Definitive hosts for E. granulosus are dogs, and other canines.
Humans are accidental hosts with the ingestion of infected embryonate eggs shed by stray dogs.
Humans become infected with E granulosus by ingesting eggs that are shed in the feces of definitive hosts.
In intermediate hosts larvae are transported through blood or lymphatics to the liver, lung and other organs, with parasites develop into hydatid cysts.
The eggs contain the infectious oncosphetes that penetrate the intestinal wall and enter into the bloodstream.
The genus Echinococcus includes six parasite species of cyclophyllid tapeworms of the family Taeniidae.
Infection results in hydatid disease, also known as echinococcosis.
Echinococcus is triploblastic – it has three layers- outermost ectoderm, middle mesoderm, and inner endoderm.
Has no anus and no digestive system.
Its body is covered by tegument.
The worm is divided into a scolex, a short neck, and three to six proglottids. Its body shape is ribbon-like.
Causes a disease called echinococcosis.
The three types of echinococcosis are cystic echinococcosis caused by E. granulosus, alveolar echinococcosis caused by E. multilocularis, and polycystic echinococcosis caused by E. vogeli or E. oligarthrus.
A worm’s incubation period is long and can be up to 50 years.
Cystic echinococcosis is mostly found in South and Central America, Africa, the Middle East, China, Italy, Spain, Greece, Russia, and the western United States of Arizona, New Mexico, and California.
Echinococcosis is a zoonosis.
Cystic, echinococcodid is caused by infection with the larval stage of the tapeworm called E agranulosus.
More than 1 million people annually are infected with E. Granulosus worldwide.
Endemic areas of involvement include western China, Central Asia, South America, Mediterranean countries, and east Africa. Cystic.
Echinococcosis is rare in the US and typically occurs in immigrants from endemic areas.
Definitive hosts for E granulosis, are domestic or wild dogs and wolves, who acquire the infection after eating animal organs containing hydatid cysts.
Humans are dead-end hosts.
The definitive hosts are carnivorous predators, to include dogs, wolves, foxes, and lions.
The adult tapeworm lives in their small intestines and delivers eggs to be excreted with the stool.
The intermediate hosts are infected by ingesting eggs and include: Sheep, goats, cattle, camels, pigs, wild herbivores, and rodents are the usual intermediate hosts, but humans can also be infected.
The egg hatches in the digestive system of the intermediate host, producing a larva, which penetrates the intestinal wall and is carried by bloodstream to liver, lung, brain, or another organ.
The larva settles in an organ and turns into a bladder-like structure called hydatid cyst.
Prrotoscoleces which are scoleces with invaginated tissue layers, bud and protrude into the fluid filling the cyst.
Protoscoleces turn inside out, attach, and give rise to adult tapeworms, completing the lifecycle.
In humans, the cysts persist and grow for years, and regularly found in the liver and other organs: spleen, kidney, bone, brain, tongue and skin.
Approximately 70% of adults with cystic echinococcosis have liver cysts, and approximately 10 to 30% have pulmonary cysts.
In children pulmonary cysts are the most common cystic manifestation.
Hydatid cysts can develop in the brain, spleen, kidney, pancreas and heart infrequently
Cysts are asymptomatic until their size produces symptoms or are accidentally discovered.
Complications of cystic echinococcosis results from compression of adjacent organs, cyst rupture superinfection, and immunologic reactions, including urticaria, angioedema, and rarely anaphylaxis.
Disruption of the cysts can be life-threatening due to anaphylactic shock.
Cysts are detected by imaging techniques.
Liver cysts typically grow over many years, but often increase in the long and children at a faster rate.
Pulmonary cysts range from 1 cm to 20 cm and are usually asymptomatic.
Symptomatic pulmonary cysts may be related to cough dyspnea, chest pain, hemoptysis and fever.
Pulmonary cysts can also cause cough when they rupture with salty tasting fluid or membrane fragments, empyema, and hydropneumothorax.
Antiechinococcus antibodies can be detected with serodiagnostic tests – indirect fluorescent antibody, complement fixation, ELISA, and Western blot.
Most oncospheres lodge in the liver and develop into hydatid cysts.
Hydatid cysts can also occur in the lungs, bones, brain, heart and muscle.
Cysts are typically unilocular.
Cyst growth rate depends on the surrounding tissue, such that liver cysts grow at a rate of approximately 1 cm in diameter per year.
Majority of hydatid cysts remain asymptomatic for years, but symptoms related to infection of the cyst can occur in approximately 25% of such persons.
Hydatid cyst of the liver can rupture into the biliary tree, cause obstruction, fibrosis, and enterocutaneous fistula.
Hydatid cysts can be associated with bacterial infection.
Rarely hydatid cysts rupture into the peritoneal cavity and can cause anaphylaxis.
Diagnostic aspiration is not recommended routinely because of the risk of fluid leakage resulting in anaphylaxis and also dissemination of the disease.
The most common used diagnostic method is the detection of echinococcal antibodies.
Rupture or leak of hydatid cyst fluid due to trauma or surgery or extreme physical activity can cause anaphylaxis.
Spontaneous rupture of hydatid cysts can lead to anaphylaxisis
Hidatid cysts are classified on the basis of x-ray features, size, septations, presence or absence of the daughter cysts, visible when non visible contents within the cyst and stability of the cyst wall.
Small, stable cyst walls and no daughter cysts may not require therapy and only be clinically observed or may be treated with antihelminthic agents alone.
Large cyst with multiple septations or daughter cysts typically require invasive surgery.
Cysts greater than 5 cm in diameter or that are complex may undergo cystectomy, partial liver resection or percutaneous aspiration procedure.
The diagnosis of E. granulosus infection, the cystic hydatid disease, is suggested by identification of a cyst-like mass in a person with a history of exposure to sheepdogs in areas where the parasite is endemic.
Cystic echinococcosis differentiatial from benign cysts, cavitary tuberculosis, mycoses, abscesses, and benign or malignant neoplasms.
Noninvasive imaging techniques such as CT scans, MRI, and ultrasound imaging are all used for detecting and defining avascular fluid-filled cysts in most organs.
Radiography permits the detection of hydatid cysts in the lungs.
In other organ sites, calcification is necessary for visualization.
Diagnosis is based on history, imaging, serology, and histology.
Typical imaging findings are pulmonary cysts on chest x-ray, CT scan, and liver cysts on abdominal ultrasound or CT.
Detection of antibodies against echinococcosis can confirm the diagnosis.
Eosinophilia occurs in approximately 25% of patients with cystic echinococcosis.
Ultrasonography is used for screening, clinical diagnosis, and monitoring of treatment of liver and intra-abdominal cysts.
Cyst viability cannot be reliably determined with X-Ray or parasite antigen detection.
Calcification can be present in all stages of cysts.
Serologic tests :enzyme-linked immunosorbent assay (ELISA) and indirect hemagglutination test, are highly sensitive methods for detecting infection.
Diagnostic confirmation can be achieved by demonstrating echinococcal antigens by immunodiffusion procedures or immunoblot assays.
Alveolar echinococcosis is more commonly diagnosed in people of an advanced age, with radiographs showing hepatomegaly and scattered areas of radiolucency outlined by calcific rings 2 to 4 mm in diameter.
CT imaging of E. multilocularis infection suggests solid tumors with central necrotic areas and perinecrotic plaque-like calcifications.
Serologic test results allows discrimination between patients infected with E. multilocularis and those infected with E. granulosus.
Incubation period of cystic echinococcosis is often several years and most cases remain asymptomatic until the cysts reach a large enough size to cause dysfunction.
Most primary infections in humans consist of a single cyst.
The liver is the most common site of the hydatid cysts, followed by the lungs, while cysts in the spleen, kidneys, heart, bone and central nervous system are less common.
In secondary echinococcosis, larval tissue spreads from the primary site and new cysts develop after spontaneous or trauma-induced cyst rupture or after release of viable parasite material during invasive treatment procedures.
Patients may present with hepatomegaly with or without a palpable mass in the right upper quadrant, right epigastric pain, nausea, and vomiting.
Rupture or leakage of hepatic cysts may result in acute or intermittent allergic manifestations.
Primary infection of alveolar echinococcosis is in the liver, and usually the right lobe.
Direct extension of alveolar echinococcosis to contiguous organs, as well as hematogenous metastases to the lungs and brain can occur.
Alveolar echinococcosis remains in the proliferative stage indefinitely.
The larval lesion resembles a malignancy in appearance and behavior.
In chronic alveolar hydatid infections, the lesion consists of a central necrotic cavity filled with a white amorphous material covered with a layer of dense fibrous tissue.
Surrounding tissue is invaded by extension of the budding and proliferating cyst wall, causing pressure necrosis.
An inflammatory and fibrous tissue reaction usually surrounds the larval mass.
Diagnosis is often delayed until an advanced and inoperable stage.
Mortality rates have traditionally been high, ranging between 50% and 75%.
In the past, surgery was the only treatment for cystic echinococcal cysts.
Chemotherapy, cyst puncture, and percutaneous aspiration, injection of chemicals and reaspiration have been used to replace surgery as effective treatments for cystic echinococcosis.
In some cases, no treatment and a watch and wait approach is best.
Treatment indications vary with cyst characteristics, including cyst type, location, size, and complications.
Surgery is considered best treatment for liver cysts that are secondarily infected or cysts located in the brain, lungs, or kidney.
Liver cysts larger than 7.5 cm are likely to have biliary communication and surgery may be the best option for these cysts.
Many abdominal cysts can be treated by injection of protoscolicidal chemical solutions into the cyst, followed by evacuation, prior to further manipulations and extirpation of cysts.
With small cysts or multiple cysts in several organs can be treated successfully with albendazole.
Approximately one third of patients treated with chemotherapy with benzimidazole drugs have been cured of the disease and even higher proportions, between 30-50%, have responded with significant regression of the cyst size and alleviation of symptoms.
Both albendazole 10 to 15 mg/kg body weight per day (max 800 mg orally in two doses) and, as a second choice for treatment, mebendazole 40-50 mg/kg body weight per day continuously for several months have been highly effective.
Prior administration of albendazole allows safe surgical manipulation of the cysts by inactivating protoscolices, altering the integrity of the cysts membranes, and reducing the turgidity of the cysts.
Percutaneous aspiration, injection of chemicals and reaspiration has been shown to be effective, and indicated for patients with relapse after surgery, failure of chemotherapy alone, or who refuse surgery.
Albendazole 400 mg orally twice a day for 1-6 months-10-15 mg/kg/day (max 800 mg) orally in two doses for 1-6 months.
Alveolar echinococcosis requires chemotherapy with or without surgery.
Effective treatment involves benzimidazoles administered continuously for at least 2 years and patient monitoring for 10 years or more since recurrence is possible.
Additional treatments include percutaneous, puncture, aspiration, injection, and re-aspiration, anti-helminth therapy and watchful, waiting for small assists.
Abendazole or abendazole-praziquantel may be considered in patients with inoperable cysts in the liver, cysts in multiple organs or isolated, small medium sized cysts.
Anti-helminth therapy as an adjunct to surgery for interventional procedures decreases the risk of Echinococcus dissemination and recurrence.
Approximately 6.5% of patients experience to relapse after treatment for cystic echinococcosis.