RabiesIntroduction Rabies
is a serious viral illness affecting the brain and saliva glands of mammals, particularly
meat eating species (carnivores) such as dogs and cats, but also wild animals
like bats, skunks, raccoons,foxes and woodchucks. There are several subtypes of
rabies viruses typical for different animal species. Typically man becomes infected
because of a bite
from a rabid dog, cat or bat and the virus, which is carried in the
saliva of the rabid animal enters into the human through the skin wound. Without
therapy it would now follow the skin nerves into the spinal cord and eventually
enter into the brain where it multiplies. It then switches from there into other
nerve pathways going to the saliva glands, the throat area and muscles used to
swallow. The virus also multiplies in the respiratory center with the neurotoxin
destroying the nerve cells there, which eventually leads to an inability to breathe
and death. Every year about 100,000 people die from rabies throughout
the world, mostly from rabid dog bites. As the rabid virus leaves very characteristic
inclusion bodies in the brain cells that are called "Negri
bodies", one of the tests to see whether a dog that has bitten
a patient, was rabid is to kill the dog and examine the dog's brain histologically
for the presence of Negri bodies. As there are blood tests available now
that are very sensitive, the procedure has changed: the dog is caught and kept
in a kennel for 10 day observation. A veterinarian can then determine whether
the dog is rabid or not. Should the dog be diagnosed clinically with rabies, it
would still have to be killed and the brain examined. However, many dogs are healthy
and do not have to be killed and can be released after the incubation period.
Signs and Symptoms: The incubation time typically
is 10 to 50 days. The rabies virus is a Lyssavirus, an RNA virus. It is the only
type of Lyssavirus that affects man (Ref. 11, p. 1812). At this stage it is important
that the physician does a thorough washout and cleaning of the wound under a local
anesthetic as this removes the majority of the virus and the bacteria from the
saliva of the animal (see below).
In
the first two to three days the wound becomes painful, the patient becomes febrile,
may vomit and may develop nausea and a loss of appetite. Due to the neurotoxin
that is circulating the patient may now develop hallucinations, confusion, anxiety,
bizarre behavior including biting. There often is an excruciating pain around
the throat and with drinking fluids so that the patient will avoid doing this,
thus the old-fashioned term "hydrophobia" for rabies. The patient is
thirsty though and is getting dehydrated quickly, which adds to the mental confusion.
As more levels of the spinal cord get involved with infection with rabies virus,there
is a progressive inability to first move the extremities, then the trunk muscles
and finally the face and neck muscles (called "paralysis of muscles").
Symptoms of encephalitis with headaches, confusion and agitation are a sign that
the brain is now infected. Death occurs from an inability to breathe and swallow
or from secondary sepsis or meningitis from other bacteria or fungi that entered
the system through the bite injury. Diagnostic tests:
A highly sensitive fluorescent antibody test on the one hand and a virus isolation
test on the other hand can replace the killing of the suspected rabid dog as already
indicated above. Arising antibody titer in a human is also a very worrisome diagnostic
test that would indicate exposure to rabies. However, the clinician should treat
the patient right away on suspicion as waiting for results is unsafe and would
jeopardize the patient's prognosis. Treatment As
death happens in almost all cases of rabies about 3 to 10 days after the onset
of symptoms, it is clear that the physician must be very aggressive in any case
suspicious for rabies exposure. After a bite wound the wound is horoughly
scrubbed and washed out under local anesthetic to reduce the potential amount
of viral load. A good amount of rabies immunoglobuline (=RIG) is then
injected into the wound area and the rest given normally by injection. The wound
is then closed. In addition an active rabies immunization is then started on the
day of the bite, but injected in another site. The old vaccines that used to be
painful are no longer used. There are now two vaccines that are used instead:
the human diploid cell rabies vaccine(=HDCV) and the rabies vaccine,
absorbed (=RVA). Either of them can be used in combination with RIG. Five
doses of HDCV or RVA have to be given on the day of the bite, at 3, 7, 14 and
28 days. The WHO recommends a 6th dose 3 months after the bite. Here is a summary
regarding the treatment after an animal bite (modified from Ref. 6, p. 1298).
| Treatment
after bite from animal with possible rabies | | Type
of animal: | What to do with
animal: | Therapy
of patient: | | cats
and dogs | observe animal for 10 days; kill
animal, if it turns rabid and look for Negri bodies | No
vaccination generally unless rabies proven in animal; if rabid, then vaccinate
immediately. | | raccoons,
foxes, bats, skunks, woodchucks | consider
wild animals as rabid unless they can be retained and proven by lab tests to be
rabies free | Immediately vaccinate |
| rats, mice, rabbits, hares, livestock | these
animals seem to have a natural immunity to rabies | contact
public health officer regarding the recommendation for the area where bite took
place, but rarely is vaccination required | More
info about rabies (questions
and answers about rabies, CDC site).
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