Echinococcus granulosus/multilocularis

Echinococcus granulosus is also called the dog tapeworm because dogs are thought to be the definitive host for the worm. Humans are infected through ingestion of the eggs of the parasite in contaminated water, food, soil, or after direct contact with an animal host such as a dog. The eggs are in the feces of the infected dog.

Echinococcus multilocularis, unlike granulosus, has a predilection for the lung are and thus the symptoms are more respiratory like. Echinococcus multilocularis produces an alveolar echininococcosis while Echinococcus granulosus produces a cystic echinococcus also known as hydatid disease or hydatidosis.

Disease / Pathology

The disease Human Echinococcosis is considered a zoonotic disease that is transferred to humans by animals. Humans are pretty much an accidental host or not considered a natural part of the parasites life cycle.

Echinococcus granulosus infections are acquired by the ingestion of the parasite eggs in contaminated water, food, soil, or after direct contact with an infected animal such as a dog. The infectious eggs are deposited in the feces of an infected animal. After the infection of the eggs the eggs undergo development and release infectious larvae. These larvae are active and can spread to different parts of the human body to produce cysts and/or cysticercosus.

The production of these cysts can occur in muscle and brain as well as to other vital organs. These cysts are called cysticerci.

When cyst formation occurs in the brain the term “neurocysticercosus” is used to describe the disease. Nuerological symptoms will occur due to damage to the brain as well as increasing cranial pressure due to the expanding size of the cyst. Cysts can also form in the lung or in/around the liver and/or other adjacent organs. Symptoms are dependent on the pressure exerted by the expanding cyst on organsm.

Liver involvement will produce abdominal pain with nausea and vomiting. While lung involvement will produce chest pain, chronic coughing, and shortness of breath. Patients may experience lethargy, loss of weight and anorexia.

Alveolar echnicococcus is a slowly progressive disease. Lung involvement may be asymptomatic for 5-15 years while incubating. The slow development of a primary tumor-like lesion around the liver is characteristic and will eventually produces symptoms such as abdominal pain, and signs of hepatic failure. Eventually dissemination of the larval metastases to other organs or distal areas … as well as the lung … will increase symptoms based on the parasites location. Left untreated it is progressive and fatal.

Surgical intervention is often needed to remove large cysts that may be located in areas that are perilous to the host. The removal procedure is performed with extreme care as the accidental bursting of the cyst can result in the release of it’s contents (hydatit sand) which is highly antigenic and can induce an anaphylactic shock that can result in death.

Location in the Host

In humans the location in the host is dependent on where the larvae migrated to and cyst formation occurs. The cyst formation is many times seen in the liver, lung, or brain but can occur adjacent to other organs as well.

Geographic Distribution

Echinococcus granulosus can be found in many parts of the world but is most common in the Mediterranean countries, northern African continent, Australia, Southwestern Asian countries, Middle Eastern countries, and select regions of southern South America.

Life Cycle

Echinococcus granulosus has the following life cycle. Important to note is that the parasite’s definitive host is the dog while it’s intermediate host is the sheep or other similar animal of prey. Humans are an accidental host and a dead end to the parasite’s cycle.

Morphology & Diagnosis

Echinococcus granulosus diagnosis is


Echinococcus granulosus protoscolex – photo courtesy of St. Mary’s Hospital Microbiology Laboratory, Waterbury, Connecticut.