Overview
Swine eperythrozoonosis is an infectious disease characterized by acute jaundice anemia and fever caused by Eperythrozoon in the rickettsia. Also known as jaundice anemia, echinococcosis, red body disease or erythroderma. The disease was first reported in India in 1932. The disease is widely distributed in many countries and regions in North America, Europe, Asia, Africa, and Oceania. Porcine erythroderma was reported in southern Jiangsu Province in 1972 and was later confirmed to be porcine erythroblastosis. With the development of large-scale pig industry in China, the complexity of the disease has increased, and pig erythropoiesis has become a prominent problem in pig production. Especially since the 1990s, the disease has become more and more popular. Seriously, reports of the disease have occurred in more than a dozen provinces and cities such as Guangdong, Hebei, Henan, Shandong, etc., which have caused great economic losses to the pig industry in China and become a common and secondary disease in pig production. .
Pathogen
Eperythrozoon is a member of the Rickettsiales, Anaplasmataceae, and Eperythrozoon. It is a polymorphic microorganism, mostly in the shape of a ring, a sphere, and an ellipse. A small number of rods, crescents, horns, beaded and other different forms. The average diameter is 0.2 to 2.5 μm and is attached to the surface of the red blood cells individually, in pairs or in a chain. Under electron microscope, the erythrocyte cell of pig is disc-shaped, coated with a membrane, without obvious cell wall and nuclear structure. There are microtubules with a diameter of lOnm under the cytoplasmic membrane, and there are ribosome-like particles. Under the dark field and phase contrast microscope, the red blood cell body can be seen in the water-immersed tablets or plasma for free movement such as advancement and retreat, flexion and extension, and multi-directional torsion. The erythrocyte body is easy to color the aniline pigment, and the Gram stain is negative. The Giemsa stain is light red or purple, and the Wright stain is light blue. Proliferation occurs on the red blood cells in a two-split manner. It has not been possible to culture Eperythrozoon cells on non-cellular media.
The erythrocyte body is sensitive to drying and chemicals. 0.5% carbolic acid can be killed at 37 ° C for 3 hours. Generally, the disinfectant can be killed in a few minutes. The erythrocyte body can be cold-resistant. The infectivity at -37 ° C in blood supplemented with 15% glycerol can be stored for 80 days; in the anticoagulant of citrate, it can be stored at 5 ° C for 15 days, and in defibrated blood at -30 ° C for 83 days. It is still infectious and can survive for 2 years after lyophilization.
Epidemiology
Pig Eperythrozoon only infects domestic pigs and does not infect wild boars. Pigs of all varieties, genders, and ages are susceptible, but are more common in piglets and sows. Among them, the morbidity and mortality of suckling piglets are higher, and piglets that are cast for several weeks after castration are particularly susceptible to infection. The infection rate of pig erythrocyte cells in pigs is very high, reaching more than 90%.
Sick pigs and recessive infected pigs are the main source of infection. In the case of stress-infected pigs with hidden stress, such as poor management, malnutrition, temperature mutations, and other diseases, the number of red blood cell bodies in the blood may increase, and obvious clinical symptoms may occur. Resistant pigs can carry the pathogen for a long time and become a source of infection. Pig erythrocyte bodies can be transmitted through various routes such as contact, blood supply, mating, vertical and vector insects (such as mosquitoes). Animals can be spread by licking wounds, biting each other or drinking blood-contaminated urine, and contaminated syringes, surgical instruments, etc.; when mating or artificial insemination, it can be transmitted through contaminated semen; infected sows can pass The uterus and placenta infect the piglets.
Porcine erythroblastosis can occur all year round, but it occurs in summer, autumn and rainy seasons, as well as in climate-changing winter and spring seasons. Stress factors such as poor weather, poor management, and diseases can lead to aggravation of the disease, an increase in the spread of the epidemic, and an increase in economic losses. Porcine erythroblastosis can be secondary to other diseases, and can also occur in combination with some diseases.
Clinical symptoms
After the pigs are infected with Eperythrozoon, they are mostly recessive. When the disease, the poor management and other stress factors cause the resistance of the pigs to decline, the disease will be outbreak. The incubation period is generally 6 to 10 days.
1. Piglets have obvious symptoms after infection, often with acute morbidity and high morbidity and mortality. In the acute phase, the skin mucous membranes are pale and jaundice. Among them, piglets less than 5 days old are mainly pale skin and jaundice; 4-week-old pigs are mainly anemia, and occasionally jaundice can be seen. Sick pigs are weak, appetite is reduced or abolished, response is slow, gait is unstable, and indigestion. The high fever reaches 42 ° C, and the limbs are especially cleft at the edge of the auricle. The shallow to dark red at the edge of the auricle is a characteristic symptom. Some can be seen in the entire auricle, tail and extremities. When the infection lasts for a long time or a persistent infection occurs, necrosis may occur at the edge of the auricle or even the auricle. Resistant piglets tend to grow poorly into stiff pigs and may re-infect. Chronic Eperythrozoonosis pigs show weight loss, paleness, and some urticaria or plaque-type allergic reactions. Generally, bleeding spots can be seen under the skin of the abdomen.
2. The fattening jaundice is typical after fattening pigs, and the symptoms of anemia are rare. Common skin flushing, microscopic erythema at the tip of the needle, especially in the ear skin, the body temperature rises above 40 °C. The spirit is sluggish and the appetite is declining. The mortality rate is low.
3. The sow is acute or chronic. Infections are common in labored sows or 3 to 4 days after delivery. In the acute phase, the sows showed loss of appetite and apathetic stagnation, sustained high fever of 42 ° C, anemia, pale mucous membranes, breast or vulvar edema for 1 to 3 days, and milk production decreased. Infected sows can develop reproductive disorders, manifested as premature birth, weak birth and stillbirth. The conception rate of sows is reduced, and there is no estrus or irregular estrus.
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Pathological changes
The necropsy lesions were jaundice and anemia, and the skin mucosa, fat and organs were significantly yellowish, often with generalized jaundice. The muscle color of the whole body is light, the blood is thin and watery, and the coagulation is poor. Systemic lymphadenopathy, flushing, yellow staining, facet valgus, liquid exudation. Thoracic and abdominal cavity and pericardial effusion. The liver is swollen and brittle, and the cells are steatotic and are yellowish or yellowish brown. The gallbladder is swollen and contains thick jelly-like bile. The splenomegaly is soft and brittle. Kidney enlargement, pale or khaki, bleeding spots under the capsule. There is a small amount of bleeding in the bladder mucosa. The lungs are swollen and bruised and edematous. Epicardial and heart fat bleeding yellow stain, a small number of needle tip bleeding, myocardium pale and soft. The pia mater is congested, the brain parenchyma is soft, and there is a small bleeding point with a large needle tip, and cerebral effusion.
Histological lesions showed focal necrosis of the liver parenchyma, infiltration of lymphocytes and monocytes, dilation of bile ducts between hepatic lobules, and hemosiderin deposition. The central spleen of the spleen is dilated and congested, and follicular cellulose proliferates. Pulmonary interstitial edema, thickened alveolar wall, capillary congestion, lymphocytic infiltration. The glomerular capsule is narrowed with red blood cells and cellulose exuding. Renal tubule degeneration and necrosis. Myocardial degeneration. The cerebral vascular endothelial cells are swollen, the surrounding interstitial is broadened, and there is serous and fibrinous exudation. The brain is softened and hemorrhage, and there are a lot of white blood cells accumulated, of which the cerebellum is the most serious.
Diagnostic identification
According to epidemiology, clinical symptoms and pathological changes, a preliminary diagnosis of the disease can be made, but a laboratory diagnosis is needed for the diagnosis.
1. Epidemiological characteristics mainly occur in the seasons when blood-sucking insects with more warm and rainy summer and autumn are infested; pigs of all ages can be infected, and the incidence and mortality of piglets are high. Piglets occur mostly after castration. A few weeks; the same group of individuals in the first frequent onset, the individual small after the onset; sows occur in the sows or 3 to 4 days after delivery; the climate is bad, poor management, disease and other stress factors induce this The disease can aggravate the disease and expand the spread of the epidemic.
2, the main points of clinical diagnosis of piglets after acute infection, jaundice, anemia, high fever; fattening pigs after infection with typical jaundice more common, anemia symptoms are less common; sick pig ears first turned purple, then body flushing Or purple red, the so-called "red pig" is a characteristic clinical symptom; infected sows can see high fever up to 42 ° C, anemia, breast and vulvar edema and birth defects, weak babies and other reproductive disorders.
3, necropsy diagnosis of the main points of the skin, mucous membrane, fat yellow stain; heart, liver, spleen, lung, kidney edema, yellow staining; abdominal cavity and pericardial effusion and other pathological features.
4, laboratory diagnosis
(1) Blood routine examination showed that the red blood cells were low, the mean value of 3 million/mm3 hemoglobin decreased by about 52%; the white blood cells increased, the mean value was 11.6 million/mm3; the monocytes increased, and the lymphocytes and neutrophils decreased.
(2) Fresh blood pressure microscopy from the ear vein of the sick pig, add the same amount of saline, add a cover glass, under 400 to 600 times microscope or dark field microscope, check for adhesion to the surface of red blood cells or free In the plasma, the worm body is spherical, comma-shaped, rod-shaped or granular. The worms in the plasma can be stretched, contracted, or swiveled. Microscopically, the morphology of red blood cells has changed, and it has irregular shapes such as pineapple, serrated, and star-shaped.
(3) Smear staining microscopy to take blood smear, perform Giemsa staining, microscopic examination, visible in pink or purple-red, irregular ring or point-like worm body.
(4) Serological examination Serological methods can not only diagnose the disease, but also conduct epidemiological investigations and disease surveillance. Common serological methods include complement binding assay, indirect hemagglutination assay, fluorescent antibody assay, and enzyme-linked immunosorbent assay.
(5) Molecular biological methods PCR or nucleic acid probes can be used to detect Eperythrozoon in blood, and PCR can be positive 24 hours after infection of erythrocytes in pigs.
(6) Animal test The blood of suspected pigs was inoculated with healthy experimental animals (mouse, rabbit, chicken, etc.) or chicken embryos. After inoculation, the reaction was observed, and blood was taken to examine the red blood cell bodies.
Prevention
(1) Treatment of tetracycline, kanamycin, doxycycline, oxytetracycline, yellow pigment, blood worm (Benil), chlorpheniramine, arsenic (dissolved acid), etc., can be used to treat the disease, Tetracycline and arsenic preparations are generally considered to work better. Early and timely treatment of porcine erythropoiesis can be very effective.
(1) Xinyi Fan Na Ming (9:14), 10 ~ 15mg per kilogram of body weight, intravenous infusion, while intravenous vitamin C, glucose. Used for 3 days;
(2) oxytetracycline, 600-800g per ton of feed, for 2 to 3 courses of treatment. Or intramuscular injection of tetracycline or oxytetracycline at a dose of 3 mg per kilogram of body weight;
(3) The diseased piglets were intramuscularly injected with sulfa-5-methoxypyrimidine injection once a day for 3 days, and the iron preparation was injected once;
(4) Benier (blood worm net), 5 to 7 mg per kilogram of body weight, deep intramuscular injection, and injection once every 48 hours. Sick pigs are ineffective for Bernier, and the initial effect is good;
(5) Ascorbic acid, 180g per ton of feed, fed for 1 week, then changed to 90g per ton of feed for 1 month.
(B), preventive measures should take comprehensive prevention and control measures for this disease.
1. Strengthen the daily feeding management of pigs, feed high-nutrient full-price materials, maintain the health of the pigs; maintain good temperature, humidity and ventilation of the pig houses; eliminate stress factors, especially in the high season of the disease, Blood-sucking insects such as cockroaches, scorpions, crickets, and ticks should be extinguished and their contact with animals should be cut off.
2, the injection needle, syringe should be strictly disinfected, regardless of vaccination, or treatment injection, should ensure a needle per pig. Sows should be strictly disinfected when they are delivered.
3. Strengthen environmental sanitation and disinfection, keep the pig house clean and hygienic, clean the manure in time, disinfect regularly, regularly deworming, reduce the chance of infection of the pigs and reduce the infection rate of the pigs.
4, drug prevention, regular addition of preventive amounts of oxytetracycline, tetracycline, doxycycline, chlortetracycline, arsenic acid in the feed, have a good preventive effect on the disease. Add chlortetracycline 48g per ton of feed or add 50mg per liter of water for 7 days to prevent the disease in large pigs. Injecting oxytetracycline (11mg/kg body weight) into sows before delivery can prevent the onset of sows. Injection of oxytetracycline 50 mg/head to 1-day-old piglets can prevent erythropoiesis in piglets.
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