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) disease results from being infected with the larval stage of Echinococcus granulosus, a tiny tapeworm (~2-7 millimeters in length) found in dogs (definitive host), sheep, cattle, goats, foxes, and pigs, amongst others (intermediate hosts). Most infections in humans are asymptomatic, but CE, also known as hydatid disease, causes slowly enlarging masses, most commonly in the liver and the lungs. Treatment can involve both medication and surgery.

Alveolar echinococcosis (AE) disease results from being infected with the larval stage of Echinococcus multilocularis, a tiny tapeworm (~1-4 millimeters in length) found in foxes, coyotes, dogs, and cats (definitive hosts). 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 AE can be fatal.

How do people get alveolar echinococcosis (AE)?

People who accidentally swallow the eggs of the Echinococcus multilocularis tapeworm are at risk for infection. People at high risk include trappers, hunters, veterinarians, or others who have contact with wild foxes, or coyotes, or their stool, or household dogs and cats that have the opportunity to eat wild rodents infected with AE. Humans can be exposed to these eggs by “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 dogs or cats infected with the Echinococcus 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.

Where is alveolar echinococcosis (AE) found?

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 Echinococcus multilocularis is found primarily in the north central region from eastern Montana to central Ohio, as well as Alaska and Canada. Rare human cases have been reported in Alaska, the province of Manitoba, and Minnesota. Prevalence among wild foxes and coyotes can be high, and may reach over 50% in some areas; however, even in these areas, transmission to humans has been low.

What are the symptoms of alveolar echinococcosis (AE)?

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.

What should I do if I think I have alveolar echinococcosis (AE)?

See your health care provider if you think you may have alveolar echinococcosis (AE). Diagnosis of AE can be made by a blood test that looks for the presence of antibodies to Echinococcus multilocularis.

How is alveolar echinococcosis (AE) treated?

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.

Can alveolar echinococcosis (AE) be prevented?

If you live in an area where Echinococcus 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 dogs and cats to wander freely or to capture and eat rodents.
• If you think that your pet may have eaten rodents, consult your veterinarian about possible preventive treatments.
• Wash your hands with soap and warm water after handling dogs or cats, and before handling food.
• Teach children the importance of washing hands to prevent infection.
• 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.

How do people get cystic echinococcosis (CE)?

People who accidentally swallow the eggs of the Echinococcus granulosus tapeworm are at risk for infection. Dogs that eat home-slaughtered sheep and other livestock become infected with the tapeworm Echinococcus granulosus and the tapeworm eggs can be found in their stool. Direct contact with infected dogs, particularly intimate contact between children and their pet dogs, may lead to human infection. Ingestion of soil, water and vegetables contaminated with infected dog feces may also lead to infections. Echinococcus granulosus eggs can survive snow and freezing conditions.

Humans can be exposed to these eggs by “hand-to-mouth” transfer or contamination.

• By ingesting food, water or soil contaminated with stool from infected dogs. This might include grass, herbs, greens, or berries gathered from fields.
• By petting or handling dogs infected with the Echinococcus granulosus tapeworm. These dogs may shed the tapeworm eggs in their stool, and their fur may be contaminated.

Where is cystic echinococcosis (CE) found?

CE is found in Africa, Europe, Asia, the Middle East, and Central and South America. Highest prevalence is found in populations that raise sheep. In North America, Echinococcus granulosus is rarely reported in Canada and Alaska, and a few human cases have also been reported in Arizona and New Mexico in sheep-raising areas. In the United States, most infections are diagnosed in immigrants from counties where CE is endemic. Risk factors for human infection include uncontrolled dogs living closely with people, uncontrolled slaughter of livestock, and unsanitary living conditions.

What are the symptoms of cystic echinococcosis (CE)?

CE is caused by cyst-like tapeworm larvae growing in the body. CE usually involves the liver or the lungs, but can also be found in other organs of the body. Because the cysts are slow-growing, infection with CE may not produce any symptoms for many years. Pain or discomfort in the upper abdominal region or chest, nausea, vomiting, or coughing may occur as a result of the growing cysts. Rupture of cyst fluid can lead to allergic reactions or even death.

What should I do if I think I have cystic echinococcosis (CE)?

See your health care provider if you think you may have cystic echinococcosis. CE can be diagnosed with imaging studies such as X-rays or MRI scans, which are helpful to see the cysts in most organs. Blood tests are available to help diagnose an infection, but may not always be accurate. If surgery is necessary, confirmation of the diagnosis can be made by the laboratory.

How is cystic echinococcosis (CE) treated?

Until recently, surgery was the only option for treatment of CE. However, now medication and a modified surgical procedure (aspiration) are increasingly used and can replace the need for surgical removal of the hydatid cysts. Even so, surgery may be necessary in certain circumstances. After surgery, medication may be needed to keep the cyst from growing back.

Can cystic echinococcosis (CE) be prevented?

If you live in an area where Echinococcus granulosus is found in sheep or cattle, take the following precautions to avoid infection:

• Wash your hands with soap and warm water after handling dogs, and before handling food.
• Teach children the importance of washing hands to prevent infection.
• Avoid ingestion of food, water or soil contaminated with stool from dogs. This might include grass, herbs, greens, or berries gathered from fields.
• Don’t allow your dogs to wander freely or to capture and eat raw meat from sheep, cattle, pigs, and goats.
• Don’t home slaughter sheep and other livestock.
• If you think your pet may have eaten infected meat, consult your veterinarian about the possible need for preventive treatments.

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.

Causal Agents

Human echinococcosis (hydatidosis, or hydatid disease) is caused by the larval stages of cestodes (tapeworms) of the genus Echinococcus. Echinococcus granulosus (sensu lato) causes cystic echinococcosis and is the form most frequently encountered. Another species, E. multilocularis, causes alveolar echinococcosis, and is becoming increasingly more common. Two exclusively New World species, E. vogeli and E. oligarthrus, are associated with “Neotropical echinococcosis”; E. vogeli causes a polycystic form whereas E. oligarthrus causes the extremely rare unicystic form.

Many genotypes of E. granulosus have been identified that differ in their distribution, host range, and some morphological features; these are often grouped into separate species in modern literature. The known zoonotic genotypes within the E. granulosus sensu lato complex include the “classical” E. granulosus sensu stricto (G1–G3 genotypes), E. ortleppi (G5), and the E. canadensis group (usually considered G6, G7, G8, and G10). Research on the epidemiology and diversity of these genotypes is ongoing, and no consensus has been reached on appropriate nomenclature thus far.

Neotropical Echinococcosis (Echinococcus vogeli, E. oligarthrus)

The Neotropical agents follow the same life cycle although with differences in hosts, morphology, and cyst structure. Adults of E. vogeli reach up to 5.6 mm long, and E. oligarthrus up to 2.9 mm. Cysts are generally similar to those found in cystic echinocccosis but are multi-chambered.

Hosts

Echinococcus granulosus definitive hosts are wild and domestic canids. Natural intermediate hosts depend on genotype. Intermediate hosts for zoonotic species/genotypes are usually ungulates, including sheep and goats (E. granulosus sensu stricto), cattle (“E. ortleppi”/G5), camels (“E. canadensis”/G6), and cervids (“E. canadensis”/G8, G10).

For E. multilocularis, foxes, particularly red foxes (Vulpes vulpes), are the primary definitive host species. Other canids including domestic dogs, wolves, and raccoon dogs (Nyctereutes procyonoides) are also competent definitive hosts. Many rodents can serve as intermediate hosts, but members of the subfamily Arvicolinae (voles, lemmings, and related rodents) are the most typical.

The natural definitive host of E. vogeli is the bush dog (Speothos venaticus), and possibly domestic dogs. Pacas (Cuniculus paca) and agoutis (Dasyprocta spp.) are known intermediate hosts. E. oligarthrus uses wild neotropical felids (e.g. ocelots, puma, jaguarundi) as definitive hosts, and a broader variety of rodents and lagomorphs as intermediate hosts.

Geographic Distribution

Echinococcus granulosus sensu lato occurs practically worldwide, and more frequently in rural, grazing areas where dogs ingest organs from infected animals. The geographic distribution of individual E. granulosus genotypes is variable and an area of ongoing research. The lack of accurate case reporting and genotyping currently prevents any precise mapping of the true epidemiologic picture. However, genotypes G1 and G3 (associated with sheep) are the most commonly reported at present and broadly distributed. In North America, Echinococcus granulosus is rarely reported in Canada and Alaska, and a few human cases have also been reported in Arizona and New Mexico in sheep-raising areas. In the United States, most infections are diagnosed in immigrants from counties where cystic echinococcosis is endemic. Some genotypes designated “E. canadensis” occur broadly across Eurasia, the Middle East, Africa, North and South America (G6, G7) while some others seem to have a northern holarctic distribution (G8, G10).

E. multilocularis occurs in the northern hemisphere, including central and northern Europe, Central Asia, northern Russia, northern Japan, north-central United States, northwestern Alaska, and northwestern Canada. In North America, Echinococcus multilocularis is found primarily in the north-central region as well as Alaska and Canada. Rare human cases have been reported in Alaska, the province of Manitoba, and Minnesota. Only a single autochthonous case in the United States (Minnesota) has been confirmed.

E. vogeli and E. oligarthrus occur in Central and South America.

Clinical Presentation

Echinococcus granulosus infections often remain asymptomatic for years before the cysts grow large enough to cause symptoms in the affected organs. The rate at which symptoms appear typically depends on the location of the cyst. Hepatic and pulmonary signs/symptoms are the most common clinical manifestations, as these are the most common sites for cysts to develop In addition to the liver and lungs, other organs (spleen, kidneys, heart, bone, and central nervous system, including the brain and eyes) can also be involved, with resulting symptoms. Rupture of the cysts can produce a host reaction manifesting as fever, urticaria, eosinophilia, and potentially anaphylactic shock; rupture of the cyst may also lead to cyst dissemination.

Echinococcus multilocularis affects the liver as a slow growing, destructive tumor, often with abdominal pain and biliary obstruction being the only manifestations evident in early infection. This may be misdiagnosed as liver cancer. Rarely, metastatic lesions into the lungs, spleen, and brain occur. Untreated infections have a high fatality rate.

Echinococcus vogeli affects mainly the liver, where it acts as a slow growing tumor; secondary cystic development is common. Too few cases of E. oligarthrus have been reported for characterization of its clinical presentation.

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.
• Teach children the importance of washing hands to prevent infection.

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.
• Avoid contact with wild animals such as foxes, coyotes and stray dogs.
• Do not encourage wild animals to come close to your home or keep them as pets.
• Wash your hands with soap and warm water after handling dogs or cats, and before handling food.
• Teach children the importance of washing hands to prevent infection.