Belonging to the family Taeniidae, the tapeworm Echinococcus is responsible for causing echinococcosis in humans. There are four species of Echinococcus known to produce infections in humans. Among these, E. granulosus and E. multilocularis are the most common ones responsible for causing cystic echinococcosis (CE) and alveolar echinococcosis (AE), respectively. On the other hand, E. vogeli and E. oligarthrus cause polycystic echinococcosis, but the incidence in humans is quite rare.
Echinococcosis is caused by infection from the parasite Echinococcus (a tapeworm). The life cycle of Echinococcus includes a definitive host (usually dogs) and an intermediate host (like sheep, goats, or swine). Humans are accidental hosts, and they do not play a part in the transmission. Adult tapeworm resides in the small intestine of the definitive host where it lays eggs containing embryos (oncospheres). These eggs expelled via feces get ingested by the intermediate or incidental host. Oncospheres after being hatched from eggs migrate via blood or lymphatics after piercing the intestinal mucosa to the liver, lungs, or other visceral organs and form cysts. Protoscoleces develop within these cysts. The life cycle gets completed when the definitive host consumes the infected organs of the intermediate host.
The epidemiology of echinococcal disease varies from species to species. Although E. granulosus is almost prevalent throughout the whole world, higher incidence rates are found in South America, the former Soviet Union, the Middle East and the eastern Mediterranean, few sub-Saharan African countries, and western China. In particular, the areas where dogs can consume organs of infected animals such as the rural and the grazing ones possess higher infection rates.
E. multilocularis is mostly limited to the Northern Hemisphere in areas such as the northern parts of Europe, Asia, and North America, as well as Central Europe. On the other hand, the remaining two species of Echinococcus, E. vogeli and E. oligarthrus, are only limited to South and Central America.
The prevalence of echinococcal disease increases with age. Older and immunocompromised people are more vulnerable to develop such infections. There is no sex predilection for hydatid cysts. While cystic Echinococcus is the disease of adulthood (average age of 30 to 40 years), alveolar Echinococcus tends to occur in old age (older than 50 years of age).
Once the eggs of the tapeworm have been ingested by a human, oncosphere larvae are released from the egg, which can pierce the lamina propria of the intestine. As it penetrates, it enters the blood or lymphatics and gets transported to the liver, lungs, or other internal organs where it develops into hydatid cysts (metacestode larvae). These cysts possess an inner germinal layer and an outer laminated layer surrounded by a fibrous capsule derived from the host. The inner cellular layer gives rise to smaller "daughter" cysts. In humans, cysts grow slowly and can be up to multiple liters in volume and contain thousands of protoscolices. Over time, septations and daughter cysts disrupt the typical unilocular pattern of echinococcal cysts.
Symptoms of E. granulosus infection depend on two factors: the size and the site of the cysts. While the small and/or calcified cysts tend to remain asymptomatic indefinitely, larger ones can produce pressure or mass effects on the surrounding structures or can rupture, leading to anaphylaxis or acquire a secondary bacterial infection.
The clinical picture of liver cysts ranges from asymptomatic to hepatomegaly associated with right upper quadrant (RUQ) pain, nausea, vomiting, biliary colic, obstructive jaundice, and pancreatitis (when a cyst ruptures into the biliary tree). Pressure effects can lead to hepatic veins, portal veins, and IVC obstruction, leading to venous obstruction, portal hypertension, and Budd Chiari syndrome. Peritonitis can also occur if the cyst ruptures into the peritoneum.
The involvement of the lungs can give rise to cough, chest pain, dyspnea, hemoptysis, and less frequently nausea, vomiting, and malaise.
Other organs involved include the heart (pericardial tamponade), the brain (seizures and signs of raised ICP), the spinal cord (spinal cord compression), the kidneys (flank pain and hematuria), and the bones (pathologic fractures).
E. multilocularis infection clinical features tend to be nonspecific. The most common complaints include malaise, weight loss, RUQ pain owing to hepatomegaly, and obstructive jaundice. It may also mimic hepatocellular carcinoma.
When obtaining medical history, risk factors of echinococcosis, especially contact with canines and cattle, should be assessed.
The diagnosis of echinococcal infection is made based on imaging and serology.
Ultrasonography is 90% to 95% sensitive for E.granulosus. Based on ultrasonographic images, echinococcal cysts have been categorized by WHO to help in guiding the correct treatment. This categorization is as follows:
Radiography can detect calcifications in up to 30% of the cases. These calcifications are generally ring-like and can progress throughout all the stages of the disease.
CT is superior to USG in terms of higher sensitivity (95 to 100%), determining size, site, and location of the cysts (extrahepatic as well), and assessing for complications.
MRI offers no major advantage over CT except in determining intra- and extrahepatic venous changes.
Serology helps in the primary diagnosis of echinococcosis as well as in the follow-up after treatment. There are numerous diagnostic serologic techniques, and among these, ELISA is the most specific and sensitive one. Few limitations to serological testing involve nonviable and calcified cysts. Also, liver cysts tend to be more seropositive than lung cysts, and serology is more specific for E. multilocularis than for E. granulosus.
Percutaneous aspiration or biopsy is preferred when other modes have proven to be inconclusive. However, because of the potential anaphylaxis and secondary spread of infection, aspiration, if required, should always be performed under the guidance of either USG or CT. If the disease involves the biliary tree, then endoscopic retrograde cholangiopancreatography (ERCP) can be used for both diagnostic as well as therapeutic purposes.
There are four modalities of treatment for echinococcal disease. These include surgery, percutaneous management, drug therapy, and observation. The WHO classification helps to choose the modality of choice for the treatment of echinococcal cysts.
For WHO stage 1 and 3a, (these cysts have a single compartment), cysts having a size less than 5 cm are treated with albendazole or PAIR (Puncture, Aspiration, Instillation, and Re-aspiration). In contrast, cysts larger than 5 cm are treated with PAIR along with the adjunctive treatment with albendazole.
For WHO stage 2 and 3b in which cysts have multiple compartments rendering PAIR ineffective, these are managed with modified catheterization technique (Non-PAIR percutaneous therapy) or surgery with adjunctive albendazole.
WHO Stage 4 and 5 require only observation as they are inactive.
Differential diagnosis of cystic echinococcus includes:
In cystic echinococcosis, the prognosis is generally good compared to alveolar echinococcosis, where the prognosis is much worse, and the cure is dependent on early detection and complete surgical excision. Prognosis is poor when sites where surgical excision of the cyst poses a difficulty, especially when the heart and spinal cord are involved.
In general, the public of endemic areas must be made aware of the transmission of Echinococcus and that they should avoid contact with dogs. Once infected, the patient should be educated regarding the complications of echinococcal cysts. Also, all the treatment options should be discussed thoroughly with the patient as to why one is superior to others. The clinician ought to inform the patient that despite the proper medical or surgical management, these cysts tend to recur. Finally, if cysts are amenable to drug therapy, then strict compliance is the key to eradicate the parasitic infection.
Endemic areas can benefit from mass screening using ultrasound as it will limit the disease in such areas.
The echinococcal disease is a very common parasitic infection, particularly among farmers and shepherds that is often first seen by the primary care provider, nurse practitioner, or the emergency department physician. These clinicians should always consult with the hepatobiliary surgeon and radiologist before starting any treatment. The disease needs to be dealt with in time to avoid morbidity and mortality. Coordination among healthcare professionals is vital for better patient outcomes.
The management and the evaluation of echinococcal disease requires an interprofessional approach as cysts resulting from this condition tend to form in different viscera of the body, thus requiring multiple consultant approaches accordingly. For instance, brain cysts require opinions from a neurologist as well as a neurosurgeon. Likewise, liver and lung cysts require consultant opinions from hepatologists and pulmonologists, respectively, other than the general surgeon. The role of radiologists is evident as the imaging not only helps in making the primary diagnosis but also guides the treatment of choice. The nursing staff is also a vital segment of the interprofessional group as they assist in educating the patient and family members about the disease. Finally, pharmacists' roles are imperative, too, particularly when drug therapy is initiated and monitored. This type of interprofessional collaboration is the key to achieving optimal patient outcomes in the cases of echinococcosis.
|||McManus DP,Zhang W,Li J,Bartley PB, Echinococcosis. Lancet (London, England). 2003 Oct 18; [PubMed PMID: 14575976]|
|||Wen H,Vuitton L,Tuxun T,Li J,Vuitton DA,Zhang W,McManus DP, Echinococcosis: Advances in the 21st Century. Clinical microbiology reviews. 2019 Mar 20; [PubMed PMID: 30760475]|
|||Langer JC,Rose DB,Keystone JS,Taylor BR,Langer B, Diagnosis and management of hydatid disease of the liver. A 15-year North American experience. Annals of surgery. 1984 Apr; [PubMed PMID: 6712316]|
|||Symeonidis N,Pavlidis T,Baltatzis M,Ballas K,Psarras K,Marakis G,Sakantamis A, Complicated liver echinococcosis: 30 years of experience from an endemic area. Scandinavian journal of surgery : SJS : official organ for the Finnish Surgical Society and the Scandinavian Surgical Society. 2013; [PubMed PMID: 23963031]|
|||International classification of ultrasound images in cystic echinococcosis for application in clinical and field epidemiological settings. Acta tropica. 2003 Feb; [PubMed PMID: 12606104]|
|||Beggs I, The radiology of hydatid disease. AJR. American journal of roentgenology. 1985 Sep; [PubMed PMID: 3895873]|
|||Stojkovic M,Rosenberger K,Kauczor HU,Junghanss T,Hosch W, Diagnosing and staging of cystic echinococcosis: how do CT and MRI perform in comparison to ultrasound? PLoS neglected tropical diseases. 2012; [PubMed PMID: 23145199]|
|||Brunetti E,Kern P,Vuitton DA, Expert consensus for the diagnosis and treatment of cystic and alveolar echinococcosis in humans. Acta tropica. 2010 Apr; [PubMed PMID: 19931502]|
|||Mansfield BS,Pieton K,Pather S, Spinal Cystic Echinococcosis. The American journal of tropical medicine and hygiene. 2019 Jan; [PubMed PMID: 30652663]|
|||Sayek I,Tirnaksiz MB,Dogan R, Cystic hydatid disease: current trends in diagnosis and management. Surgery today. 2004; [PubMed PMID: 15580379]|
|||Dhar P,Chaudhary A,Desai R,Agarwal A,Sachdev A, Current trends in the diagnosis and management of cystic hydatid disease of the liver. The Journal of communicable diseases. 1996 Dec; [PubMed PMID: 9057445]|
|||Bouraoui H,Trimeche B,Mahdhaoui A,Majdoub A,Zaaraoui J,Hajri Ernez S,Gouider J,Ammar H, Echinococcosis of the heart: clinical and echocardiographic features in 12 patients. Acta cardiologica. 2005 Feb; [PubMed PMID: 15779850]|
|||Moro P,Schantz PM, Echinococcosis: a review. International journal of infectious diseases : IJID : official publication of the International Society for Infectious Diseases. 2009 Mar; [PubMed PMID: 18938096]|
|||Macpherson CN,Bartholomot B,Frider B, Application of ultrasound in diagnosis, treatment, epidemiology, public health and control of Echinococcus granulosus and E. multilocularis. Parasitology. 2003; [PubMed PMID: 15027603]|