Psoriasis is a chronic parasitic disease caused by the parasitism of the larvae of the cow or yak on the back of the cow or yak. The disease is mainly endemic in the northwest, northeast China and Inner Mongolia regions. Because when the larvae of the skin fly burrow into the skin, the skin of the cattle is itchy, the cattle are uneasy, the gradual emaciation, and due to mechanical damage, the quality of the leather is reduced, which brings certain economic losses to the cattle industry, so the prevention and control of the bovine fly disease is particularly important.
<h1>1 Pathogen and life history</h1>
The cowhide fly belongs to the genus Offinders in the family Rhinoceros, and the adult insects are shaped like bees, with thick colored villi on the surface of the body, small compound eyes, three single eyes, and degenerate mouth organs, and cannot bite cattle. Adults can only live outside for 5 to 6 days, and female flies die after laying eggs. The cow skin fly lays eggs on the limbs, abdomen, udder and body side of the cow, while the striped fly lays eggs on the hind leg bulbs or front legs. The first stage larvae of the stinging fly burrow into the skin along the pores, move and metamorphose in the deep tissues of the skin, and after about 2.5 months, the second stage larvae of the stinging fly appear in the serous or mucosal layer of the esophagus of cattle. After 5 months, it moves along the diaphragm toward the back. The cow skin fly, on the other hand, does not pass through the esophagus and moves directly to the back. Skin flies stay under the dorsal skin for 2.5 months to develop into stage III larvae, while tattooed flies need to develop under the skin for 2 months. At this time, a nodular bump appears on the skin, with a small hole in the middle, and the posterior stomata of the larvae are ventilated to the outside world. As the third stage larva enlarges, the small hole becomes larger, and the third stage larvae mature and jump out of the small hole, land as a pupa, and feather into a fly after 1 to 2 months. It takes about 10 to 11 months for the larvae to grow and develop in the body of the cow, and the whole development takes about a year.
<h1>2 Therapeutic effect and symptoms</h1>
When the larvae of the skin fly burrow into the skin of the cow, the cow has an itchy sensation, so the cow will be restless. At the same time, when the larva migrates in the bovine, it often causes mechanical damage, such as inflammation of the serous membrane, subcutaneous connective tissue hyperplasia, nodular bulge at the parasite site, and subcutaneous cellulitis. After the skin is raised, small holes appear in the place of the bulge, when if there is a bacterial infection, it can cause suppuration and form a fistula, and the fistula will often flow out of the purulent or serous liquid until the larva leaves the body of the cow, heals, but forms a scar, which in turn affects the quality of the cow leather. Moreover, the larvae of the skin fly also produce toxins when parasitized in the body, which are harmful to the blood and blood vessels of cattle, which can cause anemia or muscle lenovoemia.
In severe infections, livestock are emaciated, growth is slow, and milk production in cows decreases. If the larvae burrow into the brain or brain feet, they can cause a range of neurological symptoms, such as hind leg movement disorders, sudden fall to the ground, syncope or paralysis, and in severe cases, death. When adult cowskin flies lay eggs, they can cause uneasiness and fear in the cattle, and the cattle will be emaciated over time, affecting the healthy development of the cattle.
<h1>3 Diagnosis</h1>
When the larvae appear on the back, they can feel the induration on the back skin of the cow, and for about a month or so, the induration becomes a protruding bag, and a small hole will appear on it, and there will be a scab formed by purulent secretions around the hole, and the connective tissue sac in the hole will be connected to the sac, and there will be a larva inside. This condition can be diagnosed.
<h1>4 Prevention and control</h1>
Killing the parasitic larvae in the bovine body is extremely important for the prevention and control of bovine fly disease, because the development of the cow skin fly is completely metamorphosed, and the whole process of development needs to go through four stages of eggs, larvae, pupae and adult worms, as long as one of the stages is cut off, the epidemic of the disease can be controlled. To control and eliminate the disease, it is also necessary to grasp the biological characteristics of the skin fly, such as the season when adult flies lay eggs, the site of larval parasitism and the time of parasitism. Only with these basic information can effective prevention and control measures be formulated.
4.1 Strengthen feeding management, ensure that the livestock house is well ventilated, and disinfect the livestock house during the spawning season of the cow skin fly, every 7 days, and the disinfectant can be a conventional disinfectant such as glutaraldehyde.
4.2 Regular deworming, the commonly used anthelmintic drug is avermectin, which is injected subcutaneously into the bovine from June to July every year, and injected with a dose of 1 mL per 100 to 200 kg of body weight.