Echinococcus: The Link Between Tapeworms and Dog Poop

Tapeworms seem a bit icky. Even worse, some people have them and don't even know it, only to find out later.

There's one particular parasite, a tapeworm, that infects one million people worldwide. Oddly enough, it involves dogs (or other animals), their poo, and the meat they eat. It isn't found everywhere, but where it is found, a dog is often the reason. The infection, Echinococcus, might come from simply petting a friendly stray dog that had eaten discarded livestock.

It could come from a salad that had a bit of soil that had been contaminated by dogs.

There are two main types of Echinococcosis. Both are spread through dogs and occasionally by other animals. Both types cause parasite infections of our livers and sometimes other organs. Both can be dangerous, especially to our livers, but both are easily preventable through simple, everyday good hygiene practices.

The name comes from the spines found on Echinococcus. The "Echino" is spiny like a spined animal, such as hedgehogs or sea urchins. The "coccus" refers to a round body, like a seed or berry. The Echinococcus can be seen (under a microscope) to have hooks within the cysts. 

How Can You Get Echinococcus and What Happens When You Do?

The parasite spreads to us when we accidentally eat its eggs. You can do this by:

  • Eating food or drinking water contaminated by the stool (or soil contaminated by the stool) of infected dogs (or other animals). This might mean lettuce or fruit farmed where dogs are.
    • Being in close contact with dogs (or other animals) infected with Echinococcus. This may mean petting, touching, or cuddling animals that may have the tapeworm eggs in their stool which can get on their fur. Note that infections can occur in coyotes, foxes, and rarely cats that eat wild animals.

    Once these eggs are eaten, the parasite can then develop and migrate from the intestines to another organ.

    In the new organ it can form a cyst. This cyst is often found in the liver but it can also be in the lungs or sometimes the spleen, kidneys, bone, heart, brain, or eyes.

    What happens with the cyst depends, in part, on what type of Echinococcus is causing the infection. This cyst can grow and cause problems simply because it gets in the way. This can lead to pain, nausea, and vomiting, especially when its in the liver. The cyst can cause even more problems if it suddenly ruptures, such as when someone is hit in their abdomen. This rupture can release the parasites, creating an allergic reaction—even a severe reaction like anaphylaxis. Other times the parasites can simply continue to invade areas where they shouldn't be, causing medical problems resembling a spreading cancer tumor.

    How Is the Disease Spread and Transmitted?

    The disease is a zoonosis. It spreads between different animals—intermediate hosts (especially sheep, but also goats, pigs, and rodents) and definitive hosts (carnivores that eat these animals, in particular dogs, but also wolves, foxes, and other animals, including sometimes cats).

    Humans just end up in this chain of infection accidentally. 

    The means of transmission depends on the specific type of Echinococcus involved. There are different types that are spread by sheep and other spread by wild rodents, in different areas.

    It's not common in the U.S. but occasionally infections happen. To spread in the U.S. dogs needs to eat infected animals. Depending on the type of Echinococcus this might mean eating infected wild rodents or meat from sheep or goats. Fortunately, livestock can be monitored for this infection and are monitored in the U.S.; dogs rarely become infected from eating meat from farm animals. They also do not usually eat enough infected rodents. The U.S., luckily then, is not at much risk for this infection, though transmission sometimes occurs. There are occasional cases in the Southwest of the US and Alaska.

    That doesn't mean it isn't a problem elsewhere. It can spread without people even being aware they are at risk. Many can get sick without knowing they are infected for years laterl, when it's too late to have stopped the infection from also spreading to friends and family who eat the same food that led to the infection.

    There are unfortunately a lot of ways that the tapeworm can spreads from dogs to people through their stool. This can be from a kid playing with an infected dog. It can be when a dog's stool ends up in a garden or a farmer's field. It's another case for being careful what you eat.

    What Specifically Does Echinococcus Cause?

    There are two different main types of echinococcosis.

    • Cystic echinococcis (CE) is hydatid disease caused by Echinococcus granulosus - also caused hydatidosis.
    • Alveolar echonococcis (AE) is caused by Echinococcus multilocularis. It is found in dogs, as well as foxes and coyotes who are infected, oftentimes by small rodents. In people it can lead to parasites invading the lungs, liver, brain, and other parts of the body. This can lead to death.

    There are also two other types that are rare. These are found in South America (such as Brazil) and Central America.

    • Polycystic echinococcosis is due to Echinococcus vogeli
    • Unicystic echinococcosis due to Echinococcus oligarthrus (which is the rarest form)

    ​The precise symptoms and the disease that follows depends on which type is causing the infection. Your doctor can discuss this with you, if you are diagnosed with this disease.

    Can I Catch Echinococcus From Someone Else?

    Nope. Dogs or other infected animals like coyotes and foxes pass the eggs in their stool. People don't.

    How Long Does Echinococcus Take to Develop?

    It can take 50 years to slowly develop into an illness. Many can carry the parasite without getting sick for years and years.

    Where Is Echinococcus Found?

    These can be found in the Americas (including the West of the US), Africa, China, the Middle East, and parts of southern Europe and Russia.

    The rates of cystic echinococcis are highest in parts of South America, as well as some parts of East Africa, Central Asia, and China. In areas at highest risk in South America, abattoirs (slaughterhouses) may have, in some cases, most animals slaughtered be infected. Prevalence can reach as high as 5-10% in the most affected communities. These most affected communities are usually in rural areas where livestock are raised. The effects include not just the impact on human health - but can also lead to economic loss as the infected animals may lead to less production value for those who depend on livestock for a living.

    Where Is It Found in the US?

    Most cases in the U.S. come from abroad. The disease can take years to develop. Those who have immigrated from (or visited) countries where it is common may develop disease years later.

    Those infected rarely die from it in the U.S. Over the course of 18 years, only 41 deaths were recorded in the US. However, both types of Echinococcus are found in the US. There are occasionally local cases of Hydatid disease (E. granulosus) - especially in Utah and California, as well as Alaska. E. multilocularis is found in wild animals in the US, especially in the Midwest and Alaska.

    How Is Echinococcus Diagnosed?

    Sometimes the infection is diagnosed when someone has liver problems or an enlarged abdomen. Other times the cysts are found by accident on an ultrasound for another reason. The diagnosis can be made through ultrasound but also through Cat Scans, MRI, or blood tests like antibody tests. Biopsies can be performed to identify what is causing the cyst, as it may be thought to be caused by another infection - or even by cancer.

    How Is Echinococcus Treated?

    If you have access to good medical care, it can be safely treated. Like with other parasites, there are now drugs that can help treat the disease. There's also surgical techniques to get rid of the parasite. 

    Good treatment costs a lot. Treatment and prevention (including losses in livestock industry) cost about 3 billion US dollars a year.

    If you or someone you know is to be treated, it's important to have access to care that will be safe and effective, depending on what type of infection is involved. Oftentimes, full surgery can be avoided and the parasites can be aspirated (or vacuumed) out, with the help of ultrasound images. Even aspiration carries risk—an unusual one in particular. Exposure to the parasites, if they were to fall out during aspiration into the abdomen, can lead to a severe allergic reaction: anaphylaxis. As such, any surgical treatment—including aspiration procedures—requires careful consideration and the facilities, supplies, and staff to make it safe.

    How Can You Prevent Echinococcis?

    This disease is a reminder of the need to wash hands, be careful what you eat, and watch out for stray (or outdoor dogs). The risk depends on which type of Echinococcus is found locally. In general though, it's a good idea to:

    • Avoid having stray dogs near farming or livestock
    • Not pet stray dogs or wild animals, like foxes and coyotes.
    • Wash your hands after touching dogs and before eating
    • Keep dogs from eating possibly infected animals (i.e. infected sheep)
    • Carefully control abattoirs 
    • Keep dogs (and cats) from eating wild animals that might be infected
    • Avoid having wild animals as pets or near your home

    On a larger scale:

    • Dogs can be dewormed
    • Food and abattoir inspections can be improved.
    • Public education campaigns can help halt the continued spread in communities where it is common
    • There is also discussion of vaccinating lambs to help halt its spread 
    • Others look to vaccinating dogs to halt the disease's continued transmission

    Sources:

    CDC. Alveolar Echinococcosis (AE) FAQs.

    Bristow BN, et al. Human echinococcosis mortality in the United States, 1990-2007. PLoS Negl Trop Dis. 2012;6(2):e1524.

    D'alessandro A, Ramirez LE, Chapadeiro E, Lopes ER, De mesquita PM. Second recorded case of human infection by Echinococcus oligarthrus. Am J Trop Med Hyg. 1995;52(1):29-33.

    Meneghelli UG, et al. Polycystic hydatid disease (Echinococcus vogeli). Clinical, laboratory and morphological findings in nine Brazilian patients. J Hepatol. 1992;14(2-3):203-10.

    WHO. Echinococcosis.

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