Parasite contamination of food and its prevention

作者：admin  点击次数：29  发布时间：2025-04-06

Parasites refer to worms that cannot survive completely independently and need to parasitize other organisms. The organisms parasitized by parasites are called hosts of parasites. Among them, the hosts parasitized by adults and sexual reproduction stages are called definitive hosts; the hosts parasitized by larvae and asexual reproduction stages are called intermediate hosts. Parasites survive in their parasitic hosts and cause harm to the hosts by competing for nutrients, mechanical damage, embolism of blood vessels, and secretion of toxins. Parasites and their eggs directly contaminate food or contaminate water or soil through the feces of patients and sick animals, and then contaminate food. People ingest foodborne parasitic diseases through oral ingestion.
(I) Contamination of food by cysticercosis
Cysicercosis refers to the larvae of hooked tapeworms, namely pork tapeworms, and hookless tapeworms, namely beef tapeworms. People can be parasitized by adults or by the larvae of pork tapeworms (cysticercosis), especially the latter, which is more harmful to humans. 1. Pathogens
The pathogens that cause human cysticercosis are pork tapeworm and beef tapeworm. Pork tapeworm belongs to the family Taeniaceae and the genus Taenia. Mature pork tapeworms are oval, milky white, translucent, and filled with fluid. The size of the cyst is (6~10)mmx5mm. It is located in the connective tissue between muscle fibers, and its long diameter is parallel to the muscle fibers. The cyst wall is a thin film. The naked eye can see mung bean-sized milky white dots on the cyst wall. They are concave into the cyst cavity and are inverted scolex. The scolex has 4 suckers and 1 apex, and there are 11~16 pairs of small hooks on the apex. Pork cysticercosis mainly parasitizes in the medial vastus muscle, deep psoas muscle, scapular muscle, masseter muscle, internal oblique muscle, diaphragm and myocardium. It can also parasitize in the brain, eyes, pleura and intercostal muscle membranes. The cysticercosis in the muscle is the size of rice or beans. Such meat is usually called "rice pork" or "bean pork". The adult pork tapeworm is ribbon-shaped, up to 2 to 8 meters long, and can be divided into scolex, prescolex and body segments, with 700 to 1000 segments. Its scolex is the same as the cysticercus, and can be firmly attached to the small intestinal wall to absorb nutrients. The neck segment is slender, closely attached to the back of the scolex, and is its growing part. The body segment is divided into three parts: immature, mature and pregnant. The eggs are dark in color, containing embryos with 3 pairs of small hooks, called hexahook larvae. Adults mainly parasitize the human small intestine. The larvae and adults of beef tapeworm are similar to those of pork tapeworm, but its scolex has no hooks and is fixed to the intestinal wall by suckers.
2. Causes and clinical symptoms
People are infected by eating raw or undercooked "rice pork". Under the action of gastric juice and bile, the scolex is turned out in the small intestine and then attached to the intestinal wall. Segments gradually grow from the neck, and develop into adults after 2 to 3 months. Gravid segments begin to be excreted with feces. The life span of an adult can reach more than 25 years. Generally, one person can be infected with 1 to 2, and occasionally 3 to 4. Patients show symptoms of loss of appetite, weight loss, chronic indigestion, diarrhea, or alternating diarrhea and constipation. In addition to being the final host of tapeworms, humans can also be intermediate hosts. In addition, pigs, wild boars, dogs, and sheep are also intermediate hosts. The eggs of tapeworms must be excysted in the stomach under the action of gastric acid before they can develop into cysticerci and infect humans. Therefore, the ways in which humans are infected with cysticercosis are: ① Heterologous infection. It is caused by eating food contaminated with eggs. ②) Autologous in vitro infection. When a person is infected with tapeworms in the body, due to poor personal hygiene habits, the eggs are ingested through hands or food, causing cysticercosis. ③ Autologous in vivo infection. The human body itself has adult parasites in the intestines. Vomiting for some reason causes the gravid segments in the intestines to reverse peristalsis and enter the stomach, which is equivalent to eating a large number of worm eggs from the mouth and causing self-infection. After the eggs hatch in the duodenum of the human body, they enter the small veins and lymphatic vessels of the mesenteric mesentery, and then sink into the body tissues with the blood flow to form cysticerci. Its symptoms are: ① Subcutaneous and muscle cysticercosis. The patient has local muscle soreness and swelling. ② Brain cysticercosis. The patient may suffer from epilepsy, meningitis, increased intracranial pressure, dementia, convulsions, paralysis and even death due to compression of brain tissue. ③ Ocular cysticercosis. Parasitism in the eyes can cause vision loss or even blindness, and may also cause changes in movement, sensation, reflexes, headaches, dizziness, nausea and other symptoms. 3. Identification and treatment of porcine cysticercosis
Identification is carried out according to the location of cysticercosis, cyst morphology, and microscopic examination of its head segment structure. If there are less than 3 (including 3) cysticerci and calcified worms found in the inspectable part of the pig within an area of ​​40cm, the whole meat carcass shall be frozen or salted before being shipped out; if there are 4 to 5 worms, they shall be shipped out after high temperature treatment; if there are 6 to 10 worms, they shall be used for industrial purposes or destroyed. If the worms can be removed, they can be used as raw materials for replicas; if there are more than 11 worms, they shall be used for industrial purposes or destroyed; the stomach, intestines and skin shall be shipped out without restrictions, and other internal organs shall be shipped out without restrictions if there are no cysticerci in the inspection; subcutaneous fat shall be refined into edible oil or used as raw materials for replicas, and body cavity fat shall be shipped out without restrictions if there are no worms in the inspection. For frozen or salted pork cysticerci meat, whether the pork cysticerci in the meat are dead or not, the activity of pork cysticerci shall be determined. The method is bile stimulation method: 10 pork cysticerci to be inspected are placed in a culture dish containing 80% bile saline and cultured in a 38℃ incubator for 1 to 3 hours. If the head section automatically turns out and can move, it indicates that the pig cysticercosis is alive and the processed pig cysticercosis is not lethal, so it must be frozen or treated at high temperature.
4. Preventive measures Strengthen the meat hygiene inspection and processing system, implement "fixed-point slaughter and centralized quarantine" for live pigs; strengthen health publicity and education in epidemic areas to make people understand the harm of tapeworm/cysticercosis, do not eat raw pork and meat products that are not fully roasted and cooked, separate raw and cooked knives, cutting boards, rags, and containers for cutting meat, and disinfect them in time. Pigs should be kept in pens to prevent pigs from cannibalism and infection; pay attention to hygiene and develop good hygiene habits, strengthen the harmless treatment of feces; raw vegetables, fruits and melons should be washed and disinfected, drinking water should be disinfected, and drinking raw water is strictly prohibited.