Echinococcosis (Hydatid disease) refers to human infection by the immature (larval) form of tapeworm, Echinococcus. One of three forms of the Echinococcus spp., E. granulosus, lives on dogs and livestock, and infects humans through contact with these animals. Allergic reactions and damage to various organs from cyst formation are the most common forms of disease in humans.
E. granulosus is found in many areas of Africa, China, South America, Australia, New Zealand, and Mediterranean and eastern Europe, as well as in parts of the western United States. The parasite lives in regions where dogs and livestock cohabitate. Direct exposure to infectious dogs as well as parasitic eggs released into the environment during shedding are both sources of human infection.
In humans, cysts containing the larvae develop after ingestion of eggs. Cysts form primarily in the lungs and liver. Cysts developing in the liver are responsible for about two-thirds of echinococcosis cases. Echinococcosis is a significant public health problem in many areas of the world, but control programs have decreased the rate of infection in some regions. In Kenya alone, the numbers of persons infected each year is as high as 220 per 100, 000 population.
Causes and symptoms
After ingestion, the eggs develop into embryos within the intestines and then travel to the liver and lungs through major blood vessels. The embryos then begin to form cysts within the liver and lungs, causing damage as they enlarge over a period of five to 20 years. Cysts may become over 8 in (20.3 cm) or more in size and contain a huge amount of highly allergenic fluid. Studies show that while the liver is most often targeted, lungs, brain, heart, and bone can also be affected.
The major symptoms are due to compression damage, blockage of vessels and ducts (such as the bile ducts), and leakage of fluid from cysts. The following symptoms are frequent.
Liver involvement causes pain and eventually jaundice or cholangitis due to blockage of bile ducts. Infection of cysts leads to abscesses in up to 20%.
Lung cysts cause cough and chest pain.
Bone cysts cause fractures and damage to bone tissue.
Heart involvement leads to irregularities of heart beat and inflammation of the covering of the heart (pericardium).
Allergic reactions occur from leakage of cyst fluid that contains antigens. Itching, fever, and rashes are frequent, and fatal allergic reactions (anaphylaxis) have been reported. Eosinophils, which are blood cells involved in allergic reactions, are increased in many patients.
David Kaminstein MD, The Gale Group Inc., Gale, Detroit,