Echinococcosis

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor-In-Chief: Mahshid Mir, M.D. [2] Cafer Zorkun, M.D., Ph.D. [3]; Kalsang Dolma, M.B.B.S.[4]

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.

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.

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.

Common risk factors in the development of echinococcosis include exposure to cattle such as deer, pigs, sheep, feces of dogs, wolves, or coyotes.

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.

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%.

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.^[1]

Physical examination findings of a patient with echinococcosis include hypotension (in cases of cyst rupture), elevated temperature, jaundice, hepatomegaly and abdominal tenderness.

 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.^[2]

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.^[3][4] Ultrasonography has been widely used for screening, clinical diagnosis, and monitoring of treatment of liver and intraabdominal cysts.

CT scan is often used to diagnose cystic echinococcosis. But the imaging technique of choice for cystic echinococcosis is ultrasonography.

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.

There are no other specific imaging findings for echinococcosis.

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.^[5]

Secondary preventive measures of echinococcosis are similar as of primary preventive measures.

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor-In-Chief: Mahshid Mir, M.D. [2] Cafer Zorkun, M.D., Ph.D. [3]; Kalsang Dolma, M.B.B.S.[4]

In 1782, Goeze was the first who described the echinococcosis cysts and the tapeworm heads. Later, in 1786, Batsch was the first who described E. granulosus with detail. In 1863, Rudolf Leuckart was the first who identified E. multilocularis.

The most important historical events considering:^[1][2][3]

• In 1782, Goeze was the first who described the echinococcosis cysts and the tapeworm heads.
• In 1786, Batsch was the first who described E. granulosus with detail.
• In 1850, Karl von Siebold was the first who conducted a series of experiments demonstrating that echinococcus cysts were causing adult tapeworms in dogs.
• In 1863, Rudolf Leuckart was the first who described E. multilocularis.
• In the early 1900s, the distinctive features of E. granulosus and E. multilocularis and their life cycles were described.
• The association between E. oligarthus and E. vogeli and human echinococcosis was made during mid-1900s.

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor-In-Chief: Mahshid Mir, M.D. [2] Cafer Zorkun, M.D., Ph.D. [3]; Kalsang Dolma, M.B.B.S.[4]

Echinococcosis is classified based on the site of infection and the type of tapeworm causing the infection, into cystic echinococcosis and alveolar echinococcosis. It can also be classified based on the ultrasound findings and appearance. Based on WHO classification, cystic echinococcus can be classified to 5 stages: CE1, CE2, CE3a, CE3b, CE4, CE5.

Based on the site of infection, echinococcosis can be classified into:^[1]

• Cystic echinococcosis
  • Due to the infection with the larvae of Echinococcus granulosus
• Alveolar echinococcosis
  • Due to the infection with the larvae of Echinococcus multilocularis

Based on an international classification, cystic echinococcosis can be classified based on the ultrasound features into 5 categories:^[1]

• Type 1 and 2
  • Active fertile cysts that contain viable protoscoleces
• Type 3
  • Transitional stage cysts, as a result of host immune response or therapy
• Type 4 and 5
  • Inactive and degenerative cysts which have lost their fertility

This classification system can be helpful for application in clinical and field epidemiological setting.

CE: cystic echinococcus.

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor-In-Chief: Mahshid Mir, M.D. [2] Cafer Zorkun, M.D., Ph.D. [3]; Kalsang Dolma, M.B.B.S.[4]

The transmission of echinococcosis from the definitive 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.

(1)The adult Echinococcus granulosus (2) Embryonated eggs (3) Oncosphere (4) Cyst (5) Protoscolices (6) Protoscolices evaginating

• The transmission of echinococcosis from the definitive host (dogs and other carnivores) to the intermediate host (sheep, goats, swine etc) occurs by the ingestion of embryonated eggs passed in the feces.
• The definitive host is infected by the ingestion of cyst containing organs of the infected intermediate host (sheep, goats, swine, etc).

• The embronated eggs are excreted in the feces of the definitive host, which include dogs and other carnivores.
• The intermediate hosts include: sheep, cattle, horses and camel. Once ingested the eggs hatch in the small bowel and release oncospheres.
• The onchospheres penetrate the intestinal wall and migrate through the vascular system to organs such as liver and lung.
• In the lungs and liver the oncospheres develop into a cyst producing protoscolices and daughter cysts which fill the interior of the cyst.
• The definite host will be infected if they ingest organs containing cysts.
• Once ingested, the protoscolices evaginate and attach the intestinal mucosa.
• In 32 to 80 days after evagination the protoscolices develop into adult tapeworm.
• The life cycle of E. multilocularis is similar to the life cycle of Echinococcus granulosus, but with the following differences: The definitive hosts are foxes, and to a lesser extent dogs, cats, coyotes and wolves. The intermediate host are small rodents and the larval growth (in the liver) remains indefinitely in the proliferative stage, resulting in invasion of the surrounding tissues.
• In the life cycle of E. vogeli the definitive hosts are bush dogs and dogs. The intermediate hosts are rodents and the larval stage in the liver, lung develops both externally and internally, resulting in multiple vesicles.
• E. oligarthrus (up to 2.9 mm long) has a life cycle that involves wild felids as definitive hosts and rodents as intermediate hosts. Humans become infected by ingesting eggs , with resulting release of oncospheres in the intestine and the development of cysts in various organs.

The most important gross pathological features of echinococcus cysts are:

• Cysts of E. granulosis (cystic hydatid disease):
  • Cysts tend to be:
    • Filled with clear fluid
    • White appearance
    • Solitary
    • Unilocular
  • Mostly involve right lobe of liver
  • Viable cysts are filled with a colorless fluid that contains daughter cysts and brood capsules with scolices
  • Daughter cysts may also be present outside the fibrous layer of the cyst, that are called as extracapsular or satellite cysts
• Cysts of E. multilocularis (alveolar hydatid disease):
  • Numerous small and irregular cysts
  • Mostly smaller than 2 cm
  • Appears infiltrative

On microscopic pathology of the tissues, the most important findings include:

• Cysts can be found in any part of the body, but are most common in the liver, lung and central nervous system
• Echinococcus granulosus cyst:
  • Cyst wall composed of an acellular laminated external layer and a thin, germinal (nucleated) inner layer
  • Brood capsule with protoscoleces inside

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor-In-Chief: Mahshid Mir, M.D. [2] ; Cafer Zorkun, M.D., Ph.D. [3]; Kalsang Dolma, M.B.B.S.[4]

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.

Human echinococcosis (hydatidosis or hydatid disease) is caused by the larval stages of cestodes (tapeworms) of the genus Echinococcus.

Different echinococcus sybtypes and the disease they are associated with are as follows:

• Echinococcus granulosus causes cystic echinococcosis (CE), the form most frequently encountered.
• E. multilocularis causes alveolar echinococcosis (AE).
• E. vogeli causes polycystic echinococcosis.
• E. oligarthrus is an extremely rare cause of human echinococcosis.

Echinococcus eggs contain an embryo that is called an oncosphere or hexcanth. The name of this embryo stems from the fact that these embryos have six hooklets. The eggs are passed through the feces of the definitive host (dogs and other carnivores) and it is the ingestion of these eggs that lead to infection in the intermediate host (sheep, cattle, horses, and camel).

From the embryo released from an egg develops a hydatid cyst, which grows to about 5–10 cm within the first year and is able to survive within organs for years.^[1] Cysts sometimes grow to be so large that by the end of several years or even decades, they can contain several liters of fluid. Once a cyst has reached a diameter of 1 cm, its wall differentiates into a thick outer, non-cellular membrane, which covers the thin germinal epithelium. From this epithelium, cells begin to grow within the cyst. These cells then become vacuolated and are known as brood capsules, which are the parts of the parasite from which protoscolices bud. Often, daughter cysts will also form within cysts.

Echinococcus adult worms develop from protoscolices and are typically 6mm or less in length and have a scolex, neck and typically three proglottids, one of which is immature, another of which is mature and the third of which is gravid (or containing eggs). The scolex of the adult worm contains four suckers and a rostellum that has about 25-50 hooks.^[2]

The major morphological difference among different species of Echinococcus is the length of the tapeworm. E. granulosus is approximately 2 to 7 mm while E. multilocularis is often smaller and is 4 mm or less.^[3] On the other hand, E. vogeli is found to be up to 5.6 mm long and E. oligarthus is found to be up to 2.9 mm long. In addition to the difference in length, there are also differences in the hydatid cysts of the different species. For instance, in E. multilocularis, the cysts have an ultra thin limiting membrane and the germinal epithelium may bud externally. Furthermore, E. granulosus cysts are unilocular and full of fluid while E. multilocularis cysts contain little fluid and are multilocular. For E. vogeli, its hydatid cysts are large and are actually polycystic since the germinal membrane of the hydatid cyst actually proliferates both inward, to create septa that divide the hydatid into sections, and outward, to create new cysts. Like E. granulosus cysts, E. vogeli cysts are filled with fluid.

• 
  Scolex of Echinococcus granulosus from hydatid cyst. From Public Health Image Library (PHIL). ^[4]
• 
  Photomicrograph reveals some of the ultrastructural morphology exhibited by an adult cestode, Echinococcus granulosus, found in a dog. E. granulosus causes “cystic echinococcosis”. From Public Health Image Library (PHIL). ^[4]

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Mahshid Mir, M.D. [2]

Cystic echinococcosis must be differentiated from other diseases presenting with right sided abdominal pain such as pyogenic liver abscess and amoebic liver abscess and fungal liver abscess.

Echinococcal cyst must be differentiated from other diseases presenting with hepatic abscess and right sided abdominal pain such as:

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor-In-Chief: Mahshid Mir, M.D. [2] ; Cafer Zorkun, M.D., Ph.D. [3]; Kalsang Dolma, M.B.B.S.[4]

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.^[1]

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.

• Echinococcosis commonly affects elderly age group above 55 years.

• Men and women are affected equally by echinococcosis.

• There is no racial predilection for echinococcosis.

• E. granulosus is present virtually worldwide since there are very few countries that are considered to be completely free of E. granulosus.^[2]
• E. multilocularis mainly occurs in the northern hemisphere, including central europe and the northern parts of europe, asia, and north america.^[3]
• The other two species of Echinococcus, E. vogeli and E. oligarthus are limited to central and south america. Furthermore, infections by E. vogeli and E. oligarthus (polycystic echinococcosis) are considered to be the rarest form of echinococcosis.^[4]

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor-In-Chief: Mahshid Mir, M.D. [2] ; Cafer Zorkun, M.D., Ph.D. [3]; Kalsang Dolma, M.B.B.S.[4]

Common risk factors in the development of echinococcosis include exposure to cattle such as cattle, deer, pigs, sheep and feces of dogs, wolves or coyotes.^[1]

People who accidentally swallow the eggs of the Echinococcus granulosus tapeworm are at risk for infection. Humans can be exposed to these eggs in two main ways that involve “hand-to-mouth” transfer or contamination. Risk factors include exposure to:^[1]

• Cattle
• Deer
• Feces of dogs, wolves, or coyotes
• Pigs
• Sheep

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor-In-Chief: Mahshid Mir, M.D. [2] ; Cafer Zorkun, M.D., Ph.D. [3]; Kalsang Dolma, M.B.B.S.[4]

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%.

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:^[1][2][3]

• Pulmonary embolism
• Focal cerebral disorders (seizures, hemiparesis, aphasia)
• Obstructive jaundice
• Adrenal dysfunction
• Small bowel obstruction
• Gastric perforation
• Secondary biliary cirrhosis
• Portal vein thrombosis
• Portal hypertension

The prognosis of echinococcosis is good with treatment. Without treatment, echinococcosis is associated with a 10-year mortality of 90%.

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