Echinococcosis or hydatidosis is a zoonotic larval infection caused by the tapeworm (cestode) Echinococcus. Geographically, the disease has a worldwide distribution with higher prevalence in the Mediterranean, Russia, China, North and East Africa, Australia, and South America. Due to the nature of the pathogen, this disease is more predominant in communities that keep dogs for guarding and herding cattle. There are several identified species of Echinococcosis, four of which are of concern in humans: Echinococcus granulosus, E. multilocularis, E. vogeli, and E. oligarthrus.
The definitive hosts of the cestode are carnivores such as dogs. Humans and other hosts ingest eggs or gravid proglottids that are excreted in the definitive host’s feces, causing the infection. As humans ingest the eggs of the tapeworm, an oncosphere larva releases from the egg, which can penetrate the intestine. Once it penetrates, it gets passively transported via blood or lymphatics to the liver, lungs, or other internal organs where they develop into hydatid cysts (metacestode larvae). In humans, cysts grow slowly and can be up to multiple liters in volume and contain thousands of protoscolices. Over time, septations and daughter cysts disrupt the typical unilocular pattern of echinococcal cysts.
Infected hosts may go on for months or years without showing any signs or symptoms of infection. Some patients have persistent cysts for years without noticing, others cysts may rupture spontaneously or due to trauma and disappear entirely. If a cyst continues growing, patients may exhibit symptoms gradually due to the cyst exerting pressure on surrounding tissue. Sudden signs and symptoms are more likely due to rupture rather than the growth of the cyst. Rupture of the cyst can induce an hypersensitivity reaction in patients, presenting as hives, mucous membrane swelling, and flushing. The reaction can be life-threatening. The nature of signs and symptoms varies depending on the site of the cyst, which is most common in the liver and lungs.
Diagnosis of hydatidosis is achieved by a combination of serologic tests and imaging, usually in conjunction with a history of exposure or immigration from an endemic area. The approach to management and treatment depends on the extent of organ involvement, the number of cysts, and other factors, such as secondary bacterial infection and haemorrhage. Management options range from expectant therapy to invasive surgical intervention: watchful waiting, medical treatment using Albendazole, PAIR (puncture, aspiration, injection, re-aspiration), and surgery in complicated cysts. Education regarding the disease and its mode of transmission is especially crucial in endemic areas. People who work with cattle and dogs should receive education on the transmissibility of the disease and proper ways of dealing with sheep viscera.
References:
Islami Parkoohi P, Jahani M, Hosseinzadeh F, Taghian S, Rostami F, Mousavi A, et al. Epidemiology and Clinical Features of Hydatid Cyst in Northern Iran from 2005 to 2015. Iran J Parasitol. 2018;13(2):310-6.
Mihmanli M, Idiz UO, Kaya C, Demir U, Bostanci O, Omeroglu S, et al. Current status of diagnosis and treatment of hepatic echinococcosis. World J Hepatol. 2016;8(28):1169-81.
Pakala T, Molina M, Wu GY. Hepatic Echinococcal Cysts: A Review. J Clin Transl Hepatol. 2016;4(1):39-46.
