New aspects of neotropical polycystic (Echinococcus vogeli) and unicystic (Echinococcus oligarthrus) echinococcosis

Abstract

Of the four species of the genus Echinococcus (Cestoda) distinguished by biological and morphological characteristics, two species, E. vogeli and E. oligarthrus, occur widely in the Neotropics. Approximately 200 cases of polycystic echinococcosis (PE) have been recorded from 12 countries in South America. Following early proliferation of E. vogeli in the human host, typically in the liver, the metacestode usually spreads in the peritoneal and pleural cavities, and numerous organs may be invaded. The clinical characteristics of PE in 81 patients with sufficient information are reviewed. Type I disease consists of polycysts in the liver and abdominal cavity (37% of the patients had this characteristic); type II is similar to type I but also includes hepatic insufficiency (26%); type III consists of cysts in liver and chest (14%); type IV consists of cysts only in the mesenteries (16%); and type V consists of cysts calcified in liver and lung (4%). The percentage of patients with polycysts in the liver was 81%, and the percentage of patients with polycysts in the chest was 14%. PE is most ready diagnosed by geographic origin of the patient and by means of ultrasound or computerized tomography scanning showing cysts and calcifications. The highest mortality was for patients with type II disease, due to hepatic failure and its complications. There were five patients who died due to surgical accidents, whereas 35 cases had uncomplicated surgery. Twenty-three patients died of PE, making the total mortality 29% (23 of 78 cases). None of the 13 patients treated only with albendazole, the most efficacious treatment, was completely cured. PE represents a severe medical problem in South America. A reevaluation of the characteristics of the metacestode of E. oligarthrus indicated that it is unicystic. Only three human cases are known (two with infection in the orbit and one with infection in the heart). The metacestode of E. oligarthrus, in contrast with that of E. vogeli, consists of a spherical, fluid-filled vesicle that enlarges concentrically and is not known to undergo exogenous proliferation.

FIG. 1.

Life cycle of Echinococcus vogeli in neotropical forests and the course of domiciliary transmission to humans.

FIG. 2.

The bush dog, final host of Echinococcus vogeli. (Reprinted with permission of the Los Angeles Zoo.)

FIG. 3.

The paca, intermediate host of Echinococcus vogeli. (Courtesy of Ignacio Borero, University del Valle, Cali, Colombia.)

FIG. 4.

Strobilar stage of Echinococcus oligarthrus (length, 2 mm) from a naturally infected jaguarundi from Colombia.

FIG. 5.

Strobilar stage of Echinococcus vogeli (length, 12 mm) from an experimentally infected domestic dog.

FIG. 6.

Metacestode of Echinococcus vogeli in the liver of a paca kept as a pet in a household in Carimagua, Colombia.

FIG. 7.

Transected metacestode of Echinococcus vogeli, showing brood capsules and other tissues, in the liver of a naturally infected paca, El Porvenir, Colombia.

FIG. 8.

Vesicles of Echinococcus vogeli in the mesentery near the caecum in a naturally infected paca, Carimagua, Colombia.

FIG. 9.

Proliferating vesicles of Echinococcus vogeli from the peritoneal cavity of an experimentally inoculated Mongolian gerbil. (Reprinted from reference with permission of the publisher.)

FIG. 10.

Polycystic echinococcosis in the human liver (fatal case, from a resident of Panama). (Courtesy of Octavio Sousa, Centro de Investigación y Diagnóstico de Enfermedades Parasitarias, Facultad de Medicina, República de Panamá.)

FIG. 11.

Portion of the wall of a polycystic lesion, showing germinal and laminated membranes (rightmost arrows) and accumulated dead eosinophils (larger arrow) between the metacestode and the fibrotic pericyst (hematoxylin-eosin stain).

FIG. 12.

Section of biopsy specimen from a human liver (from the 58-year-old female case from reference 12), containing part of a polycystic lesion, showing a granulomatous reaction with palisaded histiocytes (periodic acid-Schiff stain).

FIG. 13.

Macroscopic appearance of polycystic vesicles removed from the omentum of a patient (58-year-old female case from reference 12) by palliative surgery. (Reprinted from reference with permission from Elsevier.)

FIG. 14.

Abdominal posteroanterior X ray, showing three small, round calcifications (arrows) in a polycystic lesion involving the liver and omentum (from the 58-year-old female case from reference 12). (Reprinted from reference with permission from Elsevier.)

FIG. 15.

Ultrasonic image of a liver, showing polycystic lesions (from the 58-year-old female case from reference 12). The anechoic vesicles were round and of different sizes, with regular walls. (Reprinted from reference with permission of the publisher.)

FIG. 16.

CT scan, demonstrating vesicles of Echinococcus vogeli in the abdomen (from the 58-year-old female case from reference 12). The vesicles are hypodense and round to oval. The intestine has been displaced against the posterior wall. (Reprinted from reference with permission from Elsevier.)

FIG. 17.

Polycystic lesion of the pericardium, the frontal section (from the 22-year-old male case from reference 12). (Reprinted from reference with permission of the publisher.)

FIG. 18.

Posteroanterior X ray of the thorax, indicating right pulmonary lobe and left and right pericardial tumors (arrows). From the first X-ray study of case no. 1 (from the 22-year-old male case from reference 12), subsequently proved to be polycystic echinococcosis. (Reprinted from reference with permission of the publisher.)

FIG. 19.

CT scan, made 5 years after surgery (from the 22-year-old male case from reference 12), showing hypodense, round polycystic vesicles, mainly posterior in the right hepatic lobe and right lung. Triangular calcifications are evident in the liver. (Reprinted from reference with permission from Elsevier.)

FIG. 20.

Palpebral ptosis and chemosis in a child with a retro-ocular unicyst of Echinococcus oligarthrus. (Reprinted from reference with permission of the publisher.)

FIG. 21.

CT scan of the young patient shown in Fig. 20, indicating the liquid-filled, retro-ocular unicyst (four dots). (Reprinted from reference with permission of the publisher.)

FIG. 22.

CT scan of a patient with polycystic echinococcosis (from Brazil), treated with albendazole alone. (Top) Pretreatment, rounded, hypoechoid formations in the peritoneum and hepatic parenchyma. (Bottom) Reduction in number and size of vesicles 70 days after the beginning of treatment. (Courtesy of Ulysses G. Meneghelli, Departamento de Clinica Médica, Facultad de Medicina de Ribeirâo Preto, Brazil.)

FIG. 23.

Large rostellar hooks from protoscoleces of Echinococcus vogeli, E. oligarthrus, and E. granulosus (left to right, all at the same magnification).

FIG. 24.

Aerial view of gallery forest in the oriental plains of Colombia. (Reprinted from reference with permission of the publisher.)

FIG. 25.

Map of Central America and South America, indicating the geographic range of the bush dog, as compiled from various sources.

FIG. 26.

Map of Central America and South America, showing the geographic ranges of the paca and agoutis. (Reprinted from reference with permission from Elsevier.)

FIG. 27.

Metacestodes of Echinococcus vogeli in the liver of an adult nutria (body weight, 5.1 kg), examined 50 days after receiving gravid proglottids from a domestic dog. The dog 129 days previously had received metacestodes from a naturally infected paca captured at Carimagua, Colombia.