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Do you know the transmission routes of dermal myiasis in dairy cows?

Posted on: July 29, 2019, by Eleanor

Dermatomyiasis of dairy cows is a chronic parasitic disease, mainly caused by the parasitic larvae of Hypoderma bovis, Dermatomyza striatum and Dermatomyza Sinensis in subcutaneous tissues of the body. The main manifestation of the diseased cows is loss of body weight, which affects the growth and development of calves, and the cow's milk production decreases after the disease. The following specific to understand: Dairy cow dermatomycosis transmission routes and harm of cow dermatomycosis clinical symptoms and prevention.

Do you know the transmission routes of dermal myiasis in dairy cows
Do you know the transmission routes of dermal myiasis in dairy cows
  1. Pathogenic characteristics

  Mosquito skin flies and Hypoderma bovis have similar adult morphology. They look like bees. Their whole body is covered with villi. Their heads have large compound eyes and three single eyes. They also have non-branched antennae, and their mouthparts are not developed enough to bite and feed. Hypoderma bovis, the adult length is about 15 mm, head covered with light yellow villus, chest covered with light yellow villus at both ends, middle covered with black villus, abdomen covered with white, black and orange villus from front to back, wings covered with light grey villus. Female flies produce eggs that attach to the hair on the abdomen, upper limbs, and breasts. The eggs are round, pale yellow and glossy, ranging in size from 0.78 mm to 0.8 mm x o.22 mm to 0.29 mm. The first and second stage larvae are translucent yellow-white, the third stage larvae are brown, trapezoidal relatively large, there are a large number of spines and nodules on the body surface, and segmented, the length can reach 28 mm. The length of the adult is about 13 mm. The chest is covered with pale yellow villi. There is a black longitudinal line on the back of the chest. The abdomen is covered with gray, black and orange villi from front to back, and the wings are covered with brown villi. Female flies usually produce eggs that attach to the bulbar ganglion of the hind legs and can attach to multiple eggs on one coat. The eggs and the first and second stage larvae are similar to Hypoderma Bovis. The third stage larvae can reach 26 mm in length, with segmented body surface and small spines.

  • Ways of transmission and hazards

  Both species of skin flies have a very strong reproductive capacity, most of them live on blood-sucking, and some decaying substances can be used as a staple food. The disease is mainly transmitted in two ways, one is through blood transmission of adult skin flies, and this way can be divided into the transmission of worms to cows and dairy cows. Usually, when skin flies transmit the virus to cows, the virus is very easy to cause other cows to be infected through the air. The transmission of this chain reaction will cause very serious harm to cattle. The other is that skin flies spread by parasitic means, which, although rare, can cause greater harm. The skin flies ovulate in spring and autumn, while some of them lay eggs directly on the skin of dairy cows. Although most of the eggs die because of the harsh environment, a few of them can survive, and the hatched larvae will parasitize in the subcutaneous tissues of the body, thus causing chronic parasitism.

  • Clinical symptoms

  When the cow suffers from dermatomycosis, it mainly manifests mental malaise, loss of appetite and obvious emaciation in the clinic. Touching on the back of the cow with the hand, it will feel that there is a protuberance similar to the size of the mother's finger under the skin, and there are small holes close to the size of matchhead on the protuberance of the skin, and there are yellow pus flowing from the hole. Out, when pus dries, it cements with the hair around the pore, resulting in a markedly rough coat on the body surface. When the infection is serious, the sick cattle will be mentally depressed, and their physique will be rapidly emaciated and exhausted, or cause secondary infection and sepsis, which will directly or indirectly cause their death.

  • Prevention and control

  Fly control. In the season of frequent activity of adult flies, that is, 6-9 months of the year, we should regularly use the insecticide spray to kill flies. Besides, 1% to 2% trichlorfon can be sprayed on the body surface of dairy cows once every 10 days or 1000-1500 mg JKG pyrethroid can be sprayed once every 30 days to kill the laying female flies or the larvae hatched by the eggs.

  Kill the larvae in the body. It is very important to eliminate the parasitic larvae, especially stage 1-2 larvae, to control the disease. Therefore, it is necessary to understand and grasp the biological characteristics of dermatomycoses, such as the activity of adult flies, the spawning season, the parasitic time and the parasitic sites of larvae at different stages, and take planned large-scale control to ensure that the effect of insect repellency is better. Besides, medicines can also be used for prevention. In May-July of each year, an appropriate amount of 1% trichlorfon solution can be sprayed on the surface of cattle, once every 15 days, to inhibit the oviposition of skin flies. In mid-September and early October of each year, 2 kg of Angelica Sinensis can also be extracted and soaked in 4 000 ml vinegar. After 48 hours, the extract is applied to the back of the body. The adult cattle use about 150 ml of extract each time, and the calves use about 80 ml of extract to make the coat and skin wet. At the end of the annual mosquito-fly season, that is, in November, dairy cows can be subcutaneously injected with 0.2 mg/kg avermectin or ivermectin, or with 6-7 mg/kg this phosphorus intramuscularly injected with body weight, which can kill the larvae in vivo. If it is found that there is swelling in the back skin of dairy cows, but no perforation has been formed, that is, the larvae parasitize in the subcutaneous area. The larvae can be killed by spraying an appropriate amount of 0.25% fenthion solution or 0.05% fly venom Phosphorus Solution on the back.

  Mechanical removal of worms. If the back skin of diseased cattle has formed a skin hole, and the larvae have not drilled out, the appropriate amount of 2% trichlorfon solution can be applied to the back skin hole, the larvae can be killed, and then the larvae are taken out with tweezers. It can also be taken out directly from the skin hole with tweezers. If the body is large and difficult to take out, the body should be pierced first, then the contents of the body should be extruded, and then the body can be taken out, but attention should be paid to completely extruding the body to prevent allergic reactions.

  Wound management. The wounds of diseased cattle after mechanical removal of worms and the wounds (inflammation or suppuration) formed by mature larvae after drilling through the skin holes should be washed with 0.1% potassium permanganate solution or hydrogen peroxide solution, and then iodine tincture or iodoform should be applied.

Do you know the transmission routes of dermal myiasis in dairy cows?
Do you know the transmission routes of dermal myiasis in dairy cows?
  1. Harm

  Adult fly interference: In the season of frequent adult fly activity, although it will not bite cattle, in the process of female fly oviposition, it will make them restless, avoid everywhere, and even run, there will be sniffing, kicking and other phenomena. In severe cases, even the feeding and rest of cattle will be seriously affected, leading to physical loss and trauma, cows may cause abortion and reduce milk production after the onset of the disease and other symptoms.

  Mechanical stimulation: When larvae penetrate bovine skin, they can grow and develop subcutaneous tissues. Individuals continue to grow and move over long distances, causing severe mechanical stimulation to local skin and damaging the tissues passing through during migration, causing inflammation, connective tissue proliferation, and subcutaneous tissue inflammation, thus causing subcutaneous tissue inflammation. Cause local skin itching, accompanied by pain, make it turn upset. Diseased cows tend to develop poorly, lose weight, and deteriorate meat quality. The invasion of cows can lead to reduced milk production.

  Absorption of host nutrition: From the first stage larvae to the third stage larvae, the individual increased significantly, even more than hundreds of times, and all the nutrients needed for growth and development were obtained through the host.

  Secondary infection: When the larvae invade the cattle and develop into the third stage larvae, they will form bumps on the skin at the parasitic site, then drill out from the skin and fall to the ground, resulting in skin damage and even local scarring. It is very easy to secondary infection of pyogenic bacteria, causing an abscess, and through the fistula, there is pus discharge. Besides, pyogenic bacteria can also cause cellulitis subcutaneously. If a large area of the scar is formed and the quantity is large, the quality of leather will be reduced.

  Toxin damage: The Hypoderma fly larvae parasitized in cattle produce and excrete some substances through metabolism during their growth and development, and these substances have toxic effects on cattle.

  Damaged nerves: Individual larvae enter the body of cattle and can parasitize in the brain or the medulla, resulting in nerve compression and injury, and then show neurological symptoms, and even cause death in severe cases.

   Induce allergic reaction: The diseased cattle are often sensitized by absorbing the body fluid of the larvae crushed by mechanical insecticide or died naturally. If they are re-exposed to the antigen, they can cause an allergic reaction.

  • Life history

  The development of dermatomycoses is a complete metamorphosis process, which is generally divided into four stages: adult, eggs, larvae, and cochlea. It takes about one year to complete the whole development process, and adult flies appear in succession in 4 to 9 months. Adult flies only live for 5 to 6 days. Female flies usually lay eggs on cattle hair at noon when the sun is hot. The first stage larvae hatch in about 3 to 6 days, then enter the body through the pores, and begin to grow and develop. According to the species of skin flies, there are different ways of migration. Hypoderma bovis larvae first enter the subcutaneous tissue, and gradually migrate to the back subcutaneous tissue, and stay there for about 2-3 months, then grow and mature. Under the action of toxins produced by the insect body, the skin perforates and then discharges to the outside body. After falling to the ground, the skin begins to harden, gradually forms pupae, and then passes through. It will emerge and develop into adults in 1-2 months. After infected with the larvae of dermatome striata, the cattle can develop into the second stage larvae in pharynx and esophagus for about 2.5 months, stay in the esophageal wall for about 5 months, and finally migrate to the back subcutaneous, and continue to develop into the third stage larvae.

  • Clinical symptoms

  When adult flies lay eggs on the back of cattle, they often cause an individual or whole cattle to feel uneasy and affect their normal feeding and rest. The produced larvae move into the subcutaneous area of cattle, causing them to feel pain and itching, which leads to restlessness; when the larvae grow to a certain stage, they will form nodules on the back, even local areas will increase continuously, forming smaller tumors, which are prominent on the skin surface. If the skin is observed, the protruding top can be formed. There is a small hole in the end. Besides, it can squeeze out larvae in tumors, as big as fingers or peanuts. When the larvae are drilled out from under the skin, a small hole will be left on the skin, which is easy to secondary infection of bacteria, small abscess, so that the quality of cattle cortex is significantly reduced. If there are a large number of hypodermis maggots parasitized under the skin of cattle, many protuberances will be formed on their back, which can even cause anemia, leading to physical loss, reduced meat quality, and reduced milk production.

  • Treatment

  The diseased cattle can be treated by intramuscular injection of fenthion. The dosage of adult cattle is 1.5 ml and that of calves is 0.5-1.0 ml. Generally, the first to second stage larvae of dermatomycoses can be killed, and the insecticidal rate can exceed 95%. The drug is easy to use and is one of the good insecticides that can kill the larvae of dermatomycoses, but it is better to use this medicine in November when the effect is better. The diseased cattle can also be treated with dermatophyte, but because it can not dissolve in water, they can choose to make pills and take 100 ml orally per kilogram of body weight. The insecticidal effect of 30 ml imidophos emulsifiable concentrate on the back skin of diseased cattle per kilogram of body weight was better. The diseased cattle were given 0.2 ml ivermectin orally or subcutaneously once per kilogram of body weight. After about 7 days, the blister became soft and inelastic. After 30 days, all the larvae could be killed. Injecting 10 ml of fly venom phosphorus into the buttocks of diseased cattle per kilogram of body weight can kill the larvae in the transitional period to a certain extent. Spot injection of 60-degree liquor around the parasitic site of the diseased Hypoderma bovis larvae can kill the parasite at one time, or needle the parasitic site first, and then apply liquor. Besides, the larvae can be extruded vigorously with both hands to ensure that they are trampled to death or burned, then smeared with iodine tincture on the wound, and finally sprayed with iodoform, which can promote the wound to heal well, usually once every 10 days or so. Besides, the therapeutic effect of traditional Chinese medicine is also very good, such as taking 100g gourd tea and 25g lime, pounding and sealing in the affected area of diseased cattle.

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