Prevention and control of fascioliasis in antler deer in grassland area

Fascioliasis is a parasitic helminthiasis that can occur in cattle, sheep, horses, deer and even humans. It is also often called liver bdellosis. In the deer farms in the grassland areas, although the disease has decreased in recent years, it still occurs from time to time in the deer herds of some farmers. In areas where fascioliasis is endemic, people may suffer from fascioliasis if they do not have enough understanding of the disease and do not take necessary prevention and control measures in production. In summer and autumn, the suitable climatic conditions and the existence of intermediate host (mainly amphibious and near-terrestrial freshwater snail-small vertebra solid snail), deer grazing or feeding forage grass in low-lying land, it is easy to cause fascioliasis. Even in winter, deer can be attacked by feeding hay from contaminated pastures or lowlands.

1 clinical manifestations of diseased deer

The sick deer are in low spirits and often live alone in the enclosure. they gradually lose weight, the coat is withered and dull, and the capillaries are brittle and easy to take off. The nose is dry and the mucous membrane is yellow or pale. The amount of forage is reduced, often gnawing on the coat or licking dung, urine, masonry and other foreign bodies. The sick deer regurgitate slowly and sometimes have constipation or dysentery. The adult male deer is sick, such as in the antler-growing period, the horn disc falls off slowly, the velvet antler grows slowly, and the type and color are poor, and it often develops into a morbid dry and thin type of "lack of raising antler", which greatly reduces its medicinal and economic value. In serious cases, velvet antler can hardly grow. In addition, there are also some sick deer, often without obvious clinical symptoms, sudden death. This situation is more common when the body weight of deer decreases in winter and spring.

2 pathological changes of dead deer

After death, the liver of diseased deer is often enlarged, the edge is obtuse and round, the liver capsule has different number of punctate bleeding, and there are fibrous and exudative inflammation. Many grayish-white cicatricial "insect pathways" are often seen in the liver tissue. The parenchyma of the liver faded and hardened. The bile duct is hypertrophic and dilated, in which there are often a varying number of Fasciola hepatica. In some cases, localized suppurative foci of different sizes were also formed in the liver tissue or bile duct. There are also cases of peritonitis with a lot of mixed-blood effusion in the abdominal cavity.

3 Life history of Fasciola hepatica

The fecundity of Fasciola hepatica parasitic in the bile ducts of cattle, sheep, horses, deer and other hosts is very strong. An adult can lay 100000 eggs in one day and night. The eggs produced are excreted by the host as bile flows into the intestines and mixes with faeces. Under the environmental conditions of suitable temperature, sufficient oxygen, proper water and sunlight, the eggs hatched into cercariae after 10 to 15 days. The cercariae swim in the water, and when they encounter the intermediate host, the small vertebra solid snail, they actively drill into the snail body, develop into cystic metacercaria in the lymphatic space of the snail, and then become cercariae. At the same time, the cercariae can be seen in the liver of the snail, and then turn into cercariae in the liver tissue of the snail after 35 to 40 days (when the food of the snail is sufficient, the cercariae stage can also develop into daughter cercariae). In a snail infected with cercariae, there are often 300Mel 850 cercariae, or more. Finally, the cercaria drilled out of the snail, swam in the water, took off its tail, covered the body with its cystadenic secretions, adhered to the stems and leaves of aquatic plants or floated in the water to form metacercaria. Fascioliasis may occur when cattle, sheep, horses, deer and other animals feed on contaminated aquatic plants or drink contaminated water and swallow infectious metacercariae.

4 Prevention and treatment of Fasciola hepatica

From the life history of Fasciola hepatica, it can be seen that the larvae of Fasciola hepatica are infectious to deer only when they develop into metacercariae, while the occurrence of fascioliasis in deer is possible only after ingesting infectious metacercariae by mouth. Therefore, in order to prevent the occurrence of Fasciola hepatica in deer, the following two points must be done: one is to block the breeding way of metacercaria, the larva of Fasciola hepatica, and the other is to kill metacercariae and make them lose the ability to infect animals, or to stop the disease from entering through the mouth, so that the infected metacercariae can not enter the deer through the mouth. To this end, the following prevention and control measures can be taken.

4.1 Preventive deworming of deer with ivermectin or albendazole in spring and autumn can also be used for early treatment of diseased deer.

4.2 Deer dung was piled up and fermented, and biological heat was used to kill the eggs.

4.3 transform low-lying waterlogged grasslands and marshes into dry land, so as to destroy the development conditions of liver leech eggs and the living conditions of small vertebrae snails.

4.4 Chemical drugs such as copper sulfate or ammonia were used to kill freshwater snails.

4.5 reduce freshwater snails through @ # @ 231 snail @ and other ways.

4.6 in grasslands where fascioliasis is endemic, metacercariae may exist in water and grass. The metacercariae floating in the water are usually the most in the water surface, followed by the middle layer, and the least in the bottom layer. Therefore, when picking and cutting aquatic plants, the stubble can be left higher, about 10-15cm beyond the water surface, so that the cut aquatic plants have less metacercaria pollution as far as possible.

4.7 the metacercariae adhered to the stems and leaves of aquatic plants can maintain their infectivity for a long time with only a small amount of humidity, such as the moisture of dew in the morning and evening, and in the environment of 4 ℃ and 6 min. In wet hay or water, metacercaria can survive for more than 5 months, but under dry and direct sunlight conditions, they will die after 4 weeks. Therefore, when picking and cutting water plants, do not put the cut water plants on the surface of the water, but should be fully dried in a high dry place to kill the metacercariae that may adhere to them. In conditional deer farms, the sun-dried forage grass can be stored for 6 months before feeding.

4.8 in areas where fascioliasis is endemic, grazing deer or harvesting water grass to feed deer in low-lying grasslands, ponds, marshes or canals should be avoided. This is especially true in the warm seasons of prolonged drought and rain, rainy years and after heavy rains in summer and autumn. Because fresh Rain Water can stimulate a large number of mature cercariae to escape from the snail, which is conducive to the formation of metacercaria and aggravate its pollution to aquatic plants.

4.9 pay attention to the cleanliness of drinking water, and it is best to let deer drink deep well water or tap water.

5 discussion

5.1 in the grassland areas where Fasciola hepatica is endemic in Northeast China, it is best to carry out preventive deworming of deer twice a year: one in late autumn and early winter, and the other in late winter and early spring. If the deer is infected with Fasciola hepatica in summer and autumn, the weather becomes cold after winter, most of the nutrients in the roughage are lost, and the physique of the deer (especially the adult male deer over 3 or 4 saw age) decreases. The pathogenicity of Fasciola hepatica will be revealed. Therefore, deworming at the end of autumn and the beginning of winter can prevent Fasciola hepatica from "taking advantage of virtual chaos", which is conducive to the safety of deer through the winter. Disinfestation in late winter and early spring can further remove the Fasciola hepatica remaining in deer, which is beneficial to the fattening and rejuvenation of deer, and improve the survival rate of female deer and the antler production level of male deer.

5.2 when oral medication is given to deer herds, the sex, age and body condition of each herd should be the same, and the number of deer in each herd should not be too many, generally 15 deer, no more than 20 deer, in order to avoid excessive differences in individual drug intake during mixed feeding. At the same time, attention should be paid to the selection of safe and effective oral insect repellents, such as albendazole. However, from a practical point of view, the effect of ivermectin injection is relatively definite.

5.3 in northeast China, some deer farmers, in order to promote the early recovery of deer from cold winter and dry spring and increase antler production, often mow and feed deer early in warm seasons where aquatic plants such as river ponds and marshes flourish. However, from the history of the development of metacercaria, such aquatic plants are easily contaminated.

5.4 Deer liver fascioliasis has no special clinical manifestations, and only some simple symptoms can not be diagnosed. When there is Fasciola hepatica parasitism in deer, it may not be fascioliasis, and there is often the phenomenon of "healthy paragonimiasis". The diagnosis of fascioliasis of deer liver should be based on the comprehensive analysis of fecal examination of eggs and observation of clinical manifestations. Some related clinical symptoms of deer suffering from this disease often occur when the body weight of deer decreases in winter and spring, as well as single nutrition and poor feeding and management.