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Toxoplasmosis is a disease caused by
the protozoal parasite Toxoplasma gondii, which can affect all
warm-blooded species. People can get infected by eating raw or
undercooked meat that contains toxoplasma cysts or by ingesting
those cysts from the environment.
Cats that have been recently infected can shed infective
toxoplasma organisms in their feces, which is why many people may
associate cats with the disease. However, Dr. Graves explains that
there are many reasons cats don't deserve notoriety for the disease.
"First of all, 30 percent to 50 percent of people have already
been exposed to toxoplasma, and most of these people do not get
sick," Graves says. Most people and animals show mild or no signs of
illness when infected with toxoplasma.
People and animals most at risk for developing disease include
those with suppressed immune systems -- for example, from HIV
infection or chemotherapy treatment -- and unborn fetuses, who can
get infected through maternal blood. In these cases, toxoplasmosis
may manifest as a blood, respiratory or nervous system disease.
Additionally, the likelihood an indoor cat will shed infective
toxoplasma is very low. A cat will shed the organism only if it has
been recently exposed. This usually happens in kittenhood, if it
will happen at all. When exposed, a cat will shed the organism for
one to three weeks, and if even if it doesn't get sick, it will
develop antibodies to protect it against future infection. Once a
cat has developed these antibodies, the chances it will shed
toxoplasma again are very slim.
Finally, the developmental stage of toxoplasma found in cat feces
takes several days to mature into the infectious stage once they are
out of the cat's body. Graves says, "If litter boxes are cleaned
daily, there's little chance cat owners can be exposed to the
infectious form of the organism."
Graves points out that the immune status of the human plays a
role in whether a person or unborn fetus can become infected. A
blood serum test can determine if a person has antibodies to protect
against toxoplasmosis. If the blood contains antibodies, the person
has already been exposed and is protected from infection.
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 If a person is negative for toxoplasmosis, then his cat can also
be tested for antibodies. There are two antibodies that a
veterinarian will look for: immunoglobulin M, or IgM, which is
produced soon after infection, and immunoglobulin G, or IgG, which
doesn't increase until five weeks after the cat has been infected.
If a cat is negative, it poses no risk to owners. If the cat has
high level of IgM, it was recently infected, and owners should take
precautions against exposure. If the cat has high level of IgG, it
has been exposed, but likely has already stopped shedding the
organism.
"Pregnant women and immunosuppressed people do not have to avoid
cats," Graves says. "With some common sense and proper hygiene,
those at risk can avoid ingestion of the infectious oocytes."
Of course, the best way to protect the humans in your family from
toxoplasmosis is by protecting your cats from infection. Graves
recommends keeping pet cats indoors, and they should not eat raw
meat, such as birds or rodents.
Women who are pregnant, or plan on becoming pregnant, can be
tested and have their cats tested for antibodies. Litter boxes
should be cleaned daily, especially if antibody tests indicate that
a cat has been recently exposed to toxoplasma, and pregnant women
should avoid this household task. Toxoplasmosis is just one of many
reasons pet owners should wash their hands thoroughly after cleaning
up after their pets.
Since recently infected outdoor cats can deposit toxoplasma into
the environment, pregnant women and immunosuppressed individuals
should wear gloves when gardening or doing other outdoor work and
thoroughly wash their hands afterward. Covering sandboxes when they
not in use can prevent cats from using them as a litter box.
For more information about toxoplasmosis, consult your
veterinarian and your physician.
[University of Illinois
news release by Kim Marie Labak] |
