Control methods for fascioliasis in deer in grassland areas
Fascioliasis is a parasitic helminth disease that can occur in cattle, sheep, horses, deer, and even humans, and is also commonly called liver fluke disease. In deer farms in grassland areas, although this disease has decreased in recent years, it still occurs from time to time in the deer herds of some breeders. In areas where fascioliasis is prevalent@#@253@#@, if people lack sufficient awareness of this disease and do not take necessary control measures in production, they may suffer its harm. In grassland areas where summer and autumn climatic conditions are suitable and the intermediate host (mainly a freshwater snail that is amphibious but tends toward terrestrial life, the small lymnaeid snail) exists, deer grazing on low-lying land or fed forage from low-lying land are prone to fascioliasis. Even in winter, if deer are fed hay from contaminated pasture or low-lying land, they can also be attacked by the disease.
1 Clinical manifestations of diseased deer
Diseased deer are listless, often stand alone in a corner of the pen, gradually become emaciated, and have a dry, lusterless coat with brittle, easily shed hair. The nasal mirror is dry, and the visible mucous membranes are icteric or pale. Feed intake decreases, and they often gnaw hair or lick feces, urine, bricks, stones, and other foreign matter. Diseased deer ruminate slowly and sometimes develop constipation or diarrhea. When adult male deer are affected, if it occurs during the antler-growing period, the casting of the antler buttons is delayed, antler growth is slow, and the shape and color are poor; they often develop into abnormal, dry, thin "malnourished antlers," greatly reducing their medicinal and economic value; in severe cases, the antlers can hardly grow at all. In addition, some diseased deer often show no obvious clinical symptoms and die suddenly. This situation is more commonly seen in winter and spring when the body condition of deer declines.
2 Pathological changes in dead deer
After diseased deer die, the liver is commonly seen to be enlarged with blunt, rounded edges, and the liver capsule shows varying numbers of petechial hemorrhages, with fibrinous and exudative inflammation. In the liver tissue, many grayish-white, scar-like, cord-like "fluke tracts" are often seen. The liver parenchyma is discolored and hardened. The bile ducts are thickened and dilated, and varying numbers of Fasciola hepatica are often present within them. In some cases, localized purulent foci of different sizes also form in the liver tissue or bile ducts. Some cases also show peritonitis, with much blood-mixed fluid in the abdominal cavity.
3 Life history of Fasciola hepatica
Fasciola hepatica parasitizing the bile ducts of the liver of hosts such as cattle, sheep, horses, and deer has very strong reproductive capacity; one adult fluke can lay 100,000 eggs in a single day and night. The eggs produced flow with bile into the intestine, mix with feces, and are excreted from the host's body. Under environmental conditions of suitable temperature, sufficient oxygen, appropriate moisture, and sunlight, the eggs hatch into miracidia after 10-15 d. The miracidia swim in water, and when they encounter the intermediate host, the small lymnaeid snail, they actively burrow into the snail's body and develop into sac-like sporocysts in the snail's lymphatic spaces, then become rediae. Rediae can be seen at the same time in the snail's liver, and in the snail's liver tissue, after 35-40 d, they then become cercariae (when the snail has sufficient food, the redia stage can also develop into daughter rediae). In a snail infected with miracidia, there are often 300-850 cercariae, or more. Finally, the cercariae emerge from the snail, swim in the water, shed their tails, cover their bodies with cystogenous gland secretions, adhere to the stems and leaves of aquatic plants, or float in the water, forming metacercariae. When animals such as cattle, sheep, horses, and deer eat contaminated aquatic plants or drink contaminated water and swallow infective metacercariae, fascioliasis may occur.
4 Control of fascioliasis
From the life history of Fasciola hepatica, it can be seen that the larvae of Fasciola hepatica are infective to deer only when they develop into metacercariae; and fascioliasis in deer can occur only after they orally swallow infective metacercariae. Therefore, to prevent fascioliasis in deer, the following two points must be achieved: first, block the pathway by which the larvae of Fasciola hepatica, the metacercariae, breed; second, kill the metacercariae so that they lose the ability to infect animals, or guard the gate of "disease entering by mouth" so that infective metacercariae have no way to enter the deer's body orally. For this purpose, the following control measures can be taken.
4.1 Use preparations such as ivermectin or albendazole to carry out one preventive deworming of deer in each of spring and autumn, which can also be used for early treatment of diseased deer.
4.2 Pile deer feces for fermentation and use biological heat to kill the eggs within them.
4.3 Transform low-lying waterlogged pastures and swamps into dry land to destroy the developmental conditions for liver fluke eggs and the survival conditions for the small lymnaeid snail.
4.4 Apply chemical drugs such as copper sulfate or ammonia water to eliminate freshwater snails.
4.5 Reduce freshwater snails through methods such as @#@231@#@.
4.6 In grassland areas where fascioliasis is prevalent, metacercariae may exist both in water and on grass. Metacercariae floating in water are usually most numerous at the water surface, fewer in the middle layer, and least on the bottom. Therefore, when cutting aquatic plants, the stubble can be left taller, about 10-15 cm above the water surface, so that the cut aquatic plants are contaminated by as few metacercariae as possible.
4.7 Metacercariae adhering to the stems and leaves of aquatic plants need only a trace amount of moisture, such as the moisture of morning and evening dew, and in an environment of 4-6 degrees C, they can maintain their infectivity for a long time. On damp hay or in water, metacercariae can survive for more than 3-5 months, but under dry conditions and direct sunlight, they die after 3-4 weeks. Therefore, when cutting aquatic plants, do not place the cut aquatic plants on the water surface; place them in a high, dry place and dry them thoroughly in the sun to kill any metacercariae that may adhere to them. Deer farms with the conditions can store sun-dried forage for 6 months before feeding it.
4.8 In areas where fascioliasis is prevalent, avoid grazing deer herds or cutting aquatic plants to feed deer in low-lying waterlogged grassland, marshy land, or river and canal areas. This is especially so in warm seasons after long drought followed by rain, in rainy years, and after heavy rainstorms in summer and autumn. This is because fresh rainwater can stimulate large numbers of mature cercariae to emerge from the snail's body, promoting the formation of metacercariae and worsening their contamination of aquatic plants.
4.9 Pay attention to the cleanliness of drinking water; it is best to let deer drink deep well water or tap water.
5 Discussion
5.1 In the grassland areas of Northeast China where fascioliasis is prevalent, it is best to carry out preventive deworming of deer herds twice a year: once in late autumn and early winter, and once in late winter and early spring. If deer are infected with Fasciola hepatica in summer and autumn, after winter begins and the weather turns cold, the nutrients in roughage are largely lost, the deer's body condition declines (especially in adult male deer aged 3 or 4 antler cuttings and above), and the pathogenic effect of Fasciola hepatica will then become apparent. Therefore, deworming in late autumn and early winter can prevent Fasciola hepatica from "taking advantage of weakness to cause trouble" and helps the deer herd pass the winter safely. Deworming in late winter and early spring can further eliminate Fasciola hepatica remaining in the deer's body, help deer regain condition and strength, and improve the survival rate of fawns born to female deer and the antler production level of male deer.
5.2 When using oral drugs to deworm deer herds, the sex, age, and body condition of each pen of deer should be the same, and the number should not be too large, generally 10-15, with a maximum of no more than 20, to avoid excessive differences in the amount of drug ingested by individuals during mixed feeding. At the same time, attention should also be paid to selecting safe and effective oral dewormers, such as albendazole. However, in practice, the use of injection methods such as ivermectin injection for deworming is relatively more reliable in effect.
5.3 In Northeast China, some deer raisers, in order to help deer herds that have passed through the cold winter and barren spring regain body condition sooner and increase antler production, often go in warm seasons to places such as river ponds and marshy land where aquatic plants grow luxuriantly to cut grass early and feed it to deer; however, from the developmental history of metacercariae, such aquatic plants are easily contaminated.
5.4 Fascioliasis in deer has no specific clinical manifestations, and diagnosis cannot be made on the basis of certain single symptoms alone. When Fasciola hepatica is parasitizing in the deer's body, it does not necessarily mean the deer has fascioliasis; there is often a phenomenon of "healthy carriers." The diagnosis of fascioliasis in deer must be based on comprehensive analysis and judgment according to fecal examination for eggs, observation of clinical manifestations, and other factors. Some related clinical symptoms of deer suffering from this disease mostly appear in winter and spring when the deer's body condition declines, as well as when nutrition is single and feeding management is poor.