Hydatid Worm, Echinococcus granulosus

The Hydatid Worm (Echinococcus granulosus), also known as the Hyper Tape-Worm, is a species of cyclophyllid cestode that is found in the small intestine of adult canids (canine), but also is found in livestock and humans, which serve as intermediate hosts. This specimen causes Hydatid disease.

The adult Hydatid worm is typically less than 0.25 inches in length and has three proglottids (segments) when intact: the immature proglottid, mature proglottid and gravid proglottid. This specimen, like all cyclophyllids, has four suckers on its head (scolex). It also has a rostellum with hooks.

In canids, the Hydatid worm causes a tapeworm infection and produces eggs that are passed with the dog’s feces. Any organism that ingests the feces serve as intermediate host. In the intermediate host, the eggs hatch into oncosphere larvae that travel through the blood stream and form Hydatid cysts in tissue. These cysts can grow to the size of a softball, or even a basketball, and may contain several smaller “balloons” inside the main cyst. If the outer cyst ruptures, new cysts may form at a different location in the body. Each of these smaller sections contain several juvenile worms, and dogs may eat millions of them, resulting in heavy infection.

Hydatid cysts occur in organs such as the liver, brain and lungs, but not in subcutaneous tissue. Symptoms can include liver enlargement, hooklets in sputum and possible anaphylactic shock when the immune system reacts to ruptured cysts. Hydatid cysts are found using an ultrasound, MRI, or immunoelectrophoresis.

Hydatid disease is treated through surgery, taking care not to rupture the cyst so new cysts cannot form. Once surgery is performed, mebendazole is administered over a long period of time at low dosages. The best way to keep dogs from being infected is to prevent them from eating infected offal (the internal organs and entrails of butchered animals). It is difficult to diagnose the presence of Hydatid worms in canids through microscopy.

Image Caption: Scolex of Echinococcus granulosus from hydatid cyst. Parasite. Credit: CDC/Dr. L.L.A. Moore, Jr/Wikipedia