Alveolar Echinococcosis

Life Cycle of Echinococcus, Source: Wikimedia Commons

Epidemiology

Prevalence

AE 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 Alveolar Echinococcosis Occurs in Animals

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 catch and eat rodents often, may also become infected. Once the animal becomes infected, the tapeworm matures in its intestine, produces 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 AE.

Diagnosis

Exams and Tests for Animals

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.

Exams and Tests in Humans

See a health care provider if following to potential exposure to AE 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. ^[1]

Signs and Symptoms

AE is caused by tumor-like or cyst-like tapeworm larvae growing in the body. AE usually involves the liver, but can spread to other organs of the body. Because the cysts are slow-growing, infection with AE 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.

Treatment

Surgery is the most common form of treatment for AE, although removal of the entire parasite mass is not always possible. After surgery, medication may be necessary to keep the cyst from growing back. ^[2]

Chances of Developing Alveolar Echinococcosis

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.

Risk Factors

For 50 years, E. multilocularis was thought to be 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 AE are low, certain groups may be at greater risk.

A person may be at greater risk if he or she lives in an area where E. multilocularis 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 AE.

Prevention

If residing 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 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 cats and dogs to wander freely or to capture and eat rodents.
• If the pet may have eaten rodents, consult the veterinarian about the possible need for preventive treatments.
• After handling pets, always wash the 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.

References

1. ↑ Gottstein et al, "Improved primary immunodiagnosis of alveolar echinococcosis in humans by an enzyme-linked immunosorbent assay using the Em2plus antigen." J Clin Microbiol. 1993 February; 31(2): 373-376 [Abstract | PDF]
2. ↑ Reuter et al, "Benzimidazoles in the treatment of alveolar echinococcosis: a comparative study and review of the literature," Journal of Antimicrobial Chemotherapy (2000) 46, 451-456 Abstract | Full Text | PDF