2 English references Entamoeba histolytica
Entamoeba histolytica
Entamoeba histolytica (1903) belongs to Entamoeba of Entamoebaceae. In the past, it was thought that Entamoeba histolytica usually lived in the colon of the host, but only invaded the intestinal wall or was carried to other organs by blood flow under certain conditions to cause disease. In 1928, Brumpt proposed that there are two kinds of Entamoeba histolytica, one of which can cause amoebiasis, and the other is similar to Entamoeba dispersa in morphology and life history, but it is not pathogenic. In the late 1970s, researchers confirmed that Entamoeba histolytica and Entamoeba dispersa were indeed two different insect species by analyzing antigenicity and small subunit ribosomal RNA(SSUrRNA). Entamoeba histolytica is the cause of amoebiasis, while Entamoeba dispersa is not pathogenic.
The morphology of Entamoeba histolytica can be divided into two stages: cyst and trophozoite, and the mature 4-nuclear cyst is the infection stage.
Figure 1 Entamoeba histolytica (stained with hemlock)
3. 1 Entamoeba histolytica The size of the trophozoite is between10 and 60 mm ~ 60 mm. When it is separated from the tissues of symptomatic patients, it often contains ingested red blood cells, and sometimes white blood cells and bacteria can be seen. The trophozoite moves with the aid of one-way pseudopodia, which has a transparent outer substance and a granular inner substance, a spherical cystic nucleus with a diameter of 4 ~ 7 mm, and a single layer of chromatin particles at the edge of the thin nuclear membrane, which are evenly distributed and uniform in size. However, the trophozoites in the culture medium often have more than two nuclei, and the nucleoli is small, with a size of 0.5mm, often located in the middle, surrounded by slender colorless filamentous structures.
3.2 The process of cyst formation by cyst trophozoite in intestinal cavity is called cyst station. Trophoblasts cannot be wrapped in organs outside the intestinal cavity or outside the intestine. In the intestinal cavity, the trophozoite gradually shrinks, stops moving, becomes an approximate spherical anterior capsule, and then becomes a nucleated capsule for binary division and proliferation. There is a special nutritional storage structure in cytoplasm, that is, chromosome-like body, which is short and rod-shaped, which is of great significance to the identification of insect strains. There are glycogen vacuoles in the immature sac. The mature cyst has four nuclei, round, with a diameter of 10 ~ 16 mm and a wall thickness of 125 ~ 150 nm. The nucleus is cystic, similar to trophozoite, but slightly smaller.
The life history of Entamoeba histolytica is a suitable host for Entamoeba histolytica, and cats, dogs and mice can also be used as occasional hosts. The life history of Entamoeba histolytica includes cyst stage and trophoblast stage. The infection stage is mature tetranuclear cyst. Infectious cysts in food and drinking water contaminated by feces are ingested through the stomach and small intestine. In the neutral or alkaline environment at the end of ileum or colon, due to the movement of worms in the capsule and the action of intestinal enzymes, the wall of the capsule becomes thinner at a certain point, the worms in the capsule stretch many times, the pseudopoda expands and contracts, and the worms come out of the capsule. After three cytokinesis and one mitosis, the tetranuclear worm develops into eight trophozoites, and then it feeds on bacteria in the upper colon and undergoes binary division and proliferation. In the process of moving down in the intestinal cavity, with the dehydration of intestinal contents and the change of environment, the worm forms a round anterior capsule, secretes a thick capsule wall, and forms a tetranuclear capsule through secondary mitosis, which is discharged with feces. Cysts can survive in humid environment and remain infectious for several days to a month, but they are easy to die in dry environment.
The trophoblast can invade the intestinal mucosa, devour red blood cells, destroy the intestinal wall, cause intestinal ulcer, and also enter other tissues or organs with blood flow, causing extraintestinal amebiasis. The trophozoites that fall off with necrotic tissue and enter the intestinal cavity can be excreted with feces through intestinal peristalsis. The trophozoite can only survive for a short time in the external natural environment. Even if swallowed, it will be killed by digestive juice when passing through the upper digestive tract.
5. Pathogenicity of Entamoeba histolytica 5. 1 Pathogenesis Entamoeba histolytica trophozoites have the ability to invade host tissues or organs, adapt to host immune response and express pathogenic factors. Pathogenic factors expressed by trophozoites can destroy extracellular matrix, contact-dependent dissolve host tissue and resist the dissolution of complement, among which destroying extracellular matrix and dissolving host tissue are important ways for worms to invade. The transcription level of these pathogenic factors is an important mechanism to regulate their pathogenic potential.
Among the pathogenic factors affecting Entamoeba histolytica, three pathogenic factors have been widely studied and clarified at the molecular level: 260kDa galactose/galactosamine lectin (Gal/GalNAclectin) mediates the adsorption to host cells; Amoeba pores form pore destruction in host cells; Cysteine protease dissolves the host tissue.
The trophozoite is first adsorbed on the intestinal mucosa by 260kDa lectin, and then secretes perforin and protease to destroy the intestinal mucosal epithelial barrier and perforated cells, killing the host intestinal epithelial cells and immune cells, causing ulcers, and then leading to intestinal infection, which is the pathogenic feature of Entamoeba histolytica.
260kDa lectin mediates the adsorption of trophozoites on the colon epithelium, neutrophils and erythrocytes of the host. Lectins also play an important role in cell lysis after adsorption. In addition, this lectin is also involved in cell signal transduction. Amoeba perforin is a group of small molecular protein contained in the cytoplasm of trophozoites. Perforin can be injected into trophozoites when it comes into contact with target cells or invades tissues, so that the target cells form ion channels, which is related to the damage of host cells and the dissolution of red blood cells and bacteria. Cysteine protease is the most abundant protease in worms, which belongs to the papain family and has many isomers. It can make target cells dissolve or degrade complement C3 into C3a, thus resisting complement-mediated anti-inflammatory reaction and degrading serum and secretory IgA. Some people think that 260kDa lectin is also related to anti-complement effect.
5.2 Pathological intestinal amebiasis mostly occurs in cecum or appendix, and it is also easy to involve sigmoid colon, ascending colon and even ileum. The typical lesion is a flask-shaped ulcer with a small mouth and a large bottom. The mucosa between ulcers is normal or slightly congested and edematous, which is different from diffuse inflammatory lesions caused by bacteria. Except for severe cases, primary lesions are confined to the mucosal layer. Microscopically, tissue necrosis is accompanied by a small number of inflammatory cells, mainly lymphocytes and plasma cells. Because trophozoites can dissolve neutrophils, there are few neutrophils. In acute cases, trophozoites can break through the muscularis mucosa, causing liquefied necrotic foci, and the formed ulcers can reach the muscularis mucosa and fuse with the adjacent ulcers, causing large-scale exfoliation of mucosa. Entamoeba is a proliferative response of colonic mucosa to Entamoeba, mainly tissue granuloma with chronic inflammation and fibrosis. Although only 1% ~ 5% patients are accompanied by amebic swelling, it needs to be differentiated from tumors.
Extraintestinal amebiasis is usually aseptic liquefaction and necrosis, surrounded by lymphocyte infiltration, less neutrophils, and trophozoites are mostly located at the edge of abscess. Liver abscess is the most common. Early trophozoites invaded the small blood vessels of the liver, causing embolism, and then acute inflammatory reaction occurred. Later, the focus expanded and the center liquefied. Abscess varies in size and consists of necrotic liver cells, red blood cells, bile, fat droplets and tissue residues. Abscess can also occur in other tissues, such as lung, abdominal cavity, pericardium, brain and reproductive organs. The main pathological features are sterility and liquefactive necrosis.
5.3 The incubation period of clinical manifestations of amoebiasis ranges from 2 days to 26 days, with 2 weeks being the most common. The onset is sudden or hidden, which can be explosive or protracted, and can be divided into intestinal amebiasis and extraintestinal amebiasis.
(1) intestinal amebiasis
Entamoeba histolytica trophozoites invade the intestinal wall, causing intestinal amebiasis. The common sites are cecum and ascending colon, followed by rectum, sigmoid colon and appendix, sometimes involving all or part of ileum of large intestine. The clinical process can be divided into acute or chronic. The clinical symptoms in acute stage range from mild and intermittent diarrhea to fulminant and fatal dysentery. Typical amebic dysentery often has diarrhea, several times or dozens of times a day, and the feces are jam-colored, with a strange smell, blood and mucus. 80% patients have localized abdominal pain, discomfort, flatulence, acute diarrhea, anorexia, nausea and vomiting. Acute fulminant dysentery is a serious and fatal intestinal amebiasis, usually a pediatric disease. From acute type to acute explosive type, patients have a lot of mucus and bloody stools, fever, hypotension, extensive abdominal pain, severe and persistent diarrhea, nausea, vomiting and ascites. Intestinal perforation or extraintestinal amebiasis can occur in 60% patients. Some mild patients only have intermittent diarrhea. Chronic amoebiasis is characterized by long-term intermittent diarrhea, abdominal pain, flatulence and weight loss, which can last for more than 1 year or even 5 years. Some patients have amebic tumor, also known as amebic granuloma, which is an asymptomatic mass-like lesion. Barium meal fluoroscopy looks like a tumor, and pathological biopsy or positive serum amoeba antibody can be used for differential diagnosis.
The most serious complications of intestinal amoebiasis are intestinal perforation and secondary bacterial peritonitis, which are acute or subacute processes.
(2) Extraintestinal amebiasis.
It is caused by intestinal submucosa or muscle trophozoites entering veins and spreading to other organs through blood. Amebic liver abscess is the most common. Young men are the most common patients, and abscesses are more common in the right lobe, especially in the top of the right lobe. 10% of intestinal amoeba cases were accompanied by liver abscess. Clinical symptoms include right epigastric pain and right shoulder radiation, fever, hepatomegaly and tenderness, chills, night sweats, anorexia and weight loss, and a few patients may even have jaundice. Puncture of liver abscess shows "chocolate sauce" like pus, and trophozoites can be detected. Liver abscess can break into chest cavity (10% ~ 20%) or abdominal cavity (2% ~ 7%). In rare cases, liver abscess can rupture into pericardium, which is often fatal.
Multiple pulmonary amebiasis mainly occurs in the lower right lobe, followed by liver abscess and diaphragm perforation, mainly manifested as chest pain, fever, cough and coughing up "chocolate sauce"-like sputum. X-ray examination showed exudation, consolidation or abscess formation, pus accumulation and even bronchopulmonary fistula. Abscess can break into trachea and cause airway obstruction. If the abscess breaks into the thoracic cavity or trachea, drainage combined with drug treatment is very important, but the mortality rate is still close to 15% ~ 30%.
About 1.2% ~ 2.5% patients may have brain abscess, and 94% patients with brain abscess are complicated with liver abscess, which is often a single abscess in the central cortex. The clinical symptoms are headache, vomiting, dizziness and mental abnormality. 45% patients with brain abscess can develop meningoencephalitis. The course of amebic brain abscess progresses rapidly, and if it is not treated in time, the mortality rate is high.
Cutaneous amebiasis is rare and often spreads to * * * due to rectal lesions, and the damage to * * * will spread to * * *, * * and even the uterus; It can also occur around thoracoabdominal fistula caused by rupture of liver abscess.
The experimental diagnosis of Entamoeba histolytica mainly includes etiological diagnosis (including nucleic acid diagnosis), serological diagnosis and imaging diagnosis.
6. 1 pathogen diagnosis (1) Normal saline smear method: stool examination is still the most effective method for intestinal amoebiasis. This method can detect active trophozoites. Generally speaking, trophozoites are common in loose stools or purulent bloody stools, and ingested red blood cells can be seen in the trophozoites. However, due to the rapid death of worms after contact with urine and water, we should pay attention to rapid detection and keep the temperature above 25 ~ 30℃ to prevent urine pollution. However, it should be noted that some antibiotics, laxatives or astringents, and * * * liquid will affect the survival and activities of worms, thus affecting the detection rate.
It is also feasible to examine the abscess puncture fluid smear, but it should be noted that most worms are on the abscess wall and need puncture.
And should pay attention to the inspection. In addition, trophozoites need to be distinguished from host cells under the microscope. The main points of differentiation are as follows: ① The trophozoite of Entamoeba histolytica is larger than the host cell; ② The ratio of nucleus to cytoplasm is smaller than that of host cells; ③ The trophozoite is a vesicular nucleus with a middle nucleolus, and the staining plasmid around the nucleus is clear; ④ The cytoplasm of trophozoites can contain red blood cells and tissue fragments.
(2) Iodine smear method: For patients with chronic diarrhea, the cyst is mainly examined, and iodine staining can show the nucleus of the cyst and make a differential diagnosis. The detection rate can be increased by 40% ~ 50% by formaldehyde ether precipitation encapsulation method. In addition, for some chronic patients, stool examination should last for 1 ~ 3 weeks, and check many times to avoid missed diagnosis.
(3) In vitro culture: Culture method is of great significance for the diagnosis and preservation of insect species, and it is more sensitive than smear method. The culture is usually feces or abscess extract. Using Robinson medium, the detection rate of subacute or chronic cases is relatively high. In stool examination, Entamoeba histolytica must be distinguished from other intestinal protozoa, especially Entamoeba coli and Entamoeba hartmann. At present, there are many methods that can be used to identify Entamoeba histolytica and Entamoeba dispersa, such as isozyme analysis, enzyme-linked immunosorbent assay, polymerase chain reaction PCR and so on.
(4) Nucleic acid diagnosis: This is a sensitive and specific diagnostic method developed rapidly in recent ten years. We can use the DNA of pus, puncture fluid, feces culture, biopsy of intestinal tissue, skin ulcer secretion, purulent bloody stool and even worms in feces to shape, and then use specific primers for polymerase chain reaction. The amplified products can be distinguished from other amoebas by electrophoresis analysis.
6.2 Serodiagnosis Since the success of Entamoeba histolytica sterile culture, serological diagnosis has developed rapidly. About 90% patients can detect the corresponding specific antibodies from serum by indirect hemagglutination test (IHA), ELISA or agar diffusion method (AGD).
1997, the WHO Committee suggested that the cysts with four nuclei found under the microscope should be identified as Entamoeba histolytica/Entamoeba dispersa; Entamoeba histolytica infection should be highly suspected when trophozoites containing red blood cells are detected in feces. Serological examination results show that high titer positive should be highly suspected of entamoeba histolytica infection; Amoebiasis is only caused by Entamoeba histolytica.
3. Imaging diagnosis? Ultrasound examination and computed tomography (CT) can be used for extraintestinal amebiasis, such as liver abscess, and X-ray examination is the main method for lung lesions. Imaging diagnosis should be combined with serological test, DNA amplification analysis and clinical symptoms in order to make early and accurate diagnosis.
4. Differential diagnosis? Intestinal amebiasis should be differentiated from bacillary dysentery, with acute onset, fever, poor general condition, many white blood cells in feces, effective antibiotic treatment and negative amoeba trophozoite. Amebic liver abscess should be mainly differentiated from bacterial liver abscess, which usually occurs in people over 50 years old, with poor general condition, fever and pain, previous history of gastrointestinal diseases, and negative amoeba trophozoite test. At the same time, amebic liver abscess should also be differentiated from liver cancer, hepatitis or other abscesses.
7. Epidemic and control of Entamoeba histolytica 7. 1 The epidemic and spread of Entamoeba histolytica is worldwide, but it is common in tropical and subtropical regions, such as India, Indonesia, Sahara Desert, tropical Africa and Central and South America. According to the domestic 1988 ~ 1992 survey, the national average infection rate is 0.949%, and the estimated number of infected people is10.69 million, mainly distributed in northwest, southwest and north China. Among them, the incidence of amoebiasis in Yunnan, Guizhou, Xinjiang and Gansu is more closely related to sanitary conditions and socio-economic conditions than climate factors. There is no gender difference in intestinal amoebiasis, but there are more men than women with amoebic liver abscess, which may be related to diet, living habits and occupation. In recent years, the infection rate of amoeba among gay men is particularly high, which was reported to be 40% ~ 50% in 1970s, and 20% ~ 30% in Europe, America and Japan. In Europe and the United States, Entamoeba dispersus is the main species, while among Japanese homosexuals, Entamoeba histolytica is the main species. The high-risk groups suffering from amoebiasis include tourists, floating population, mentally retarded people and homosexuals, and serious infections often occur in children, especially newborns, pregnant women, lactating women, patients with low immune function, patients with malnutrition or malignant tumors, and patients who take adrenocortical hormone for a long time. The peak age of infection is 14 children and adults over 40 years old.
The source of infection of amoebiasis is cyst carriers or cyst passers-by. The cyst has strong resistance, can survive for several weeks at suitable temperature and humidity, and remains infectious, but it is not resistant to dryness and high temperature. Cysts passing through the digestive tract of flies or cockroaches are still contagious. Entamoeba histolytica has poor resistance to trophozoites and can be killed by gastric acid without spreading. The main route of human infection is oral infection, which can be infected by eating food contaminated with feces containing mature cysts, drinking water or using contaminated tableware. Foodborne outbreaks are caused by unsanitary eating habits or eating food prepared by cyst carriers. In addition, for people who have oral sex and anal sex, cysts in feces can directly invade through the mouth, so amebiasis is listed as a sexually transmitted disease (STD) in Europe, America, Japan and other countries, but it has not been reported in China, but it should be paid attention to.
7.2 Metronidazole is the first choice for the treatment of amoebiasis. It is suitable for patients with acute and chronic invasive intestinal amoeba, and is absorbed almost 100% orally. Besides, tinidazole, ornidazole and secnidazole seem to have the same effect. However, some data show that metronidazole or tinidazole is mainly used for tissue infection and has no radical effect on intestinal pathogens, so it is not suitable for treating asymptomatic cyst patients.
Generally speaking, asymptomatic cyst carriers do not need treatment if they are infected with Entamoeba histolytica. However, because the methods and techniques for distinguishing Entamoeba histolytica from Entamoeba histolytica have not been widely used, and 65,438+00% of cyst carriers are infected with Entamoeba histolytica, it is still recommended to treat asymptomatic cyst carriers. In addition, because the surface lectin of amoeba can replicate HIV, HIV-infected people infected with amoeba should be treated regardless of whether they are pathogenic or not.
For the treatment of cyst patients, we should choose drugs that are not easily absorbed by intestinal wall and have little side effects, such as paromomycin, iodoquine and desLasanyi.
The treatment of extraintestinal amoebiasis, such as liver, lung, brain and skin abscess, is mainly metronidazole, and chloroquine is also an effective drug. Drug therapy combined with surgical puncture and drainage can achieve good results in patients with liver abscess. Allicin and Pulsatilla chinensis also have certain curative effects, but it is difficult to achieve the goal of radical cure simply with traditional Chinese medicine.
7.3 The prevention of amoebiasis is a worldwide public health problem. While treating diseases, comprehensive measures should be taken to prevent infection. The specific method includes harmless treatment of feces to kill cysts; Protect water and food from pollution; Do a good job in environmental sanitation and drive away harmful insects; Strengthen health education and improve self-protection ability.