Detection of parasites in food of animal origin - double-chamber flukes

Dicrocoelium lanceatum and Dicrocoelium chinense are bilocarminal fluoros, often parasitic in the bile ducts and gallbladders of livestock livers, which can cause zoonotic parasitic diseases——— bilosullar fluke disease, also known as bilocal trematodiasis. The disease occurs throughout the country, especially in the northwest, Inner Mongolia and northeast China. Insects can parasitize sheep, goats, cattle, deer, camels, pigs, horses, dogs, rabbits, monkeys, etc., and are occasionally seen in humans. But the disease mainly harms ruminants, and severely infected sheep sometimes even die.

1 Etiological features

The body of the spear-shaped ambiguity flux is flat, transparent, brownish red, and visible to the internal organs with the naked eye; the surface is smooth, the front end is thin, the posterior end is blunt, and the spear-shaped; the body length is 5 to 15 mm, and the width is 1.5 to 2.5 mm. The ventral suction cup is larger than the mouth suction cup. 2 testicles, nearly rounded or slightly lobed, diagonally or juxtaposed anteriorly and posteriorly after the ventral suckers. To the right of the posterior side of the testicles are the ovaries and fertilized vesicles, and the yolk glands are small granular and distributed on both sides of the central part of the worm. The posterior part of the worm body is a zigzag uterus filled with worm eggs. The eggs are ovate or oval, dark brown, thick shell, slightly asymmetrical on both sides, and are (38 to 45) μm in size× (22 to 30) μm. The eggs have a distinct egg cap at one end and contain trichoderma.

The body of the Chinese cavity flux is flat and transparent, the front body of the abdominal suction cup is head-conical, and the posterior sides are wider, like shoulder-like protrusions; the body length is 3.5 to 9.0 mm, and the width is 2.63 to 3.09 mm. The two testicles are irregularly rounded with irregular margins or slightly lobed, juxtaposed after the abdominal suction cups. The testicles are followed by the ovaries. The yolk glands are arranged on either side of the central part of the worm. The posterior part of the worm body is filled with uterus. Eggs are similar to spear-shaped ambiguity trematodes eggs.

2 Epidemiological features

The disease is distributed almost all over the world and is mostly endemic. In China, it is mainly distributed in the northeast, north China, northwest china and southwest provinces, especially in the northwest provinces and Inner Mongolia. The host animals are extremely extensive, with more than 70 species of mammals recorded so far, and many wild ungulates can be infected in addition to domestic animals such as cattle, sheep, camels, deer, horses and rabbits. In the warm and humid southern region, the first and second intermediate host snails and ants can be active throughout the year, so animals can be infected almost all year round; and in the cold and dry northern region, because the middle dwelling is mainly hibernating, animal infection obviously has the characteristics of spring and autumn, but animal diseases are mostly in winter and spring. With the increase of animal age, its infection rate and infection intensity also gradually increase, and the number of infected insects can reach thousands or even tens of thousands, which indicates that the animal's acquired immunity is poor. Eggs are more resistant to external environmental conditions, remain infectious after months of survival in soil and feces, and are more resistant to low temperatures. Eggs and stages of larvae in the first and second intermediate hosts can overwinter without losing infectivity.

3 Hazards

Bilumen flukes are distributed worldwide and are widely distributed in China. The intermediate hosts of bilocarp flukes are snails and ants, terrestrial species that do not depend on water and whose eggs can survive for several months on dry pastures. Human infection with the disease is mainly opportunistic, inadvertently swallowing ants and being infected, so the infection rate of the population is low, mainly manifested as symptoms of dyspepsia. Livestock as the terminal host infection of the disease is mainly caused by swallowing an intermediate host containing mature tail larvae, adult parasitizes the bile ducts and gallbladder of the terminal host livestock, mild infection is asymptomatic, severe infection causes bile duct fibrosis and sclerosis, sometimes the bile ducts are significantly dilated.

4 Domestic and foreign health requirements

In the process of meat quarantine, if double-chamber fluke disease meat is found, the damaged organs will be systemized, and other parts will not be restricted from leaving the factory (field).

5 Detection methods

Pathogenic testing

Live animal testing

Clinical symptoms vary depending on the intensity of infection in livestock after infection with biloxazoata. Mildly infected livestock are usually asymptomatic; in severe cases, they manifest as visible mucosal yellowing, submandibular edema, digestive disorders, diarrhea and gradual loss of weight, and may even die of extreme exhaustion. Live animals mainly rely on fecal water washing and precipitation to find insect eggs.

Meat testing after slaughter

After the animal is slaughtered, the internal organs are examined by autopsy, and the insect body is found in the bile duct and gallbladder to make a diagnosis. The main lesions on autopsy are catarrhal inflammatory changes in the bile ducts and hypertrophy of the bile duct wall, hyperplasia of connective tissue around the bile ducts, and the bile ducts inhabited by insects often have a coarse cord of uniform thickness. The liver becomes hard and enlarged, and scars form on the surface of the liver, most notably in the marginal parts. The larger bile ducts are incised to show that the worm body flows out with the bile. The liver can be shredded in water and the worm body can be examined by continuous washing. For details, see "Test methods for parasites in imported and exported food" (SN/T1748-2006).