Echinococcosis

Men approximately equal to women.

Echinococcus granulosus causes cystic echinococcosis (hydatid disease) in people exposed to feces of dogs and other canids in endemic areas of nearly every continent.

E. multilocularis causes alveolar echinococcus in people exposed to feces of infected foxes living in colder regions of the northern hemisphere. Cases of alveolar echinococcus continue to expand over the past 2 decades, despite increased awareness of the disease.

E. vogeli and E. oligarthrus cause polycystic echinococcosis in people exposed to feces of infected dogs and wild carnivores in rural Central and South America.

Hydatid cyst rupture leads to anaphylaxis and spread of encapsulated organisms, which implant in exposed tissues (e.g., peritoneal cavity), later causing disseminated hydatidosis (bowel obstruction, cachexia, death)

Failure to resect all echinococcal tissue due to microscopic or extensive disease extension

Hemorrhage (if cyst attached to liver or major blood vessel)

Systemic reactions to toxic agents instilled into cyst cavity; air embolism if cyst attached to a vein or hydrogen peroxide instilled into cyst cavity

Postop jaundice, cholangitis, bacterial superinfection, vascular compression, and hepatic failure

Parasitic disease caused by organism classified as flatworm (adult stage). Parasite cycles through four different stages (adult tapeworm, egg, oncosphere, metacestode) each adapted to maximize survival in the two host organisms:

• Definitive host: Carnivore; intestines contain adult flatworms releasing eggs into feces.

• Intermediate host: Herbivore/omnivore (sheep, small rodents, man); ingests minute amount of feces of definitive host; eggs hatch in stomach and release oncospheres (first larval stage), which penetrate gut blood vessels and distribute to potentially any organ, especially liver and lung. Develop into slowly expanding fluid-filled cysts (metacestodes). Inner (germinal) layer of metacestode buds off tiny encapsulated protoscolices (Gk: juvenile heads) which accumulate to form hydatid sand.

A definitive host eats infected organs of intermediate host; protoscolices are released into intestinal lumen; these evaginate; anterior parts attach to intestinal epithelium and become adult tapeworms.

Adult E. granulosus (2–11 mm) inhabits small intestine of canid (dog, wolf, coyote, dingo, jackal); eggs distribute to grass eaten by sheep, goats, camels, yaks, cattle, pigs, horses, marsupials; man becomes infected via hand-to-mouth contact with fecally contaminated object. Cysts of volume up to 1000 mL form within intermediate host (or man—sometimes called dead end host), physically compromising organ function.

Adult E. multilocularis (1–5 mm) inhabits small intestine of fox (occasionally dog, bush dog, rarely cat); intermediate host usually a rodent. Cysts become multiple and invade target organs.

E. vogeli and E. oligarthrus rarely cause human disease (if present of polycystic type).

Echinococcus granulosus:

• Medical: Cyst instillation with nonspecific histotoxic solution (hypertonic NaCl, alcohol, silver nitrate, povidone-iodine, formaldehyde, hydrogen peroxide, chlorhexidine) in sequence of PAIR. Not appropriate if multiple cysts, cyst architecture subdivided into daughter cysts, or cysts balloon out via narrow passages to form satellite cysts. Increasing in popularity; complications include biliocutaneous fistula and bacterial superinfection of residual cyst cavity. Technique variants include percutaneous evacuation (sometimes using cutting-aspiration device), cyst catheterization/continuous irrigation.

• Laparoscopic: Cystotomy, toxin irrigation, partial cystectomy (± use of aspirator-grinder); 77.16% of hydatid cyst surgeries are laparoscopic, regardless of location; cysts near major vascular structures require open technique.

• Open: Complete resection for concealed, extensive, or invasive disease; attempt to avoid spilling contents; histotoxic solutions often used in conjunction.

Echinococcus multilocularis:

• Exhibits cancer-like growth behavior. Specific immunologic tests in combination with high-performance imaging techniques promise substantial improvements in early diagnosis of alveolar echinococcosis, which is essential for curative treatment, staging, and follow-up. Radical open surgical resection if possible; liver transplantation considered if disease confined to liver. Prevent recurrence by treating infected family companion animals with oral anthelmintic and praziquantel.