Rabies
Rabies virus is a negative strand RNA virus.
How does Rabies virus get access into humans?
Rabies is generally transmitted by a bite from an infected animal (bat, skunk, fox, dog or cat).
In many areas of the world, the dog is the most important vector of the rabies virus to humans.
Other important sources of disease are the wolf in eastern Europe, the mongoose in Africa, the fox in western Europe, and the bat in Latin America and the United States.
Inhalation of heavily contaminated material, such as bat droppings, can also cause infection.
How does the rabies virus spread from the site of inoculation?
Rabies virus first replicates in striated muscle tissue at the site of inoculation.
It then enters the peripheral nervous system at the neuromuscular junctions and spreads up the nerves to the central nervous system, where it replicates exclusively within the gray matter.
It then passes centrifugally along autonomic nerves to reach other tissues, including the salivary glands, adrenal medulla, kidneys, and lungs.
Passage into the salivary glands in animals facilitates further transmission of the disease by infected saliva.
What is the incubation period for rabies?
The incubation period ranges from 10 days to a year, depending on the amount of virus introduced, the amount of tissue involved, the host immune mechanisms, and the distance the virus must travel from the site of inoculation of the central nervous system.
Thus, the incubation period is generally shorter with face wounds than with leg wounds. Immunization early in the incubation period frequently aborts the infection.
What clinical symptom did this patient have which is classic for
rabies (but is not always present)?
Refusal of liquids with apparent fear of
water (agoraphobia) is a classically described symptom of rabies.
How do you make a laboratory diagnosis of rabies?
Laboratory diagnosis of rabies in animals or deceased patients is accomplished by indirect or direct demonstration of virus in brain tissue or scalp biopsy.
Viral antigen can be demonstrated rapidly by immunofluorescence procedures.
Intracerebral inoculation of infected brain tissue or secretions into suckling mice results in death in 3 to 10 days.
Histologic examination of their brain tissue shows Negri bodies; both Negri bodies and rhabdovirus particles may be demonstrated by electron microscopy.
Specific antibodies to rabies virus can be detected in serum,
but generally only late in the disease.
What are the measures for post exposure prophylaxis?
Postexposure prophylaxis requires careful evaluation and judgment. Every year more than one million Americans are bitten by animals, and in each instance a decision must be made whether to initiate postexposure rabies prophylaxis. In this decision the physician must consider
whether the individual came into physical contact with saliva or another substance likely to contain rabies virus
whether there was significant wounding or abrasion
whether rabies is known or suspected in the animal species and area associated with the exposure
whether the bite was provoked or unprovoked (i.e., the circumstances surrounding the exposure)
whether the animal is available for laboratory examination.
If the animal is available
Any wild animal or ill, unvaccinated, or stray domestic animal involved in a possible rabies exposure, such as an unprovoked bite, should be captured and killed.
The head should be sent immediately to an appropriate laboratory, usually at the state health department, for search for rabies antigen by immunofluorescence.
If examination of the brain by this technique is negative for rabies virus, it can be assumed that the saliva contains no virus and that the exposed person requires no treatment.
If the test is positive, the patient should be given postexposure prophylaxis. It should be noted that rodents and rabbits are not important vectors of rabies virus.
The incubation period of rabies in dogs is short. Therefore, the animal can be observed and if it remains healthy for 10 days, it can be considered non-rabid.
To the individual bitten by the animal
Postexposure prophylaxis is based on immediate, thorough washing of the wound with soap and water
passive immunization with hyperimmune globulin, of which at least half the dose should be instilled around the wound site; and active immunization with antirabies vaccine.
With human diploid vaccine, five doses given on days 1,3, 7, 14 and 28 are recommended.
Once symptoms appear, vaccine and immune globulin are
ineffective.
Physicians should always seek the advice
of the local health department when the question of rabies prophylaxis
arises.
What is pre exposure prophylaxis? Who should routinely receive rabies virus vaccine?
Preexposure prophylaxis is recommended for individuals at high risk of contact with rabies virus, such as veterinarians, spelunkers, laboratory workers, and animal handlers.
The vaccine currently used in the United States for preexposure prophylaxis employs an attenuated rabies virus grown in human diploid cell culture and inactivated with β-propiolactone.
Preexposure prophylaxis consists of two subcutaneous injections of vaccine given 1 month apart, followed by a booster dose several months later.
How do you treat rabies?
Intensive supportive care has resulted in two or three long-term survivals; despite the best modern medical care, however, the mortality still exceeds 90%.
In addition, because of the infrequency of the disease, many cases die without definitive diagnosis.
Prevention is the mainstay of controlling human rabies.
Human hyperimmune antirabies globulin, interferon and vaccine do not alter the diseases once symptoms have developed.
Should the patients wit rabies be isolated?
The patient should be in strict isolation to prevent transmission of rabies virus in her secretions (especially saliva) from infecting health care workers.
What is to be done for exposed contacts?
All health care workers that came into contact with this patient should be given post-exposure prophylaxis.