Rabies and Rabies-Related Viruses

SECTION 8 Clinical Microbiology: Viruses

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Rabies and Rabies-Related Viruses MARY J. WARRELL  |  DAVID A. WARRELL

KEY CONCEPTS • Rabies encephalitis due to canine rabies virus is 100% fatal in unvaccinated patients. • No deaths have been reported in anyone who had had both pre-exposure vaccination and postexposure boosting. • Pre-exposure immunization should be encouraged for residents of, and travelers to, dog rabies enzootic countries. • Dog rabies is the source of 98% of human rabies deaths. • Rabies virus types found in bats in the Americas appear to be less pathogenic in humans. • There is not yet any specific treatment for rabies encephalitis. • Intensive care therapy is only recommended for certain encephalitis patients, those previously immunized or if infected by an American bat rabies virus. • Palliation is advised for the vast majority of symptomatic patients.

Nature Rabies is a zoonosis of dogs and other mammals that is occasionally transmitted to humans, causing fatal encephalomyelitis. Dog rabies virus is universally fatal in unvaccinated humans causing more than 98% of human rabies deaths. However, prophylaxis can be 100% effective, so all human deaths represent failure of prevention. Lyssaviruses are members of the large Rhabdoviridae family infecting animals and plants. The Lyssavirus classification and terminology have changed from genotypes to species. Rabies virus is the type species, species 1 of the genus, which also contains 11 rabies-related Lyssavirus species. They are divided into three phylogroups. All six species known to cause the typical fatal encephalitis in man are in phylogroup I. (See end of chapter.)

Structure The bullet-shaped virions contain a nonsegmented negative strand of rabies RNA encoding five proteins. The RNA is coiled with a nucleoprotein, a phosphoprotein and an RNA-dependent RNA polymerase to form a helical ribonucleoprotein complex or nucleocapsid. This is covered by a matrix protein. An outer envelope studded with the viruscoded, glycoprotein-bearing, club-shaped projections is acquired by budding through a host cell lipid membrane. Rabies virus strains from different vector species and geographic areas are distinguished by nucleotide sequencing.

Epidemiology ANIMAL RABIES Rabies is enzootic in most parts of the world. Globally, the domestic dog is the most important reservoir species and is the dominant vector in Asia, Africa and some areas of Latin America1 including Bolivia, Brazil, Haiti and the Dominican Republic. Separate reservoirs of enzootic infection occur in certain wild mammalian species (Table 171-1). Sylvatic rabies2 predominates in North America, Europe, parts of southern Africa and the Caribbean. All mammals are potentially susceptible, and infection may be transmitted to other species, including

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domestic animals, especially cats, and to humans. Lyssaviruses have not been reported from a few areas including Iceland, Italy, Cyprus, some other Mediterranean islands, Singapore, Sabah, Sarawak, New Guinea, New Zealand, Antarctica, Oceania, Hong Kong islands, Japan and some Caribbean islands. Although these countries have no apparent current indigenous rabies, infected animals cross national boundaries and so infection may be imported. Rabies (species 1) infects terrestrial mammalian reservoir species and bats in the Americas. Western Europe and Australia are free of rabies in terrestrial mammals, but rabies-related lyssaviruses are found in bats (see end of chapter). As the epizootiology changes constantly, up-to-date local advice should be sought for detailed information.

HUMAN RABIES Estimates of human rabies mortality are notoriously unreliable in tropical areas where about 99% of the deaths occur. The much quoted estimate of 55 000 deaths annually in Asia and Africa was deduced and extrapolated from data on the incidence of human dog bites. A welldesigned Indian verbal autopsy survey discovered 12 700 furious encephalitic rabies deaths annually.3 This estimate excluded paralytic cases. Other areas of high incidence include Bangladesh and Pakistan. There is very little surveillance in Africa. In Europe over the last 10 years, the average annual mortality was nine deaths, predominantly in Russia and Ukraine.4 Ten percent were imported, mainly from Asia or Africa. In the USA, an average of three cases are diagnosed annually. About 60% of cases are indigenous, of which 95% are caused by insectivorous bat rabies virus. Although fewer than 20 percent of such North American patients remember a bat bite, possible bat contact is more often reported.

Pathogenicity TRANSMISSION Human infection usually results from bites by rabid dogs or other mammals. Virus in saliva can enter via broken skin or intact mucous membranes, and so scratches or licks by a rabid animal may cause infection. On two occasions, human rabies may have resulted from inhalation of virus in caves in Texas that were densely populated by insectivorous bats. Unnoticed skin contact was a more likely route of infection.5 However, inhalation of virus aerosols has occurred in rare laboratory accidents. The saliva, respiratory secretions and tears of rabies patients contain virus,6 which could infect another person but the only documented instances of human-to-human transmission have been through human tissue transplants from donors in whom rabies had not been suspected. At least 11 cases of infection by corneal graft have been reported. In the USA and Germany, three donors transmitted rabies to eight recipients of solid organ transplants (kidney, liver, lung, pancreas) and one patient received only a segment of artery.7–9 Several women with rabies encephalitis have delivered healthy infants. Only one case of neonatal rabies has been reported, although vertical transmission is documented in animals.

PATHOGENESIS (Figure 171-1) Rabies virus attaches to a variety of cellular receptors, but in a bite wound, competitive binding to acetylcholine receptors may concentrate virus at neuromuscular junctions where it is poised for entry into a peripheral nerve pre-synaptic axon terminal.10 The virus or viral components then travel to the cell soma by retrograde axonal transport.11 Experimentally, infection can be halted by sectioning the nerve



Chapter 171  Rabies and Rabies-Related Viruses

TABLE

171-1 

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Distribution of Rabies Reservoir Species

Africa

Domestic dog (Canis familiaris) Black-backed jackals (Canis mesomelas) Yellow mongoose (Cynictis penicillata) Bat-eared fox (Otocyon megalotis) Frugivorous and insectivorous bats – (bat lyssaviruses)

Widespread dominant reservoir Southern Africa Southern Africa Southern Africa see Table 171-3

Asia

Domestic dog (Canis familiaris) Wolf (Lupus lupus) Chinese ferret badgers (Melogale moschata)

Widespread dominant reservoir Middle East China, Taiwan

Americas

Arctic fox (Alopex lagopus) Red fox (Vulpes fulva) Gray fox (Urocyon cinereoargenteus) Striped skunk (Mephitis spp.) Raccoon (Procyon lotor) Insectivorous bats Vampire bat (Desmodus spp.) Frugivorous bats Mongoose (Herpestes spp.) Domestic dog (Canis familiaris)

Alaska, northwest Canada Western Canada and northeast USA Texas, Arizona Texas, central USA, California Eastern USA, southeast Canada Very widespread Mexico, Trinidad and Tobago, Isla de Margarita, northern South America South America Puerto Rico, Granada, Cuba, Dominican Republic Mexico, parts of central and South America eg. Haiti, Bolivia, Brazil, Dominican Republic

Australia

Flying foxes or fruit bats (Pteropus spp.) Insectivorous bats – (Australian bat Lyssavirus see Table 171-3)

Eastern coastal area

Europe

Red fox (Vulpes vulpes) Arctic fox (Alopex lagopus) Raccoon dog (Nyctereutes procyonoides) Wolf (Lupus lupus) Domestic dog (Canis familiaris) Insectivorous bats – (European bat lyssaviruses)

Eastern Europe, Russian Federation Northern Russian Federation Eastern Europe Eastern Europe, Russian Federation Turkey (act as vectors in Eastern Europe and Russian Federation) Widespread see Table 171-3

Pathogenesis of rabies Infection

Route of infection

Incubation

Disease

Incubation period 20–90 days Salivary gland

Broken skin Intact mucosa (Respiratory tract) Tissue transplant

Centripetal retrograde axonal transport of virus to CNS

Rabies encephalomyelitis Intracellular viral replication

Clinical effects:

Inclusion (Negri) body formation

Behavioral changes,

Trans-synaptic viral spread

hydrophobia, paralysis,

Host gene expression altered

autonomic dysfunction

Neuronal dysfunction

Centrifugal axonal transport

Virus may replicate in muscle at bite site. Viral binding at nerve endings especially at motor end plates

Extracellular virus appears Virus produced in salivary glands Dissemination also to lungs, heart, adrenal and lacrimal glands, skin and cardiac muscle

Figure 171-1  The pathogenesis of rabies.

or by poisoning microtubular function. The route of viral entry into the central nervous system (CNS) after superficial inoculation by bats is unknown. Viral replication is intraneuronal. Accumulations of viral proteins form inclusions, such as classic Negri bodies (Figure 171-2). The virus spreads up the spinal cord towards the brain, passing intraneuronally

by budding from synaptic membranes, during which it acquires its glycoprotein envelope. Rabies virus remains confined to neurons where it evades immune recognition throughout the incubation period. Experimentally, neurophysiological disturbance is indicated by abnormal neurotransmitter activity, electroencephalograph patterns

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Appropriate rabies control strategies are based on surveillance to determine the principal domestic or wild reservoir species, with laboratory diagnosis to confirm the local prevalence of infection. Sylvatic rabies has been eliminated in the red fox, Vulpes vulpes, in Western Europe by distributing oral vaccine in suitable baits around the countryside.15 Repeated campaigns of oral vaccination are needed over many years, using live attenuated rabies, vaccinia or adenovirus recombinant vaccine expressing rabies glycoprotein. In North America, raccoons, foxes and skunks, and in southern Africa, jackals, have been similarly immunized. Control of vampire bat rabies, a cause of human and many cattle deaths in Latin America, is attempted by treating cattle with small doses of anticoagulant in order to poison the bats. Vaccination of cattle is possible but expensive. No active measures are taken to control rabies in insectivorous or fruit bats in the Americas, Europe, Africa or Australia, but the population is educated to avoid direct contact with these animals. Figure 171-2  Negri bodies in cerebellar Purkinje cells in a human victim of rabies encephalitis. The intracytoplasmic, dark-staining Negri bodies are marked with arrows. (Courtesy of Armed Forces Institute of Pathology, Bethesda, USA.)

and ion-channel function. The demonstrated viral effects on host gene expression include upregulation of genes which could enhance viral spread and replication, and downregulation of genes related to cell protein synthesis. The latter will impair cell metabolism and innate immune responses and contributes to the widespread dysfunction of intact neurons.12 Viral pathogenicity correlates with low levels of rabies glycoprotein expression, a minimal inflammatory response and little if any apoptosis. Pathological features of diffuse encephalomyelitis may be minimal or even absent in humans. Rabies virus spreads centrifugally via peripheral and autonomic nerves to many tissues including the salivary and lacrimal glands where replication produces extracellular virus that may initiate an immune response (Figure 171-1).

IMMUNOLOGY Following infection, rabies virus evades the immune system.13 No immunological response can be detected in unvaccinated patients before signs of encephalitis develop. Rabies antibody does not appear until 1–2 weeks after the onset of symptoms, if at all, and later in the CSF. Rabies-specific IgM is not detectable any earlier than IgG. The presence of neutralizing antibody is diagnostic in unvaccinated patients, but low levels of apparent immunofluorescent (IF) antibody can result from cross-reaction with other viral antigens. The virus is immunosuppressive, as reflected by the minimal histopathological changes in the brain. Interferon production in humans is very low, and high levels of IFN-α and IFN-β in animal brains did not protect them against death. The role of cellular immunity is not clear in human disease, but specific T lymphocytes are found experimentally in rabid animals with paralytic but not encephalitic signs. Surprisingly, apoptosis of immune reactive CD3+ T cells has been observed in mouse brains.13 In animals, clearance of virus from the brain and recovery is associated with early induction of neutralizing antibody, increased expression of viral glycoprotein, a greater inflammatory response, early appearance of IFN-γ and very little neuronal apoptosis. Neurons cleared of virus still have abnormal gene expression.

Control The elimination of rabies virus from domestic dogs would prevent 98% of human rabies deaths, obviating the need for expensive prophylaxis. This has been achieved, for example, in Western Europe, North America, Japan, several urban areas of Latin America1 and even in one study area in India.14 Mass killing of reservoir species is ineffective, but campaigns of dog vaccination and population control can be successful, if accompanied by enthusiastic education and publicity supported by adequate funding. Although oral vaccination of dogs is possible, it remains impractical.

Clinical Features The incubation period (bite to first symptom) ranges from 4 days to a documented 19 years, but in about 75% of cases it ranges 20–90 days. Of the many reported prodromal symptoms, only itching, pain or paresthesiae, radiating proximally from the site of the healed causative bite wound, suggest imminent encephalomyelitis. After 1–7 days of generally nonspecific symptoms, features of furious or paralytic rabies develop. The pathognomonic symptom of furious rabies is hydrophobia16 – jerky, violent inspiratory muscle spasms associated with an inexplicable terror provoked by water – or aerophobia – an identical response provoked by a draught of air on the skin. The hydrophobic response may be provoked by attempts to drink liquid or by the sight, sound or mere mention of water. An hydrophobic spasm may end in extreme opisthotonos, reminiscent of severe tetanus; in generalized convulsions; or in cardiorespiratory arrest. Other features of furious rabies include periods of excitement, sometimes with hallucinations or, rarely, with aggression; interspersed with lucid intervals during which victims can be aware of their terrible predicament; fever; tachycardia and other arrhythmias; hypersalivation; lacrimation; sweating; and fluctuating temperature and blood pressure; and priapism. These features suggest stimulation of the autonomic nervous system as in severe tetanus. Hypersexuality in rabies patients may be attributable to hippocampal or amygdaloid lesions as in Klüver–Bucy syndrome. Conventional neurological examination may prove surprisingly normal, unless hydrophobia is provoked, but meningism, cranial nerve lesions (especially III, VI, VII, IX–XII), upper motor neuron lesions, fasciculations, myoclonus and other involuntary muscular contractions are sometimes detected. Paralytic or dumb rabies is underdiagnosed but was recognized during an epidemic of rabies transmitted by vampire bats in Trinidad in the 1920s and 1930s. Although associated particularly with vampire bat rabies, it is also seen in patients infected by other species. After the prodromal symptoms described above, often with fever and headache, local paresthesiae and flaccid paralysis develop, usually in the bitten limb, and ascend symmetrically or asymmetrically. There is accompanying pain and fasciculation in the affected muscles and mild objective sensory disturbances. Death follows paralysis of the muscles of deglutition and respiration; there is usually no evidence of hydrophobia or aerophobia. Patients with rabies whose lives are prolonged by intensive care may develop a variety of respiratory, cardiovascular, neurological and gastrointestinal complications including fatal cardiac arrhythmias, pneumothorax, cerebral edema, diabetes insipidus, syndrome of inappropriate secretion of antidiuretic hormone (SIADH), hypo- or hyperpyrexia, diffuse axonal neuropathy and Mallory–Weiss hematemesis.

DIFFERENTIAL DIAGNOSIS Severe and unusual neurological symptoms, whether encephalitic or paralytic, should suggest the possibility of rabies in any unimmunized



Chapter 171  Rabies and Rabies-Related Viruses

person who has had contact with mammals in rabies-endemic areas. Children may not report animal contact and rabies patients infected by bats in the USA often deny exposure to bats. Rabies in children has been misdiagnosed as cerebral malaria. Furious rabies can be mimicked by the pharyngeal form of cephalic tetanus (‘hydrophobic tetanus’); however, severe tetanus usually has a shorter incubation period than rabies and there is sustained muscle rigidity, often associated with trismus. Delirium tremens and the excitatory effects of some plant toxins and recreational drugs7 have been confused with rabies. Paralytic rabies is indistinguishable from other encephalitides, and the many causes of Landry-type ascending paralysis, including postvaccinal encephalomyelitis complicating the use of obsolete nervous tissue rabies vaccines, and Guillain–Barré syndrome. No convincing or diagnostically useful differences have been proven between the clinical features of rabies encephalitis acquired from terrestrial mammals, classic (species 1) rabies compared to those from bats infected with rabies-related species (Table 171-3).

PROGNOSIS AND RECOVERY Without intensive care, victims of furious rabies encephalitis usually die within a few days, but some patients with paralytic rabies have survived for as long as 1 month, even without this support. During the virological era, only 10 documented cases of recovery or prolonged survival with neurological deficits after rabies encephalomyelitis have been reported. In two of them, rabies polymerase chain reaction (PCR) or antigen was detected and in eight, the diagnosis was based on detection of very high neutralizing antibody levels. Six had been infected by dogs and had received at least one dose of vaccine postexposure before the onset of symptoms.17,18 A seventh, who inhaled an attenuated vaccine virus, had received pre-exposure nervous tissue vaccine. Six of these seven suffered debilitating residual neurological sequelae but one has recently recovered: a 17-year-old Turkish shepherd who was bitten on the forearm and shoulder by a proven rabid dog. Four days later he was given a single dose of Vero cell vaccine, but 20 days after that he developed typical symptoms of rabies including hydrophobia. PCR on saliva and IFA corneal smear tests were positive for rabies, with high serum-neutralizing antibody. Equine rabies immunoglobulin and vaccine were given, and he was discharged after 66 days, apparently fully recovered.19 Three of the survivors were bitten by bats. One was bitten by a vampire bat in Brazil. He received postexposure prophylaxis, was diagnosed by PCR and has neurological sequelae. Another was a 6-year-old boy bitten on the thumb by a big brown bat (Eptesicus fuscus) in 1970 in Ohio, USA.20 He started having duck embryo rabies vaccine 4 days later but developed an encephalitic illness with

TABLE

171-2 

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very high rabies neutralizing antibody in the serum and CSF. After intensive care but no specific treatment he recovered completely in 6 months. The most surprising case, the only unvaccinated person known to have survived, is a 15-year-old girl in Wisconsin, USA, bitten by a bat in 2004.21 She developed paresthesiae of the bitten hand and features of paralytic rabies: progressive cranial nerve paralyses and leg weakness, with fever and hypersalivation. Rabies antibody had appeared by the sixth day after the onset of symptoms, but no virus or antigen was detected. Her intensive treatment included ketamine-induced coma and the antiviral agents ribavirin and amantadine. She made a slow recovery with only minor residual neurologic deficits, and she graduated from high school. This case has features similar to the boy in Ohio. It is likely that they both had rabies antibody present at, or soon after, the onset of symptoms. The American bat viruses are all rabies (species 1), which has a different pattern of infection from the dog rabies strains experimentally. It is slower to evolve and progress and there is relatively little neuronal apoptosis. The Milwaukee treatment protocol that was apparently effective in the Wisconsin girl, has not proved effective in at least 30 other patients infected by bats or dogs. It is not recommended by the World Health Organization (WHO). There is no evidence that it is superior to normal intensive care unit (ICU) therapy. Two patients initially reported to have recovered from rabies in the USA were diagnosed by finding low levels of IFT antibody. They are now considered to have been misdiagnoses due to a nonspecific serological cross-reaction.18 In summary, no unvaccinated patient is known to have survived rabies encephalitis if infected by a terrestrial mammal. Three people have recovered: two were vaccinated, after being bitten by a dog or bat, and a single unvaccinated patient recovered from a bat infection. All other survivors were left with severe neurological sequelae.

Diagnosis Confirmation of the diagnosis of rabies encephalitis should be possible within a day, if optimal samples are supplied to a specialist laboratory (Table 171-2). Rapid identification of antigen can be followed by virus isolation and, in unvaccinated patients, by detecting neutralizing antibody.22 Skin, saliva, respiratory secretions, CSF, tears and brain are all suitable samples, but a full-thickness skin biopsy is the most likely to yield a rapid result. A punch biopsy is taken from a hairy area, usually at the nape of the neck. Frozen sections show the characteristic IF staining of rabies antigen visible in nerve fibers around the base of hair follicles.23 With controls to ensure specificity and examination of many

Rabies Diagnostic Methods

Diagnostic Sample

Aim

Method

Antigen detection

IFA test on frozen section RT-PCR

Saliva Tears CSF

Virus isolation and antigen detection

Tissue culture Mouse inoculation test RT-PCR

Serum

Antibody test

Detectable antibody is diagnostic in unvaccinated patients Save sample for comparison later if vaccinated previously

CSF

Antibody test

Test in parallel with serum

Full-thickness skin* punch biopsy

REPEAT skin and saliva samples daily until a diagnosis is confirmed Brain post-mortem: needle biopsy† or autopsy sample brain stem and cerebellum

*Bold, most important, potentially helpful, samples. † See text for details.

Virus isolation and antigen detection

Tissue culture Mouse inoculation test IFA test-impression smear RT-PCR

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sections, sensitivity is 60–100%. False-positive results have not been reported, whereas the corneal impression test is insensitive and falsepositive results do occur. RT-PCR can be performed on the samples mentioned. Skin and saliva are the most likely to be positive. Viral isolation in tissue culture is the ideal method. Genetic analysis will indicate the likely reservoir species and geographic origin of the virus. Tests should be repeated until the diagnosis of rabies is excluded. In unvaccinated patients, diagnostic seroconversion may occur in the second week of illness or thereafter.24 In vaccinated patients, high levels of antibody both in the serum and in the CSF have been considered diagnostic.20 To confirm the diagnosis post-mortem, brain samples should be cultured, but antigen can readily be detected by IF staining of impression smears, enzyme immunoassay or RT-PCR. Without a full autopsy, a needle necropsy sample of brain can be obtained by inserting a long biopsy needle percutaneously through the medial canthus of the eye and the superior orbital fissure, the foramen magnum, the nose and ethmoid sinus or, in young children, through an open fontanelle.

TREATMENT OF MAMMAL BITES, SCRATCHES OR LICKS

Management

RABIES VACCINES Vaccines of Nervous Tissue Origin

No antiviral or ancillary treatments have proved effective in animal models and, in unvaccinated people, rabies of canine origin remains 100% fatal. Patients should be admitted to hospital so that their agonizing symptoms can be palliated with adequate doses of analgesic and sedative drugs.25 Friends, family and medical staff in close contact with the patient should be vaccinated as reassurance, even though such person-to-person transmission has not been documented. Intensive care should be considered for previously vaccinated patients, or those infected by an American bat virus. A better prognosis is associated with previous good health, early presentation and seroconversion. Novel approaches to rabies antiviral methods are needed, perhaps with immunological enhancement. Intrathecal injection of a live attenuated rabies virus is currently the most promising experimental method. Until a treatment has proved effective in animals, intensive care therapy is usually inappropriate, especially in low- to middleincome countries (LMIC).

Prevention POSTEXPOSURE PROPHYLAXIS

26-28

In rabies-endemic areas, the risk of infection, and hence the decision to give postexposure prophylaxis, depends on the species of animal, its behavior and the circumstances of contact. An unprovoked attack by a known local vector suggests a high risk of exposure to rabies, especially if the animal is unvaccinated, unusually excitable, partially paralyzed or if a wild animal is unusually tame. Vaccinated animals have, however, transmitted rabies. The virus gains access through any bite, scratch or contamination of broken skin or mucous membrane, but intact skin is an adequate barrier against infection. Bites or scratches by bats may pass unnoticed. The risk of infection is greatest from bites on the head, neck and hands, and multiple bites carry a higher risk than single bites. Before vaccines were available, the mortality from proven rabid dog bites in India was 35–57%. The biting animal’s brain should be tested for rabies. The routine IF test for antigen may give a false-negative rate of 1–2%. This test is unreliable for rabies-related lyssaviruses, and so viral culture and PCR are important in highly suspicious cases. Postexposure prophylaxis should not await laboratory results but must be started immediately, irrespective of the time that has elapsed since the bite. Postexposure prophylaxis aims to inactivate rabies virus in the wound and to stimulate immunity to kill the virus before it enters the nervous system, where it is protected from immune attack. Postexposure therapy includes urgent wound treatment, active prophylaxis with vaccine and passive immunization with rabies immune globulin (RIG). The complete therapy is very effective, and failures of optimal treatment started on the day of exposure are very rare. However, many deaths occur because treatment is often delayed, unaffordable, inadequate or incomplete.

The treatment can be summarized as follows: 1. Scrub wounds vigorously with soap or detergent and water, reaching into the depth and removing foreign material. Local or even general anesthesia may be necessary, especially for children. 2. Swab with a virucidal agent: povidone iodine or 40–70% ethanol. (The virucidal effect of quaternary ammonium compounds is neutralized by soap, and so they are not recommended.) 3. Suturing of wounds should be avoided or delayed for fear of inoculating virus deeper into the wound. 4. Tetanus prophylaxis (tetanus immune globulin or toxoid booster plus metronidazole) must not be forgotten. Antibiotic prophylaxis against other potential wound pathogens is recommended in the case of bites on the hands. 5. If there is a risk of rabies, start specific postexposure prophylaxis immediately.

Human rabies vaccines contain killed virus. Vaccines produced from infected sheep, goat or suckling mouse brain (SMB) should no longer be used. However, Fermi vaccine is still produced in Ethiopia and SMB in Peru. These are weak antigens and neurological reactions still occur.

Purified Tissue Culture Vaccines Tissue culture-grown vaccines are in general use. The original human diploid cell vaccine (HDCV) Imovax, Sanofi Pasteur has given way to vaccines of equivalent efficacy and safety, including German and Indian purified chick embryo cell vaccines (PCECV) Rabipur. RabAvert GSK, and a French purified Vero cell vaccine (PVRV), Verorab, Sanofi Pasteur which meet the WHO standards. Several other Indian and Chinese tissue culture vaccines are exported whereas Russian and Japanese vaccines are used locally.

Immunological Response to Vaccination The presence of serum-neutralizing antibody is the best available indicator of protection against rabies. It appears 7–14 days after starting a primary course of a modern rabies vaccine. A level of 0.5 IU/mL is considered satisfactory, although the protective level cannot be determined in humans. Only the viral surface glycoprotein molecules induce neutralizing antibody. They also stimulate helper and cytotoxic T-lymphocyte responses. The speed and size of the antibody response to vaccine vary, influenced by genetic factors. Relatively delayed, lower antibody levels are found in about 3% of vaccinees. Increasing age and immunosuppression, including by HIV infection also impair the response. The induction of neutralizing antibody is related to the amount of antigen (within limits) and the route of inoculation. Intradermal (ID) injection delivers antigen into the dermis, rich in antigen-presenting dendritic cells which stimulate T lymphocytes to initiate antibody production, an advantage over intramuscular (IM) inoculation.

POSTEXPOSURE VACCINE REGIMENS Intramuscular Vaccine Regimens

• The standard five-dose intramuscular (Essen) regimen is one

dose of vaccine (1 mL or 0.5 mL, depending on the product) into the deltoid on days 0, 3, 7, 14 and 28. A recent change, to omit the final dose, has been sanctioned in the USA for otherwise healthy patients if RIG is also given. • An alternative 2-2-1 (Zagreb) regimen is two doses intramuscularly into deltoids on day 0 and one dose on days 7 and 21.

Intradermal Vaccine Regimens The five-dose intramuscular regimen is unaffordable by the vast majority of patients in LMIC. Multiple-site ID vaccination is economical but only recommended using specified vaccines – PVRV, PCECV

and HDCV. The manufacturers’ instructions must be used for all other vaccines. The four-site ID 1-month regimen28,29 is the original eight-site regimen30 adapted by halving the number of injection sites and doubling the intradermal (ID) dose per site. The regimen is: • Day 0: four ID injections – the entire contents of the vial are divided between four sites: the deltoid and either the thigh or suprascapular areas. The ID dose depends on the volume per vial: for 0.5 mL/vial PVRV vaccine the ID dose is 0.1 mL/site, and for less concentrated 1.0 mL/vial PCECV vaccine it is 0.2 mL/ site. • Day 7: two ID injections in deltoid areas [0.1/ 0.2 mL] • Day 28: one ID injection in a deltoid area [0.1/ 0.2 mL]. If there is difficulty injecting 0.2 mL ID, the needle is withdrawn and the remainder injected nearby. This four-site regimen meets the WHO criteria of immunogenicity and supersedes the eight-site regimen, recognized as highly immunogenic and recommended by WHO for many years. The regimen is as immunogenic as the five-dose IM Essen method. It requires three visits and is the most economical, both for the patient and the healthcare provider. It is practical in rural areas because on the first crucial day a whole vial of vaccine is used. Vaccine wastage can be minimized by asking the patient to bring relatives with them on day 7, in case there is any left-over vaccine available for pre-exposure immunization. The timing of the day 28 dose may be adjusted to enable sharing of vials. • A two-site ID regimen is: on days 0, 3, 7 and 28, two 2 ID injections in deltoid areas [0.1 mL]. (Although originally 0.1 or 0.2 mL depending on the vaccine.) This regimen has been used in thousands of patients in urban areas in Thailand, the Philippines and Sri Lanka, where RIG treatment is likely to be available.

PASSIVE IMMUNIZATION WITH RABIES IMMUNE GLOBULIN Except in the case of trivial exposures, every primary postexposure vaccine course should be accompanied by RIG to cover the first 7–10 days before vaccine-induced immunity appears. RIG treatment is especially important after bites on the head, neck or hands, or multiple bites. A dose of 20 IU/kg of human RIG or 40 IU/kg of equine RIG is given, preferably with analgesia, at the same time as the first dose of vaccine. As much as possible is infiltrated into and around the wound, but care is needed when injecting into fingers or other tight tissue compartments. Any remaining vaccine is injected intramuscularly, avoiding the gluteal region. Increasing the dose of RIG may impair the response to vaccine, but if the volume is insufficient for infiltration, it can be diluted in saline two- or threefold in order to infiltrate all wounds. Skin testing with equine RIG does not predict early (anaphylactic) reactions and is no longer recommended.26 Adrenaline (epinephrine) should always be ready in case of very rare anaphylaxis. Reactions occur in 1.8% of equine RIG recipients and serum sickness is seen in 0.7%, but not after human RIG therapy.31

Postexposure Boosting of Previously Vaccinated Patients Treatment is always urgent. Provided that the patient has previously had a complete pre-exposure or postexposure course of tissue culture vaccine or if a neutralizing antibody level >0.5 IU/mL has been recorded anytime previously, only booster vaccination is needed without RIG. • Two-dose intramuscular regimen: one dose on days 0 and 3. • Single day four-site ID regimen:26four ID injections in deltoid and thigh or suprascapular areas.

SIDE EFFECTS OF TISSUE CULTURE VACCINES32 The incidence of minor symptoms is very variable. Local pain or erythema occurs in about 15% of people vaccinated and irritation is more

Chapter 171  Rabies and Rabies-Related Viruses

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common following intradermal injections. Generalized nonspecific symptoms are reported by about 7% of patients and transient maculopapular and urticarial rashes are occasionally seen. Neurologic symptoms, either Guillain–Barré-like or local limb weakness, are extremely rare, and the incidence following treatment is no greater than those following other routine vaccines. No complications have been observed in pregnancy.

PRE-EXPOSURE PROPHYLAXIS26–28 Pre-exposure vaccination is recommended for anyone at risk of exposure to rabies virus, particularly veterinary surgeons, animal handlers, zoologists, all bat handlers, laboratory staff working with rabies, wildlife officers and people living in or traveling33 to rabies-endemic areas where dogs are the dominant reservoir species. A total of three doses of cell culture vaccine are needed on days 0, 7 and day 28. The last dose can be advanced towards day 21 if time is short. The dose can be intramuscular or 0.1 mL ID. Families or student groups who cannot afford intramuscular vaccine can share ampoules economically if inoculated the same day. If immunosuppression is suspected, or if taking chloroquine, give vaccine intramuscularly rather than ID. A single booster dose after 1 or 2 years prolongs the antibody response, which usually lasts 5–10 years.34 Unnecessary boosters can be avoided if antibody is detected. Booster doses are not needed for travelers who will have access to vaccine if exposed. If not, boost after 5 years. Serologic testing is useful to determine the need for booster injections and is advised if immunosuppression is suspected.

Rabies-Related Viruses Infecting Humans With one exception, these are viruses of bats. Five of the six are phylogroup I viruses, causing typical rabies-like encephalitis (Table 171-3). New unclassified lyssaviruses are emerging.

AFRICA2 Duvenhage virus, a bat virus, is fatal in humans2,35,36 (Table 171-3). Its true prevalence is uncertain as the diagnosis of human rabies is normally made on clinical grounds and rabies-related viruses may give a weak or negative result with the routine diagnostic rabies IF test.

EUROPE There are two species of European bat lyssaviruses2 (EBLVs): EBLV type 1 is widely distributed in insectivorous bats across Europe and EBLV type 2, which is rare. There are four reports of EBLV fatal rabieslike encephalitis following bat bites in Europe (see Table 171-3).2,37–39 Irkut virus caused a human death in Eastern Russia.40

AUSTRALIA Australian bat Lyssavirus,2 found in flying foxes or fruit bats (Pteropus spp.) and other bats, has caused three human deaths.41

CHINA AND ASIA In China there is serological evidence of lyssaviruses in bats, but only a single isolate of Irkut virus from a bat which fatally infected a woman.40 Rabies was diagnosed clinically in one other victim of a Chinese bat bite. There is indirect evidence of bat lyssaviruses in India. A case of typical furious rabies followed a bat bite in Andhra Pradesh in 1954 and an untyped Lyssavirus was isolated from a bat in Chandigarh in 1978. In South East Asia, seropositive bats have been found in the Philippines, Thailand, Cambodia, Bangladesh and Vietnam. References available online at expertconsult.com.

1464 TABLE

171-3 

SECTION 8  Clinical Microbiology: Viruses

Rabies and Rabies-Related Lyssaviruses Known to Infect Humans Animal Reservoirs (Potential Vectors)

Lyssavirus Species*

Phylogroup

Virus Distribution§

1 Rabies

I

Widespread

Dogs, some wild mammals and bats in the Americas

Tens of thousands annually

3 Mokola

II

South Africa, Nigeria, Cameroon, Ethiopia (rare)

Shrews, rodents (cat, dog)

Child febrile convulsion;† recovered2 Child encephalitic signs;‡ died2 Vaccinated laboratory worker, mild illness; recovered

4 Duvenhage

I

South Africa, Zimbabwe, Kenya (very rarely identified)

Insectivorous/fruit bats (cats)

Man bitten by a bat, signs of typical furious rabies; died2 Man scratched by a bat, signs of classic rabies encephalitis; died35 Woman scratched by a bat, signs of rabies encephalitis; died36

5 European bat Lyssavirus EBLV type1a EBLV type 1b

I

Northern and Eastern Europe Western Europe

Insectivorous bats

Girl had bat bite, had acute ascending paralysis and encephalitis; died (clinical diagnosis only) Girl had bat bite, signs of furious rabies; died of EBLV 1a37

6 European bat Lyssavirus EBLV type 2a EBLV type 2b

I

Netherlands, UK, Germany, France Switzerland, Finland

Insectivorous bats (Myotis spp.)

Bat conservationist bitten by bats, typical signs of rabies encephalitis; died of EBLV 2a38 Zoologist bitten by sick bat, signs of furious rabies; EBLV type 2b39

7 Australian bat Lyssavirus

I

Australia

Fruit bats (Pteropus spp.), insectivorous bats

Woman bat carer, scratched by bats, typical signs of rabies encephalitis; died Woman, bitten by a fruit bat, signs of paralytic rabies; died39 Boy scratched by bat, developed typical rabies encephalitis; died41

10 Irkut

I

Eurasia, China

Insectivorous bats

Woman bitten on lip by bat, paralytic rabies-like encephalitis, died40

Disease in Humans

*Bat Lyssavirus species not found in humans. In Africa, Phylogroup II: 2 Lagos bat virus; 12 Shimoni bat virus. In Eurasia: Phylogroup I: 8 Aravan; 9 Khujand virus; Phylogroup III: West Caucasian bat virus. § There is serologic evidence of lyssaviruses in bats in the Philippines, Cambodia, Thailand, Bangladesh and Vietnam. † Doubtful diagnosis. ‡ Alternative diagnosis possible.

KEY REFERENCES Gautret P., Parola P.: Rabies in travelers. Curr Infect Dis Rep 2014; 16:394. Helmick C.G., Tauxe R.V., Vernon A.A.: Is there a risk to contacts of patients with rabies? Rev Infect Dis 1987; 9:511-518. Jackson A.C., Warrell M.J., Rupprecht C.E., et al.: Management of rabies in humans. Clin Infect Dis 2003; 36:60-63. Nel L.H., Markotter W.: Lyssaviruses. Crit Rev Microbiol 2007; 33:301-324.

Noah D.L., Drenzek C.L., Smith J.S., et al.: Epidemiology of human rabies in the United States, 1980 to 1996. Ann Intern Med 1998; 128:922-930. Schnell M.J., McGettigan J.P., Wirblich C., et al.: The cell biology of rabies virus: using stealth to reach the brain. Nat Rev Microbiol Jan 2010; 8:51-61. Warrell D.A., Davidson N.M., Pope H.M., et al.: Pathophysiologic studies in human rabies. Am J Med 1976; 60:180-190.

Warrell M.J.: Current rabies vaccines and prophylaxis schedules: preventing rabies before and after exposure. Travel Med Infect Dis 2012; 10:1-15. Warrell M.J., Riddell A., Yu L.-M., et al.: A simplified 4-site economical intradermal post-exposure rabies vaccine regimen: a randomised controlled comparison with standard methods. PLoS Neglect Trop Dis 2008; 2(4): e224.



Chapter 171  Rabies and Rabies-Related Viruses 1464.e1

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