R Sehgal, Yashwant Kumar, Sunil Arora, Central Research Institute, Kasauli, Himachal Pradesh 

Address for correspondence

Dr. R. Sehgal, Director, Central Research Institute, Kasauli, District Solan (H.P) -173204

I have seen agony in death only once, in a patient with rabies; he remained acutely aware of every stage in the process of his own disintegration over a twenty four- hour period, right up to his final moment.   

                                                                                                                    Lewis Thomas. The lives of a cell.
                                                                                                                    New York, bantam books, 1974.

Rabies is an acute viral encephalitis transmitted from animal to animal or from animal to human by exposure to saliva, containing Rabies virus. The Virus if present in the saliva, attaches to the peripheral nerve endings and travels to the brain through the nervous system. In nature, rabies is a disease of mammals, involving the Canidae (dogs, wolves, foxes, coyotes, and jackals), Procyonidae (raccoons), Viverridae (mongooses), Mephitadae (skunks), and Chiroptera (bats) as reservoirs or vectors. All mammalian species are believed to be susceptible. Human infection with rabies is nearly always secondary to animal bite, although exposures through the inhalation of virus or through the transplantation of infected corneas have occurred. Rabies infection may also occur through small cuts, abrasions, scratches and contamination of mucous membranes by licking of the rabid dog.  

Although different hypothesis have been given, about the aetiology of rabies since 1300 B.C., obviously much of the credit for rabies research goes to Pasteur but one must not overlook the contributions of his collaborators, Roux, Chamberland, and Thuillier. 

Hydrophobia is the main clinical symptom of rabies. Attempts to drink or eat may produce severe painful spasms of the pharynx and larynx and precipitate an episode of hyperactivity that is extremely frightening to the patient. Subsequently, simply the sight of liquids may precipitate episodes of pharyngeal spasms. Bright lights, loud noises, or air currents also may precipitate spasms. Other abnormalities during the acute and neurologic phase include muscle fasciculation (particularly near the site of the exposure), hyperventilation, hypersalivation, focal or generalized convulsions, and, rarely, priapism or increased libido. Death in rabies is usually due to respiratory paralysis, while the patient is fairly cautious.  Unless the patient dies abruptly, paralysis generally becomes the major problem. Paralysis may be symmetric; asymmetric with maximal involvement of the bitten extremity; or ascending, as in the Guillain-Barré syndrome.1 

To date, there are fewer than 10 cases of known survival among humans who showed signs of disease, all of whom recovered with sequelae and one with severe psychogenic disturbance.2-7 All survivors had received either preexposure or postexposure rabies vaccination, except one. Despite trials of steroids, interferon, and other antivirals, there is no therapy of proven value.8 

Rabies virus belongs to the family Rhabdoviridae, genus Lyssavirus, consisting of genetically related enveloped viruses with a single, nonsegmented, negative-stranded RNA. The virus is shaped like a bullet, 200 nm long and 75 nm wide. The virus contains multiple copies of the following five structural proteins: virion transcriptase (L), lycoprotein (G), nucleoprotein (N), nucleocapsid phosphoprotein (NS or P), and matrix protein (M). 

When inoculated in a wound, rabies virus may take days or weeks to reach the central nervous system. Usually the incubation period in rabies, in most cases, is 1-12 months, but can vary from less than a week to several years. The length of the incubation period appears to be dependent on the bite site, proximity to the central nervous system (CNS), severity of the bite, type and quantity of virus and the immune status of the host.  It is this fact that makes post-exposure prophylaxis possible. During this early period, the virus is susceptible to VNAs and even to mechanical removal by washing. There is some evidence that initial replication may occur in muscle cells surrounding the wound, providing an amplification of the original inoculum. However, experimental data show that central nervous system entry can occur without any prior replication in the muscle.9 Another site proposed for possible persistence of rabies virus before entry into the central nervous system is the macrophage, from which the virus could reactivate to cause disease,10 but the importance of replication in non-nerve cells to the pathogenesis of rabies remains controversial.11 In any event, at some point in time, the virus attaches to receptors, which may include the nicotinic acetylcholine receptors of the neuromuscular junction or lipoproteins on the membrane (see later), and begins a passive journey to the cytosol, where it replicates and spreads within the central nervous system.12,13 Dietzschold and colleagues14 have demonstrated that the action of rabies VNAs is not exerted solely outside of the cell. In an animal model, the effectiveness of antibody was associated with entry into the cell by endocytosis and inhibition of viral transcription. Whether the antibody acts directly or by signal transduction to inhibit viral protein synthesis is unclear.15

Rabies is a disease of both domestic and wild mammals, particularly dogs and related species, raccoons, mongooses, skunks, and bats. In areas in which animal control programs are not extensively developed, dogs and cats account for most of the rabid animals reported and cause the majority (90%) of human rabies exposures. After effective domestic animal rabies control programs in these areas, the numbers of rabid dogs and cats markedly decrease, as illustrated in the United States from the 1940s to the 1960s. Wildlife is then recognized as the main reservoir of rabies virus. In the United States since 1960, the majority of cases of animal rabies has been in wildlife species, and most of the human rabies cases have been secondary to bites by rabid wildlife, including bats.1,16 Curiously, bats do not often transmit virus to dogs or cats.17 The situation is similar in western Europe, where domestic species accounted for only 28% of 8155 reported rabid animals. Of the wild species, foxes accounted for 83% and raccoon dogs 11%.18           

The most important reservoir of rabies in Europe is the red fox. The vampire bat is a major threat to cattle in Latin America and has been involved in many biting incidents in humans. Rabid cattle also may excrete rabies virus in saliva.19 Like all mammals, rodents, squirrels, and voles are susceptible to infection12  

Travelers are at risk, as confirmed by the report of seven cases of rabies in the United States acquired abroad between 1990 and 2001.20 

Nonbite transmission has been reviewed by Gibbons,21 who found 27 well-documented cases of transmission by means other than bites, and 17 other less well-documented cases. Of the total 44 cases, 18 were caused by improperly inactivated vaccine in Brazil, 8 from corneal transplants, 8 from contamination of skin whose integrity had been  impaired, 4 by aerosols created in laboratory or bat-infested caves, and 6 from human to human. Among the alleged causes of human-to human transmission were transplacental passage, lactation, kissing, intercourse, and providing health care. Gibbons94 also found three reports of transmission by human bites. 

Infection by aerosol has been suspected in caves inhabited by rabies infected bats, and under laboratory conditions.1,22 Unwitting corneal transplantation from patients deceased from rabies also has resulted in transmission.1,23  Human-to-human transmission by bite is extremely rare, but transmission has been reported after kissing, intercourse, and maternal rabies.21,24,25 A case of a child biting its parents is also on record. Similarly, oral transmission by ingestion of infected meat has also been demonstrated.  

In the United States alone, a million dog bites occur each year,26 and the situation is worse in some other parts of the world.27 Human rabies has been reported from all continents except Antarctica, but the majority of cases occur in countries where canine rabies is not well controlled. The World Health Organization (WHO) estimate of humans vaccinated for exposure to rabies exceeds 10 million annually.28 The WHO also estimated between 35,000 and 50,000 human rabies cases in 1997, most of them in India.29 The annual incidence of rabies deaths per 100,000 population has been calculated as 3 in India, 0.01 to 0.2 in Latin America, and an uncertain 0.0001 to 13 in Africa, respectively.24  

Vaccination is the only method of prevention of rabies apart from animal control. Although passive immunization with antiserum is available it alone will not prevent rabies and is not recommended except in combination with vaccine.

There are different vaccines available for the prevention of rabies:

• Avian:

• PDEV (Purified duck embryo vaccine).

• Cell culture:

• HDCV (Human diploid cell culture vaccine

• Vero cell vaccine.).

• Chick embryo vaccine.

• Hamster kidney vaccine.

• Duck embryo vaccine.

• Fetal Rhesus monkey vaccine.

These vaccines are available for both pre-exposure and post-exposure treatment in different dose schedule. Normally intramuscular route of administration of vaccine is employed but now more emphasis is given to intra-dermal administration due to several benefits of this route of administration.

Intradermal Route of vaccination:

The higher cost of cell culture vaccines has induced physicians to look for ways of reducing doses. Accordingly, Warrell et. al. and Wilde et. al. have developed vaccination schedule by using the intradermal route. The principles that allow intradermal vaccination are the better response to an equal volume of antigen when placed in contact with the langerhans cells of the epidermis and the use of multiple sites of vaccination to obtain maximum drainage of the antigen presenting cells to the lymph nodes. The expense of a full regimen of intramuscular HDCV (about $600 in the United States for a five-dose regimen) led to attempts to reduce the cost by taking advantage of the intradermal route. Aoki, Turner, Nicholson, and their colleagues demonstrated that rapid antibody responses could be induced by various intradermal regimens, including multisite postexposure inoculations.30-32 Although injection by the intramuscular and subcutaneous routes results in higher titers, intradermal administration for preexposure or booster vaccinations appears to be adequate.26,33 Two intradermal doses of 0.1 mL successfully boosted titers in those previously given DEV.26,34 Intradermal postexposure regimens have now undergone extensive evaluations and are indicated in the circumstances of insufficient vaccine, insufficient funds, and the availability of staff experienced in intradermal injection technique.35,36  

The vaccines that may be used by this route are HDCV, PVRV, PCECV, and PDEV. The antigenic content of the rehydrated vaccine should always be at least 0.25 IU/0.1 mL. The injection should be given with use of a 1.0-mL syringe and a 25- or 27-gauge needle, with the needle introduced parallel to the skin into the epidermal layer. A papule should always be produced at the site of the injection.37 For pre-exposure immunization, three doses are necessary.38 Intradermal injection has been widely used to immunize veterinary students and others at high risk of rabies exposure. Antibody titers are lower after intradermal than after intramuscular inoculation but still adequate.

Local reactions are annoying but tolerable after intradermal vaccination, and systemic reactions are virtually absent. However, the death in Kenya in 1983 of a Peace Corps volunteer who had been preimmunized with HDCV by the intradermal regimen raised questions regarding the efficacy of this route.39 Intensive review of immunization records revealed that people vaccinated overseas, whether intramuscularly or intradermally, often had lower and shorter lived antibody responses than expected from observations made in people immunized in the United States. One factor shown to be significantly associated with lower immunologic responses is the concurrent  administration of chloroquine for antimalarial chemoprophylaxis.40 People receiving concurrent antimalarial chemoprophylaxis or other immunogens are now recommended to receive the intramuscular and not the intradermal regimen for antirabies pre-exposure immunization. Moreover, those who receive an intradermal pre-exposure regimen in developing countries should have titers checked after immunization.41  

The situation in the United States is now complicated by the removal of the intradermal formulation from the market. Whereas 0.1-mL intradermal doses can be withdrawn from vials containing the 1.0-mL intramuscular dose, this is an off-label use justified only when there are numerous persons to vaccinate on the same day.

Studies conducted:

However, postexposure intradermal immunization using vaccine from intramuscular vials is licensed in Thailand and is used in developing countries to make CCVs more readily available for rabies exposures.  

Warrell and colleagues42,43 developed the concept of multiple intradermal vaccinations. In their scheme, HDCV or PCECV is given intradermally at eight different sites (deltoid, suprascapular, thigh, and abdominal wall on day 0; four 0.1-mL doses over the deltoid and thigh on day 7; and single doses over the deltoid on days 28 and 91).44 However, antibodies are not induced any more rapidly by this regimen than by others, and concomitant antiserum is still indicated.45  

An economical post-exposure regimen of Merieux human diploid cell strain vaccine (HDCSV) was compared with Semple vaccine (SV). 155 patients bitten by animals proved to be rabid, received either conventional courses of SV and HDCSV, 0.1 ml intradermally at eight sites on day 0, at four sites at day 7 and severely bitten patients were given equine antirabies serum (EARS) 80 IU/Kg on day 0. There were no death in either group. Follow up was 97.5% at 1 year and 93% at 2 years.43 

88% of patients given HDCSV alone had detectable neutralizing antibodies on day 7 in contrast to 2% given SV alone. Antibody persisted until 1 year in all sera tested from HDCSV patients in contrast to only 48% of SV sera. The high dose of EARS resulted in  pronounced suppression of response to HDCSV. There were no serious side effects but local side effects but local side effects were significantly more common in SV group. The multiple site intradermal HDCSV regimen was atleast as effective as SV. The amount of HDCSV used was 30% of the conventional dose. 43   

Phanuphak and associates48 developed another intradermal schedule that is now the standard regimen used in Thailand. PVRV, PCECV, or PDEV is given over both deltoids in a volume of 0.1 or 0.2 mL on days 0, 3, and 7, followed by single injections on days 30 and 90. The volume of injection in the Thai regimen is decided by the volume of reconstitution: 0.1 mL from a 0.5-mL vial (in practice, this is PVRV) and 0.2 mL from a 1.0-mL vial.35  

The efficacy of purified duck embryo rabies vaccine (Lyssavac-N) has been conducted under the WHO recommended regimen for intradermal route. In this study the dose was increased from 0.1 ml to 0.2 ml and satisfactory titers were obtained. 

The two intradermal regimens were compared in India, where the eight-site regimen induced higher antibody titers, particularly at 7 days.46 Intradermal vaccination is considerably less expensive than the full intramuscular use of HDCV and has been demonstrated to be protective in Thailand.47,48,49,50  

In Thai practice the vaccine is sometimes reconstituted and stored for a week under refrigeration in order to use the same vial for the first three injections of vaccine. So far, this practice has not resulted in treatment failures.51 

 Neutralizing responses after intradermal vaccination with HDCV or PVRV were compared in Thailand.49 All vaccinees in both groups were seropositive at day 14, whereas at day 90, adequate VNA levels were found in 95% of PVRV recipients and 96% of HDCV recipients.  

A comparison of intradermal PVRV or PCECV with intramuscular PCECV showed no important differences in antibody responses 52  

In addition, Thai workers simulated two-dose postexposure booster vaccination in subjects previously vaccinated intradermally or intramuscularly with PVRV. The subjects vaccinated and boosted intradermally all developed anamnestic responses, although these were slower and of lower magnitude than in the all-intramuscular group.53  

Conversely, a booster study done with a four site intradermal regimen showed higher titers than after intramuscular immunization.54 Using the Thai regimen, PDEV was shown to be immunogenic by the intradermal route if the intradermal dose was 0.2 mL.55 PDEV given by either intramuscular or intradermal routes was studied in the Philippines.53 By day 90, 94% of the intradermal vaccines and 98% of the intramuscular vaccinees had antibodies above 0.5 IU, and the GMTs were about 3 IU in both groups. PCECV was also studied in Thailand,56 both with and without concomitant administration of HRIG. Neutralizing antibodies peaked at a GMT of about 10 IU in both groups, and there were no failures. About 40 patients exposed to rabies were all protected by PCECV.  

Thai workers keep the reconstituted vaccine at 4ºC for 1 week in order to provide patients with the first three doses from the same vial.57  

Determination of the minimum vaccine potency per intradermal required to elicit an adequate immune response using the Thai red cross (TRC) regimen (2-2-2-0-1-1) was done. These results confirm that the current WHO recommendations for vaccine potency are sufficient for use in the Thai Red Cross intradermal regimen.58  

Currently in India, intradermal vaccination is practiced with the four WHO-approved vaccines, enabling a reduction in cost from $81 for the intramuscular regimen to about $13 for an intradermal regimen.59

Modified Thai schedule: 

Pakamatz et. al. (2006)60 have revised the Thai red cross intradermal post-exposure regimen by eliminating the 90-day booster injection. Praphan Phanuphak’s original Thai Red Cross regimen (TRC-ID) consisted of two intradermal injections of 0.1 ml tissue culture rabies vaccine at two sites (usually both deltoid regions or lateral thighs) on days 0,3,7 and one injection on days 28 and 90. it required five clinical visits. 

It has been experienced that 11% of 187,000 potentially rabies exposed patients missed the day-90 booster injection and that 6-9% of these were WHO category III (Severe) exposures treated at Queen Saovabha Memorial Institute during the past two decades. No treatment failures (rabies deaths) were reported from this defaulting group. The immunogenicity studies in an effort to determine the immune response if the 90-day booster injection is omitted gave promising results.     

Dosage and dose schedule: 

One dose (0.1 ml) should be given at each of the two sites, either the forearm or upper arm, on days 0, 3 and 7, and one dose at one site on days 30 and 90. this regimen considerably lowers the cost of vaccination against rabies, as the total volume of the vaccine required is much less than that required for intramuscular regimens. Separate syringes and needles must be used for each dose. Intradermal injections should be administered by staff who have been trained in this technique. Vaccine vials should be stored between 4ºC to 8ºC after vaccination and the total contents should be used as soon as possible.61  Two intradermal (I.D) regimens have been demonstrated to be immunogenic. They are 2 site intradermal and 8 site intradermal method.62 

1. Two site intradermal schedule: for use with PVRV, PCECV and PDEV. The volume of an intramuscular dose after reconstitution is 0.5ml for PVRV, 1ml for PCECV and PDEV. The volume of intradermal dose is one-fifth of the intramuscular dose i.e., if I.M dose is 0.5ml then I.D dose will be 0.1ml.

        2-site intradermal regimen (2-2-2-0-1-1)         

Rabies immunoglobulin Less than 2 vials 5 visits

2. Eight site intradermal schedule: For use with human diploid cell vaccine (HDCV) and purified chick embryo cell vaccine (PCECV) Where intramuscular dose is 1ml after reconstitution. On day 0, 0.1ml of reconstituted vaccine is given at each of 8 sites using contents of the whole vial. Inject intradermally over deltoid, lateral thigh, suprascapular region and lower quadrant of the abdomen. On day 7, 0.1ml of vaccine is given at each of 4 sites over deltoid and thighs. On days 28 and 90, 0.1ml of vaccine is given at one site over deltoid.

 8-site intradermal regimen (8-0-4-0-1-1)   

Rabies immunoglobulin Less than 2 vials  4 visits

Passive immunization/Treatment of dog/animal bite cases: 

Use of rabies immune serum or globulin of equine origin in the post exposure immunization of man has been accepted in medical practice only during the past two decades. 

Administration of rabies immunoglobulins is recommended along with vaccine in class III exposures (single or multiple transdermal bites or scratches, contamination of mucous membrane by saliva). Administration of RIG is especially useful when the incubation period is anticipated to be short,  Wounds on head, face and neck, wounds on fingers and toes, wounds in children and multiple lacerated wounds. However, 90% of the post exposure patients worldwide receive no passive immunization with HRIG or ERIG. If there is complete post exposure or pre-exposure treatment in the past one year with tissue culture vaccine, there is no need of administration of RIG. 

When to start passive immunization:  

• Administration of RIG should be done as early as possible after exposure (preferably on day 0).

• Rig can be administered irrespective of interval between time of exposure and initiation of post exposure treatment.

If vaccination has already been started RIG can be given upto 7 days after administration of first dose of vaccine. Beyond this period, administration of RIG may interfere with antibody production by the host following vaccination.

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