Clinical Information

Echinococcosis, also referred to as hydatidosis or hydatid disease, is 1 of the 17 neglected tropical diseases recognized by the World Health Organization and affects over 1 million people worldwide. Echinococcus species are tapeworms or cestodes, and 2 main species infect humans: Echinococcus granulosus and Echinococcus multilocularis.

With respect to geographic distribution, E granulosus can be found worldwide but, more frequently, is found in rural grazing areas where dogs may feed on infected sheep or cattle carcasses. E multilocularis is largely localized to the northern hemisphere. The definitive hosts for E granulosus are dogs or other canids, while the definitive host for E multilocularis are foxes and, to a much lesser extent, canids. Echinococcus tapeworms reside in the small intestine of definitive hosts and release eggs that are passed in the feces and ingested by an intermediate host, typically sheep or cattle in the case of E granulosus or small rodents for E multilocularis. The eggs hatch in the small bowel, releasing an oncosphere that penetrates the intestinal wall and migrates through the circulatory system to various organs where it develops into a cyst that gradually enlarges, producing protoscolices and daughter cysts, which fill the interior. The definitive host becomes infected following ingestion of these infectious cysts. Humans become accidentally infected following ingestion of Echinococcus eggs.

In humans, E granulosus (cystic echinococcal disease) cysts typically develop in the lungs and liver. The infection may remain silent or latent for years (5-20 years) prior to cyst enlargement and symptom manifestation. Symptomatic manifestations include chest pain, hemoptysis, and cough for pulmonary involvement and abdominal pain and biliary duct obstruction for liver infection. E multilocularis (alveolar echinococcal disease) infections manifest more rapidly than those of E granulosus and similarly to a rapidly growing, destructive tumor, resulting in abdominal pain and biliary obstruction. Rupture of cysts can produce fever, urticaria, and anaphylactic shock.

Diagnosis of echinococcal infections relies on characteristic findings by ultrasound or other imaging techniques and serologic findings. Fine-needle aspirates of cystic fluid may be performed; however, they carry the risk of cyst puncture and fluid leakage, potentially leading to severe allergic reactions. Importantly, infected individuals do not shed eggs in stool.