Ear infections, chronic WORLD OF MICROBIOLOGY AND IMMUNOLOGY172•
two weeks, and terminate naturally as the body’s immune
defenses successfully cope with the infection. Usually no per-
manent damage results from the infection. However in those
who are immunocompromised and in children, the disease can
become more disseminated. Damage to the kidney can be so
devastating that complete loss of kidney function occurs. If
not treated the death rate from hemolytic anemia is high. Even
with rapid diagnoses and treatment that includes antibiotics,
blood transfusions and kidney dialysis, the death rate is still
three to five percent.
Approximately ten to fifteen per cent of those infected
with strain O157:H7 develop hemolytic anemia. The syn-
drome is the leading cause of sudden-onset kidney failure in
children in the world. As well, the elderly can develop a con-
dition known as thrombocytopenic purpura, which consists of
a fever and nerve damage. In the elderly, this malady can kill
almost half of those who become infected.
The chances of infection from E. coliO157:H7 are
greatly lessened by proper food preparation, washing of food
surfaces that have been exposed to raw ground meat, and
proper personal hygiene, especially hand washing. Also, since
the bacterium is very sensitive to heat, boiling suspect water
prior to drinking the water is a sure way to eliminate the risk
of infection from the bacteria and to inactivate the toxins.
Also, a vaccinefor cattle is in the final testing stages
prior to being approved for sale. Approval is expected in 2002.
The vaccine blocks the binding and pedestal formation by the
bacteria in cattle. The bacteria remain free in the intestinal
tract and so are washed out of the cow. Eliminating the reser-
voir of the organism lessens the spread of O157:H7 infection
to humans.See alsoAnti-adhesion mechanisms; Escherichia coli; Food
safety; VaccinationEEar infections, chronicAR INFECTIONS, CHRONIC
Chronic ear infection, which is also referred to as chronic oti-
tis media, is a recurring infection of the middle ear that occurs
in animals and in humans. In humans, children between a few
months of age and about six years of age are the most suscep-
tible. The infection can be caused by bacteriaand, occasion-
ally, by viruses.
The ear consists of outer, middle, and inner regions.
The outer ear is the visible portion that channels sound vibra-
tions to the middle ear. The middle ear contains three small
bones that pass on the vibration to the nerve endings housed
in the inner ear. The middle ear is connected to the nasal cav-
ity and the throat by a drainage tube known as the Eustachian
tube. Improper drainage from the Eustachian tubes result in a
retention of fluid in the middle ear, which can become
infected by bacteria.
Such infections are common in children. Each year in
the United States, over 10 million children are treated for ear
infections. However, ear infections tend to be infrequent and
disappear as the construction of the ear changes with age.
Specifically, the Eustachian tube becomes more slanted inorientation, which promotes drainage that is more efficient.
However, in some children the normally short-term (or
acute) middle ear infections begin to recur. For these chil-
dren, many ear infections can occur in the first six or so years
of life. Chronic ear infections affects about two out of every
10,000 people.
In some cases, surgical intervention is necessary to
install a plastic drainage tube (a procedure called myrin-
gotomy) or to remove infected adenoids or tonsils, which can
swell and block the eustachian tube. Myringotomy is one of
the most common operations that are performed in the United
States. As the ear matures structurally and the eustachian tube
acquires the ability to drain more freely, the tube is removed.
As with other chronic bacterial infections, the symp-
toms associated with chronic ear infections can be less severe
and uncomfortable than those of the acute form of the infec-
tion. Chronic infections may thus escape detection for long
periods of time.
Usually a chronic ear infection is more inconvenient
and uncomfortable than a health threat. However, in some
cases, the chronic bacterial or viral ear infections can lead to
complications that are much more serious. The infection can
spread into the bones of the ear. Also, the increased pressure
from the build-up of fluid can rupture the eardrum. Such dam-
age can produce permanent impairment of hearing.
Another damaging aspect of chronic ear infections,
which is shared with other chronic bacterial infections, is the
damage to tissues that results from a prolonged immune
response to the infection. The failure to clear the infection can
produce a prolonged immune response. This response, partic-
ularly inflammation, can be damaging to tissue.
Treatment consists of decongestants or antihistamines
to promote drainage through the Eustachian tube, and of
antibioticsin the case of a bacterial infection. Even with treat-
ment a chronic infection can take weeks or months to com-
pletely clear. Adherence to the treatment schedule is critical,
especially since the symptoms of chronic ear infections can
pass before the infection is fully cleared. Stopping therapy
when the symptoms fade may allow the bacteria that are still
surviving to become re-established as another infection.
Moreover, because the bacteria were exposed to an antibacte-
rial agent, resistance to that agent can develop, making the
recurrent infection harder to eradicate.See alsoBacteria and bacterial infectionEEbola virusBOLA VIRUS
The Ebola virus is one of two members of a family of viruses
that is designated as the Filoviridae. The name of the virus
comes from a river located in the Democratic Republic of the
Congo, where the virus was discovered.
The species of Ebola virus are among a number of
viruses that cause a disease that is typified by copious internal
bleeding and bleeding from various orifices of the body,
including the eyes. The disease can be swiftly devastating and
results in death in over 90% of cases.womi_E 5/6/03 2:11 PM Page 172