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Alveolar Hydatid Disease
(al-VEE-oh-ler HIGH-dad-id)
What is Alveolar Hydatid
disease (AHD)?
AHD (al-VEE-oh-ler
HIGH-dad-id) disease results from being infected with the larval stage of Echinococcus
multilocularis, a microscopic tapeworm (1-4 millimeters) found in
foxes, coyotes, dogs, and cats. Although human cases are rare, infection
in humans causes parasitic tumors to form in the liver, and, less
commonly, the lungs, brain, and other organs. If left untreated, infection
with AHD can be fatal.
Where has AHD been found?
AHD is found worldwide,
mostly in northern latitudes. Cases have been reported in central Europe,
Russia, China, Central Asia, Japan, and North America. In North America E.
multilocularis is found primarily in the north central region from
eastern Montana to central Ohio, as well as Alaska and Canada. Human cases
have been reported in Alaska, the province of Manitoba, and Minnesota.
Prevalence among wild foxes and coyotes is high, and may reach over 50% in
some areas; however, even in these areas, transmission to humans has been
low.
How does infection occur in
foxes, coyotes, dogs, and other cats?
Wild foxes, coyotes,
and cats get infected when they eat Echinococcus multilocularis
larvae in infected rodents, field mice, or voles. Cats are less
susceptible than dogs, but because they probably catch and eat rodents
more often, may also become infected. Once the animal becomes
infected, the tapeworm matures in its intestine, lays eggs, and the
infected animal passes eggs in the stool. These tapeworm eggs, which are
directly infectious to other animals, are too tiny to see, and will stick
to anything with which they come in contact. Coyotes, foxes, dogs, and
cats are not harmed by the tapeworm and do not have symptoms of AHD.
Can animals be tested for E.
multilocularis tapeworms?
Routine fecal
examinations are not sufficient to diagnose E. multilocularis
infection. Infection with the E. multilocularis tapeworm and other
tapeworms may occur at the same time. Eggs of Taenia species
tapeworms and Echinococcus tapeworms are similar in shape and size
and are very difficult to tell apart. If you live in an area where this
parasite occurs or you are concerned about your dog or cat being infected
with E. multilocularis or other tapeworms, see your veterinarian
who can answer your questions and assess the risk of possible infection.
How can I be infected with AHD?
By accidentally
swallowing the eggs of the E. multilocularis tapeworm. Humans can
be exposed to these eggs in two main ways, both of which involve
"hand-to-mouth" transfer or contamination:
- By directly
ingesting food items contaminated with stool from foxes or coyotes.
This might include grass, herbs, greens, or berries gathered from
fields.
- By petting or
handling household cats and dogs infected with the E.
multilocularis tapeworm. These pets may shed the tapeworm eggs in
their stool, and their fur may be contaminated. Some dogs "scent
roll" in foreign material (such as wild animal feces) and may
become contaminated this way.
How likely am I to contract
AHD?
For 50 years, E.
multilocularis was confined to the Alaskan coast and Canada. Now,
because wild coyotes, foxes, and wolves are being trapped and transported
to states where E. multilocularis has not previously been found,
there is increased risk of spreading the disease to animals and humans.
Wild animals carrying the tapeworm could set up the transmission cycle and
expose animals not already infected. Many states prohibit this movement of
wild animals, but trapping and movement of infected wild canines still
occurs. If the transportation and relocation of these animals continues,
the risk of human transmission will increase. Although the chances of
contracting AHD are low, certain groups may be at greater risk.
You may be at greater
risk if you live in an area where AHD is found (see above). People at high
risk include trappers, hunters, veterinarians, or others who contact wild
foxes, coyotes, or their stool, or household cats and dogs who have the
opportunity to eat wild rodents infected with AHD.
What are the symptoms of AHD?
AHD is caused by
tumor-like or cyst-like tapeworm larvae growing in the body. AHD usually
involves the liver, but can spread to other organs of the body. Because
the cysts are slow-growing, infection with AHD may not produce any
symptoms for many years. Pain or discomfort in the upper abdominal region,
weakness, and weight loss may occur as a result of the growing cysts.
Symptoms may mimic those of liver cancer and cirrhosis of the liver.
How can I find out if I have
AHD?
See your health care
provider if you think you may have been exposed to AHD by one of the ways
listed above. He or she can order a blood test for the presence of the
parasite or antibodies to E. multilocularis.
What is the treatment for AHD?
Surgery is the most
common form of treatment for AHD, although removal of the parasite mass is
not usually 100 % effective. After surgery, medication may be necessary to
keep the cyst from growing back.
How can I prevent AHD?
If you live in an area
where E. multilocularis is found in rodents and wild canines, take
the following precautions to avoid infection:
- Dont touch a fox,
coyote, or other wild canine, dead or alive, unless you are wearing
gloves. Hunters and trappers should use plastic gloves to avoid
exposure.
- Dont keep wild
animals, especially wild canines, as pets or encourage them to come
close to your home.
- Dont allow your
cats and dogs to wander freely or to capture and eat rodents.
- If you think that
your pet may have eaten rodents, consult your veterinarian about the
possible need for preventive treatments.
- After handling pets,
always wash your hands with soap and warm water.
- Fence in gardens to
keep out wild animals.
- Do not collect or
eat wild fruits or vegetables picked directly from the ground. All
wild-picked foods should be washed carefully or cooked before eating.
For more information:
- Hildreth MB, Johnson
MD, Kazacos KR. Echinococcus multilocularis: a zoonosis of
increasing concern in the United States. Supplement to the Compendium
of Continuing Education for the Practicing Veterinarian 1991;13:
727-741.
- Leiby PD, Kritsky
DC. Echinococcus multilocularis: a possible domestic life cycle
in central North America and its public health implications. J
Parasitol 1972;58: 1213-1215.
- Schantz PM, Chai J,
Craig PS, Eckert J, Jenkins DJ, Macpherson CNL, Thakur A. Epidemiology
and Control. In: Echinococcosis and Hydatid Disease, R.C.A. Thompson
and A.J. Lymbery, eds., London, CAB International, 233-331.
- Stehr-Green JK,
Stehr-Green PA, Schantz PM, Wilson JF, Lanier A. Risk factors for
infection with Echinococcus multilocularis in Alaska. Am J Trop
Med Hyg 1988;38: 380-385.
- WHO. Guidelines for
treatment of cystic and alveolar echinococcosis in humans. Bull World
Health Organization 1996;74: 231-242.
- Wilson JF, Rausch RL.
Alveolar hydatid disease: a review of clinical features of 33
indigenous cases of Echinococcus multilocularis infection in
Alaskan Eskimos. Am J Trop Med Hyg 1980;29: 1340-1355.
*This
information was prepared in association with the American Association of
Veterinary Parasitologists (AAVP).
This fact sheet is for
information only and is not meant to be used for self-diagnosis or as a
substitute for consultation with a health care provider. If you have any
questions about the disease described above or think that you may have a
parasitic infection, consult a health care provider.
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