Echinococcosis overview On the Web
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Echinococcosis is a chronic infection caused by the larval stage of several animal cestodes (tapeworms) of the genus Echinococcus. There are two predominant forms of echinococcosis, cystic echinococcosis caused primarily by E. granulosus and alveolar echinococcosis caused by E. multilocularis. The disease is transmitted to humans by infected domestic or wild dogs, which are the definitive hosts, and is seen most commonly in livestock-producing areas of the Middle East, Africa, Australia, New Zealand, Europe, and the Americas, including the southwestern U.S. Uncomplicated cystic echinococcosis is generally asymptomatic but may cause mass effect with signs of an enlarging mass lesion in a visceral site such as the liver, lungs, kidneys, bone, or CNS. Occasional cyst rupture may cause allergic manifestations such as urticaria, angioedema, or anaphylaxis that bring the patient to medical attention. Additionally, in the case of rupture, secondary bacterial infection may occur, or fistulas may develop (for example, cystobiliary). In the patients suspected of echinococcosis, enzyme-linked immunosorbent assay (ELISA) and the indirect hemagglutination test are highly sensitive procedures for the initial screening of serum for cystic echinococcosis. Treatment modalities for echinococcosis include percutaneous intervention, surgery, chemotherapy, and observation.
Goeze accurately described the echinococcosis cysts and the tapeworm heads for the first time in 1782. Later Batsch gave a detailed description of E. granulosus in 1786. Rudolf Leuckart identified E. multilocularis for the first time in 1863.
Echinococcosis is classified based on the site of infection and the type of tapeworm causing the infection into cystic echinococcosis and alveolar echinococcosis. Echinococcosis can also be classified based on the ultrasound findings and appearance.
The transmission of echinococcosis from the definite host to the intermediate host is by ingestion of embryonated eggs passed in the feces. Once the eggs are ingested they hatch in the small intestine and develop into onchospheres. There oncospheres reach various organs by migration through the vascular system and develop into cysts producing protoscolices. The definitive host is infected by ingestion of the organs infected with the cysts. After ingestion of the cysts they evaginate and invade the intestinal mucosa and develop into adult worms.
Human echinococcosis (hydatidosis or hydatid disease) is caused by the larval stages of cestodes (tapeworms) of the genus Echinococcus. Echinococcus granulosus causes cystic echinococcosis (CE), the form most frequently encountered; E. multilocularis causes alveolar echinococcosis (AE); E. vogeli causes polycystic echinococcosis; and E. oligarthrus is an extremely rare cause of human echinococcosis. Echinococcus eggs contain an embryo that is called an oncosphere or hexcanth. From the embryo released from an egg develops a ''hydatid cyst'', which is able to survive within organs for years. Echinococcus adult worms develop from protoscolices and are typically 6mm or less in length and have a scolex, neck and typically three proglottids.
Differentiating Echinococcosis from other Diseases
Cystic echinococcosis must be differentiated from other diseases presenting with similar features of right sided abdominal pain such as pyogenic liver abscess and amoebic liver abscess and fungal liver abscess.
Epidemiology and Demographics
In endemic areas such as eastern part of the Mediterranean region, Northern Africa, Southern and Eastern Europe, at the southern tip of South America, in Central Asia, Siberia and Western China, the incidence of echinococcosis is more than 50 per 100,000 persons.
According to WHO guidelines, screening for echinococcosis is recommended for all the population in endemic areas who are at risk. Portable ultrasound machines are frequently used for screening patients in communities. Sometimes a serological testing (ELISA) is often employed which is followed by a western blot in all positive cases.
Natural History, Complications and Prognosis
If left untreated, alveolar echinococcosis is progressive and can disseminate to other organs systems eventually leading to various clinical syndromes that can lead to death. Complications that can develop as a result of echinococcosis are pulmonary embolism, focal cerebral disorders (seizures, hemiparesis, aphasia), obstructive jaundice, adrenal dysfunction. The prognosis of echinococcosis is good with treatment. Without treatment, echinococcosis is associated with a 10-year mortality of 90%.
History and symptoms
Persons with echinococcosis often remain asymptomatic. The clinical presentation of echinococcosis infection depends upon the site of the cysts and their size. The cysts are mainly found in the liver and lungs but can also appear in the brain, eyes, spleen, kidneys, heart, bone, and central nervous system. Cyst rupture is most frequently caused by trauma and may cause mild to severe anaphylactic reactions, even death, as a result of the release of cystic fluid.
In the patients suspected of echinococcosis enzyme-linked immunosorbent assay (ELISA) and the indirect hemagglutination test are highly sensitive procedures for the initial screening of serum for cystic echinococcosis. In case of alveolar echinococcosis serologic test results are usually positive at high titers. Comparing a patient’s titers with both purified-specific and shared antigens permits the serologic discrimination between patients infected with E. multilocularis and those infected with E. granulosus.
Radiography imaging permits the detection of hydatid cysts in the lungs; however, in other organ sites, calcifications can be visualized. On a chest X-ray, cysts are well defined as a rounded mass with uniform density.
The imaging technique of choice for cystic echinococcosis is ultrasonography since it is not only able to visualize the cysts in the body’s organs but it is also inexpensive, non-invasive and gives instant results. Ultrasonography has been widely used for screening, clinical diagnosis, and monitoring of treatment of liver and intraabdominal cysts.
Both MRI and CT scans can and are often used although an MRI is often preferred to CT scans when diagnosing cystic echinococcosis since it gives better visualization of liquid areas within the tissue.
Other imaging findings
Other diagnostic studied
There are no additional diagnostic fidings for echinococcosis.
Both cystic echinococcosis and alveolar echinococcosis are complicated to treat, sometimes requiring extensive surgery and/or prolonged drug therapy. There are 3 options for the treatment of cystic echinococcosis: anti-infective drug treatment, percutaneous treatment of the hydatid cysts with the PAIR (Puncture, Aspiration, Injection, Re-aspiration) technique and surgery.
Surgery for echinococcosis is indicated if the cyst is non-echoic and greater than 5 cm in diameter (CE1m and l), contains daughter cysts (CE2), and/or is associated with the detachment of membranes (CE3), consists of multiple cysts that are accessible to be punctured, are infected or in the patients who fail to respond to chemotherapy alone. Puncture, aspiration, injection and re-aspiration, also known as the PAIR protocol, is utilized for the surgical treatment of echinococcal cysts.
Effective measures for the primary prevention of echinococcosis include discouraging feeding of raw offal to work dogs, employing basic hygiene practices like thoroughly cooking food and vigorous hand washing before meals and regular "worming" of farm dogs with the praziquantel also helps kill the tapeworm.
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