Echinococcus granulosus (and multilocularis) Sarah Richards Max Karpyak

Three Species  Echinococcus granulosus: causing hydatid disease  Echinococcus multilocularis: causing alveolar hydatid disease  Echinococcus vogeli: causing hydatid disease

Echinococcus multilocularis vs Echinococcus granulosus  Both produce hydatid disease in many mammals, including rodents and humans  Unlike E. granulosus, E. multilocularis produces many small cysts that spread throughout the infected animal

Geographic Distribution  Worldwide  Higher prevalence in South America (Argentina, Uruguay), Europe (Mediterranean bassin), Northern Africa, Middle East, South Central and East Asia

Larvae Stage  E. granulosus  Hydatid cysts are large, roughly spherical, fluid filled hollow bladders containing numerous protoscolices.  They vary in size; those found in the liver are aprox. 20 cm in diameter, but those found in the peritoneal cavity are usually larger  E. multilocularis  The cyst grows invasively by external budding, forming a diffuse growth through the infected organ, replacing that organs tissues. In contrast to E. Granulosus this growth is very rapid, infective prosocialises being present only 2 to 3 months.

Adult Stage  E. multilocaris  Slightly smaller than E. granulosus (max. length of aprox 4 mm and consisting of 4-5 proglottids).  E. granulosus  The adult parasites in the dog represent one of the smallest of the tapeworms (3-9 mm in length, usually with 3 proglottids).  Scolex is globular in shape and has a prominent rostellum

Definitive Hosts E. granulosus  Dogs  Coyotes  Wolves E. multilocularis  Mostly foxes

Intermediate Hosts E. granulosus  Sheep  Horses  Camels  Pigs  Humans E. multilocularis  Small rodents

Life Cycle: E. granulosus  The adult is in the small bowel of the definitive host  Gravid proglottids release eggs that are passed in the feces  In the intermediate host the egg hatches in the small bowel and releases an oncosphere  The oncosphere penetrates the intestinal wall and moves through the circulatory system to various organs  In the organs they develop into cysts and enlarge gradually  The cysts produce protoscolices and daughter cysts  Definitive host eats the infected organs and becomes infected  After ingestion, the protoscolices evaginate, attach to the intestinal mucosa and develop into adult stages  In days, the cycle starts over

Life Cycle: E. multilocularis  The life cycle is basically the same E. granulosus Except  There are different definitive and intermediate hosts  Larval growth in the liver remain indefinitely in the proliferative stage, which causes invasion of the surrounding tissues (sometimes this can take over the whole organ)

Life Cycle (cont’d)

Diagnosis  Diagnosis in the definitive host is difficult by ordinary microscopy because it will look a lot like Taenia and Echinococcus eggs  Detection of antigens in feces by ELISA is currently the best available technique  Newer techniques like polymerase chain reaction (PCR) is also used to identify the parasite from DNA isolated from eggs or feces

Treatment  Surgery: with the goal of leaving the cyst intact so new cysts do not form  Mebendazole can be taken over a long period of time at low dosages  Praziquantel

Prevention  The best way to keep dogs from being infected is to prevent them from eating infected feces, or contaminated meat  The best way to avoid human infection is to avoid ingesting food or other substances contaminated with dog feces

Prevention (cont’d)  The best method is to disrupt the lifecycle  Basic hygiene practices  Avoid feeding raw offal (internal organs of butchered animals) to dogs  By doing this hydatids have been virtually eliminated in New Zealand (a once common place for this parasite)

QUESTIONS

 1. What are the main differences between the larvae stage of E. granulosus and E. multilocularis?

 E. granulosus  Hydatid cysts are large, roughly spherical, fluid filled hollow bladders containing numerous protoscolices.  They vary in size; those found in the liver are aprox. 20 cm in diameter, but those found in the peritoneal cavity are usually larger  E. multilocularis  The cyst grows invasively by external budding, forming a diffuse growth through the infected organ, replacing that organs tissues. In contrast to E. Granulosus this growth is very rapid, infective prosocialises being present only 2 to 3 months.

2. What are the definitive hosts for each parasite?

E. granulosus  Dogs  Coyotes  Wolves E. multilocularis  Mostly foxes