker to predict outcomes in patients.

Ante-mortem diagnosis of human rabies is essential for patient management and public health measures. The detection of virus specific antibodies in the CSF/serum of patients with suspected rabies is thought to have a limited diagnostic role owing to late seroconversion and short survival in rabies. We examined the diagnostic and prognostic utility of antibody detection by rapid fluorescent focus inhibition test (RFFIT) in CSF/serum samples received from clinically suspected human rabies cases (2015–2017). RFFIT (in CSF and/or serum) could confirm ante-mortem diagnosis in 45 (34.6%) of the 130 clinically suspected cases, accounting for 81.8% of the total 55 laboratory confirmed cases. The sensitivity of CSF RFFIT increased with the day of sample collection (post-onset of symptoms) and was found to be 100% after 12 days of illness. Patients who had received prior vaccination had an increased likelihood of a positive RFFIT and negative PCR result. Patients who were positive by RFFIT alone at initial diagnosis had longer duration of survival, although with poor functional outcomes. Antibody detection by RFFIT in CSF/serum was found to have a diagnostic utility especially in patients who survived beyond a week and a limited prognostic role in human rabies.

Case Report: Failure of Therapeutic Coma in Rabies Encephalitis

Rabies encephalitis is a fulminant, almost universally fatal infection involving the central nervous system. A unique treatment protocol, including anti-exicitotoxic therapy and induced coma was credited with the survival of a vaccinated teenager with bat rabies encephalitis in 2005. However, multiple efforts to replicate this expensive and intense protocol have not been successful. In this article, we report the failure of the protocol in Indian patients with canine-acquired rabies and elucidate the potential explanations for the failure of the protocol in our patients.

Rabies

Rabies is a life-threatening neglected tropical disease: tens of thousands of cases are reported annually in endemic countries (mainly in Africa and Asia), although the actual numbers are most likely underestimated. Rabies is a zoonotic disease that is caused by infection with viruses of the Lyssavirus genus, which are transmitted via the saliva of an infected animal. Dogs are the most important reservoir for rabies viruses, and dog bites account for >99% of human cases. The virus first infects peripheral motor neurons, and symptoms occur after the virus reaches the central nervous system. Once clinical disease develops, it is almost certainly fatal. Primary prevention involves dog vaccination campaigns to reduce the virus reservoir. If exposure occurs, timely post-exposure prophylaxis can prevent the progression to clinical disease and involves appropriate wound care, the administration of rabies immunoglobulin and vaccination. A multifaceted approach for human rabies eradication that involves government support, disease awareness, vaccination of at-risk human populations and, most importantly, dog rabies control is necessary to achieve the WHO goal of reducing the number of cases of dog-mediated human rabies to zero by 2030.

Perspectives in Diagnosis and Treatment of Rabies Viral Encephalitis: Insights from Pathogenesis

Rabies viral encephalitis, though one of the oldest recognized infectious disease of humans, remains an incurable, fatal encephalomyelitis, despite advances in understanding of its pathobiology. Advances in science have led us on the trail of the virus in the host, but the sanctuaries in which the virus remains hidden for its survival are unknown. Insights into host-pathogen interactions have facilitated evolving immunologic therapeutic strategies, though we are far from a cure. Most of the present-day knowledge has evolved from in vitro studies using fixed (attenuated) laboratory strains that may not be applicable in the clinical setting. Much remains to be unraveled about this elusive virus. This review attempts to re-examine the current advances in understanding of the pathobiology of the rabies virus that modulate the diagnosis, treatment, and prevention of this fatal disease.

Human rabies in India: an audit from a rabies diagnostic laboratory

OBJECTIVES

Rabies, an acute progressive encephalomyelitis, continues to be a serious public health problem in India and many other countries in Asia and Africa. The low level of commitment to rabies control is partly attributable to challenges in laboratory diagnosis and lack of adequate surveillance to indicate the disease burden. A laboratory audit of human rabies cases was undertaken to disseminate information on the clinical, demographic, prophylactic and most importantly the laboratory diagnostic aspects of rabies.

METHODS

A retrospective analysis of all clinically suspected human rabies cases, whose samples were received at a rabies diagnostic laboratory in South India in the last 3 years, was performed. Clinical and demographic details of patients were obtained. The clinical samples included cerebrospinal fluid (CSF), serum, saliva and nuchal skin biopsy collected antemortem, and brain tissue obtained post-mortem. Various laboratory tests were performed for diagnosis.

RESULTS

Clinical samples from 128 patients with suspected rabies, from 11 states in India, were received for diagnostic confirmation. About 94% of the victims reported dog-bites, more than a third of them were children and most of the victims did not receive adequate post-exposure prophylaxis. Antemortem confirmation of rabies by a combination of laboratory diagnostic assays (detection of viral RNA in CSF, skin and saliva, and neutralising antibodies in CSF) could be achieved in 40.6% cases.

CONCLUSIONS

Increasing awareness about adequate post-exposure prophylaxis, additional rabies diagnostic facilities, and enhanced human and animal rabies surveillance to indicate the true disease burden are essential to control this fatal disease.

Critical Appraisal of the Milwaukee Protocol for Rabies: This Failed Approach Should Be Abandoned

The Milwaukee protocol has been attributed to survival in rabies encephalitis despite a lack of scientific evidence supporting its therapeutic measures. We have reviewed the literature with reference to specific treatment recommendations made within the protocol. Current literature fails to support an important role for excitotoxicity and cerebral vasospasm in rabies encephalitis. Therapies suggested in the Milwaukee protocol include therapeutic coma, ketamine infusion, amantadine, and the screening/prophylaxis/management of cerebral vasospasm. None of these therapies can be substantiated in rabies or other forms of acute viral encephalitis. Serious concerns over the current protocol recommendations are warranted. The recommendations made by the Milwaukee protocol warrant serious reconsideration before any future use of this failed protocol.

Interplay between rabies virus and the mammalian immune system

Rabies is a disease caused following infection of the brain by the rabies virus (RABV). The principle mechanism of transmission is through a bite wound. The virus infects peripheral nerves and moves to the central nervous system (CNS). There appears to be little involvement of other organ systems and little detectable immune stimulation prior to infection of the CNS. This failure of the mammalian immune system to respond to rabies virus infection leads, in the overwhelming majority of cases, to death of the host. To some extent, this failure is likely due to the exclusive replication of RABV in neurons and the limited ability to generate, sufficiently rapidly, an anti-viral antibody response in situ. This is reflected in the ability of post-exposure vaccination, when given early after infection, to prevent disease. The lack of immune stimulation during RABV infection preceding neural invasion is the Achilles heel of the immune response. Whilst many viruses infect the brain, causing encephalitis and neuronal deficit, none are as consistently fatal to the host as RABV. This is in part due to prior replication of many viruses in peripheral, non-neural tissue by other viruses that allows timely activation of the immune response before the host is overwhelmed. Our current understanding of the correlates of protection for rabies suggests that it is the action of neutralising antibodies that prevent infection and control spread of RABV. Furthermore, it tells us that the induction of immunity can protect and understanding how and why this happens is critical to controlling infection. However, the paradigm of antibody development suggests that antigen presentation overwhelmingly occurs in lymphoid tissue (germinal and non-germinal centres) and these are external to the CNS. In addition, the blood-brain-barrier may provide a block to the delivery of immune effectors (antibodies/plasma B-cells) entering where they are needed. Alternatively, there may be insufficient antigen exposure after natural infection to mount an effective response or the virus actively suppresses immune function. To improve our ability to treat this fatal infection it is imperative to understand how immunity to RABV develops and functions so that parameters of protection are better defined.

Rabies: Rare Human Infection - Common Questions

Rabies is an acute, rapidly progressive encephalitis that is almost always fatal. Prophylaxis is highly effective but economics limits disease control. The mechanism of death from rabies is unclear. It is poorly cytopathic and poorly inflammatory. Rabies behaves like an acquired metabolic disorder. There may be a continuum of disease severity. History of animal bite is rare. The diagnosis is often missed. Intermittent encephalopathy, dysphagia, hydrophobia and aerophobia, and focal paresthesias or myoclonic jerks suggest rabies. Laboratory diagnosis is cumbersome but sensitive. Treatment is controversial but survivors are increasingly reported, with good outcomes in 4 of 8 survivors.

Virology, immunology and pathology of human rabies during treatment

BACKGROUND

Rabies is an acute fatal encephalitis caused by all members of the Lyssavirus genus. The first human rabies survivor without benefit of prior vaccination was reported from Milwaukee in 2005. We report a second unvaccinated patient who showed early recovery from rabies and then died accidentally during convalescence, providing an unparalleled opportunity to examine the histopathology as well as immune and virological correlates of early recovery from human rabies.

METHODS

Case report, rapid fluorescent focus inhibition test, enzyme-linked immunosorbent assay, indirect and direct fluorescent antibody assays, reverse-transcriptase polymerase chain reaction, phylogenetic reconstruction, isolation in tissue culture, pathology and immunohistochemistry.

RESULTS

The 9 year old died 76 days after presenting with rabies of vampire bat phylogeny transmitted by cat bite. Antibody response in serum and cerebrospinal fluid was robust and associated with severe cerebral edema. No rabies virus was cultured at autopsy. Rabies virus antigen was atypical in size and distribution. Rabies virus genome was present in neocortex but absent in brainstem.

CONCLUSIONS

Clinical recovery was associated with detection of neutralizing antibody and clearance of infectious rabies virus in the central nervous system by 76 days but not clearance of detectable viral subcomponents such as nucleoprotein antigen or RNA in brain.

Why we can prevent, control and possibly treat – but will not eradicate – rabies

ABSTRACT 

Rabies is an acute, progressive viral encephalitis. Despite historical recognition, millions still remain exposed annually. Most fatalities are of children, although this zoonosis is a vaccine-preventable disease. All developed countries interrupted canine transmission and increasingly, Asian and African communities recognize what Latin Americans demonstrated – dog rabies can be eliminated – by mass application of veterinary vaccines. Realistically, rabies is not a candidate for eradication. Management is lacking for major reservoirs, such as bats. Increasing pre-exposure immunization of individuals at risk, simplification of postexposure schedules, enhancing vaccine delivery by alternative routes, development of less expensive biologics and antiviral drugs, may lessen its impact if applied strategically in a One Health context.

Current status of rabies and prospects for elimination

Rabies is one of the most deadly infectious diseases, with a case-fatality rate approaching 100%. The disease is established on all continents apart from Antarctica; most cases are reported in Africa and Asia, with thousands of deaths recorded annually. However, the estimated annual figure of almost 60,000 human rabies fatalities is probably an underestimate. Almost all cases of human rabies result from bites from infected dogs. Therefore, the most cost-effective approach to elimination of the global burden of human rabies is to control canine rabies rather than expansion of the availability of human prophylaxis. Mass vaccination campaigns with parenteral vaccines, and advances in oral vaccines for wildlife, have allowed the elimination of rabies in terrestrial carnivores in several countries worldwide. The subsequent reduction in cases of human rabies in such regions advocates the multidisciplinary One Health approach to rabies control through the mass vaccination of dogs and control of canine populations.

Diagnosis, management and post-mortem findings of a human case of rabies imported into the United Kingdom from India: a case report

BACKGROUND

Human rabies infection continues to be a significant public health burden globally, and is occasionally imported to high income settings where the Milwaukee Protocol for intensive care management has recently been employed, with limited success in improving survival. Access to molecular diagnostics, pre- and post-mortem, and documentation of pathophysiological responses while using the Milwaukee protocol, can add useful insights for the future of rabies management.

CASE PRESENTATION

A 58-year-old British Asian woman was referred to a regional general hospital in the UK with hydrophobia, anxiety and confusion nine weeks after receiving a dog bite in North West India. Nuchal skin biopsy, saliva, and a skin biopsy from the site of the dog bite wound, taken on the day of admission, all demonstrated the presence of rabies virus RNA. Within 48 hours sequence analysis of viral RNA confirmed the diagnosis and demonstrated that the virus was a strain closely related to canine rabies viruses circulating in South Asia. Her condition deteriorated rapidly with increased agitation and autonomic dysfunction. She was heavily sedated and intubated on the day after admission, treated according to a modified Milwaukee protocol, and remained stable until she developed heart block and profound acidosis and died on the eighth day. Analysis of autopsy samples showed a complete absence of rabies neutralizing antibody in cerebrospinal fluid and serum, and corresponding high levels of virus antigen and nucleic acid in brain and cerebrospinal fluid. Quantitative PCR showed virus was also distributed widely in peripheral tissues despite mild or undetectable histopathological changes. Vagus nerve branches in the heart showed neuritis, a probable Negri body but no demonstrable rabies antigen.

CONCLUSION

Rapid molecular diagnosis and strain typing is helpful in the management of human rabies infection. Post-mortem findings such as vagal neuritis highlight clinically important effects on the cardiovascular system which are typical for the clinical course of rabies in humans. Management guided by the Milwaukee protocol is feasible within well-resourced intensive care units, but its role in improving outcome for canine-derived rabies remains theoretical.

Diagnosis, management and post-mortem findings of a human case of rabies imported into the United Kingdom from India: a case report

BACKGROUND

Human rabies infection continues to be a significant public health burden globally, and is occasionally imported to high income settings where the Milwaukee Protocol for intensive care management has recently been employed, with limited success in improving survival. Access to molecular diagnostics, pre- and post-mortem, and documentation of pathophysiological responses while using the Milwaukee protocol, can add useful insights for the future of rabies management.

CASE PRESENTATION

A 58-year-old British Asian woman was referred to a regional general hospital in the UK with hydrophobia, anxiety and confusion nine weeks after receiving a dog bite in North West India. Nuchal skin biopsy, saliva, and a skin biopsy from the site of the dog bite wound, taken on the day of admission, all demonstrated the presence of rabies virus RNA. Within 48 hours sequence analysis of viral RNA confirmed the diagnosis and demonstrated that the virus was a strain closely related to canine rabies viruses circulating in South Asia. Her condition deteriorated rapidly with increased agitation and autonomic dysfunction. She was heavily sedated and intubated on the day after admission, treated according to a modified Milwaukee protocol, and remained stable until she developed heart block and profound acidosis and died on the eighth day. Analysis of autopsy samples showed a complete absence of rabies neutralizing antibody in cerebrospinal fluid and serum, and corresponding high levels of virus antigen and nucleic acid in brain and cerebrospinal fluid. Quantitative PCR showed virus was also distributed widely in peripheral tissues despite mild or undetectable histopathological changes. Vagus nerve branches in the heart showed neuritis, a probable Negri body but no demonstrable rabies antigen.

CONCLUSION

Rapid molecular diagnosis and strain typing is helpful in the management of human rabies infection. Post-mortem findings such as vagal neuritis highlight clinically important effects on the cardiovascular system which are typical for the clinical course of rabies in humans. Management guided by the Milwaukee protocol is feasible within well-resourced intensive care units, but its role in improving outcome for canine-derived rabies remains theoretical.

Survival from rabies encephalitis

Rabies is a major public health problem in Asia and Africa, with nearly 60,000 deaths every year, and represents a substantial economic burden. Neurologists frequently encounter atypical cases, and need to make informed decisions regarding diagnosis and management. No therapy has been shown to unequivocally improve survival in rabies till date. Despite the overwhelmingly fatal nature of this disease, a small number of patients have been reported to survive acute rabies encephalitis with varying degrees of neurological sequelae. This paper presents the eleventh documented case of survival from rabies, which developed after being bitten by a stray dog, albeit with severe neurological residua. Similar to patients in previous reports, this man demonstrated a robust immune response as indicated by peripheral viral clearance and very high serum and cerebrospinal fluid antibody titres. Immunologically-mediated virus clearance therefore appears to be a prerequisite for survival. A detailed review of previously reported survivors, as well as descriptions of the host response and viral clearance in human rabies, current therapy for this disease and future directions in improving the currently dismal prognosis are provided.

Laboratory diagnosis of human rabies: recent advances

Rabies, an acute progressive, fatal encephalomyelitis, transmitted most commonly through the bite of a rabid animal, is responsible for an estimated 61,000 human deaths worldwide. The true disease burden and public health impact due to rabies remain underestimated due to lack of sensitive laboratory diagnostic methods. Rapid diagnosis of rabies can help initiate prompt infection control and public health measures, obviate the need for unnecessary treatment/medical tests, and assist in timely administration of pre- or postexposure prophylactic vaccination to family members and medical staff. Antemortem diagnosis of human rabies provides an impetus for clinicians to attempt experimental therapeutic approaches in some patients, especially after the reported survival of a few cases of human rabies. Traditional methods for antemortem and postmortem rabies diagnosis have several limitations. Recent advances in technology have led to the improvement or development of several diagnostic assays which include methods for rabies viral antigen and antibody detection and assays for viral nucleic acid detection and identification of specific biomarkers. These assays which complement traditional methods have the potential to revolutionize rabies diagnosis in future.

Utility of real-time Taqman PCR for antemortem and postmortem diagnosis of human rabies

Rabies, a fatal zoonotic viral encephalitis remains a neglected disease in India despite a high disease burden. Laboratory confirmation is essential, especially in patients with paralytic rabies who pose a diagnostic dilemma. However, conventional tests for diagnosis of rabies have several limitations. In the present study the utility of a real-time TaqMan PCR assay was evaluated for antemortem/postmortem diagnosis of rabies. Human clinical samples received for antemortem rabies diagnosis (CSF, saliva, nuchal skin biopsy, serum), and samples obtained postmortem from laboratory confirmed rabies in humans (brain tissue, CSF, serum) and animals (brain tissue) were included in the study. All CSF and sera were tested for rabies viral neutralizing antibodies (RVNA) by rapid fluorescent focus inhibition test (RFFIT) and all samples (except sera) were processed for detection of rabies viral RNA by real-time TaqMan PCR. All the 29 (100%) brain tissues from confirmed cases of human and animal rabies, and 11/14 (78.5%) CSF samples obtained postmortem from confirmed human rabies cases were positive by real-time TaqMan PCR. Rabies viral RNA was detected in 5/11 (45.4%) CSF samples, 6/10 (60%) nuchal skin biopsies, and 6/7 (85.7%) saliva samples received for antemortem diagnosis. Real-time TaqMan PCR alone could achieve antemortem rabies diagnosis in 11/13 (84.6%) cases; combined with RVNA detection in CSF antemortem rabies diagnosis could be achieved in all 13 (100%) cases. Real-time TaqMan PCR should be made available widely as an adjunctive test for diagnosis of human rabies in high disease burden countries like India.

Imported human rabies cases worldwide, 1990-2012

Sixty cases of human rabies in international travelers were reviewed from 1990-2012. A significant proportion of the cases were observed in migrants or their descendants when emigrating from their country of origin or after a trip to visit friends and relatives or for other reasons (43.3%). The cases were not necessarily associated with long-term travel or expatriation to endemic countries; moreover, cases were observed in travelers after short trips of two weeks or less. A predominance of male patients was observed (75.0%). The proportion of children was low (11.7%). Cases from India and Philippines were frequent (16 cases/60). In a significant proportion of cases (51.1%), diagnosis was challenging, with multiple missed diagnoses and transfers from ward to ward before the final diagnosis of rabies. Among the 28 patients whose confirmed diagnosis was obtained ante-mortem, the mean time between hospitalization and diagnosis was 7.7 days (median time: 6.0 days, range 2-30) including four cases with a diagnosis delayed by 15 or more days. In five cases, a patient traveled through one or more countries before ultimately being hospitalized. Three factors played a role in delaying the diagnosis of rabies in a number of cases: (i) a low index of suspicion for rabies in countries where the disease has been eradicated for a long time or is now rare, (ii) a negative history of animal bites or exposure to rabies, and (iii) atypical clinical presentation of the disease. Clinical symptomatology of rabies is complex and commonly confuses physicians. Furthermore, failure in diagnosing imported cases in more developed countries is most likely related to the lack of medical familiarity with even the typical clinical features of the disease.

Current and future approaches to the therapy of human rabies

Human rabies has traditionally been considered a uniformly fatal disease. However, recent decades have seen several instances in which individuals have developed clinical signs of rabies, but survived, usually with permanent neurologic sequelae. Most of these patients had received prophylactic rabies vaccine before the onset of illness. The best outcomes have been seen in patients infected with bat viruses, which appear to be less virulent for humans than strains associated with other rabies vectors. In 2003, an article by rabies experts suggested that survival might be improved through a combination of vaccine, anti-rabies immunoglobulin, antiviral drugs and the anesthetic ketamine, which had shown benefit in an animal model. One year later, a girl in Milwaukee who developed rabies after bat exposure was treated with some of these measures, plus a drug-induced (therapeutic) coma, and survived her illness with mild neurologic sequelae. Although the positive outcome in this case has been attributed to the treatment regimen, it more likely reflects the patient's own brisk immune response, as anti-rabies virus antibodies were detected at the time of hospital admission, even though she had not been vaccinated. This conclusion is supported by the failure of the "Milwaukee Protocol" to prevent death in numerous subsequent cases. Use of this protocol should therefore be discontinued. Future research should focus on the use of animal models to improve understanding of the pathogenesis of rabies and for the development of new therapeutic approaches.

Metabolomics of cerebrospinal fluid from humans treated for rabies

Rabies is a rapidly progressive lyssavirus encephalitis that is statistically 100% fatal. There are no clinically effective antiviral drugs for rabies. An immunologically naïve teenager survived rabies in 2004 through improvised supportive care; since then, 5 additional survivors have been associated with use of the so-called Milwaukee Protocol (MP). The MP applies critical care focused on the altered metabolic and physiologic states associated with rabies. The aim of this study was to examine the metabolic profile of cerebrospinal fluid (CSF) from rabies patients during clinical progression of rabies encephalitis in survivors and nonsurvivors and to compare these samples with control CSF samples. Unsupervised clustering algorithms distinguished three stages of rabies disease and identified several metabolites that differentiated rabies survivors from those who subsequently died, in particular, metabolites related to energy metabolism and cell volume control. Moreover, for those patients who survived, the trajectory of their metabolic profile tracked toward the control profile and away from the rabies profile. NMR metabolomics of human rabies CSF provide new insights into the mechanisms of rabies pathogenesis, which may guide future therapy of this disease.

Developments in rabies vaccines

The development of vaccines that prevent rabies has a long and distinguished history, with the earliest preceding modern understanding of viruses and the mechanisms of immune protection against disease. The correct application of inactivated tissue culture-derived vaccines is highly effective at preventing the development of rabies, and very few failures are recorded. Furthermore, oral and parenteral vaccination is possible for wildlife, companion animals and livestock, again using inactivated tissue culture-derived virus. However, rabies remains endemic in many regions of the world and causes thousands of human deaths annually. There also remain no means of prophylaxis for rabies once the virus enters the central nervous system (CNS). One reason for this is the poor immune response within the CNS to infection with rabies virus (RABV). New approaches to vaccination using modified rabies viruses that express components of the innate immune system are being applied to this problem. Preliminary reports suggest that direct inoculation of such viruses could trigger an effective anti-viral response and prevent a fatal outcome from RABV infection.

Rabies: still a uniformly fatal disease? Historical occurrence, epidemiological trends, and paradigm shifts

Rabies has the highest case fatality of any infectious disease. Pathobiological and clinical insights have questioned the assertion that death is inevitable after onset of acute encephalomyelitis. Relying upon national laboratory-based surveillance, we reviewed records of human rabies acquired in the United States during 1960-2009. Changes in the epidemiology of human rabies were notable, due to improved animal management, safer and more efficacious biologics, and revisions in prevention guidelines. Historically, domestic animals were the most important source of infection. Since the 1990s, more human cases were associated with rabid bats. Prior to 1980, postexposure prophylaxis failures were reported. After development of modern rabies immune globulin and vaccines, none occurred. Of 75 human cases identified, only four patients survived. Rabies remains an extremely high consequence zoonosis, but the disease is not uniformly fatal, per se. Rabies is essentially preventable when primary exposures are averted, or appropriate prophylaxis occurs before illness.

Sufficient virus-neutralizing antibody in the central nerve system improves the survival of rabid rats

Background

Rabies is known to be lethal in human. Treatment with passive immunity for the rabies is effective only when the patients have not shown the central nerve system (CNS) signs. The blood–brain barrier (BBB) is a complex functional barrier that may compromise the therapeutic development in neurological diseases. The goal of this study is to determine the change of BBB integrity and to assess the therapeutic possibility of enhancing BBB permeability combined with passive immunity in the late stage of rabies virus infection.

Methods

The integrity of BBB permeability in rats was measured by quantitative ELISA for total IgG and albumin levels in the cerebrospinal fluid (CSF) and by exogenously applying Evans blue as a tracer. Western blotting of occludin and ZO-1, two tight junction proteins, was used to assess the molecular change of BBB structure.

The breakdown of BBB with hypertonic arabinose, recombinant tumor necrosis factor-alpha (rTNF-γ), and focused ultrasound (FUS) were used to compare the extent of BBB disruption with rabies virus infection. Specific humoral immunity was analyzed by immunofluorescent assay and rapid fluorescent focus inhibition test. Virus-neutralizing monoclonal antibody (mAb) 8-10E was administered to rats with hypertonic breakdown of BBB as a passive immunotherapy to prevent the death from rabies.

Results

The BBB permeability was altered on day 7 post-infection. Increased BBB permeability induced by rabies virus infection was observed primarily in the cerebellum and spinal cord. Occludin was significantly decreased in both the cerebral cortex and cerebellum. The rabies virus-specific antibody was not strongly elicited even in the presence of clinical signs. Disruption of BBB had no direct association with the lethal outcome of rabies. Passive immunotherapy with virus-neutralizing mAb 8-10E with the hypertonic breakdown of BBB prolonged the survival of rabies virus-infected rats.

Conclusions

We demonstrated that the BBB permeability was altered in a rat model with rabies virus inoculation. Delivery of neutralizing mAb to the infected site in brain combined with effective breakdown of BBB could be an aggressive but feasible therapeutic mode in rabies when the CNS infection has been established.

Rabies in the critical care unit: diagnostic and therapeutic approaches

Worldwide, human rabies is prevalent where there is endemic dog rabies, but the disease may present unexpectedly in critical care units when suggestive clinical features have passed. In North America transmission from bats is most common and there is often no history of a bat bite or even contact with bats. Laboratory diagnostic evaluation for rabies includes serology plus skin biopsy, cerebrospinal fluid, and saliva specimens for rabies virus antigen and/or RNA detection. Rare patients have survived rabies, and most received rabies vaccine prior to the onset of illness. Therapeutic coma (midazolam and phenobarbital), ketamine, and antiviral therapies (dubbed the "Milwaukee Protocol") were given to a rabies survivor, but this therapy was likely not directly responsible for the favorable outcome. There have been many subsequent failures of similar therapeutic approaches. There is no scientific rationale for the use of therapeutic coma in human rabies. New approaches to treating human rabies need to be developed.

Rabies vaccination for international travelers

Rabies prevention in travelers is a controversial issue. According to experts, the decision to vaccinate results from an individual risk assessment based on the duration of stay, the likelihood of engagement in at-risk activities, the age of the traveler, the rabies endemicity and access to appropriate medical care in the country of destination. However, no detailed information is available regarding the last two determinants in many regions. Twenty-two cases of rabies were reported in tourists, expatriates and migrant travelers over the last decade, including three cases following short-term travel of no more than two weeks. Studies on rabies post-exposure prophylaxis (PEP) in travelers show that overall, 0.4% (range 0.01-2.3%) of travelers have experienced an at-risk bite per month of stay in a rabies-endemic country, while 31% of expatriates and 12% of tourists were vaccinated against rabies before traveling. The main reason cited by travelers for not being vaccinated is the cost of the vaccine. The majority of patients who sustained a high risk injury was not vaccinated against rabies before traveling and were not properly treated abroad. From available studies, the following risk factors for injuries sustained from potentially rabid animals may be identified: traveling to South-East Asia, India or North Africa, young age, and traveling for tourism. The duration of travel does not appear to be a risk factor. It should be noted that "at-risk activities" have not been addressed in these studies. Detailed rabies distribution maps and information on the availability of rabies biologics are urgently needed in order to identify those travelers who need pre-travel vaccination. Meanwhile, cost-minimization of rabies pre-exposure vaccination may be achieved in several ways, notably by using the intra-dermal method of vaccination.

Evolutionary history of rabies in Ghana

Rabies virus (RABV) is enzootic throughout Africa, with the domestic dog (Canis familiaris) being the principal vector. Dog rabies is estimated to cause 24,000 human deaths per year in Africa, however, this estimate is still considered to be conservative. Two sub-Saharan African RABV lineages have been detected in West Africa. Lineage 2 is present throughout West Africa, whereas Africa 1a dominates in northern and eastern Africa, but has been detected in Nigeria and Gabon, and Africa 1b was previously absent from West Africa. We confirmed the presence of RABV in a cohort of 76 brain samples obtained from rabid animals in Ghana collected over an eighteen-month period (2007-2009). Phylogenetic analysis of the sequences obtained confirmed all viruses to be RABV, belonging to lineages previously detected in sub-Saharan Africa. However, unlike earlier reported studies that suggested a single lineage (Africa 2) circulates in West Africa, we identified viruses belonging to the Africa 2 lineage and both Africa 1 (a and b) sub-lineages. Phylogeographic Bayesian Markov chain Monte Carlo analysis of a 405 bp fragment of the RABV nucleoprotein gene from the 76 new sequences derived from Ghanaian animals suggest that within the Africa 2 lineage three clades co-circulate with their origins in other West African countries. Africa 1a is probably a western extension of a clade circulating in central Africa and the Africa 1b virus a probable recent introduction from eastern Africa. We also developed and tested a novel reverse-transcription loop-mediated isothermal amplification (RT-LAMP) assay for the detection of RABV in African laboratories. This RT-LAMP was shown to detect both Africa 1 and 2 viruses, including its adaptation to a lateral flow device format for product visualization. These data suggest that RABV epidemiology is more complex than previously thought in West Africa and that there have been repeated introductions of RABV into Ghana. This analysis highlights the potential problems of individual developing nations implementing rabies control programmes in the absence of a regional programme.

Update on rabies

Human rabies is almost invariably fatal, and globally it remains an important public health problem. Our knowledge of rabies pathogenesis has been learned mainly from studies performed in experimental animal models, and a number of unresolved issues remain. In contrast with the neural pathway of spread, there is still no credible evidence that hematogenous spread of rabies virus to the central nervous system plays a significant role in rabies pathogenesis. Although neuronal dysfunction has been thought to explain the neurological disease in rabies, recent evidence indicates that structural changes involving neuronal processes may explain the severe clinical disease and fatal outcome. Endemic dog rabies results in an ongoing risk to humans in many resource-limited and resource-poor countries, whereas rabies in wildlife is important in North America and Europe. In human cases in North America, transmission from bats is most common, but there is usually no history of a bat bite and there may be no history of contact with bats. Physicians may not recognize typical features of rabies in North America and Europe. Laboratory diagnostic evaluation for rabies includes rabies serology plus skin biopsy, cerebrospinal fluid, and saliva specimens for rabies virus antigen and/or RNA detection. Methods of postexposure rabies prophylaxis, including wound cleansing and administration of rabies vaccine and human rabies immune globulin, are highly effective after recognized exposure. Although there have been rare survivors of human rabies, no effective therapy is presently available. Therapeutic coma (midazolam and phenobarbital), ketamine, and antiviral therapies (known as the "Milwaukee protocol") were given to a rabies survivor, but this therapy was likely not directly responsible for the favorable outcome. New therapeutic approaches for human rabies need to be developed. A better understanding of basic mechanisms involved in rabies pathogenesis may be helpful in the development of potential new therapies for the future.

Therapy of human rabies

Preventive therapy for rabies, including wound cleansing and active and passive immunization after a recognized exposure, is highly efficacious. Unfortunately, there is no established therapy that is effective for patients who develop rabies encephalomyelitis. There have been several survivors from rabies and all but one received rabies vaccine prior to the onset of clinical illness. Aggressive approaches to therapy of human rabies may be appropriate in certain situations. There is no scientific rationale for the use of therapeutic coma, and there are many reports of failures using this approach. Therapeutic coma should be abandoned for the therapy of rabies. New approaches such as therapeutic hypothermia should be evaluated, in combination with other therapeutic agents. More basic research is needed on the mechanisms involved in rabies pathogenesis, which will hopefully facilitate the development of new therapeutic approaches in the future for this ancient disease.

Reassessing the risk from rabies: a continuing threat to the UK?

The threat of re-introduction of rabies virus into the United Kingdom exists on several levels. Firstly, importation of live animals into the UK continues to challenge the regulations in place to ensure that the virus does not enter the country. Secondly, the indigenous bat population is known to carry a virus genetically related to rabies virus, the European bat lyssavirus (EBLV). Molecular characterization of this virus has further characterized it as being EBLV type 2, genetically distinct from a similar virus that has caused several human deaths across Europe. Finally, a lack of awareness of the threat of rabies and related viruses to travelers visiting endemic areas also constitutes a re-introduction threat to the UK population. This review will address the most recent cases of lyssavirus infection, in both humans and animals, either contracted within the UK or from abroad. We highlight the current diagnostic necessity for testing indigenous and foreign cases and comment on current UK government policy in light of a European call to harmonise rabies legislation across Europe.