Echinococcus
Echinococcus is a genus of tapeworms that primarily infects carnivorous animals, particularly dogs and foxes, and can lead to serious health issues in humans and herbivores acting as intermediate hosts. The disease caused by Echinococcus is known as echinococcosis, which manifests in several forms depending on the species involved. Echinococcus granulosus is responsible for cystic echinococcosis (CE), characterized by large, fluid-filled cysts that can develop in the liver and lungs, often going undetected for years. Echinococcus multilocularis leads to alveolar echinococcosis (AE), a more aggressive form with multilocular cysts that can be fatal if untreated. E. vogeli and E. oligarthus are associated with polycystic echinococcosis (PE), a less common condition. Transmission typically occurs through the ingestion of eggs shed in the feces of infected carnivores, highlighting the importance of maintaining hygiene in areas where humans and animals coexist. Treatment for echinococcosis often involves a combination of chemotherapy and surgical intervention, with the medications albendazole, mebendazole, and praziquantel being commonly used. Awareness and preventive measures are vital for limiting the spread of these parasites, particularly in regions where livestock and wild animals are present.
Echinococcus
- TRANSMISSION ROUTE: Ingestion
Definition
Echinococcus species are tapeworms of carnivores that cause serious disease in humans and herbivores as intermediate hosts. This disease is known as echinococcosis.
Natural Habitat and Features
Echinococcus species are cestodes (tapeworms) with complex life cycles requiring two mammalian hosts. Their definitive hosts (where sexual reproduction occurs) are carnivores, commonly dogs and foxes. In definitive hosts, the worms remain small, usually less than 6 millimeters in size, and consist of a head and three egg packets or proglottids. Proglottids pass with feces and contaminate the environment, where they are ingested by the intermediate species, typically herbivores and sometimes humans.
After ingestion by herbivores, Echinococcus species eggs develop into oncospheres that can penetrate intestinal epithelium. Once there, they pass into blood or lymph vessels and then travel passively to target organs, usually the liver or lung, but occasionally the spleen, brain, heart, and kidneys. Once there, they form metacestodes, reproductive structures called hydatid cysts. These cysts grow to between 5 and 10 centimeters within one year and can persist and remain viable for years, growing, on occasion, so large they contain several liters of fluid. The cysts contain protoscoleces (called hydatid sand) and are ingested by carnivores, where they develop into adult Echinococcus cestodes.
Pathogenicity and Clinical Significance
The different species of Echinococcus cause different syndromes of disease in humans. E. granulosus causes the oldest known disease, cystic echinococcosis (CE). CE cysts are large, unilocular, and fluid-filled. CE occurs most commonly in humans living pastoral lives in contact with sheep, goats, and dogs. Signs of CE often take years to develop and include abdominal pain occurring when cysts have grown large enough to displace organs. Allergic signs and anaphylaxis can occur with cyst rupture. Treatment is usually a combination of chemotherapy and the surgical removal of cysts. CE is a disease of the Northern Hemisphere, although it can also be found in the Southern Hemisphere as well.
E. multilocularis was recognized as a separate parasite in the nineteenth century that caused a syndrome known as alveolar echinococcosis (AE). E. multilocularis is most often found in foxes and rodents. AE cysts differ from CE because they are multilocular, solid, and frequently pulmonary. Signs are similar to CE, but pulmonary AE also causes coughing. AE is more likely to be fatal. Treatment of AE is usually a combination of chemotherapy and the surgical removal of cysts. AE is a disease of the Northern Hemisphere and suburban regions where humans and wildlife are close.
E. vogeli and E. oligarthus cause polycystic echinococcosis (PE). PE cysts tend to be small. The disease is not well characterized because it has only recently been recognized; also, only a few cases have been described. Treatment is usually chemotherapy. PE occurs in Central America and South America.
Drug Susceptibility
Albendazole, mebendazole, and praziquantel are drugs used to treat echinococcosis. High doses are used, and treatment may last for years or even be lifelong.
Bibliography
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Marie, Chelsea, and William A. Petri, Jr. "Echinococcosis - Merck Manual Professional Edition." Merck Manuals, Nov. 2023, www.merckmanuals.com/professional/infectious-diseases/cestodes-tapeworms/echinococcosis. Accessed 8 Nov. 2024.
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