form
Echinococcus granulosus
Adult is one of the smallest tapeworms, with a body length of 2 ~ 7 mm and an average of 3.6 mm. Except for the head and neck, the whole chain has only one young node, one mature node and one pregnant node, and even one. The head section is slightly pear-shaped, with a protrusion and four suction cups. The apical process is rich in muscle tissue and has strong elasticity. There are 28 ~ 48 small hooks with two circles of different sizes arranged radially. There are a group of spindle cells in the parietal gland, and their secretions may be antigenic. Each paragraph is long and narrow. The structure of the knot is slightly similar to that of tapeworm tapetum, and the reproductive hole is located at the middle and rear of one side of the knot. There are 45 ~ 65 testes, which are evenly distributed around the horizontal line of the genital foramen. The reproductive foramen of the pregnancy knot is farther back, and the uterus has irregular branches and lateral sacs, containing 200 ~ 800 eggs.
Eggs are basically the same as Taenia solium and Taenia solium, so it is difficult to distinguish them under light microscope.
Larvae, hydatid disease, is a round cystic body, and its diameter can range from less than 1cm to several 10cm, depending on the parasitic time, parasitic site and host. Echinococcus is a single-chamber cyst, which consists of cyst wall and cyst contents (germinal cyst, protocercaria, cyst fluid, etc.). Some people also have ties and grandchildren. The capsule wall is surrounded by the fibrous tissue of the host. The capsule wall is divided into two layers, the outer layer is a laminated layer, about 1mm thick, milky white, translucent, powdery, fragile and easy to break. Under the optical microscope, there is no cell structure, but there are multiple layers of texture. The inner layer is mucus layer, also called mucous layer, which is about 20μm thick and has nucleus. The mucus layer is close to the stratum corneum, and countless hairs extend into the stratum corneum from the mucus layer under the electron microscope. The cystic cavity is filled with cystic fluid, also known as hydatid fluid. The capsule fluid is colorless, transparent or yellowish, with a specific gravity of 1.0 1 ~ 1.02 and a pH value of 6.7 ~ 7.8. It contains a variety of protein, inositol, lecithin, urea and a small amount of sugar, inorganic salts and enzymes, and has antigenicity to human body.
The mucous layer (germ layer) grows a large number of protoscolices into the capsule. The original cephalic segment is oval or round, with the size of 170× 122μm, which means that the cephalic segment is turned inward. Its top protrusion and suction cup are invaginated, protecting dozens of small hooks. In addition, lime corpuscles can be seen. The difference between protocercaria and adult cephalic segment is that it is small in size and has no apical gland.
The germinal sac, also known as fertile sac, is a small sac with a mucous layer, with a diameter of about 1mm, which is developed from nucleated cells in the mucous layer. It has been observed that cells initially germinate from mucous layer to cyst. After these cells are hollowed out, they form cysts and grow stalks connected with the germ layer. Different numbers of protocysts are produced on the wall of microspore cysts, many of which can reach 30 ~ 40. The protocysticercus can grow into or out of the embryo sac as ectoplasmic protocysticercus.
The daughter cyst can grow directly from the mucus layer of the mother cyst (hydatid cyst), or it can develop further from the original cyst or germinal sac. The structure of the sac is similar to that of the mother sac, and the wall of the sac has a horny cortex and a mucus layer. There can also be protocysticercosis, embryo sacs and small sacs similar to the ascocyst structure, which are called granddaughter sacs. Some female cysts have no scoliosis and germinal cysts. This is the so-called dark side.
Protocercaria, embryo sac and ascocyst can shed from the germ layer and be suspended in cyst fluid, which is called cyst sand or hydatid sand.
Echinococcus granulosus
biography
The ultimate hosts of Echinococcus granulosus are carnivores such as dogs, wolves and jackals. The intermediate hosts are cloven-hoofed animals such as sheep, cattle, camels, pigs and deer, and can occasionally infect horses, kangaroos, some rodents, primates and people.
Adults parasitize the upper part of definitive host's small intestine, and are fixed in the crypt at the base of intestinal villi with small hooks and suckers on the apical process, and pregnant nodes or eggs are discharged with the feces of the host. The pregnancy node has strong mobility and can crawl along grass or plants, so that eggs pollute animal fur and surrounding environment, including pasture, barn, vegetables, soil, water and so on. When the intermediate host devours eggs and is pregnant, the coccidiosis hatches in its intestine, then burrows into the intestinal wall, circulates through the blood to organs such as liver and lung, and develops into echinococcosis with a diameter of 1 ~ 3 cm after 3 ~ 5 months. With the size and development of hydatid cysts, there are thousands to tens of thousands or even millions of protoscolices in the cysts. The original scoliosis can spread in the intermediate host to form a new echinococcosis, and can develop into an adult in the final host.
After echinococcosis is swallowed by dogs, wolves and other final hosts, every protoscolex contained in it can develop into an adult. So dogs and wolves have thousands to tens of thousands of adults in their intestines. It takes 8 weeks to ovulate from infection to maturity to save pregnancy. Most adults can live for about 5-6 months.
People can be used as the intermediate host of Echinococcus granulosus. When people eat eggs by mistake, hexagonal worms invade tissues through the intestinal wall with blood circulation, causing acute inflammatory reaction. If the larvae are not killed, they will gradually form a fibrous outer envelope and gradually develop into echinococcosis inside, so there is a fibrous membrane to separate the echinococcosis from the host. Generally, the cyst diameter reaches 0.5 ~ 1.0 cm after half a year of infection, and then it will increase by 1 ~ 5 cm every year, reaching 10cm at the longest. Echinococcus can survive in human body for 40 years or even longer. However, in the case of secondary infection or trauma, degeneration, decay, turbid cystic fluid may occur, and finally calcification will be absorbed.
Echinococcus can be found in almost all parts of the human body, the most common part is the liver (69.9%), mostly in the right lobe, followed by the lung (19.3%), in addition to abdominal cavity (3%) and primary liver metastasis to various organs (5.3%). Other sites were brain (0.4%), spleen (0.4%), pelvic cavity (0.3%), kidney (0.3%), chest cavity (0.2%), bone (0. 1%) and gallbladder (0.65438+). Echinococcus grows rapidly in lung and spleen. In bone tissue, it grows very slowly. Giant hydatid cyst is more common in abdominal cavity, which can occupy the whole abdominal cavity, push the diaphragm and even shrink a lung lobe. Echinococcus is generally a single parasite in human body, but multiple parasites are not uncommon, accounting for more than 20% of patients.
Pathogenesis and clinical symptoms
Echinococcosis is commonly known as echinococcosis. The harm of echinococcosis to human body is mainly mechanical injury, and the severity depends on the volume, quantity, parasitic time and location of echinococcosis. Because echinococcosis grows slowly, it often takes 5 ~ 20 years to show symptoms after infection. The primary infection of echinococcosis is mostly single, and the secondary infection is often multiple, which can involve multiple organs at the same time. Due to the continuous growth of echinococcosis, the surrounding tissues and organs are oppressed, resulting in atrophy and necrosis of tissues and cells. Therefore, the clinical manifestations are extremely complicated, and the common symptoms are:
Echinococcus granulosus
1, with symptoms of local compression and stimulation, slight pain and swelling. If the liver is involved, there may be symptoms of lung respiratory irritation such as liver pain, shortness of breath and chest pain, headache, vomiting and even brain epilepsy. Bone echinococcosis usually occurs in the center of pelvis, vertebral body and metaphysis of long bones, which can destroy bones and easily cause fractures or bone fragments. Echinococcus with superficial position can form a mass on the body surface, which is tough to touch and elastic to press, and has a trembling feeling when detained. If the tumor presses the portal vein, it can cause ascites, and pressing the bile duct can cause obstructive jaundice and cholecystitis.
2. Allergic symptoms usually include urticaria, angioneurotic edema and anaphylactic shock.
3, poisoning and gastrointestinal dysfunction such as loss of appetite, weight loss, emaciation, developmental disorders and cachexia.
Hydatid cyst once ruptured can cause secondary infection. For example, the rupture of hepatic hydatid cyst can enter the biliary tract, causing acute inflammation, biliary colic, chills, high fever, jaundice and so on. Invasion of abdominal cavity can cause acute diffuse peritonitis. Pulmonary echinococcosis can cough up small hair follicles, cysts and keratin fragments if it breaks into bronchi. A large amount of cystic fluid overflow can produce allergic reactions, such as entering the blood circulation, which can cause severe anaphylactic shock and even death.
diagnose
Asking about the medical history, knowing whether the patient is from an epidemic area, and the contact history with dogs, sheep and other animals and fur has certain reference value for diagnosis. X-ray, B-ultrasound, CT, MRI and isotope scanning are also helpful for the diagnosis and localization of echinococcosis. In particular, CT and MRI can not only diagnose asymptomatic carriers early, but also accurately detect various pathological images. However, the diagnosis should be based on the results of etiology, that is, surgical removal of echinococcosis, or discovery of echinococcosis fragments or scoliosis from sputum, pleural effusion, ascites or urine.
Immunological test is an important auxiliary diagnostic method. Commonly used methods include intradermal test and serological examination, such as ELISA, convection immunoelectrophoresis (CIEP), IHA, avidin-biotin-enzyme complex enzyme-linked immunosorbent assay (ABC-ELISA) and dot enzyme-linked immunosorbent assay (Dot-ELISA).
The epidemic Echinococcus granulosus has extensive host adaptability and is distributed all over the world. Mainly for the circulation between dogs and cloven-hoofed livestock. In China, it is mainly sheep/dog animal cycle, and yak/dog cycle is only found in alpine meadows and foothills of Qinghai-Tibet Plateau and Gansu Province.
China is one of the countries with the most serious echinococcosis epidemic in the world. The main epidemic areas are in the vast agricultural and pastoral areas in the west and north of China, namely Xinjiang, Qinghai, Gansu, Ningxia, Tibet, Inner Mongolia and Sichuan, followed by parts of Shaanxi, Shanxi and Hebei. In addition, there are sporadic cases in three northeastern provinces, Henan, Shandong, Anhui, Hubei, Guizhou and Yunnan. Up to now, 23 provinces, municipalities and districts in China have confirmed local infected patients. According to the incomplete statistics of several key endemic provinces, the population threatened by echinococcosis in China is about 50 million, with about 500,000 to 600,000 patients. Preschool children are the most susceptible to infection (15 accounts for 32. 1% of the 5289 patients in Xinjiang). The infection rate of sheep, the intermediate host of main animals, is between 3.3% and 90%, and that of domestic dogs is between 7% and 71%. With the implementation of the western development strategy, the prevention and treatment of the disease has increasingly become an important task.
Echinococcus granulosus
Epidemic factors mainly include the following three points:
1, the pollution of eggs to the environment, the dog infection in pastoral areas is usually heavier, and the amount of eggs in dog feces is large, which causes serious environmental pollution with animal activities and the spread of dust, wind and water. Eggs have strong resistance to external low temperature, dryness and chemicals. It can survive for 2.5 years in water at 2℃ and 4 months in ice, and it is still contagious after severe winter (-12 ~- 14℃). Ordinary chemical disinfectants can't kill eggs.
2. Infections of children in pastoral areas like close contact with domestic dogs and are easy to be infected. Shearing, milking and processing fur can all cause adult infections. In addition, they can be infected by eating water, vegetables or other foods contaminated by eggs. Infections of domestic dogs and wild animals are often caused by feeding the internal organs of sick animals to dogs or littering them everywhere, resulting in infections of wild dogs, wolves and jackals. , thus aggravating the infection of sheep and cattle and making the epidemic situation more and more serious.
In non-endemic areas, people are infected by occasional contact with infected dogs or contact with animal fur from endemic areas. With the rapid development of China's economy, a large number of livestock products from epidemic areas have flowed to the mainland, and new pastures and grasslands have been opened up in various places, and a large number of livestock have been introduced and raised. New pollution areas may be formed. Therefore, it is necessary to strengthen the prevention and treatment of the disease.
Prevention and control principle
Epidemic areas should take comprehensive preventive measures, mainly including the following aspects:
1, strengthen health education, publicize and popularize echinococcosis knowledge, raise the awareness of disease prevention of the whole people, strengthen personal protection in production and life, and avoid infection.
2, strengthen the construction of health regulations and health quarantine, strengthen the public health behavior norms, and eradicate the bad habits of feeding dogs with sick animals and littering. Strengthen the quarantine of slaughterhouses and individual butchers, and deal with the internal organs of sick animals in time.
3. Regularly deworm domestic dogs and herding dogs to reduce the source of infection.
On 1992, the Ministry of Health promulgated the National Echinococcosis Prevention and Control Plan. After years of implementation in epidemic areas, remarkable results have been achieved, and the infection rate of domestic dog sheep in many places has dropped rapidly.
Surgery is the first choice for the treatment of echinococcosis, and attention should be paid to taking out the cyst during the operation to avoid anaphylactic shock or secondary abdominal infection caused by the overflow of cyst fluid. The early stage of mucro coccidiosis can be treated with drugs. At present, albendazole has the best effect, and praziquantel and mebendazole can also be used.