TABLE 1.

Forms of echinococcosis in humans^a

Name of disease (according to WHO/OIE; [223])	Cystic echinococcosis	Alveolar echinococcosis	Polycystic echinococcosis
Causative agent	E. granulosus	E. multilocularis	E. vogeli	E. oligarthrus
Other names of the disease	Hydatid disease, hydatidosis	Alveolar hydatid disease	E. vogeli echinococcosis, neotropical echinococcosis	E. oligarthrus echinococcosis, neotropical echinococcosis
Adult parasite
Length (mm)	2.0-7.0	1.2-4.5	3.9-5.6	2.2-2.9
No. of proglottids	3 (4-6)	5 (2-6)	3	3
Definitive hosts	Domestic dog, wild canids (coyote, dingo, red fox, etc.)	Red fox, arctic fox, raccoon dog, coyote, domestic dog, cat	Bush dog, domestic dog	Wild felidae: pampas cat, Geoffroy's cat, ocelot, jaguar, cougar, jaguarundi, puma, bobcat
Intermediate hosts	Primarily ungulates, also marsupials	Rodents, other small mammals	Rodents: paca and agouti	Rodents: agouti, spiny rat, paca
Geographic distribution of the parasite	Worldwide	North America, northern and central Eurasia	Central and South America	Central and South America
Larval parasite in humans
Organ localization	Visceral, predominantly liver and lungs	Visceral, primarily liver, metastases in lungs, brain, bones, etc.	Visceral, mainly liver, abdomen, lungs	Orbita, heart
Morphology	Fluid-filled mostly solitary (and less frequently multiple) cysts, unilocular or multichambered, diam 1->15 cm (Fig. 2); often with protoscoleces	Masses of numerous small cysts (diam microscopic up to 3 cm), often interconnected, surrounded by dense connective tissue, no cyst fluid, appearance of cheeselike mass, sometimes with central necrosis (Fig. 7); rarely a few protoscoleces	Polycystic; fluid-filled cysts, diam up to 4-6 cm, solitary, but often aggregated, interconnected and multichambered; thick laminated layer; protoscoleces frequently present	Fluid-filled cysts with tendency for multicystic development, less subdivision than in E. vogeli, and laminated layer thinner; protoscoleces formed.
Type of growth in humans	Concentric expansion	Exogenous proliferation, tumorlike, infiltrative	Exogenous and endogenous proliferation	Expansive, no indication of exogenous proliferation

^aData from references 156 to 158 and 194.