| disease | Echinococcosis |
| alias | Echinococcosis, Echinococciosis? |
Echinococcosis, also known as hydatid disease, is a chronic parasitic infection caused by the larval stage of Echinococcus tapeworms. The clinical manifestations of this disease vary depending on the location, size of the hydatid cysts, and the presence of complications. For a long time, echinococcosis has been considered a zoonotic disease, referred to as an animal-derived disease. However, recent epidemiological studies have shown that it is also an endemic parasitic disease, characterized by occupational hazards in endemic areas and classified as an occupational disease for certain populations. Globally, echinococcosis is a common and frequently occurring disease, particularly among ethnic minorities or religious tribes.
bubble_chart Epidemiology
This disease is globally distributed, primarily prevalent in pastoral areas. In China, it is commonly found in Gansu, Ningxia, Qinghai, Xinjiang, Inner Mongolia, Tibet, western Sichuan, and Shaanxi. Sporadic cases have also been reported in Hebei and northeastern provinces.
(1) Source of pestilence: The main source of pestilence for this disease is dogs. Although wolves, foxes, and jackals are also definitive hosts, their significance as sources of pestilence is minimal. In endemic areas, echinococcosis is often present in sheep flocks, and residents frequently feed dogs with sheep or other livestock offal, providing dogs with the opportunity to ingest hydatid cysts. Infections are often severe, with the number of Chinese Taxillus Herb worms in the intestines reaching hundreds to thousands. The gravid proglottids are motile and can crawl on the skin and hair, causing anal itching. When dogs lick or bite, they crush the proglottids, and the eggs in the feces often contaminate the entire skin and hair. Close contact with such dogs can easily lead to infection.
(2) Transmission routes: Direct infection mainly occurs through close contact with dogs, where eggs on the skin and hair contaminate fingers and are then ingested orally. If eggs in dog feces contaminate vegetables or water sources, especially when humans and livestock share the same water source, indirect infection can also occur. In arid and windy regions, eggs can be carried by the wind, potentially leading to respiratory infections.(3) Susceptibility: Human infection is primarily related to environmental hygiene and poor hygiene habits. Patients are mostly farmers and herders, with ethnic minorities being significantly more affected than the Han Chinese. Since hydatid cysts grow slowly, infections generally occur in childhood, with noticeable symptoms appearing in adulthood. There is no significant difference in incidence rates between males and females.
Echinococcosis is a disease caused by the larvae of species in the genus Echinococcus. Currently recognized species include Echinococcus granulosus, E. multilocularis, E. vogeli Rausch, and E. oligarthrus. Their morphology, hosts, and distribution areas vary slightly, with Echinococcus granulosus being the most common.
Echinococcus granulosus is only 1.5–6 mm long and consists of a scolex and three body segments. The adult Chinese Taxillus Herb resides in the small intestine of dogs, but wild animals such as wolves, foxes, and jackals can also serve as definitive hosts. The eggs are round, with a double-layered embryonic membrane, resembling the eggs of Taenia species, and are relatively resistant to the external environment. When the eggs are excreted in dog feces, they contaminate pastures, livestock pens, vegetables, soil, and water. Upon ingestion by humans, sheep, or other intermediate hosts, the eggs pass through the stomach into the duodenum. Under the action of digestive fluids, the oncosphere hatches, penetrates the intestinal wall, and enters the portal venous system. Most larvae are trapped in the liver, where they develop into hydatid cysts (echinococcal cysts); some may escape to the lungs or spread throughout the body to develop into hydatid cysts in various organs. When dogs ingest the viscera of sheep or other intermediate hosts containing hydatid cysts, the protoscoleces enter the crypts of the small intestine wall and develop into adults (approximately 7–8 weeks) to complete their life cycle. The definitive hosts of E. multilocularis are primarily foxes and dogs, and the larvae (alveolar hydatid cysts) mainly Chinese Taxillus Herb in the liver of intermediate hosts such as rodents or humans.
This disease is globally distributed, primarily prevalent in pastoral areas. In China, it is commonly found in Gansu, Ningxia, Qinghai, Xinjiang, Inner Mongolia, Tibet, western Sichuan, and Shaanxi. Sporadic cases have also been reported in Hebei and northeastern provinces.
(1) Source of Pestilence: The main source of pestilence for this disease is dogs. Although wolves, foxes, and jackals are also definitive hosts, they are of little significance as sources of pestilence. In epidemic areas, echinococcosis is often present in sheep flocks, and residents frequently feed dogs with sheep or other livestock offal, providing dogs with the opportunity to ingest hydatid cysts. Infections are often severe, with the number of Chinese Taxillus Herb worms in the intestines reaching hundreds to thousands. The pregnant segments are mobile and can crawl on skin and hair, causing anal itching. When dogs lick or bite, the segments are crushed, and the eggs in the feces often contaminate the entire skin and hair. Close contact with such dogs can easily lead to infection.
(2) Transmission Routes: Direct infection mainly occurs through close contact with dogs, where eggs on their skin and hair contaminate fingers and then enter the mouth. If eggs in dog feces contaminate vegetables or water sources, especially when humans and animals share the same water source, indirect infection can also occur. In arid and windy areas, eggs can be carried by the wind, potentially leading to respiratory infections.
(3) Susceptibility: Human infection is mainly related to environmental hygiene and poor hygiene habits. Patients are mostly farmers and herders, with ethnic minorities being far more affected than the Han Chinese. Because hydatid cysts grow slowly, infections generally occur in childhood, with significant symptoms appearing only in adulthood. There is no significant difference in incidence between males and females.
Echinococcosis can persist in the human body for several years to several decades. The clinical manifestations vary depending on the location of the Chinese Taxillus Herb, the size of the cyst, and the presence or absence of complications. Due to the different species of Chinese Taxillus Herb, the clinical presentation can be cystic echinococcosis (unilocular echinococcosis), alveolar echinococcosis (multilocular echinococcosis), or mixed echinococcosis. The latter is caused by the larvae of Echinococcus vogeli or Echinococcus oligarthrus, which are found in Central and South America but have not been reported domestically.
(1) Hepatic echinococcosis: When the hydatid cyst in the liver becomes extremely enlarged, a mass may appear in the right upper abdomen, and the patient may experience a sense of fullness and dragging, along with possible compressive symptoms. Most cysts are located in the right lobe, often on the surface, with only 1/4 located in the left lobe. When the cyst is located in the central part of the right lobe, the liver may show diffuse enlargement. Upward growth can compress the thoracic cavity, leading to reactive pleural effusion, atelectasis, etc.; downward and forward growth can cause bulging into the abdominal cavity. Most patients are found to have an extremely enlarged liver upon physical examination, with a local, round, smooth cystic sensation. In a few cases, a tremor may be heard upon percussion of the cyst. Liver function is mostly normal, with an inverted albumin-globulin ratio. Liver B-ultrasound, liver isotope scanning, and liver CT scans all show space-occupying lesions in the liver. The condition caused by Echinococcus granulosus is usually referred to as unilocular echinococcosis, while that caused by Echinococcus multilocularis is called multilocular echinococcosis, also known as alveolar echinococcosis (alveococcosis). The proliferation of hydatid cysts is invasive, resembling malignant tumors. Hepatic alveolar echinococcosis can also metastasize through the lymphatic or blood pathways, leading to secondary pulmonary or cerebral alveolar echinococcosis, hence it is referred to as malignant echinococcosis. The liver becomes hard and the surface uneven.
(2) Pulmonary echinococcosis: The lung tissue is relatively loose, so hydatid cysts grow faster, often presenting with symptoms such as dry cough and hemoptysis. Two-thirds of patients have lesions in the right lung, mostly in the lower lobe. In cases without complications, chest X-rays may show single or multiple round, oval, or multicyclic masses with clear and smooth edges (edges may become blurred with secondary infection). The cysts deform with respiration, rarely calcify, and vary in size, with the largest potentially occupying one lung field. If the cyst ruptures and the fluid is completely expelled, it may appear as a cavity on X-ray; if the cyst ruptures into the thoracic cavity, severe hydropneumothorax may occur. About half of the patients have cysts that rupture into the bronchi, with the fluid being coughed out, leading to self-healing. Occasionally, a large amount of fluid overflow can cause asphyxiation.
(3) Cerebral echinococcosis: The incidence is low (1-2%), mostly seen in children, with the parietal lobe being the most common site. Clinical manifestations include epileptic seizures and symptoms of increased intracranial pressure. The cysts are usually single, mostly located subcortically. In extensive cases, the lateral ventricles may be involved, and the skull may be compressed or eroded, leading to skull protrusion. Cerebral angiography, brain CT, and brain MRI are helpful for diagnosis.
(4) Skeletal echinococcosis: This is relatively rare, with foreign reports accounting for about 1-2% of all echinococcosis cases, while domestic reports are much lower, at around 0.2%. The pelvis and spine have the highest incidence, followed by long bones of the limbs, skull, scapula, and ribs. After Echinococcus granulosus invades long bones, the infection usually starts at the bone end, with the spongy bone being the first to be affected. Due to the hardness of the cortical bone and the narrow, tubular nature of the medullary cavity, the development of the hydatid cyst is restricted, leading to a slow progression of the disease. In advanced stages, pathological fractures, osteomyelitis, or limb dysfunction may occur. X-rays can aid in diagnosis.
In addition, echinococcosis of the pericardium, kidney, spleen, muscles, pancreas, etc., is rare, with symptoms resembling benign tumors.
After infection with echinococcosis, individuals often become sensitized due to the absorption of small amounts of antigen. If the cyst ruptures or fluid spills during surgery, it can cause allergic reactions such as rash, fever, shortness of breath, abdominal pain, diarrhea, syncope, delirium, and unconsciousness. Severe cases may die from anaphylactic shock.
bubble_chart Auxiliary Examination
(1) Blood Picture: Eosinophilia is observed in half of the cases, generally not exceeding 10%, and occasionally reaching up to 70%. After the rupture of hydatid cysts or post-surgery, there is often a significant increase in eosinophils in the blood.
(2) Intradermal Test: Inject 0.1 ml of cyst fluid antigen into the inner forearm and observe the reaction after 15-20 minutes. A positive reaction shows a local red papule, possibly with pseudopodia (immediate reaction), which begins to subside after 2-21/2 hours, followed by redness and induration after about 12-24 hours (delayed reaction). When there are sufficient antibodies in the patient's blood, the delayed reaction often does not occur. In cases of simple sexually transmitted diseases, both immediate and delayed reactions are positive. After puncture, surgery, or infection, the immediate reaction remains positive, but the delayed reaction is suppressed. The positive rate of the intradermal test is between 80-90%. However, false positives can occur; other Chinese Taxillus Herb infections, especially tapeworm diseases, have higher non-specific reactions, and cross-reactions can also be seen in malignant tumors and abdominal subcutaneous nodes.
(3) Serum Tests: Serological tests are used to detect antibodies in the patient's serum. There are various methods, but indirect hemagglutination and enzyme-linked immunosorbent assays are the most commonly used, with a positive rate of about 90%. False negatives or false positives can also occur. The positive rate of serological tests for pulmonary cystic echinococcosis is lower than that for hepatic cystic echinococcosis. The complement fixation test has a positive rate of 80%, with about 5% showing false positive reactions (there is cross-immunity between this disease and fluke disease and cysticercosis). Other tests include latex agglutination and immunofluorescence tests, which can be selected based on specific circumstances.
(4) Imaging Diagnosis: Includes X-ray examination, ultrasound, CT, and radionuclide scanning. Although these are important tools for diagnosing echinococcosis, results should be combined and comprehensively analyzed to aid diagnosis. For example, chest X-rays help in locating pulmonary echinococcosis. Hepatic echinococcosis shows round or oval low-density shadows of varying sizes on liver CT, with possible calcification inside or on the cyst wall. The edge of the low-density shadow shows wheel-like round cyst shadows of varying sizes, indicating the presence of multiple daughter cysts inside. B-type ultrasound is useful for the widespread screening of echinococcosis in endemic areas, preoperative localization of hydatid cysts, and postoperative dynamic observation.
The diagnosis relies on the following three points:
(1) Epidemiological data: This disease is seen in pastoral areas, and most patients have a history of close contact with dogs, sheep, etc.
(2) Clinical signs: If the above-mentioned patients have a slowly developing, painless abdominal mass (firm, smooth, cystic) or symptoms such as cough and hemoptysis, this disease should be suspected. Further examinations such as X-ray, ultrasound, CT, and radionuclide scans should be conducted to establish the diagnosis.
(3) Laboratory tests: The intradermal test has strong sensitivity but poor specificity. Among serological tests, immunoelectrophoresis and enzyme-linked immunosorbent assay (ELISA) have high sensitivity and specificity. However, the specificity and sensitivity of various immunological diagnostic methods are influenced not only by their inherent characteristics but also by factors such as the antigen used, operational methods, criteria for positive reactions, the impact of intradermal tests on serum reactions, as well as the location of the hydatid cyst, duration of infection, time since surgery, and individual immune responsiveness.
This disease should be differentiated from non-Chinese Taxillus Herb benign liver cysts, liver abscess, mesenteric cysts, giant hydronephrosis, lung abscess, subcutaneous pulmonary nodules, brain tumors, bone tumors, etc. Based on the unique characteristics of each disease, the diagnosis is generally not difficult to make.
bubble_chart Treatment Measures
Surgical operation is the preferred method for radical treatment of this disease and should be performed before the occurrence of compression symptoms or complications. During the operation, the cystic fluid is first aspirated with a fine needle (carefully preventing the overflow of cystic fluid), and then the inner cyst is removed. The inner cyst and the outer cyst have only grade I adhesion, which is very easy to peel off, and can often be completely removed. Echinococcosis in the lungs, brain, bones, and other parts should also be treated with surgical removal.
Before surgical removal of the hydatid inner cyst, 10% formalin solution is injected into the hydatid cyst to help kill the protoscoleces. Due to its irritant and occasional toxic side effects on lung tissue, it is particularly unsuitable for ruptured pulmonary or hepatic hydatid cysts. Some foreign researchers use cetrimide to kill protoscoleces, considering it an ideal scolicidal agent with low toxicity and good efficacy. Before human hydatid cyst removal, an appropriate amount of 0.1% cetrimide is injected into the cyst in two doses, each lasting 5 minutes. A 10-year follow-up report of 378 cases showed no recurrence of hydatid disease, whereas the recurrence rate was 10% before the use of cetrimide.
Benzimidazole compounds have been the focus of anti-echinococcosis drug research in recent years, both domestically and internationally, and have shown certain efficacy in clinical trials based on animal experiments. According to WHO, albendazole and mebendazole are both listed as the first-line drugs for anti-echinococcosis. Some authors believe that their indications are as follows: ① Secondary abdominal or thoracic echinococcosis, often occurring after the rupture of primary hepatic or pulmonary cystic echinococcosis, or due to inadequate protection during hydatid surgery, or misdiagnostic puncture leading to the spillage of hydatid fluid and secondary dissemination, making surgical eradication difficult. ② Multiple or multi-organ cystic echinococcosis, or recurrent echinococcosis, where patients are unwilling or unable to undergo repeated surgeries. ③ Elderly or weak patients, or those with organic diseases of important organs, who have poor surgical tolerance. ④ Advanced stage hepatic alveolar echinococcosis found during surgical exploration or that cannot be radically treated, or secondary pulmonary or cerebral metastases, where drug treatment can alleviate symptoms and prolong survival. ⑤ For both cystic and alveolar echinococcosis, chemotherapy as an adjunct before and after surgery can reduce recurrence rates and improve efficacy.
After the introduction of fenbendazole, there has been a trend to replace mebendazole in the treatment of echinococcosis. Albendazole is better absorbed, with serum concentrations 100 times higher than mebendazole. Its concentration in hydatid fluid is 60 times higher than mebendazole. For the treatment of cystic echinococcosis, the dose is 10-40mg/kg per day, divided into two doses, with a 30-day course, which can be repeated for several courses depending on the condition. Its efficacy is superior to mebendazole, especially for pulmonary echinococcosis. For alveolar echinococcosis, some domestic researchers recommend long-term high-dose albendazole treatment, with a daily dose of 20mg/kg, and the course can range from 17 months to 66 months (average 36 months). Long-term follow-up has shown significant improvement on CT scans, with most cases showing complete calcification of the original lesion area and a cure rate of 91.7%. Most patients can tolerate long-term treatment without serious toxic side effects, but liver and kidney function and bone marrow should be monitored during treatment. It is contraindicated in pregnant women.
The dosage and treatment course of mebendazole vary internationally. The dosage ranges from 20 to 200 mg/kg per day, with 40 to 50 mg/kg per day generally recommended, divided into three oral doses. The treatment course is one month, followed by a half-month break before starting another course, typically lasting three months in total. Some believe that treating cystic echinococcosis requires medication for 1 to 6 months, while treating alveolar echinococcosis may require an extended course, potentially lasting 3 to 5 years. Reports on efficacy vary, with some cystic echinococcosis patients potentially achieving a cure, and pulmonary echinococcosis showing better treatment outcomes than hepatic echinococcosis. Mebendazole has poor absorption, with only about 1% absorbed when taken on an empty stomach. To enhance efficacy, it is recommended to take the medication with a fatty meal, as the drug is more easily absorbed with fat. Reports indicate that absorption rates can increase to 5-20% when taken with a fatty meal.
The prognosis of this disease depends on factors such as the location and size of the hydatid cyst, as well as the presence of complications. The prognosis for echinococcosis in the brain and other vital organs is relatively poor.
Echinococcosis is a zoonotic disease, with intermediate hosts including livestock and wild animals. Its prevention is not only a complex issue within the field of biology but also a serious social problem. Comprehensive measures should be taken, including:
(1) Strengthening the management and control of dogs in epidemic areas. Cattle are a critical link in preventing human echinococcosis infection. In echinococcosis epidemic areas, stray dogs should be eradicated, and domestic dogs should be strictly controlled. Essential dogs such as sheepdogs, hunting dogs, or police dogs must be registered and tagged. Regular deworming and drug monitoring should be established as routine systems. According to reports from New Zealand, in Grade III epidemic areas, deworming medication should be administered every 6 weeks, while in Grade I epidemic areas, it should be administered every 3 months.
(2) Strict meat hygiene inspection. Meat processing plants or slaughterhouses must rigorously implement meat hygiene inspections. Organs such as the liver and lungs of infected animals must be properly inactivated, using methods such as centralized incineration, deep burial, or chemical treatment, and must not be fed to dogs.
(3) Vigorously promoting health education. The methods of education can be diversified, and the content should be simple, easy to understand, and practical. It is essential to fully mobilize the public to ensure that everyone is aware and informed.
It is often the initial symptom when patients seek medical attention. The main complications are: ① Cyst rupture: Hepatic hydatid cysts can rupture due to trauma or puncture. When rupturing into the abdominal cavity, it can be misdiagnosed as an acute abdomen, with severe abdominal pain accompanied by shock, followed by allergic symptoms. Therefore, liver puncture should be considered a strict contraindication in patients with hepatic echinococcosis. The pressure inside the hydatid cyst is very high, and puncture can not only lead to cyst fluid fistula disease and anaphylactic shock but also cause the protoscoleces to implant in the abdominal cavity, resulting in secondary hydatid cysts. If the cyst ruptures into the intrahepatic bile ducts, the fragmented cyst wall can cause bile duct obstruction, often leading to biliary colicky pain and jaundice. ② Infection: About 1/5 to 1/4 of hepatic hydatid cysts have secondary infections, mostly originating from the biliary tract. Pulmonary hydatid cysts with secondary infections are also quite common. Infection can promote the death of the hydatid but also significantly exacerbates the condition.
