Rabies: Recent advances in pathogenesis and control

SPECIAL ARTICLE

Rabies: Recent Advances in Pathogenesis and Control

Aaron Miller, MD, and Neal Nathanson, M D

Current knowledge of rabies is reviewed, with emphasis on recent developments in virology, immunology, pathogenesis, treatment, and prophylaxis. Although only a few cases of human rabies occur annually in the United States, the infection is enzootic in wildlife, and an estimated 30,000possible exposures requiring treatment occur each year.

Rabies belongs to the family rhabdovirus, and its molecular anatomy and biochemistry of replication have been described in some detail. There have been advances in measurement of antirabies antibodies, and techniques for measuring celIular immune response have recently been developed. Early stages of infection are more fully understood, with a hypothesis to explain peripheral sequestration of virus during prolonged incubation periods. Rabies was once thought to be uniformly fatal, but a few patients have survived with aggressive supportive measures. A newly developed vaccine (soon to be licensed in the United States) has been shown highly potent for preexposure immunization and promises to be very effective for postexposure prophylaxis. Current Public Health Service recommendations for postexposure treatment are summarized. Recent research has suggested a novel approach to control of wildlife rabies through oral immunization.

Miller A, Nathanson N: Rabies: recent advances in pathogenesis and control. Ann Neurol 2:5 11-5 19, 1977

The haunting image of the mad dog and its potential to cause the frightening disease we now know as rabies (hydrophobia, lyssa, or, as the French so vividly say, “la rage”) has tormented mankind for millennia. De- scriptions of the behavior of apparently rabid canines exist in the pre-Mosaic code of ancient Mesopotamia, approximately 4,000 years ago, as well as in the Babylonian Talmud [63]. Summer, marked by the brightness of the dog star Sirius, which supposedly added its heat to the sun, came to be known to the ancients as “dog days” because of the belief that, at these times, dogs were especially liable to madness [ 3 5 , 381. Descriptions of the disease were offered by both Democritus (cad50 BC) and Aristotle (322 BC), but Celsus (100 AD) was the first to recognize the relation- ship of hydrophobia in humans to rabies in animals.

Fortunately, beginning with the seminal work of Louis Pasteur in the 1880s, progressive improvements over the Talmudic prescription for care of the dog bite victim have been added to the physician’s armamen- tarium. The rabbinical scholars had urged chat the patient write prayers on the skin of a male hyena or leopard, then strip off his clothes and bury them at a crossroads for 12 months. After that period he was to remove the garments, burn them, and scatter the ashes. During the 12-month period the patient must drink only from a copper tube “lest he see the shadow of the demon and be endangered.” To drink from

another vesgel might cause him to see the reflection of a mad dog in the water and thus be further seized by cramps in the throat and inability to drink (hydrophobia) (631.

Pasteur discovered that the true infectious agent of rabies could be recovered from the brains of animals dying of the disease. He accurately forecast the ul- tramicroscopical nature of the agent, which we now recognize to be a member of the family rhabdovirus. In 1884 Pasteur demonstrated the now widely recognized phenomenon that the pathogenicity of a virus for its natural host can be altered by serial intracere- bra1 passage in another host species. By repeatedly passing the rabies agent through rabbits, Pasteur obtained a preparation that caused a rather uniform, short incubation period and sterotyped clinical illness. H e called this “fixed” virus, in contrast to the natural infection caused by “street” virus. This development of fixed virus was critical for the subsequent preparation of the Pasteur vaccine and its successors [551.

Epidemiology Most neurologists in North America may never see a clinical case of rabies. Nonetheless, chroughout much of the world-especially in underdeveloped na- tions-rabies remains an unabated terror. Even in the United States, Canada, and Western Europe, the threat of rabies continues and is even spreading at [he

From the Division of Infectious Diseases, Department of Epdemi- AcceDteci for mblication Tune 2. 1977 ~ ~, ~, .

ology, The Johns Hopkins University School of Hygiene an: Public Health, and the Department of Neurology, The Johns Hopkins University School of Mcdicine, Baltimore, MD.

Address reprint requests to Dr Nathanson, Department of Epide- miology, The Johns Hopkins University School of Hygiene and Public Health, Baltimore, MD 21205.

511

present time. Israel was declared a danger area by health officials in December, 1976, after a rabid dog bit 50 persons and 17 dogs (NY Times, Jan 16,1977).

The scope of the problem may be indicated by the fact that while 430 human deaths were recorded by the World Health Organization in 1973, an estimated 15,000 deaths occur annually in India alone, according to Schwabe [68]. Discrepant figures similarly cloud the issue of postexposure vaccination. However, whether one accepts the W H O estimate that more than 1 million persons were immunized in 1973 [62] or the claim that more than 3 million are vaccinated in India [76], the public health impact of rabies can be appreciated. In Latin America the risk of rabies is aIso high, necessitating the vaccination of more than 300,000 persons annually [6 1 I.

While the incidence of rabies is highest in such countries as India, the Philippines, and Brazil, the virus is virtually ubiquitous. The very few locales completely free of the disease are mainly islands sur- rounded by protective ocean barriers, such as Britain [62]. Despite this, the United Kingdom has practiced intensive surveillance and quarantine procedures to prevent introduction of the disease in the face of a spreading epizootic in Western Europe over the past thirty years.

Throughout most of the world the primary animal reservoir of rabies is the dog. Dog bites constitute the major route for transmission of the disease to humans, and control of canine rabies represents the most important step in reducing the human illness. According to WHO, “in countries where dog rabies is still the major problem, rabies can be controlled by adequately vaccinating the dog population and by de- stroying strays. One of the most effective weapons in rabies control is the prophylactic vaccination of pet dogs” [62].

That such measures can be extremely effective is amply illustrated by the situation in the United States, where reported cases of dog rabies steadily declined from 1946 to 1960, a period when such control measures were applied to the canine population. From 1946 to 1960 there were 236 human deaths from rabies, but since 1760 the mortality rate has decreased to an average of 1 or 2 deaths a year. In both the United States and Canada, wildlife rabies cases now far outnumber those in canines. Thus, in 1975, of 2,677 cases of laboratory-confirmed rabies in the United States and Puerto Rico, only 5% occurred in dogs. In contrast, in Mexico, where stray and unvacci- nated dogs remain a major health hazard, nearly 90% of 4,275 confirmed cases were in dogs [621.

The largest wildlife reservoir in the United States at present is the skunk, which accounts for 465% of the total incidence. Foxes, which caused 10% of cases in the United States in 1975, are the largest single reser-

voir in Canada, responsible for approximately 25% of the 2,274 cases [62l. The raccoon is a potential source of human exposure, but cases involving this species (7% of the total) occur almost exclusively in Georgia and Florida. Rabies is enzootic in the mongoose in Puerto Rico and other parts of the Caribbean, where it has become a significant public health hazard [23].

Following an outbreak of rabies in Trinidad in 1729, vampire and frugivorous bats were demonstrated to have the capability of transmitting rabies. In 1734 Pawan [54l made the important discovery that insec- tivorous bats (the only type found in the continental United States) have similar ability. Although the largest number of virus isolations in this country have been obtained in the Southwest from the Mexican free-tailed bat [4 1 3, of greater significance is the fact that bats (accounting in 1975 for 17% ofwildlife cases in the United States) represent the most widely dis- tributed host geographically. Furthermore, antibody surveys of bat populations, virus isolations, and experimental investigations suggest the possibility that both abortive infections (shown to occur in some experimental models 1461) and asymptomatic carrier states may be present in certain species of bats [5, 12, 741.

Rather convincing evidence now exists that rabies may, o n occasion, be transmitted other than through bites. Following the deaths of 2 persons who had entered the Frio Cave in Texas and who denied knowledge of bat or other bites, Constantine [18] demonstrated that sentinel animals housed in such heavily bat infested caves and screened from direct contact with bats or other animals uniformly developed rabies after incubation periods of 28 to 109 days. In addition, a well-documented rabies infection has occurred in a laboratory worker who was exposed to a brain homogenate prepared in a kitchen type blender that was subsequently shown capable of producing viral aerosols [17, 851.

Of great concern at present is a propagating epizootic of fox rabies in Western Europe. Rabies in foxes was first observed in Poland in 1739, and westward progression through Europe has been well documented since 1945. Fox rabies rapidly spread to Germany and Denmark (1964); Austria, Belgium, and Luxembourg (1766); Switzerland (1767); and France (1968) [76]. The epizootic front continues to advance into uninfected areas at a rate of approximately 20 to 60 km per year. Most European biologists believe that the occurrence of rabies in red foxes is self supporting. Reduction of the fox population density to fewer than 1 per square kilometer has been demonstrated to stop the spread of the disease, but effective population control has been difficult to achieve [45, 731.

The importance of fox rabies has led to extensive efforts to develop oral vaccines for field application.

512 Annals of Neurology Vol 2 No 6 December 1977

Attention is now focused primarily on the use of attenuated live virus vaccine incorporated into sausage baits. Acceptance of these baits and successful immunization have been demonstrated experimentally [6,79,84]. Before the immunization technique can be field tested, however, it will be necessary to demon- strate nonpathogenicity of the live virus vaccine for nontarget species, including man.

A recent development in the management of animal bite victims in the United States has been the attempt to determine rabies-free areas. Approximately 30,000 courses of postexposure prophlyaxis, many of which may be unnecessary, are administered annually in the United States. Philadelphia and New York City have now been declared free of terrestrial rabies. Thus, the vast majority of animal bite victims in these cities- and in future areas similarly deemed to be rabies free-need not receive rabies postexposure prophylaxis [47, 621.

Clinical Features Rabies assumes protean clinical forms in man. Nonetheless, several features are quite characteristic of the disease. After an incubation period usually lasting 2 1 to 60 days (range, 6 days to 14 months) [22,30,34, 771, the illness often begins with a few days of nonspecific constitutional symptoms such as chills and fever, fatigue, headache, photophobia, and musculo- skeletal pains. Many patients complain of an abnormal sensation around the wound site as one of the earliest symptoms. These complaints may include pain or dysesthetic sensations such as itching, burning, numbness, or paresthesias. In a review of 49 cases by Dupont and Earle [221,46% presented with pain and 125% with paresthesias.

Two major clinical patterns can be disringuished [38,801 although individual case reports indicate considerable variation among patients. The majority of patients suffer “furious” rabies. Hydrophobia, the most characteristic and widely recognized symptom and sign of the disease, occurs in 17 to 50% of patients. This symptom is often described as difficulty in swallowing, often painful, marked by pharyngeal spasm. The presence of an intense psychic reaction or terror precipitated by attempts to drink, or at times even by the sight of water, is typical. Severe inspiratory spasms lasting 5 to 15 seconds are an integral part of the hydrophobic response [Sl], and these may lead to respiratory arrest orgeneralized fatal convulsions [80, 8 11. Warrell et a1 [811 have suggested that these respiratory signs may be related to respiratory myoclonus [ 591 and be caused by brainstem lesions rather than occurring as a conditioned reflex arising from severe throat pain.

Despite the widespread view that rabies is an atypi- cal encephalitis, the majority of patients do manifest signs of delirium at some point in the clinical course.

These may range from mild memory disturbance through Severe alterations of mental status to coma. Other neurological signs that may occur include meningismus; cranial nerve pareses leading to dip- lopia, ptosis, dysphagia, and dysarthria; limb paresis, sometimes with clear signs of pyramidal tract lesions; reflex alterations; and involuntary movements. Lum- bar puncture usually shows normal or only mildly elevated opening pressure, and protein concentration may be slightly increased. Cell counts usually reveal a mild pleocytosis of predominantly mononuclear cells [22, 30, 38, 801.

Autonomic disturbances such as hyperpyrexia, hypotension, excessive sweating, piloerection, hyper- salivation, pupil dilation, and tachycardia frequently develop. The pathophysiology of these signs is uncer- tain, but some may be related to the severe hypothalamic involvement seen not infrequently at necropsy. Alternatively, these abnormalities may re- flect dysfunction of the autonomic nerves themselves, since these have been experimentally demonstrated by immunofluorescence studies to contain rabies antigen [531.

The second clinical form of rabies infection in man, occurring in fewer than 20% of the cases, presents a neurological picture comparable to the Landry- Guillain-Barre syndrome. This pattern of “dumb” or “paralytic” rabies has been noted most frequently, but not exclusively, following vampire bat bites and after postexposure prophylaxis has been attempted [80]. In the latter cases the illness must be distinguished from allergic postvaccinal encephalomyelitis or neuritis. After a typical prodromal period, the paresis often begins in the bitten extremity and then spreads either symmetrically or asymmetrically. Fasciculatioris and pain as well as mild sensory disturbances have been noted [80].

Pathogenesis Recent studies have characterized the anatomy and synthesis of rabies virus in some detail [50, 671. The mature virion is a bulletshaped particle, 75 by 180 nm, with a helical nucleoprotein capsid enclosed within a lipid envelope from which project numerous glyco- protein spikes that carry the major antigenic determi- nants of the virus.

Although rabies infection may rarely be acquired by other routes [17, 181, the overwhelming majority of cases are due to the bite of a rabid mammal. The pathogenesis of the subsequent infection is summarized in the Figure.

I t has long been recognized that the site of the wound influences the risk of acquiring clinical rabies. Most sources 1693 report a greater incidence of rabies with bites on the face, head, and arms than on the legs. In Iran prior to 1955, approximately 4096 of persons

Miller and Nathanson: Recent Advances in Rabies 5 13

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virus budr ond infectr additional cells

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virol genomes enhr spinol cord or brainrtem

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[musclo spindle) of peripherol nerver in

interferon or replication in murcle interferon inducor -----

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bitten on the head by rabid wolves died compared with about 2% of those bitten on the limbs and trunk [ I 11.

Perhaps the most puzzling aspect of rabies infection has been the long incubation period. The usual inter- val between the bite and the onset of clinical illness in man is between 1 and 2 months. However, much longer incubation periods have been reported [30, 771.

Where the virus is harbored during this period has long been a mystery. Baer and Cleary [7], studying the pathogenesis of street virus infection in mice by footpad inoculation, noted that a marked reduction in mortality rate could be obtained by amputating the foot as long as 18 days after injection, thus implying that the virus remains at the local wound site for a considerable period. Using intramuscular or footpad inoculation of young hamsters, Murphy et a1 [51-531 have used immunofluorescence techniques to demon- strate a temporal progression of rabies infection beginning in striated muscle cells as early as 36 to 40 hours after inoculation of fixed virus. Electron microscopy confirmed the productive infection of these muscle fibers, with shedding of virus into the extracel- lular space. Sequential studies then showed progressive involvement of neuromuscular and neurotendinal spindles near the inoculation site, followed by peripheral nerve, dorsal root ganglia, and lumbar spinal cord [52]. The authors further suggest the possibility that the early myotropism of the virus may represent an amplifying phase that provides a sufficient

Puthogmew of rabtes. begzrinziig with n bite (bottom of figure). Dotted arrows Indicate point3 ojpotentiaf modulatton

amount of virus for successful invasion of the peripheral nervous system.

The necessity of intact nerves for central propaga- tion of the virus was indicated by the sparing effect of sciatic neurectomy when carried out prior to footpad inoculation [S]. Electron microscopy confirmed ear- lier evidence that infection in peripheral nerves is limited to axons, and Schwann cells were never seen to contain rabies virus [39]. Within axons “viral maturation was prominent only where axonal cytoplasm contained organelles, that is the intracytoplasmic membranes necessary for viral budding” [521. Such structures occur especially at nodes of Ranvier.

Once rabies virus has gained the central nervous system, budding may be observed from the plasma membranes of neurons and glia [58], with almost every CNS neuron infected at the time of death [24, 531. Iwasaki et a1 [36,37] found fewviralparticles free in the intercellular spaces, but direct cell-to-cell transmission of virus within the brain was noted [36, 371. The latter effect may have major implications for the failure of host immunological defense mechanisms to eradicate an established CNS infection with street virus. Centrifugal neural spread of virus occurs, reach- ing the retina and cornea; peripheral nerve endings of the skin, especially around hair follicles; intestine; adrenal medulla (including chromaffin cells); taste


buds; and olfactory neuroepitheiium. Extraneural sites of infection, including salivary gland epithelium, pancreas, brown fat, and myocardium, are also seen D31.

Diagnosis and Treatment The differential diagnosis of the clinical syndrome of furious rabies includes hysteria, tetanus, other encephalitides, and delirium tremens. Patients with rabies phobia very seldom reproduce the inspiratory spasms characteristic of true hydrophobia. Tetanus generally has a shorter incubation period (less than 2 weeks), patients do not manifest hydrophobia, and the cerebrospinal fluid is invariably normal. In contrast to rabies, other encephalitides are more likely to entail abnormal CSF and are not characterized by hydrophobia. “Retained consciousness in the presence of severe brain stem irritation and ‘furious’ behavior is most unusual except in rabies encephalitis” [SO].

One of the most difficult problems, at times, is distinguishing postvaccinal (allergic) neuritis and encephalomyelitis from dumb or paralytic rabies. The former also may assume protean forms, but clinical signs and symptoms generally appear within 2 weeks of the first dose of vaccine. Landry-Guillain-Bar& syndrome, poliomyelitis, and acute transverse myeli tis must also be ruled out as diagnostic possibilities.

Until very recently the antemortem diagnosis of rabies was, of necessity, based almost solely on clinical grounds in a patient with known or presumed exposure to a proved or potentially rabid animal. The short duration of illness after onset of clinical signs-a mean of 7.4 days [22]-precluded the possibility of obtain- ing diagnostic laboratory studies. Diagnosis of human cases antemortem may be facilitated by several recently developed techniques. Antibody determina- tions may now be made i n 24 hours by a fluorescence technique 1721. The presence of any antibody i n a nonimmunized patient, very high serum neutralizing antibody titers, or significant antibody levels in CSF are all evidence of rabies infection.

Experimental studies have demonstrated the presence of rabies antigen by immunofluorescence in cutaneous nerve fibers, especially around hair follicles and in corneal smears early in the course of rabies infection [13, 661. Identification of rabies antigen has now been made antemortem in some human cases employing these methods 114, 431. Attempts to isolate virus from saliva and CSF bj7 passage in mice may be made, but such efforts are seldom successful. Isola- tions also have the disadvantage of requiring a minimum of 6 days, and possibly much longer, before the test animals sicken and die.

Historically, rabies has been regarded as invariably fatal, and survival after onset of symptoms was seldom much longer than a week [22, 30,801. However, with

the use of intensive supportive care in recent years, several cases of prolonged survival have been reported. In 1972 Hattwick and colleagues [32] described the first known human survivor without neurological sequelae, a 6-year-old boy bitten on the left thumb by a bat in Ohio. A second convincing recovery without neurological deficit was recently reported in an Argentinian woman who was the victim of a dog bite [61]. These two reports of recovery after intensive supportive care offer some slight hope to victims of rabies. Unfortunately, the experience of others 116, 26,48,80] suggests that such cases will remain rare ex- ceptions; and the observations made by Moses Maimonides in his Treatise on Poisons (1 198) remain, in general, discouragingly valid today: “Everything mentioned in the literature against the bite of a mad dog is useful, if at all, only when applied before the Rabies sets in. When such is the case I have as ye t seen nobody who escaped with his life. . .” [63]. Until such time as effective, nontoxic antiviral agents are developed, emphasis must remain on prompt, improved prophylaxis.

The postmortem diagnosis of rabies in both man and animals for many years depended on the demonstration of Negri bodies in the brain. These structures, originally described by Negri in 1903, appear on light microscopy with Seller’s methylene blue- basic fuchsin stain as intracytoplasmic eosinophilic inclusions generally measuring 1 to 27 p,m in diameter [581. They show a heterogeneous matrix and an inner basophilic core [22]. Structures lacking this inner body but otherwise appearing similar to Negri bodies are often found in great numbers in rabid brains. Such inclusions, called lyssa bodies, were originally thought to be an intracellular phase of the parasite En- cephalitozoon lyssae 1221. Both Negri bodies and lyssa bodies in rabies infection have been demonstrated to correspond with sites of viral replication 1491. However, lyssa bodies are now widely recognized to be nonspecific for rabies since similar structures have been found in normal animals of many species, in human senescense, and in some human degenerative diseases such as myotonic dystrophy [ I l l . The specificity of even the Negri body has recently been questioned after Derakhshan [21] reported finding identical inclusions in the brain of a 5-year-old patient dying of Reye’s syndrome. How- ever, unlike Negri bodies in rabies [421, the inclusions in Derakhshan’s patient stained positively with periodic acid-Schiff.

Even if the traditional dogma of Negri specificity is valid, the problem remains that in more than 25% of naturally occurring cases of rabies, Negri bodies are not found. Rabies is predominantly a disease of gray matter and, other than manifesting the “pathog- nomonic” Negri body, is not dissimilar to other viral


encephalomyelitides, including poliomyelitis. Peri- vascular mononuclear cell infiltrates are found almost universally and tend to occur most extensively in the spinal cord and brainstem; a mild leptomenin- geal inflammation is frequently observed also [22]. At times, such inflammatory changes are sparse and may be overlooked without careful inspection. Although gross cell disruption is seldom seen in naturally occurring rabies, some degree of neuronophagia is frequently present, along with perineuronal inflammatory cells [58]. These infiltrates have come to be known as Babe’s nodules, after the French pathologist who originally described them in 1872.

A critical breakthrough occurred in 1958, when Goldwasser and Kissling [27] described a fluorescence technique for demonstration of rabies antigen in nerve tissue. Used with appropriate controls, this technique is highly sensitive and specific. The procedure has revolutionized the pathological diagnosis of rabies and is in widespread use in public health laboratories throughout the world. The mouse inoculation test is also important, for it leads to positive virus isolation in some 20% of brains that contain no Negri bodies and confirms the fluorescent antibody test [221.

Prophylaxis In the early 1880s, Louis Pasteur dried the spinal cords of rabbits infected with fixed rabies and then exposed dogs to daily subcutaneous injections of doses of graded infectivity over 10 days. He found that the dogs were resistant to natural virus infection [56]. Following this success, in 1885, a severely exposed peasant boy was vaccinated in the same manner and remained well [38]. O n the basis of this single case, Pasteur was overwhelmed with demands for the treatment. In the first 15 months following his success with young Joseph Meister, Pasteur and his associates treated 2,940 persons. The clamor produced such a burden on his laboratory that no further experiments were done to prove the efficacy of the regimen [35].

This pioneering work of Pasteur’s has remained the basis of human postexposure prophlaxis throughout the world up to the present. Fermi in 1908 became the first to use chemical treatment of suspensions of fixed virus for preparation of the vaccine, though his vaccine still contained some residual live virus. In 1919 Semple modified the phenolization procedure so that the virus could be rendered completely noninfectious. Even today, much of the vaccine employed throughout the world in man is prepared by similar methods from the nervous tissue of an infected animal, such as sheep, goat, or rabbit, and administered in a course not dissimilar to that used by Pasteur [201.

Despite the prevalent use of the inexpensive and easy to prepare Semple vaccine, convincing data on the efficacy of such postexposure prophylaxis is

scarce. The best evidence suggesting that therapy with Semple vaccine is beneficial comes from a thorough retrospective study by Veeraraghavan [78] demon- strating that in more than 800 persons bitten by dogs that were each known to have caused at least 1 human rabies infection, the incidence of disease was reduced from 57 to 75% after a complete 14-day course of vaccination. In contradistinction, however, is evidence from two naturally occurring experiments in Iran. These studies, using only vaccine, showed virtually no reduction in the usual mortality rate of approximately 4 0 p for persons bitten on the head by rabid wolves [ 10, 11, 281.

A major drawback to nerve tissue vaccines, of course, is the production in a large number of patients of the human counterpart of experimental allergic encephalomyelitis. The incidence of serious neurological disturbances after treatment with Semple type vaccines has ranged as high as 1 per 600 persons, with a fatality rate of 10 to 25% [65]. The occurrence of such demyelinating syndromes has led to a search for safer effective vaccines. Because sensitization to myelin basic protein has been thought responsible for the neurological syndromes, Fuenzalida [25] in 1755 introduced a vaccine prepared from suckling mouse brain, presumably containing only minimal amounts of CNS myelin. This preparation is now widely used in Latin America for both preexposure vaccination of domestic animals and postexposure prophylaxis in man. While the use of suckling mouse brain vaccine has been associated with a marked reduction in the incidence of neuroparalytic accidents, such syndromes do continue to occur [ l , 3, 15, 331.

An alternative vaccine produced in duck embryos (DEV) was introduced by Peck and co-workers in 1756 [571 in another attempt to avoid neurological complications. Presently the only commercial vaccine licensed in the United States and the United King- dom, DEV has gained widespread acceptance for use in both postexposure and occasional preexposure prophylaxis [75]. Although use of this vaccine has reduced the frequency of serious neurological reactions to approximately 1 per 25,000 patients with a 10% fatality rate, cases of anaphylaxis are not rare (0.5-0.7%), and discomforting local reactions are almost universal [64, 651.

Of greatest concern with all the aforementioned vaccines, however, is their effectiveness in preventing rabies infection. With the possible exception of suckling mouse brain vaccine, none produces very high titers of serum neutralizing antibody, and most inves- tigators agree that they are of highly questionable protective value after serious rabies exposure. Kop- rowski and Black [44] in 1754 found that nerve tissue vaccine therapy alone, initiated 24 hours after inoculation of street virus, failed to protect guinea pigs. In contrast, hyperimmune serum with or without vaccine


prevented disease. Treatment with serum plus vaccine after rabid wolf bites in Iran seemed to substantiate these experimental data [1 11. As a result of such reports, WHO incorporated the use of hyperimmune rabies serum, usually of equine origin, into its recommendations for therapy after severe exposure [86].

The use of equine antiserum, while undoubtedly reducing the risk of rabies infection in man, has led to the major iatrogenic complication of serum sickness. This syndrome is characterized by a generalized erup- tion, usually urticarial, appearing 1 to 2 1 days after the injection of serum; less frequently fever, lymph- adenopathy, and joint swelling occur. Karliner and Belaval [40], reporting on 526 patients who received equine antirabies serum alone, found an overall incidence of 16.3%, increasing to 46.3% in patients over the age of 15 years. This incidence is much higher than that seen, for example, after treatment with tetanus antitoxin. The difference may lie in methods of production of the respective antisera or in the considera- bly larger antigenic mass of the rabies preparation [do]. The recent commercial availability of adequate supplies of hyperimmune human antirabies serum will undoubtedly eliminate this complication, albeit with a rise in the cost of treatment from approximately $20 to about $170 per patient.

A second recognized problem with the administration of passive antibody is suppression of the patient's natural humoral response. This has been demonstrated in experimental animals and humans for both duck embryo vaccine and nerve tissue vaccines [2, 4, 191. Furthermore, some evidence exists that the use of homologous human hyperimmune serum may be associated with even more pronounced suppression of active immunity than is heterologous serum [2, 19, 29, 3 11. Awareness of this immunosuppression phenomenon has resulted in the recommendation that booster doses of vaccine be given when serum is employed. Current recommendations of the Advisory Commit- tee o n Immunization Practices for postexposure rabies prophylaxis follow.

Postexposure Antirabies Treatment Guide I. Local treatment of wounds

Immediate and thorough local treatment of all bite wounds and scratches is perhaps the most effective rabies preventive. Experimentally, the incidence of rabies in animals can be markedly reduced with local therapy alone. A. First-aid treatment to be carried out immediately:

The wound should be thoroughly cleansed with soap and water.

B. Treatment by or under direction of physician: 1. The wound should be thoroughly cleansed im-

mediately with soap solution. 2. Tetanus prophylaxis and measures to control

bacterial infection should be given as indicated.

11. Specific treatment The following recommendations are only a guide. They should be applied in conjunction with knowledge of the animal species involved, circumstances of the bite or other exposure, vaccination status of the animal, and presence of rabies in the region.

Condition of Treatment Species of' Animal at of Exposed Animal Time of Attack Human

Wild (skunk, Regard as rabid RIG -t DEVa fox, coyote, raccoon, bat)

Dog He a1 t h y None

Cat Rabid or RIG + DEVa suspected rabid

Other Consider individually [831

Domestic

Unknown (escaped) RIG + DEV

"Discontinue vaccine if fluorescent antibody tests ofanimal killed at time of attack are negative. hBegin RIG + DEV at first sign of rabies in biting dog or cat during holding period (10 days).

RIG = rabies immune globulin; DEV = duck embryo vaccine.

Source: Adapted from Morbidity and Mortality Weekly Report. Washington, DC, US Public Health Service, 1976, vol 25, pp 403-406

Perhaps the most revolutionary development in rabies postexposure prophylaxis since Pasteur's otigi- nal vaccine has been the recent production of a con- centrated tissue culture vaccine derived from growth of rabies virus in human diploid cells. This inactivated virus vaccine has now been thoroughly tested in both the laborarory and the field. Numerous studies have demonstrated a dramatic increase in the levels of serum neutralizing antibody elicited in comparison with conventional vaccines [GO, 70, 821. Experiments in primates have shown a protective effect of such a vaccine used in conjunction with antiserum [7 11, and most recently, field trials in Iran [ 9 ] have achieved uniformly successful results in postexposure treatment of 45 persons bitten by proved rabid dogs or wolves. Rabies was prevented in all bite victims by a regimen of human diploid cell vaccine administered on days 0, 3, 7, 14, 30, and 90 and heterologous antiserum on day 0. Extraordinary too was the fact that antirabies treatment was not initiated until 3 to 8 days after exposure in the majority of patients, and as long as 14 days in 1 case. In the past, such delays frequently resulted in unfortunate failures of postexposure prophylaxis [9].

One caveat to this optimistic development is derived from early experiments with a similar vaccine in which inadequately protected primates died after shorter incubation periods than control animals [7 11. This early death phenomenon raises the possibility of


immunological acceleration of the pathological pro- cess.

Because it is grown in human cells, the vaccine preparation is of much lower allergenic potential than any of the previously available vaccines. To date the vaccine has been extremely well tolerated, producing only mild local irritation and virtually no serious reactions. Preparations are currently available commer- cially in both France and Germany, and licensing is pending in the United States. I t is to be hoped that the availability of such a vaccine will greatly reduce the still grave risk of rabies in many parts of the world. Unfortunately, the high cost of producing such a con- centrated tissue culture vaccine and, even more im- portantly, the inadequacy of current health delivery systems remain ominous barriers to rapid control of human rabies in the underdeveloped world.

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Supported i n part by US Public Health Service Grants NS07077 and A112017 and a fellowship grant from che National Multiple Sclerosis Society.

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