Echinococcus multilocularis

Echinococcus multilocularis is a species of tapeworm that is classified within the Platyhelminthes phylum. It is one of a few worms that cause echinococcosis, a disease that affects many canid species including wolves, coyotes, foxes, jackals, domesticated dogs. Humans can also contract this disease. Adult members of this species can reach an average length of .2 inches, and like other species of tapeworm, its body is segmented by three proglottids. Its head, or scolex, is equipped with suckers and hooks. It is thought that the worm is spreading through Europe and America, although it has not been previously abundant in this area.

Echinococcus multilocularis requires two types of hosts to mature properly. The first is an intermediate or secondary host, which is typically a rodent of some sort, but can be a human. The intermediate host consumes the eggs after feeding on infected food. The eggs travel to the lungs, liver, and other internal organs where they develop into multilocular cysts. Once an intermediate host is consumed by a canid species, the segment or segments eaten move into the small intestine, where they become attached to the tissues and grow. When humans become intermediate hosts, they rarely move the worm forward in development, because canid species do not often eat humans.

Humans that are infected by Echinococcus multilocularis may not show symptoms for several years. After this period, however, hosts may experience nausea, vomiting, headaches, and abdominal pain. Other symptoms include hepatomegaly and jaundice, although this is not common in human hosts. A severe infection in humans, known as alveolar echinococcosis, is caused by larvae of this species and is often deadly. It is common in Europe, China, and Siberia. The infection first attacks the liver, causing a hepatic disorder that resembles a cancer. Like cancer, the disease metastases, spreading throughout the body if not treated quickly. This and other similarities make the disease difficult to treat.

The World Health Organization Informal Working Group on Echinococcosis and the European Network for Concerted Surveillance of Alveolar Echinococcosis have collaborated to create a system of diagnosis, following the Tumor-Node-Metastasis (TNM) that is used in diagnosing stages of liver cancer. This system is called the “PNM” system, and consists of three stages known as parasitic mass, involvement of neighboring organs, and metastasis. It looks at many factors in a host including regional involvement and the abundance of the species in the liver.

Diagnosing a host with an Echinococcus multilocularis infection can be relatively easy, because there is a wide range of tests available to use. These include serological tests like the ELISA test, antibody tests, and indirect hemaglutination (IHA) tests. Other tests include MRI’s, cat scans, X-rays, and ultrasounds. A Casoni test, which looks for intradermal allergic reactions, can also be used to diagnose an infection. Surgery can be used to treat an infection, but it can be difficult to remove all signs of the parasite. Because of this, using a strict treatment of medicines is more common. These medicines include benzimidazoles like albendazole, which stops the spread of the worm but does not kill it, and 2-ME2, which is a natural metabolite of estradiol. This does not kill the worm either, but has shown great promise in treating an infection if used with albendazole. Preventing an infection of this parasite is done by using good hygiene methods like washing food and hands that may have encountered egg infested feces or an infected animal.

Image Caption: Gross pathology of cotton rat infected with Echinococcus multilocularis. First E. locularis isolated in the United States proper. Necropsy. Credit: CDC/Dr. I. Kagan/Wikipedia