Echinococcus on the rise in Bashkiria, Russia
Echinococcus granulosus, the cause of hydatid disease/hydatosis in people, is on the rise in the Bashkiria (Bashkortostan) region of Russia. Fifty-three cases were identified in Bashkiria in 2008, 1.7 times the number of cases reported the year before. Over 500 cases of human infection with Echinococcus are reported in Russia annually.
The original article (translated from Russian) states that the people at risk are those in contact with cattle and other domestic animals. Echinococcus actually causes the same type of disease in cattle and livestock as it does in people – it forms slow-growing cysts in the lungs, liver or other tissues. When the cysts are small they usually don’t cause a problem, but eventually (sometimes even years later) they can grow to a size that interferes with normal organ and body functions. However, people do NOT become infected by contact with cattle, sheep or other intermediate hosts. The infection can only be spread to humans (and livestock) by the definitive host - dogs, including domestic dogs and wild canids. In dogs, the parasite lives in the intestine in the form of a tiny adult tapeworm, and the tapeworm eggs are shed in the dog’s stool. When the eggs are swallowed by an intermediate host, the immature form of the parasite penetrates the intestinal wall and migrates through the body tissues to the site where it ultimately forms a hydatid cyst. If the animal dies or is killed, and the cyst is eaten by a dog, then the cycle begins again.
The most probably reason for the increased number of human infections in this case is an increase in the number of dogs in the same area, particularly those used for herding sheep. This may be equivalent to the dog-reindeer cycle present in Siberia. Echinococcus infection in dogs can be treated with common deworming agents that kill other tapeworms, but it is likely that dogs in these areas are not dewormed as often as they should be to prevent this disease.
The article reiterates some sound recommendations for decreasing the risk of Echinococcus infection. These may sound familiar, because many of them also help decrease the risk of transmission of infectious diseases in general:
- Wash your hands after contact with animals.
- Wash your hands after working in orchards where cattle have wandered (not the most widely applicable recommendation for people living in North America, but is along the same lines as our recommendation to wash your hands after working outside, particularly with soil).
- Do not consume unwashed greens or vegetables (all fruits and vegetables should be thoroughly washed with potable water before being processed or eaten).
- Do not drink water from untreated sources.
More information about Echinococcus and other tapeworms is available in the Worms & Germs Archives.
Photo: Central Asian Shepherd Dog (Sredneaziatskaya Ovcharka), click here for source (Wikipedia).
More about Echinococcus tapeworms in dogs
Echinococcus granulosus is a tapeworm of dogs that causes a condition known as hydatid disease or hydatidosis in humans. The parasite is found in many parts of the world, and is very common in some regions of southern South America, the Mediterranean, the Middle East, southwestern Asia, northern Africa and Australia. To the best of our knowledge, E. granulosus does not occur in southern Ontario, but it is present in other parts of Canada including the western provinces and northern Ontario. A related, but much nastier, tapeworm called Echinococcus multilocularis is much less commonly found in North America.
A previous Worms & Germs post described what is known as the sylvatic cycle of Echinococcus granulosus, which is thought to be a common route of infection for dogs in Canada. In the sylvatic cycle, dogs become infected with Echinococcus by eating the internal organs (usually lungs and liver) of wild game such as moose and caribou. The dogs then pass tapeworm eggs in their stool, which can cause infection in other wild animals (thus continuing the cycle) or in people who accidentally swallow the eggs. In humans, Echinococcus forms slow-growing cysts (called hydatid cysts) in different organs of the body which can be very difficult to remove or treat in some cases.
Echinococcus also has a pastoral or domestic cycle. In this cycle, dogs acquire the parasite by eating the internal organs of infected sheep, and sometimes other livestock such as cattle and swine. This cycle is potentially very important in areas where there is a lot of sheep farming. In some areas of Latin America, 20-95% of sheep at slaughter may have evidence of hydatid cysts in their organs.
It is much more difficult to tell when a dog is infected with Echinococcus compared to other tapeworms such as Taenia or Dipylidium. An adult Echinococcus is tiny - only a few milimetres long (see picture right), very unlike the long, stringy white tapeworms that most people picture. Dogs can carry hundreds, even thousands of these tiny tapeworms without showing any signs of illness at all. The eggs can sometimes be difficult to detect on fecal examinations, and when they are seen they cannot be differentiated from Taenia eggs. Nonetheless, this is still the best way to detect infection, so fecal examinations should be performed regularly.
Remember:
- In areas where Echinococcus is known to exist, it's important to have your veterinarian perform fecal examinations on your dog's stool more frequently than the usual once-a-year, because of the serious zoonotic potential of this parasite.
- Always wash your hands well after handling dog stools.
- Do not let your dog eat uncooked meat, or the organs from farm animals or wild game.
For more information on Echinococcus, see Worms & Germs post entitled Echinococcus and hydatid disease - not your average tapeworm. There is also information available on the Michigan State Department of Natural Resources site.
Lower photo credit: Ontario Veterinary College
Echinococcus and hydatid disease - not your average tapeworm
A previous Worms & Germs post talked about the (very low) zoonotic risk of the tapeworm most commonly found in dogs and cats, Dipylidium caninum. Dogs can also carry other species of tapeworm, such as Taenia pisiformis, which cannot be naturally transmitted to people. But dogs can also carry tapeworms from the genus Echinococcus, the most common of which is E. granulosus. Echinococcus multilocularis is much less common in North America, and can also be carried by cats.
In Canada, dogs tend to be exposed to E. granulosus when they eat certain animals, particularly wild herbivores like moose and caribou. In other parts of the world, eating sheep organs is the most common way dogs are exposed. The immature form of the worm is found in the animal’s lungs, liver and other tissues. After being eaten by the dog, the worm matures in the intestine, and tapeworm eggs can soon be found in the dog’s stool. Tapeworm segments, as seen with Dipylidium infection, are usually not seen in the stool with Echinococcus. Under a microscope, it is possible to tell Dipylidium eggs from Echinococcus eggs, but it is not possible to tell Echinococcus eggs from Taenia eggs.
If a moose, caribou, sheep or another suitable “intermediate host” swallows the eggs from the dog stool, the parasite migrates through the animal’s body and forms cysts in various tissues which contain the immature form of the worm. If the animal dies or is killed, and a dog (or a wolf or coyote or related species) eats the cysts, the cycle begins again.
Unfortunately, humans can also be an “intermediate host” for these tapeworms. If a person ingests Echinococcus eggs from dog stool, the parasite can form cysts (called hydatid cysts) in many tissues and organs, including the liver, lungs, brain and heart. If the cysts are small and there are only a few, they may not cause any problems for years, and the person may never know they’re there. But as the cysts grow, they can get very large and start to interfere with the function of organs, or their size alone may be a problem, depending on where they are located. Treatment can be difficult – drugs are frequently not effective, and large problematic cysts may need to be surgically removed, if the surgery can be done safely. If a cyst bursts it can cause anaphylactic shock, which is very dangerous.
In Canada, Echinococcus infection and hydatid disease are most common in the western provinces. Nonetheless, everyone can take a few simple steps to help prevent exposure of people to Echinococcus:
- Always wash your hands after handling dog stool, even if you use a plastic bag or a scoop to pick it up.
- Your dog should have a fecal examination for intestinal parasites at least once per year, or more frequently if your dog is at increased risk of exposure to Echinococcus. If tapeworm eggs are identified, your veterinarian can prescribe medication to treat the infection.
- Monthly heartworm preventatives that are effective against other intestinal worms are not effective against tapeworms!
- Do not let your dog eat uncooked meat, especially the organs of sheep or wild game such as moose and caribou.
More information on Echinococcus and hydatid disease is available on the CDC’s Echinococcosis webpage.
Tapeworms in dogs and cats
People typically realize their pet has tapeworms when they see small tapeworm segments in the animal's stool. These whitish, rice-sized pieces (called proglottids, see the picture on the right) are parts of the adult tapeworm, which break off and are passed in the stool.
Tapeworms are not usually harmful to dogs and cats, particularly if only one or a few worms are present. In some situations, weight loss can occur. Affected animals may 'scoot' (drag their rear end across the ground) because of irritation from tapeworm segments that are passed in the stool.
Diagnosis of a tapeworm infestation is easiest through identification of tapeworm segments in stool. Identification of tapeworm eggs in stool samples through routine testing used for other intestinal parasites is less useful, as the bare eggs are infrequently shed in stool. Therefore, a negative fecal egg examination does not rule out tapeworms.
Dipylidium infections are extremely rare in people. Children are at greatest risk. Disease in people, if present, is usually mild and easily treated. However, finding tapeworms in a person's stool can be distressing to the individual (and their family). Dipylidium cannot be transmitted directly from animals to people. People and pets get infected by ingesting a flea that is infected with tapeworm larvae. Therefore, flea control is the most important aspect of tapeworm prevention. People that find tapeworm segments in their stool should contact their physician to determine whether they are actually tapeworms (people often mistake other things for tapeworm segments) and to determine whether any treatment is needed.
There are specific dewormers that can be prescribed by your veterinarian to eliminate tapeworms in pets. It is also important to take measures to control fleas and prevent dogs and cats from catching and eating animals that might be carrying fleas.
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