[Overview
Trichinosis (trichinosis, trichinellosis) is a zoonotic parasitic disease caused by Trichinella spiralis (Trichinella spiralis), which is prevalent among mammals, and people are infected by eating raw or semi-cooked pork containing Trichinella encysted. The main clinical manifestations are gastrointestinal symptoms, fever, myalgia, edema and blood eosinophilia.
【Diagnosis】.
Diagnosis based on.
① history of ingestion of raw pork, etc. 1 to 2 weeks (1 to 40 d) before the disease;
The clinical features are mainly fever, muscle pain and edema, rash, etc. Initially, there may be gastrointestinal symptoms, significant increase in total blood leukocytes and eosinophils, etc;
③Confirmation of diagnosis depends on muscle biopsy to find larvae or (and) serological examination.
Treatment measures
(a) General treatment Those with obvious symptoms should be bed rested and given adequate nutrition and water. Analgesics may be given for significant myalgia. Severe patients with significant anisotropic protein reactions or myocardial or central nervous system involvement may be given adrenocorticosteroids, preferably together with insecticides. The general dose of prednisone is 20-30mg per day for 3-5d, which can be extended if necessary; hydrocortisone 100mg/d can also be used as above in an IV course.
(B) pathogenic treatment benzimidazole drugs to albendazole as the first choice, its efficacy, light side effects. Domestic doses of 15mg/kg/day, 24-32mg/kg, divided into 2-3 oral doses, a course of 5d (10d for the longest) of different programs, have achieved good results. If necessary, 1 or 2 courses of treatment can be repeated every 2 weeks. Generally in 2-3d after taking the drug body temperature decreased, myalgia reduced, swelling disappeared, a few cases in the 2-3d after taking the drug, the body temperature response due to.
Thiabendazole has the effect of killing both adult and larvae (migratory stage and encapsulation stage); the dose is 25mg/kg, twice a day for 5-7d, and the treatment can be repeated after several days if necessary; this product may occasionally cause dizziness, nausea, vomiting, abdominal discomfort, dermatitis, decreased blood pressure, slowed heart rate, increased serum transaminases and other reactions, and the addition of prednisone can reduce the reaction. The efficacy of mebendazole on all stages of Trichinella larvae is up to 95%, but the efficacy on adult worms is slightly lower; the adult dose is 100mg, taken 3 times a day for 5-7d (larvae) or more than 10d (adults).
Pathogenesis】
The female trichinella is 3-4mm long, and the male is only 1.5mm long, usually parasitized in the duodenum and upper jejunum wall, and after mating, the female dives into the mucosa or reaches the mesenteric lymph nodes and discharges the larvae. The latter are distributed throughout the body by lymphatic vessels or blood vessels through the liver and lungs, but only those reaching the transverse muscles can continue to survive. The diaphragm, gastrocnemius, buccinator, deltoid, biceps and lumbar muscles are most susceptible, followed by the abdominal muscles, eye muscles, pectoral muscles, collar muscles and gluteus muscles.
At 5 weeks after infection, the larvae form 0.4×0.25(mm) olive-shaped sacs between the fibers, which mature within 3 months (as infective larvae) and calcify within 6 months to 2 years, but because of their small size, they are not easily detected by X-ray. The larvae in the calcified encysts can live for 3 years (11 years for those in pigs). After the mature capsule is swallowed by the animal, the larvae escape from the capsule in the upper part of the small intestine and burrow into the intestinal mucosa, where they develop into adults after four exfoliations. Adult and larvae are parasitized in the same host.
Epidemiology
(A) Infectious source
Other carnivores such as rats, cats, dogs, sheep and many wild animals such as bears, wild boars, wolves and foxes can also be infected by killing each other and swallowing or eating the carcasses of animals containing Trichinella cysts. Two transmission rings of the disease have been proposed, namely the domestic animal ring and the wild animal ring. Humans are collateral to these two rings, and both rings can operate independently in the absence of human infection.
(ii) Transmission routes
Humans become infected by swallowing pork, dog, lamb or wild boar containing encapsulated meat. The outbreak is closely related to the habit of eating raw meat.
(C) Susceptible people
People are generally susceptible to the disease and can develop significant immunity after infection, and those who are reinfected are far less ill than those who are first infected.
(D) Epidemic situation
Trichinosis is scattered around the world, with a high incidence in Europe and the United States. Domestic prevalence is mainly in Yunnan, Tibet, Henan, Hubei, Northeast, Sichuan and other places, Fujian, Guangdong, Guangxi and other places where the disease also occurs. In recent years, the infection rate of pigs is generally 0.1-0.2%, and the detection rate in some areas is 2% or 7%, and the detection rate of pigs sent to slaughter in some areas is as high as 50%. The rate of infection and the degree of infection in rats is also higher and heavier.
Clinical manifestations
The strength of the pathogenic effect of Trichinella on humans is related to the number of ingested larval encysts and their vitality, as well as the host’s immune function status and other factors. In mild cases, it can be asymptomatic, but in severe cases, it can be fatal. The infection process of Trichinella in humans can be divided into the following three phases.
(a) Invasive stage (small intestine stage, about 1 week) The decapitated larvae burrow into the intestinal wall and mature, causing extensive duodenal inflammation, mucosal congestion and edema, bleeding and even superficial ulceration. About half of the patients have gastrointestinal symptoms such as nausea, vomiting, diarrhea (dilute stool or watery stool, 3-6 times a day), constipation, abdominal pain (mainly in the upper abdomen or umbilicus, with vague pain or burning sensation), loss of appetite, accompanied by weakness, chills and fever within a week after infection. A few patients may have respiratory symptoms such as chest pain, chest tightness and cough.
(B) Larval migration period (2-3 weeks) In the second week after infection, the female produces a large number of larvae, which invade the blood circulation and migrate to the transverse muscle. A vascular inflammatory reaction may occur at the site of larval migration, causing a significant heterogeneous protein response. Clinically, flaccid hyperthermia occurs, lasting from 2 d to 2 months (average 3-6 weeks), with a few cases of saddle fever. Some patients have a rash (maculopapular rash, urticaria, or scarlet fever-like rash).
Trichinella larvae can invade any transverse muscle causing myositis: loss of myocyte transverse muscle, degeneration, infiltration of lymphocytes, macromonuclear cells, neutrophils and eosinophils, and even epithelioid cells around the larvae; clinically there is muscle soreness and localized edema with pressure pain and significant weakness. Myalgia usually lasts 3 to 4 weeks, and some can last more than 2 months. Myalgia is severe and generalized. Most of those with rash have ocular symptoms. In addition to ocular myalgia, there is often eyelid and facial swelling, bulbar conjunctival congestion, blurred vision, diplopia, and retinal hemorrhage.
In severe infections, the lung, myocardium and central nervous system are also involved, resulting in focal (or extensive) pulmonary hemorrhage, pulmonary edema, bronchopneumonia and even pleural effusion; myocardial and endocardial congestion, edema, interstitial inflammation and even myocardial necrosis and pericardial effusion; non-suppurative meningoencephalitis and increased intracranial pressure. Blood eosinophils are often significantly increased (except for very heavy cases).
(C) Intramuscular capsule formation period (1 to 2 months after infection) with the formation of intramuscular capsule, acute inflammation subsides, systemic symptoms reduce, but myalgia can continue for a long time, but there is no definite basis for turning chronic. Severe patients may be cachectic, deflated, or die due to toxemia and myocarditis.
Auxiliary examination
(A) Blood picture The white blood cell count and eosinophils increase significantly in the early migratory phase, reaching 1-20,000/mm3, but eosinophils may not increase in severe patients.
(B) Muscle biopsy A small slice of muscle near the tendon of the deltoid or gastrocnemius muscle (or the part with swelling and most significant myalgia) was taken in the fourth week after infection, placed in two slides and compressed, and observed under low magnification. Muscle biopsy is affected by the limitations of the extracted tissue and it is not easy to detect larvae in early and mildly infected cases. If the infection is mild and the microscopic examination is negative, the muscle slice can be digested with pepsin and dilute hydrochloric acid, and the larvae can be examined after centrifugation and precipitation.
(C) Immunological examination Trichinella antigens can be divided into worm antigens, worm soluble antigens (there are two kinds of soluble crude antigens and soluble antigens extracted from alpha particles in the rod cells of infected larvae), surface antigens (soluble antigens extracted or stripped from the surface of the worm), and excretory secretory antigens (or metabolic antigens).
A variety of immunological examination methods have been tried at home and abroad, including intradermal test, complement binding test, saponin (also known as American clay, bentonite) flocculation test, convective immunoelectrophoresis, cyclic larval precipitation test, indirect fluorescent antibody test (IFA), indirect hemagglutination test (IHA), enzyme-linked immunosorbent assay (ELISA) and indirect immunoenzymatic staining test (IEST). The latter four of them are highly specific, highly sensitive and can be used for early diagnosis.
①IFA has diagnostic value for both early and mild infections. Using whole larvae as antigen, a fluorescent precipitate around the larval cortex or at the mouth of the larvae is a positive reaction. Patients can show positive reactions 2-7 weeks after infection.
②IHA was used to detect antibodies in the patient’s serum with freeze-dried sensitized sheep red blood cells and IHA. There is no significant difference in the results with filter paper dried blood drops instead of serum, which is suitable for epidemiological investigation.
ELISA is more sensitive than IFA and often uses saline leachate as antigen.
④IEST uses frozen sections of infected mouse muscle as antigen, and IEST is used to detect antibodies in patient serum. The serological test starts to be positive at 2-4 weeks after infection and is mostly positive at 7 weeks after infection. The reaction is particularly diagnostic if it changes from negative to positive, or if the antibody potency increases fourfold. Serological examination has achieved good results in the detection of antibodies, but after human and animal infection with Trichinella, antibodies persist in the serum, which is not conducive to the assessment of efficacy. In recent years, monoclonal antibodies to Trichinella larvae have been successfully prepared at home and abroad.
Using the soluble antigen of the worm, excreted secretory antigen combined with monoclonal antibody, polyclonal antibody – indirect double antibody sandwich ELISA method to detect the circulating antigen in the patient’s serum, antigen-positive results suggest that the current infection, and has the value of efficacy assessment.
Differential diagnosis
The disease should be differentiated from food poisoning (initial stage), eosinophilic diseases such as polyarteritis nodosa, rheumatic fever, dermatomyositis, leptospirosis, and epidemic hemorrhagic fever. Epidemiological information has important reference value for differential diagnosis.
Prevention
(a) Strengthen health education
Not eating raw or undercooked pork and other mammalian meat or meat products is the simplest and most effective preventive measure.
(B) Control and manage the source of infection
Improve I pig methods, advocate circle I, isolate and treat sick pigs; exterminate rats to prevent rodent feces from contaminating pens; cook feed to prevent pigs from infection.
(C) strengthen meat inspection
Without inspection is not allowed to sell. Stock pork by low-temperature freezing treatment, refrigerated at -15 ℃ for 20d, or -20 ℃ for 24h, can kill the larvae.