Echinococci belong to cestodes and are parasitic in canines.
Cystic echinococcosis is caused by Echinococcus granulosus and alveolar echinococcosis by Echinococcus multilocularis. In addition, 6 other, more rare Echinococcus species have been characterized.
Transmission
Dogs and other canines (raccoon dogs, wolves, foxes) act as the final hosts of echinococci and the eggs are excreted in their faeces.
The intermediate hosts (e.g. sheep, reindeer, moose, small rodents, and also humans as incidental hosts) acquire the infection by ingestion of food that has been contaminated with faeces of the final host. The larval stages of the parasite are transported through the intestinal wall, usually into the liver and lungs, where they form a hydatid cyst. Over the years, the cyst may reach a diameter of several centimetres.
The meat of the intermediate host (e.g. reindeer, moose) is not infective for humans. Dogs and other canines may become infected by eating contaminated meat, including offal.
Epidemiology
Cystic echinococcosis is encountered worldwide, especially in areas where dogs are fed with offal.
Alveolar echinococcosis is encountered in the northern hemisphere, especially foxes and arctic foxes being the principal hosts, but also other canines may act as hosts. In many Central European countries, alveolar echinococcosis is the most common tissue parasitic disease. In Scandinavia, it is rare in animals; sporadic fox infestations have been reported in Sweden.
Symptoms
Cystic echinococcosis
The cysts cause no symptoms for a long time and are often found accidentally, e.g. in ultrasonography of the liver. A cyst may be as large as over 10 cm in diameter.
The cysts may cause compression symptoms depending on their location, most often in the liver or lungs but also in the central nervous system, bones etc.
A cyst rupture may result in anaphylactic reaction or haemoptysis (pulmonary cyst).
Alveolar echinococcosis
In humans, the disease caused by Echinococcus multilocularis progresses more rapidly and is more difficult to treat than cystic echinococcosis.
The cysts formed by the parasite are multilocular and have an invasive mode of growth.
Also otherwise, the infection has a cancer-like character and may, for example, send ”metastases” to other organs.
Diagnosis
The diagnosis is based on finding a typical cyst with radiographic imaging (ultrasound, chest radiograph, CT or MRI) in a patient with a history of exposure.
Differential diagnostics concerning other, usually more common cystic diseases is important.
The presence of echinococcus antibodies confirms the diagnosis, but a negative assay does not rule out echinococcosis.
Cyst specimens obtained by surgery or aspiration can be examined in a parasitologic laboratory. Puncture with albendazole protection (to prevent spreading) is a possible procedure but rarely used without concomitant PAIR treatment (see below). A consultation with a parasitologist is recommended before sample taking.
Inspection of a faecal sample for the presence of parasites is of no value.
Echnicoccosis is in some countries a notifiable disease. Find out about local policy.
Treatment options
The choice of therapeutic approach is based on the size, location and structure of the cyst.
The main treatment options in cystic echinococcosis include follow-up observation without treatment, chemotherapy with albendazole (may require special license), PAIR procedure Aspiration of Hepatic Hydatid Cysts (puncture and aspiration of the cyst in albendazole coverage under ultrasound control, fill-up with hypertonic saline solution and reaspiration), aspiration through a catheter (under albendazole coverage), or surgical excision of the intact cyst (in albendazole coverage; breakage should be avoided).
At the initial stage of alveolar echinococcosis, extensive surgical removal is the only good treatment option. There are no good alternatives, even if albendazole has been reported to be beneficial in some cases.
Proper food hygiene, especially appropriate slaughtering procedures, inspection of game meat
References
Tamarozzi F, Nicoletti GJ, Neumayr A et al. Acceptance of standardized ultrasound classification, use of albendazole, and long-term follow-up in clinical management of cystic echinococcosis: a systematic review. Curr Opin Infect Dis 2014;27(5):425-31. [PubMed]