Chapter 3Infectious Diseases Related To Travel
Pedro L. Moro, Peter M. Schantz
Echinococcosis (hydatid disease) is the infection of humans by the larval stages of taeniid cestodes of the genus Echinococcus. Of 6 species recognized, 4 are of public health concern: Echinococcus granulosus, causing cystic echinococcosis; E. multilocularis, causing alveolar echinococcosis; and E. vogeli and E. oligarthrus, both causing polycystic echinococcosis.
E. shiquicus in small mammals from the Tibetan plateau and E. felidis in African lions are 2 recently identified species whose zoonotic transmission potential is unknown.
MODE OF TRANSMISSION
The life cycle of Echinococcus species involves carnivores as final hosts and herbivores as intermediate hosts. Certain human activities (such as the widespread rural practice of feeding viscera of home-butchered sheep to dogs) facilitate transmission of the parasite, and consequently raise the risk that humans will become infected. Dogs infected with Echinococcus tapeworms pass eggs in their feces, and humans become infected through fecal-oral contact, particularly in the course of playful and close contact between children and dogs. Indirect transfer of eggs, either through contaminated water and uncooked food or through the intermediary of flies and other arthropods, can also result in infection of humans.
E. granulosus is prevalent in broad regions of Eurasia, several South American countries, and Africa. In North America, most cases are diagnosed in immigrants from endemic countries. The disease seems to have reemerged in Bulgaria, where the incidence of cystic echinococcosis in children increased from 0.7 to 5.4 per 100,000 population per year between the 1970s and the mid-1990s, after the collapse of control efforts. In Wales, the prevalence of infected dogs more than doubled between 1993 (3.4%) and 2002 (8.1%), after the implementation of policy changes favoring health education over weekly dosing of dogs with praziquantel. E. multilocularis is endemic in the central part of Europe, parts of the Near East, Russia, the Central Asian Republics, China, northern Japan, and Alaska. Recent findings show major endemic areas for E. granulosis and E. multilocularis in China. E. vogeli is indigenous to the humid tropical forests in central and northern South America. In endemic areas, hunting dogs are often fed the raw viscera of pacas; dogs thus infected may then expose humans. A small number of polycystic echinococcosis cases in these geographic areas are caused by E. oligarthrus.
Cystic Echinococcosis or Cystic Hydatid Disease
In humans, hydatid cysts of E. granulosus are slowly enlarging masses comparable to benign neoplasms; most human infections remain asymptomatic. The clinical manifestations are variable and are determined by the site, size, and condition of the cysts. Hydatid cysts in the liver and the lungs together account for 90% of affected localizations.
Alveolar Echinococcosis or Alveolar Hydatid Disease
The embryo of E. multilocularis seems to localize invariably in the liver of the intermediate host. The hepatic parenchyma is gradually invaded and replaced by fibrous tissue in which great numbers of vesicles, many microscopic, are embedded. Patients eventually succumb to hepatic failure, invasion of contiguous structures, or less frequently, metastases to the brain.
Polycystic Echinococcosis or Polycystic Hydatid Disease
Relatively large cysts develop over years and are primarily found in the liver and occasionally in the thorax or abdominal cavity. Those who are symptomatic may present with a painful right hypochondrial mass, progressive jaundice, or as in the other forms of disease, with liver abscess.
A presumptive diagnosis can be made on the basis of imaging studies, such as a CT scan, and sometimes lesions are found incidentally in an asymptomatic person. Serologic assays may also be performed, and newer ones are under development. Additional information and diagnostic assistance is available through CDC’s Division of Parasitic Diseases and Malaria (www.dpd.cdc.gov/dpdx).
Travelers should consult an infectious disease or tropical medicine specialist for diagnosis and treatment. Surgical removal of hydatid cysts remains the treatment of choice in many countries, and it is the preferred treatment when liver cysts are large (>10 cm in diameter), secondarily infected, or located in certain organs (brain, lung, or kidney). Puncture, aspiration, injection, reaspiration (PAIR) is a minimally invasive technique used to treat liver cysts and other abdominal locations. It is less risky and less expensive than surgery. Approximately 30% of patients treated with albendazole become cured after 3–6 months (complete and permanent disappearance of cysts), and even higher proportions (30%–50%) demonstrate significant regression of cyst size and alleviation of symptoms. However, 20%–40% of cases do not respond favorably. Albendazole should be given orally at a dose of 10–15 mg/kg/day, in 2 divided doses, with a fat-rich meal to increase bioavailability. It should be administered continuously. An intermittent treatment schedule has been recommended in the past, but evidence suggests that continuous treatment may be equally effective. Benzimidazoles (albendazole, mebendazole) should be given to prevent recurrence after surgery or PAIR. With or without surgery, alveolar hydatid disease has a high case-fatality rate. Long-term treatment with a benzimidazole inhibits growth of larval E. multilocularis, reduces metastasis, and enhances both the quality and length of survival; prolonged therapy may eventually be larvicidal in some patients. The principles of management for cystic and alveolar echinococcoses also apply to polycystic echinococcosis.
PREVENTIVE MEASURES FOR TRAVELERS
No vaccine is available for humans, and no drugs are recommended as chemoprophylactic agents. Travelers should avoid contact with dogs or wild canids while in endemic areas. Untreated water from streams, canals, lakes, and rivers may contain Echinococcus eggs. Heating potentially contaminated food and water at >140°F (60°C) for at least 30 minutes destroys the eggs.
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- Wilson JF, Rausch RL. Alveolar hydatid disease. A review of clinical features of 33 indigenous cases of Echinococcus multilocularis infection in Alaskan Eskimos. Am J Trop Med Hyg. 1980 Nov;29(6):1340–55.
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