Food contamination by Trichinella spiralis

作者：admin  点击次数：25  发布时间：2025-04-07

Trichinella spiralis is a roundworm (trichinella spiralis). Its adult parasitizes in the intestine, called intestinal trichinella, and its larvae parasitize in the striated muscle and form cysts, called muscle trichinella. Humans and almost all mammals (such as pigs, dogs, cats, mice, wild boars, etc.) can be infected. The trichinellosis caused by it is an important zoonosis parasitic disease, which is very harmful.
1. The pathogen Trichinella spiralis belongs to the class Nematoda, the order Trichocera, and the family Trichoderma. It is a small nematode with male and female bodies. The size of male worms is (1.4~1.6) mmx(0.04~0.05) mm, and the size of female worms is (3~4) mm x0.06 mm. The adult worms are short white velvety filamentous nematodes observed with the naked eye. When the larvae are just born, they are slender and cylindrical. The worm body parasitizing in the striated muscle is spirally curved, covered with an oval cyst parallel to the muscle fibers, with cyst fluid inside, which can contain 1~2 larvae. The cysts in the muscles are generally (0.25~0.3)mmx(0.4~0.7)mm, and appear white and needle-like when observed with the naked eye. The main parasitic sites are the diaphragm, tongue muscle, myocardium, pectoralis major and intercostal muscles, with the diaphragm being the most common. The cysts have strong resistance to the external environment and can withstand low temperatures. The cysts in pork will not die until 20 days of storage at -15℃, and can remain active for 57 days at -12℃; the cysts can also survive for more than 100 days in rotten meat. Processing methods such as smoking, pickling and sun exposure cannot kill the cysts, but heating to 70℃ can kill them. Trichinella spiralis is a permanent parasite. The same animal is both its final host and its intermediate host. It does not need to develop in the external environment or in the intermediate host.
2. Causes and clinical symptoms
Humans are infected with Trichinella spiralis because they eat raw or undercooked pork or wild boar meat. A few people are also infected by eating other human meat (such as dogs, sheep, horses, etc.). Causes of infection: First, it is related to the habit of eating meat. Surveys show that more than 90% of the cases are related to eating raw pork; second, it is caused by meat scraps contaminating tableware, fingers and food, especially when cooking and processing are not distinguished between raw and cooked; third, the larvae of Trichinella spiralis in feces, soil and insects may also become the source of infection. When people ingest animal muscles containing larval cysts, the cysts are digested, the larvae escape, drill into the mucosa of the duodenum and jejunum, and develop into adults within 2 days. Larvae begin to be produced 7 to 10 days after mating. Each female worm can produce 1,000 to 10,000 larvae with a lifespan of 4 to 6 weeks. The larvae pass through the intestinal wall and circulate in the blood to reach the striated muscles of various parts of the human body, and generally form cysts within 1 month after infection. The cysts begin to calcify within a few months to 1 to 2 years. The calcification of the cysts does not affect the life of the worm (if the worm dies, it will also be calcified). The lifespan of muscle Trichinella spiralis can reach several years.
In the early stage of human infection with Trichinella spiralis (adult parasitic stage, about 1 week), enteritis will occur, and most patients will experience symptoms such as nausea, vomiting, abdominal pain, and blood in the stool. In the middle stage (larval migration stage, 2-3 weeks), acute vasculitis and muscle inflammation will occur, manifested as headache, high fever, fear of cold, and itching of muscles all over the body, especially in the limbs and waist; after the pain occurs, edema of the eyelids, face, limbs or lower limbs will occur, and the skin of the edematous area will be red and shiny. In addition, solid organs such as the heart, liver, lungs and kidneys can cause functional damage to varying degrees, accompanied by peripheral neuritis, visual and hearing impairment, hemiplegia, etc. The terminal stage (cyst stage, 4-16 weeks) manifests as dull muscle pain, and severe cases may die from toxemia or complications.
3. Identification and treatment of trichinosis in pigs
Take the diaphragmatic foot of the pig and tear the membrane to check for small white spots as big as a needle tip and necrotic foci. Compress the tablets and examine the 24 meat particles for Trichinella spiralis cysts and worm bodies. It can also be tested by the sample digestion method.
If no more than 5 cysts or calcified Trichinella are found in 24 meat samples, the striated muscle and heart will be processed at high temperature and then exported; if more than 5 are found, the striated muscle and heart will be used for industrial purposes or destroyed. However, subcutaneous and intermuscular fat can be refined into edible oil, and body cavity fat can be shipped without restrictions.
4. Preventive measures
Strengthen health publicity, popularize knowledge about Trichinella, change eating habits, do not eat raw or half-cooked pork and other animal meat to prevent infection; strengthen meat hygiene inspection and processing system; strengthen pig feeding management, pigs should be kept in pens, and pigs should not be fed with raw or mixed with meat scraps; eliminate rodents to reduce the source of infection.