Detection of parasites in food of animal origin – roundworms

Roundworm is a collective name for ascarididae nematodes, which can cause parasitic diseases ——— ascarworm diseases in animals, especially juveniles, which are common and frequent diseases of livestock and poultry parasitic diseases, and are extremely prevalent and widely distributed, and the harm to livestock and poultry is extremely serious. Different species of roundworms have different intrinsic hosts (obligate hosts), such as as the ascaris suum, which does not parasitize neither equine animals nor ruminants. Horse roundworms parasitize only horses, mules, and donkeys, not pigs. Zoonotic roundworm diseases include swine ascariasis and tondosa in dogs and cats. Pig roundworms are mainly parasitic in pigs, occasionally infected with people and calves, pig roundworm infection is common, widely distributed, mainly harmful to 3 to 6 months old pigs, so that pigs are stunted, serious can cause death, high infection rate, up to 50% or more. Swine ascariasis is one of the most common and frequent important diseases in piglets, and it is also one of the parasitic diseases with the greatest loss in the pig industry. Studies have shown that human roundworms and pig roundworms are two different species of insects. Human ascarworm disease is a common disease caused by ascaris lumbricoides parasitizing the human small intestine or other organs, and the majority of patients are children, and most of them have no obvious self-conscious symptoms clinically.

1 Etiological features

Pig roundworms parasitize the small intestines of pigs and are a large nematode with a fresh body of reddish or yellowish body that turns pale after death. The body is thick in the middle and slightly thinner at both ends, resembling an earthworm. There are 3 lip pieces at the tip of the head, 1 with a larger dorsal lip and 2 smaller ventral lips, arranged in a "pin" glyph. Males are smaller than females, generally 15 to 25 cm long, with a diameter of about 0.3 cm at the widest point, and the tail end is curved towards the ventral surface, resembling a fish hook. The opening of the cloaca is closer to the tail end and there are 1 pair of intersecting syrup. The female is 20 to 40 cm long and has a diameter of about 0.5 cm at its widest point. The body is straighter , the tail is blunter , and the reproductive organs are bi-tubular.

Pig roundworm eggs: Fertilized eggs and unfertilized eggs are morphologically different. The fertilized eggs are short oval in shape, with a size of (50 to 75) μm× (40 to 80) μm, yellow-brown, thick egg shell, and protein membranes. Unfinished eggs are long, narrow, oblong-shaped, with an average size of 90 μm×40 μm, a thin shell, and most have no protein membrane. The size of human roundworms and their eggs is similar to that of pig roundworms and their eggs.

Pig roundworm life history: roundworms do not require an intermediate host for development. His life history includes three stages: the development of the eggs outside, the migration and development of the larvae in the host, and the parasitism of the adults in the small intestine.

After the eggs are excreted with feces, the unfertilized eggs cannot develop, and the fertilized eggs are in the external environment of humidity, shade, oxygen adequacy and suitable temperature (28 ~ 30 ° C), after about 10 days, the egg cells develop into stage 1 larvae, and then after a period of growth and metamorphosis, becoming stage 2 larvae. This egg is not yet infectious to the host, and it must go through a maturation process of 3 to 5 weeks in the outside world to reach the infectious stage, which is an infectious egg.

After the infected eggs are swallowed by pigs, they hatch in the small intestine, hatch the 2nd stage larvae into the liver, develop into the 3rd stage larva after the 2nd molting, the 3rd larvae enter the lungs with the blood, and after the 3rd molting, they become the 4th larvae, grow rapidly in the lungs, the 4th stage larva reaches the small intestine through the trachea, and after the 4th molt, it gradually grows and becomes an adult. It takes 2 to 2.5 months for the eggs of the self-infected worm to be swallowed into adult worms in the small intestine. Porcine roundworms are excreted with feces after 7 to 10 months of parasitism in the host, and if the host is no longer infected, roundworms can be excreted in the 12th to 15th months. After a person is infected with roundworms, the adult roundworms usually survive in the human body for about 1 year.

2 Epidemiological features

Swine ascariasis is widespread, with piglet ascariasis being particularly common. Roundworms have a strong reproductive capacity, and each female can lay an average of 200,000 eggs per day. The eggs are very resistant to various environmental factors, and in addition to the certain humidity required by the eggs, the temperature has a greater impact on them. Oxygen is a necessary factor for the development of eggs, which develop rapidly in oxygen-rich environments but survive in hypoxic environments. Pig roundworm eggs can survive for 2 to 3 years in moist arable land or garden soil. Pig roundworm eggs die within days of tropical sandy surfaces and in direct summer sunlight.

Roundworm eggs are also very resistant to various chemicals, such as in 2% formaldehyde, the eggs can develop normally. Therefore, the epidemic of swine ascariasis is closely related to feeding management and environmental health, in poor feeding management, poor sanitary conditions and overcrowded pig farms, in the case of nutritional deficiencies such as lack of vitamins and minerals in feed, 3 to 5 months old piglets are most likely to be infected with roundworms in large numbers, the symptoms are also serious, and often die.

Pig infection with roundworms is mainly due to the feeding of feed and drinking water infected by infected eggs, and the sow's udder is easily contaminated with insect eggs, making the piglets infected when sucking milk.

Pig roundworms occasionally infect cattle, causing acute atypical interstitial pneumonia, which can lead to cattle death. It can also infect lambs, clinical pneumonia and liver leukoplakia lesions.

There have been a few cases of human infection with swine roundworms, and pig roundworm larvae can invade the human liver, lungs and small intestine, which can produce serious symptoms, but the insect body generally cannot reach sexual maturity in the human body. For people who frequent and live on pig farms, swine roundworms may become an important pathogen of their occasional infection.

3 Hazards

3.1 Hazards to Animals

Adult worms parasitize the small intestine of pigs, the damage to the mucous membrane is not obvious, the number of insects can cause intestinal obstruction, sometimes the worm body can migrate to the bile ducts, causing obstructive jaundice, most animals due to gastrointestinal function is destroyed, often have loss of appetite, teeth grinding and slow growth and other manifestations. The harm of larvae to pigs stems from the migration of in vivo, causing damage to organs and tissues, of which the harm to the liver and lungs is greater. When roundworms develop to sexual maturity, the pathogenic effect is significantly weakened, and in severe infection, due to the mechanical stimulation and obstruction caused by the insect body seizing nutrients, its wandering characteristics, and the absorption of toxic substances, causing serious harm and even causing death. Adult worms enter the stomach, bile ducts, pancreatic ducts, can cause obstruction, vomiting, jaundice and digestive disorders, the insect volume caused intestinal obstruction, seriously lead to intestinal rupture, intestinal perforation, and secondary peritonitis, causing death. Toxic substances and metabolites secreted by roundworms cause allergic symptoms, paroxysmal spasms, excitement and paralysis, manifested by wasting, stunting and growth stoppage, often caused by reduced resistance and caused complications and even death.

3.2 Harm to persons

When a person is infected with roundworms, adults parasitize in the small intestine, mainly in the jejunum and upper ileum. Pathogenic effects of adult worms:

(1) Damage to the intestinal mucosa The mechanical effect of roundworms' lips and teeth and the chemical stimulation of metabolites can damage the intestinal mucosa and cause inflammatory lesions; ascaria parasitizes in the small intestine can damage the intestinal mucosa, mainly the jejunal mucosa.

(2) Plundering nutrients, causing malnutrition Roundworms feed on semi-digested materials in the human intestinal lumen, coupled with digestive and absorption disorders caused by intestinal mucosal damage, causing malnutrition, especially affecting children's absorption of protein, fat, carbohydrates and vitamins, so that children have malnutrition.

(3) Toxic effects of adult roundworms Roundworms can cause allergic reactions in the human body, such as urticaria, fever, asthma, conjunctivitis, angioedema, skin itching, abdominal pain, diarrhea, etc., and even cause degeneration of internal organs.

(4) Complications Roundworms have drilling habits, often causing ectopic damage, mainly manifested as intestinal perforation, intestinal necrosis, intussusception, intestinal volvulus, etc. Adults can burrow into the common bile duct, causing bile duct ascariasis.

4 Domestic and foreign health requirements

Hygiene requirements and treatment: when the damage to the liver, lungs and intestines is minor, the damage part will be removed, and the other parts will not be restricted from leaving the factory (field); if the damage is serious, the entire organ will be made or destroyed. Diseased pork with jaundice is prepared or destroyed.

5 Detection methods

A comprehensive diagnosis is based on epidemiology, clinical symptoms, adult infection, and fecal egg testing.

5.1 Etiologic methods

Eggs in the feces are detected by pathogenic examination, which can be made a rapid diagnosis. Commonly used saline direct smear method, due to the large amount of eggs laid by roundworms and easy to identify, the detection rate of 1 smear can reach about 80%, and the detection rate of 3 smears can reach 95%. For mildly infected patients or those who need quantitative diagnosis and efficacy assessment, the concentration method can be selected, and the current commonly used methods are modified Kato method and saturated brine floating method. The diseased pig was diagnosed before death, and the saturated saline floating egg collection method was mostly used for feces. In 1 g of feces, when the number of eggs reaches 1000, it can be diagnosed as ascariasis.

5.2 Immunological methods

Due to the large amount of ovulation of female roundworms every day, the pathogenic diagnosis can be obtained by simple stool testing, so the research and application of immunodiagnostic techniques has been slow. At present, the methods used include live larva precipitation reaction, IHA and ELISA, but most of them are still in the experimental stage.

5.3 Molecular biology methods

When distinguishing between human ascariasis and swine ascariasis, the isoenzyme lactate dehydrogenase (LDH enzyme), malate dehydrogenase MDH enzyme) and esterase profile can be analyzed by enzymatic profiles. It is also possible to analyze 17 amino acids of human roundworms and porcine roundworms and body wall protein components, as well as DNA nucleic acid analysis. According to the existing research conclusions, the protein profiles of female adult adults of human and pig roundworms were analyzed by two-dimensional polyproprylamide gel electrophoresis (2D-PAGE), and the protein composition of the two roundworms was different, but the DNA content was not different.