Alveolar hydatid disease: Abbreviated AHD. A parasitic disease caused by the larval stage of a microscopic tapeworm Echinococcus multilocularis.
AHD is found worldwide, mostly in northern latitudes. 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 in 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.
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.
Infection can occur 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 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.
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.
People at high risk for AHD 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.
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.
The diagnosis is made by a blood test for the presence of the parasite or antibodies to E. multilocularis.
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.
If you live in an area where E. multilocularis is found in rodents and wild canines, take the following precautions to avoid infection:
- Don't 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.
- Don't keep wild animals, especially wild canines, as pets or encourage them to come close to your home.
- Don't 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.