Updated: Oct 9, 2008
Rabies is a viral infection of the central and peripheral nervous systems that causes encephalitis with or without paralysis; it is virtually uniformly fatal.
Epidemiology and transmission
Bat (avian) rabies appears to be widespread in the 49 continental states. Bat rabies has been implicated in most human rabies cases acquired domestically in the United States during the last 25 years.1 Cases of rabies have been reported in humans exposed to aerosols of bat guano during recreational caving or to aerosolized laboratory strain virus. Recently, rabies has occurred secondary to virus transmission from infected transplanted solid organs in the United States.2,3 Statistics compiled by the Centers for Disease Control and Prevention (CDC) in the United States confirm that most human deaths from rabies not associated with foreign travel are from bat strains of rabies.4,5
In the United States, terrestrial rabies is most common in raccoons on the eastern coast and in skunks, foxes, coyotes, and dogs on the Texas-Mexico border. Canine rabies and bat rabies are significant problems in Mexico and around the world.
Five antigenic variants of rabies strains are recognized in the United States. The single raccoon strain is the predominant strain (see Media file 1).6,7 A single case of human rabies has resulted from the raccoon rabies strain in the United States.8
The only rodent in the United States that can carry rabies long enough to transmit to humans is the groundhog. Other small rodents (eg, squirrels, chipmunks, rats, mice) and lagomorphs (eg, rabbits, hares) usually die before being able to transmit rabies virus to humans, and human disease has never been transmitted by these mammals.
Domestic animals usually succumb to the virus strain predominant in their geographic region. Cats are the most common domestic animals reported by health departments as being rabid because of the high number of unvaccinated strays with possible contacts with bats and other mammals.9,10
Since 1980, most endemic rabies cases in humans in the United States have been associated with bat strains. Other cases have been associated with dog or animal bites in travelers returning from abroad, especially in countries where wild canine rabies is endemic. In other countries, canines are the most common source of rabies. Other animals, such as mongooses, jackals, ferrets, and domestic farm animals, may be common sources. Human-to-human transmission has only occurred with corneal and other organ transplants.3,2 Transmission of virus in saliva through mucous membranes, open wounds, or scratches is possible but rarely documented.
Rabies-free areas of the world are recognized. The island nations of the Caribbean are free of terrestrial rabies but may have bat rabies.11 Updates of this information can be found through the World Health Organization (WHO) and the CDC.
When the rabies virus enters muscles, it replicates locally and is then transported through peripheral sensory nerves to the spinal ganglia, where it replicates and travels up the spinal cord to the brain. The virus migrates to the gray matter of the brain and predominates in the neurons of the limbic system, midbrain, and hypothalamus. Efferent nerves transport virus to the acinar glands of the submaxillary salivary glands, where it achieves high concentrations.12
This transit time is presumably shorter if the initial wound is severe with a high load of virus and is proximal to the head.13,14
The reported incubation period in human beings has ranged from as short as 5 days to as long as 7 years; average incubation is 1-3 months prior to onset of symptoms. In rare cases, human rabies with an extended incubation period (2-7 y) has been reported.15,16
During 1990-1998, 22 cases of human rabies were reported in the United States. Potential exposures are not uncommon in the United States; an estimated 20,000-30,000 people per year receive treatment for potential rabies exposures. Exact exposures can only be determined if an animal is submitted for testing.1,17
Worldwide, endemic countries with wild animal vectors may have death rates as high as 40,000-50,000 per year (eg, Asia, Africa).
Rabies is 100% fatal if postexposure treatment is not administered. A single survivor who was treated with an intensive care protocol to induce a controlled coma has been reported in the United States.18 Since then, others have tried to repeat use of this intervention without success.19
No racial predilection is observed.
Encounters with rabid animal vectors may be increased in males, who may have greater contact in certain geographic areas. Evidence to support this is found in data on dog bites, which are observed more frequently in males than females.
No age predilection is noted.
Include the following in any examination of a patient who has been bitten by an animal:
Other encephalitides (especially herpes simplex encephalitis because it is treatable)
Guillain-Barré syndrome, transverse myelitis, and poliomyelitis (Patients may present with similar paralytic features.)
Tetanus (Rigidity of tetanus contractions is more prolonged, with mental status usually normal.)
Epilepsy
Poisoning with atropinelike compounds
Pseudohydrophobia (hysterical reaction to animal bites)
Mainstays of therapy include the rabies vaccine and human rabies immune globulin (HRIG). Equine-derived rabies immunoglobulin may be the only immunoglobulin available outside of the United States. Vaccine and other biological product shortages can be found at the US Food and Drug Administration (FDA) Web site.
Rabies vaccines are produced in tissue culture cell lines and are inactivated.
Human rabies immunoglobulin is produced from individuals who have been vaccinated.
Equine rabies immunoglobulin is produced from immunized horses. Previously, the equine variety had a high reactogenicity rate with serum sickness reactions. Modern production includes more purification steps, and serum sickness reaction rates have been reduced to 1-2% of recipients. For countries other than the United States, equine immunoglobulin is more widely available and cheaper. Recently, shortages of all immunoglobulin products around the world have been a problem.
Provides passive protection to individuals exposed to rabies virus. Heat-treated and cold alcohol–fractionated Ig is derived from pooled human plasma from individuals immunized with human diploid cell rabies vaccine. Infiltrate as much of the dose as possible at the site of wounds and administer the remainder IM in the gluteal region. If the volume is >5 mL, use more than one injection site. Administer no more than the recommended dose because this may partially suppress the patient's active production of antibody. The dose of HRIG, calculated by body weight, may be of insufficient volume to infiltrate all the wounds. The HRIG may be diluted with sterile saline so that more volume can be used without exceeding the total recommended dose.
20 IU/kg IM once after exposure, preferably with first dose of vaccine
Administer as in adults
Through an antigen-antibody antagonism, RIG may diminish antibody response to MMR vaccine; administer live virus vaccines 14-30 d before or 6-12 wk after immunoglobulin administration; antibody response to rabies vaccine may be delayed if administered simultaneously with rabies Ig
Documented hypersensitivity; administration in repeated doses (once the rabies vaccine treatment has been initiated, to prevent interference with a maximum active immunity from rabies vaccine, do not administer repeated doses); known specific IgA deficiency
B - Fetal risk not confirmed in studies in humans but has been shown in some studies in animals
Caution in thrombocytopenia or bleeding disorders; obtain antibody testing after vaccination in individuals with immunosuppression, including those on corticosteroids, to determine immune response; in previously vaccinated individuals who have a subsequent rabid exposure injury, RIG does not need to be administered; administer vaccine on days 0 and 3 only; all human Ig products may have a low risk of transmission of other infectious agents, therefore, explain risks to patients prior to treatment
For use in postexposure rabies prophylaxis regimens in combination with wound cleansing and rabies vaccination. Administer only to patients who have not been previously vaccinated with rabies vaccine. Produced by cold ethanol fractionation from human donors hyperimmunized with rabies vaccine. It is purified and heat-inactivated. Contains no preservative. Do not administer more than the recommended dose because this may partially suppress the patient's active production of antibody.
20 U/kg IM once after exposure, preferably with first dose of vaccine; infiltrate as much of the dose as possible at the site of wounds and administer the rest IM in the gluteal region; if the volume is >5 mL, use more than one injection site
Administer as in adults
Through an antigen-antibody antagonism, may diminish antibody response to MRR vaccine; administer live virus vaccines 14-30 d before or 6-12 wk after Ig administration; antibody response to rabies vaccine may be delayed if administered simultaneously with rabies Ig
Documented hypersensitivity; administration in repeated doses (once the rabies vaccine treatment has been initiated, to prevent interference with a maximum active immunity from rabies vaccine, do not administer repeated doses)
C - Fetal risk revealed in studies in animals but not established or not studied in humans; may use if benefits outweigh risk to fetus
Caution in thrombocytopenia or bleeding disorders; caution with known isolated IgA deficiency; human immunoglobulin products may have a low risk of transmission of other infectious agents, therefore, explain risks to patients prior to treatment
Rabies HDCV. Inactivated forms of virus that promote immunity by inducing an active immune response. May be used as part of preexposure or postexposure prophylaxis for rabies. Inactivated virus administered IM, packed to be used as single-dose vials. Check antibody titer q6mo in individuals at high risk and administer boosters as 1 mL IM to keep titer RFFIT at 1:5. In infants and small children, the mid lateral thigh may be preferable to the deltoid. Do not administer HDCV in the gluteal region.
Preexposure immunization: 1 mL IM for 3 doses on days 0, 7, and 21-28 and then q2-5y depending on antibody titers
Postexposure prophylaxis (patients who are previously unvaccinated): 20 IU/kg RIG as soon as possible after exposure, then 1 mL IM (not ID) for 5 doses on days 0, 3, 7, 14, and 28
Postexposure prophylaxis (patients who were previously immunized): 1 mL IM on days 0 and 3; do not administer RIG
Administer as in adults
High-dose corticosteroids, antimalarials, and radiation therapy may inhibit immunization, and patients may remain susceptible despite vaccination; avoid use of immunosuppressants during postexposure therapy, if possible
Life-threatening hypersensitivity reactions (carefully consider a patient's risk of developing rabies before deciding to discontinue immunization)
C - Fetal risk revealed in studies in animals but not established or not studied in humans; may use if benefits outweigh risk to fetus
When postexposure prophylaxis must be administered to an immunosuppressed person, serum should be tested for production of rabies antibody; inject only in deltoid area; vaccination may fail if injected into gluteal area; use IM route for Imovax rabies vaccine; administer rabies vaccine for rabies exposure during pregnancy (in many countries, large numbers of women who are pregnant have safely received postexposure prophylaxis); preexposure prophylaxis may also be indicated in a woman who is pregnant if substantial risk of exposure is determined; immune complex–like reactions, including urticaria, arthritis, arthralgia, nausea, vomiting, and fever, have occurred in persons previously vaccinated who receive a booster dose (onset may be from 2-21 d after booster injection)
However, no cases have been life-threatening; they may occur in up to 6% of booster doses; other reactions that may occur are mild (eg, local erythema, swelling, itching, headache, nausea, myalgias, dizziness), are usually transient, and should not prevent completion of prophylaxis injections
Inactivated form of virus grown in primary cultures of chicken fibroblasts; offers active immunity and, when used in combination with HRIG and local wound treatment, protects patients of all age groups who have been exposed; also used for preexposure immunization in both primary series and booster dose. Fourteen days after initiating immunization series, antirabies antibody titers reach levels well above minimal protective level of 0.5 IU/mL. Vaccine must be injected IM and never SC, ID, or IV. In adults, inject into deltoid muscle area. In small children, administer into anterolateral zone of thigh.
Preexposure immunization: 1 mL IM on days 0, 3, 7, 14, and 28, and then q2-5y depending on antibody titers
Postexposure prophylaxis (patients who were previously unvaccinated): 20 IU/kg RIG as soon as possible after exposure, then 1 mL IM for 5 doses on days 0, 3, 7, 14, and 28
Postexposure prophylaxis (patients who were previously immunized [documented titers]): 1 mL/d IM on days 0 and 3; do not administer RIG
Administer as in adults
Corticosteroids, antimalarials, and other immunosuppressive agents may reduce protective efficacy of vaccine
None reported for postexposure immunization
C - Fetal risk revealed in studies in animals but not established or not studied in humans; may use if benefits outweigh risk to fetus
When postexposure prophylaxis must be administered to an immunosuppressed person, serum should be tested for production of rabies antibody; if alternative products are not available, caution in persons known to be sensitive to neomycin, amphotericin B, chlortetracycline, processed bovine gelatin, and chicken protein because trace amounts of these products may be present in the vaccine; caution in documented hypersensitivity (may pretreat such patients with antihistamines); never inject rabies vaccine in gluteal area; epinephrine injection (1:1000), volume replacement, oxygen, and corticosteroids must be immediately available to counteract anaphylactic reactions that may occur; type III (immune complex–like) hypersensitivity reactions have not been reported with this vaccine preparation; rare reactions (eg, encephalitis, transient paralysis, myelitis) have been temporally associated with administration
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rabies, terrestrial rabies, hydrophobia, mad dog disease, bat rabies, avian rabies, paralytic rabies, dumb rabies, furious rabies, rabies virus, rhabdovirus, Lyssavirus, Rhabdoviridae, encephalitis, raccoon bite, bat bite, paralysis, altered mental status, anxiety, hyperactivity, hypertension, hypersalivation, hyperthermia, hyperventilation
Donna J Fisher, MD, Assistant Professor, Department of Pediatrics, Division of Pediatric Infectious Diseases, Tufts University School of Medicine and Baystate Children's Hospital, Baystate Medical Center
Donna J Fisher, MD is a member of the following medical societies: American Academy of Pediatrics, American Society for Microbiology, Infectious Diseases Society of America, and Pediatric Infectious Diseases Society
Disclosure: Nothing to disclose.
Rosemary Johann-Liang, MD, Medical Officer, Infectious Diseases and Pediatrics, Division of Special Pathogens and Immunological Drug Products, Center for Drug Evaluation and Research, Food and Drug Administration
Rosemary Johann-Liang, MD is a member of the following medical societies: American Academy of Pediatrics, American Medical Association, and Infectious Diseases Society of America
Disclosure: Nothing to disclose.
Mary L Windle, PharmD, Adjunct Assistant Professor, University of Nebraska Medical Center College of Pharmacy, Pharmacy Editor, eMedicine
Disclosure: Pfizer Inc Stock Investment from broker recommendation; Avanir Pharma Stock Investment from broker recommendation
Leslie L Barton, MD, Professor, Program Director, Department of Pediatrics, University of Arizona School of Medicine
Leslie L Barton, MD is a member of the following medical societies: American Academy of Pediatrics, Association of Pediatric Program Directors, Infectious Diseases Society of America, and Pediatric Infectious Diseases Society
Disclosure: Nothing to disclose.
Robert W Tolan Jr, MD, Chief, Division of Allergy, Immunology and Infectious Diseases, The Children's Hospital at Saint Peter's University Hospital; Clinical Associate Professor of Pediatrics, Drexel University College of Medicine
Robert W Tolan Jr, MD is a member of the following medical societies: American Academy of Pediatrics, American Medical Association, American Society for Microbiology, American Society of Tropical Medicine and Hygiene, Infectious Diseases Society of America, Pediatric Infectious Diseases Society, Phi Beta Kappa, and Physicians for Social Responsibility
Disclosure: GlaxoSmithKline Honoraria Speaking and teaching; MedImmune Honoraria Consulting; MedImmune Honoraria Speaking and teaching; Merck Honoraria Speaking and teaching; Novartis Honoraria Speaking and teaching; sanofi pasteur Grant/research funds Unrestricted research grant; sanofi pasteur Consulting; sanofi pasteur Honoraria Speaking and teaching; Tap Honoraria Speaking and teaching
Russell W Steele, MD, Head, Division of Pediatric Infectious Diseases, Ochsner Children's Health Center; Clinical Professor, Department of Pediatrics, Tulane University School of Medicine
Russell W Steele, MD is a member of the following medical societies: American Academy of Pediatrics, American Association of Immunologists, American Pediatric Society, American Society for Microbiology, Infectious Diseases Society of America, Louisiana State Medical Society, Pediatric Infectious Diseases Society, Society for Pediatric Research, and Southern Medical Association
Disclosure: None None None
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