Echinococcus granulosus

Cystic echinococcosis is caused by infection with the larval stage of a tapeworm called Echinococcus granulosus. More than 1 million people annually are infected with E granulosus worldwide. Endemic regions include western China, Central Asia, South America, Mediterranean countries, and east Africa. Cystic echinococcosis is rare in the United States and typically occurs in immigrants from endemic countries. 

Definitive hosts for E granulosus are domestic or wild dogs and wolves (canids), who become infected after eating animal organs containing hydatid cysts. Inside canids, the cysts develop into adult tapeworms, which shed eggs in their stool. Intermediate hosts, such as sheep, goats, pigs, and cattle become infected after ingesting tapeworm eggs in contaminated soil, food, or water. After ingestion, the eggs hatch and penetrate the intestinal wall, migrate through blood or lymph vessels to organs, where they develop into hydatid cysts that enlarge and produce more cysts. 

Approximately 70% of adults have liver cysts and 10 to 30% have pulmonary cysts. Children more commonly have pulmonary cysts. Less commonly, cysts develop in the brain, spleen, kidney, pancreas, and heart. Complications arise from organ compression, cyst rupture, superinfection, and allergic reactions such as urticaria, angioedema, and anaphylaxis. Ruptured pulmonary cysts result in productive cough, empyema, and hydropneumothorax. 

The diagnosis of cystic echinococcosis relies on history, imaging, cytology, and serology. Approximately 25% of patients have eosinophilia. Fine needle aspirates of cystic fluid can be performed, but increase the risk of cyst puncture and leakage, producing severe allergic reactions. 

The diagnosis can be confirmed by detection of IgG antibodies to Echinococcus by an enzyme linked immunoassay. A negative result indicates the patient has not been exposed to this tapeworm. Positive results suggest infection with Echinococcus. Cysts localized to the lungs, brain, or spleen are less likely to stimulate detectable antibody concentrations. False positive reactions may occur in patients infected with other helminths such as Tania, Schistosome, and Strongyloides species. 

References

Shen Y, et al. A child with large pulmonary and liver cysts. JAMA, July 25, 2023, 330:372-373.

Agudelo Higuita NI, Brunetti E, McCloskey C. Cystic Echinococcosis. J Clin Microbiol. 2016;54(3):518-523

Sarkari B, Rezaei Z. Immunodiagnosis of human hydatid disease: Where do we stand? World J Methodol. 2015;5(4):185-195