Affects: Dogs
Echinococcosis is a parasitic disease caused by tapeworms of the Echinococcus type. The two main types of the disease are cystic echinococcosis and alveolar echinococcosis. Less common forms include polycystic echinococcosis and unicystic echinococcosis.
The disease often starts without symptoms and this may last for years. The symptoms and signs that occur depend on the cyst's location and size. Alveolar disease usually begins in the liver but can spread to other parts of the body, such as the lungs or brain. When the liver is affected, the patient may experience abdominal pain, weight loss, along with yellow-toned skin discoloration from developed jaundice. Lung disease may cause pain in the chest, shortness of breath, and coughing.
The infection is spread when food or water that contains the eggs of the parasite is ingested or by close contact with an infected animal. The eggs are released in the stool of meat-eating animals that are infected by the parasite. Commonly infected animals include dogs, foxes, and wolves. For these animals to become infected they must eat the organs of an animal that contains the cysts such as sheep or rodents. The type of disease that occurs in human patients depends on the type of Echinococcus causing the infection. Diagnosis is usually by ultrasound though computer tomography (CT) or magnetic resonance imaging (MRI) may also be used. Blood tests looking for antibodies against the parasite may be helpful as may biopsy.
Signs And Symptoms: In the human manifestation of the disease, E. granulosus, E. multilocularis, E. oligarthrus and E. vogeli is localized in the liver (in 75% of cases), the lungs (in 5–15% of cases), and other organs in the body such as the spleen, brain, heart, and kidneys (in 10–20% of cases). In people who are infected with E. granulosus and therefore have cystic echinococcosis, the disease develops as a slow-growing mass in the body. These slow-growing masses, often called cysts, are also found in people who are infected with alveolar and polycystic echinococcosis.
The cysts found in those with cystic echinococcosis are usually filled with a clear fluid called hydatid fluid, are spherical, typically consist of one compartment, and are usually only found in one area of the body. While the cysts found in those with alveolar and polycystic echinococcosis are similar to those found in those with cystic echinococcosis, the alveolar and polycystic echinococcosis cysts usually have multiple compartments and have infiltrative as opposed to expansive growth.
Depending on the location of the cyst in the body, the person could be asymptomatic even though the cysts have grown to be very large or be symptomatic even if the cysts are tiny. If the person is symptomatic, the symptoms will depend largely on where the cysts are located. For instance, if the person has cysts in the lungs and is symptomatic, they will have a cough, shortness of breath, and/or pain in the chest.
On the other hand, if the person has cysts in the liver and is symptomatic, they will experience abdominal pain, abnormal abdominal tenderness, hepatomegaly with an abdominal mass, jaundice, fever, and/or anaphylactic reaction. In addition, if the cysts were to rupture while in the body, whether during surgical extraction of the cysts or by trauma to the body, the person would most likely go into anaphylactic shock and have high fever, pruritus (itching), edema (swelling) of the lips and eyelids, dyspnea, stridor, and rhinorrhea.
Unlike intermediate hosts, definitive hosts are usually not hurt very much by the infection. Sometimes, a lack of certain vitamins and minerals can be caused in the host by the very high demand of the parasite.
Cause: Like many other parasite infections, the course of Echinococcus infection is complex. The worm has a life cycle that requires definitive hosts and intermediate hosts. Definitive hosts are normally carnivores such as dogs, while intermediate hosts are usually herbivores such as sheep and cattle. Humans function as accidental
hosts, because they are usually a dead end for the parasitic infection cycle, unless eaten by dogs or wolves after death.
Transmission: As one can see from the life cycles illustrated above, all disease-causing species of Echinococcus are transmitted to intermediate hosts via the ingestion of eggs and are transmitted to definitive hosts by eating infected, cyst-containing organs. Humans are accidental intermediate hosts that become infected by handling soil, dirt, or animal hair that contains eggs.
While there are no biological or mechanical vectors for the adult or larval form of any Echinococcus species, coprophagic flies, carrion birds and arthropods can act as mechanical vectors for the eggs.