Echinococcosis is a parasitic disease caused by infection with tiny tapeworms of the genus Echinocococcus. Echinococcosis is classified as either cystic echinococcosis or alveolar echinococcosis.
Cystic echinocccosis (CE), also known as hydatid disease, is caused by infection with the larval stage of Echinococcus granulosus, a ~2-7 millimeter long tapeworm found in dogs (definitive host) and sheep, cattle, goats, and pigs (intermediate hosts). Although most infections in humans are asymptomatic, CE causes harmful, slowly enlarging cysts in the liver, lungs, and other organs that often grow unnoticed and neglected for years.
Alveolar echinococcosis (AE) disease is caused by infection with the larval stage of Echinococcus multilocularis, a ~1-4 millimeter long tapeworm found in foxes, coyotes, and dogs (definitive hosts). Small rodents are intermediate hosts for E. multilocularis. Although cases of AE in animals in endemic areas are relatively common, human cases are rare. AE poses a much greater health threat to people than CE, causing parasitic tumors that can form in the liver, lungs, brain, and other organs. If left untreated, AE can be fatal.
Cystic echinococcosis (CE) is caused by infection with the larval stage of Echinococcus granulosus. CE is found in Africa, Europe, Asia, the Middle East, Central and South America, and in rare cases, North America. The parasite is transmitted to dogs when they ingest the organs of other animals that contain hydatid cysts. The cysts develop into adult tapeworms in the dog. Infected dogs shed tapeworm eggs in their feces which contaminate the ground. Sheep, cattle, goats, and pigs ingest tapeworm eggs in the contaminated ground; once ingested, the eggs hatch and develop into cysts in the internal organs. The most common mode of transmission to humans is by the accidental consumption of soil, water, or food that has been contaminated by the fecal matter of an infected dog. Echinococcus eggs that have been deposited in soil can stay viable for up to a year. The disease is most commonly found in people involved in raising sheep, as a result of the sheep’s role as an intermediate host of the parasite and the presence of working dogs that are allowed to eat the offal of infected sheep.
Alveolar echinococcosis (AE) is caused by infection with the larval stage of Echinococcus multilocularis. AE is found across the globe and is especially prevalent in the northern latitudes of Europe, Asia, and North America. The adult tapeworm is normally found in foxes, coyotes, and dogs. Infection with the larval stages is transmitted to people through ingestion of food or water contaminated with tapeworm eggs.
Persons with cystic echinococcosis often remain asymptomatic until hydatid cysts containing the larval parasites grow large enough to cause discomfort, pain, nausea, and vomiting. The cysts grow over the course of several years before reaching maturity and the rate at which symptoms appear typically depends on the location of the cyst. The cysts are mainly found in the liver and lungs but can also appear in the spleen, kidneys, heart, bone, and central nervous system, including the brain and eyes. Cyst rupture is most frequently caused by trauma and may cause mild to severe anaphylactic reactions, even death, as a result of the release of cystic fluid.
Alveolar echinococcosis (AE) is characterized by parasitic tumors in the liver and may spread to other organs including the lungs and brain. In humans, the larval forms of E. multilocularis do not fully mature into cysts but cause vesicles that invade and destroy surrounding tissues and cause discomfort or pain, weight loss, and malaise. AE can cause liver failure and death because of the spread into nearby tissues and, rarely, the brain. AE is a dangerous disease resulting in a mortality rate between 50% and 75%, especially because most affected people live in remote locations and have poor health care.
The presence of a cyst-like mass in a person with a history of exposure to sheepdogs in an area where E. granulosus is endemic suggests a diagnosis of cystic echinococcosis. Imaging techniques, such as CT scans, ultrasonography, and MRIs, are used to detect cysts. After a cyst has been detected, serologic tests may be used to confirm the diagnosis.
Alveolar echinococcosis is typically found in older people. Imaging techniques such as CT scans are used to visually confirm the parasitic vesicles and cyst-like structures and serologic tests can confirm the parasitic infection.
In the past, surgery was the only treatment for cystic echinococcal cysts. Chemotherapy, cyst puncture, and PAIR (percutaneous aspiration, injection of chemicals and reaspiration) have been used to replace surgery as effective treatments for cystic echinococcosis. However, surgery remains the most effective treatment to remove the cyst and can lead to a complete cure. Some cysts are not causing any symptoms and are inactive; those cysts often go away without any treatment. The treatment of alveolar echinococcosis is more difficult than cystic echinococcosis and usually requires radical surgery, long-term chemotherapy, or both
Cystic echinococcosis is controlled by preventing transmission of the parasite. Prevention measures include limiting the areas where dogs are allowed and preventing animals from consuming meat infected with cysts.
- Prevent dogs from feeding on the carcasses of infected sheep.
- Control stray dog populations.
- Restrict home slaughter of sheep and other livestock.
- Do not consume any food or water that may have been contaminated by fecal matter from dogs.
- Wash your hands with soap and warm water after handling dogs, and before handling food.
Alveolar echinococcosis can be prevented by avoiding contact with wild animals such as foxes, coyotes, and dogs and their fecal matter and by limiting the interactions between dogs and rodent populations. Do not allow dogs to feed on rodents and other wild animals.