Epidemiological characteristics and symptom characteristics of porcine pseudorabies
All mammals are susceptible to pseudorabies, and rodents play an important role in spreading pseudorabies. Pigs infected with pseudorabies for the first time without immunity will have disastrous consequences and can be transmitted to the whole pig herd within 1 week. More than 90% piglets died of infection, adult pigs showed symptoms of respiratory infection, and pregnant sows aborted. The virus can be transmitted through placenta, vaginal mucus, semen and milk, and is often sporadic.
symptom
The main symptoms of pseudorabies are body temperature of 4 1.0 ~ 42.0℃, shortness of breath, refusal to eat, occasional vomiting or diarrhea, death in lethargy, or excitement, foaming at the mouth, nervous system symptoms such as ataxia, rotation and convulsion, depression, paresis or paralysis or loss of consciousness in the later stage, vision, hoarseness, constipation and respiratory symptoms, all of which are fatal infections.
pathological change
Pathological changes of pseudorabies pigs at autopsy are mainly seen in non-suppurative encephalitis, cerebral congestion, hemorrhage and edema, yellow-white necrotic spots with the size of 65438±0 ~ 2mm in liver, kidney and heart, pulmonary congestion and edema, catarrhal and hemorrhagic inflammation of upper respiratory tract, massive hemorrhage of gastric fundus, necrotizing placental inflammation in aborted sows and blood spots on fetal surface.
Syndrome Differentiation of Pseudorabies in Pigs
1. When a sow aborts or stillbirths, it should be differentiated from porcine parvovirus, porcine reproductive and respiratory syndrome, porcine Japanese encephalitis, porcine brucellosis and porcine chlamydia.
(1) Porcine parvovirus: There is no seasonality. Abortion almost only occurs in the first fetus. Sows are asymptomatic except for abortion, and mummified fetus is very obvious. Other pigs are asymptomatic even if they are infected.
(2) Porcine Reproductive and Respiratory Syndrome (PRRS): Pigs infected with this disease have flu-like symptoms in the early stage. In addition to sow abortion, premature delivery and stillbirth, sick piglets have high dyspnea and high mortality within 1 week. The main lesion is interstitial pneumonia.
(3) Japanese encephalitis in pigs: The disease only occurs in the season when mosquitoes and flies are active. In addition to abortion and stillbirth in pregnant sows, unilateral testicular swelling may occur in boars. Piglets show neurological symptoms such as elevated body temperature, listlessness and mild paralysis of limbs.
(4) Chlamydia suis: Most of the sick sows have no warning before abortion. Boars show orchitis and epididymitis, while piglets show symptoms such as chronic pneumonia, keratitis and polyarthritis. Microscopic examination showed that the inclusion bodies of chlamydia could be seen in the cells.
(5) Brucellosis in pigs: The disease generally occurs in brucellosis endemic areas. In addition to the abortion and stillbirth of pregnant sows, orchitis can also occur in boars. The serum was taken for brucellosis agglutination test, and it was positive.
2. Sick piglets should be differentiated from salmonellosis, epidemic diarrhea, listeriosis and stress syndrome of weaned piglets.
(1) Salmonellosis in pigs: It rarely occurs in piglets of small age and pigs over 6 months old. There are purple spots under the abdomen, chest and ears, secretions in the eyes, thin feces, pale yellow or grayish green with blood or false membrane, and foul smell. Autopsy showed swelling, dark blue, hard as rubber, blue-red section, redness around white pulp and swelling of mesenteric lymphatic cord. The cecum and colon are thick, and the mucosa is covered with a dirty yellow-green pseudomembrane. After removing the false membrane, a red ulcer surface appears with uneven edges. Microscopic examination of pathological material smear showed that Gram-negative bacteria were oval or oval at both ends and did not move. No spore formation, Salmonella capsulata.
(2) Swine epidemic diarrhea; It only happens in pigs, and other animals will not be infected. No neurological symptoms. At autopsy, the intestinal wall became thinner, and the length of intestinal villi and crypt decreased from normal 7: 1 to 3: 1. The small intestine tissue and intestinal contents of sick pigs were made into suspension, and then inoculated into experimental pigs. If the experimental pig is sick, the small intestine tissue is taken for immunofluorescence test (high sensitivity and specificity) for diagnosis.
(3) Swine listeriosis. General weakness, course of disease 1-3d(3-4 months old pseudorabies pigs have low mortality and can fully recover in a few days). Microscopic examination of pathological material smear shows that? v？ Or? y？ Gram-positive bacilli are arranged in type A.
(4) Stress syndrome of weaned piglets: a non-infectious disease, which generally occurs within 7- 10d of weaned piglets. Suddenly he fell to the ground and shouted, his muscles trembled and his eyes turned up. Most of the symptoms are relieved or static after 30-60 minutes. If treated in time, it can be cured. If they were inoculated with rabbits, there would be no itching and biting.
Prevention and treatment of pseudorabies in pigs
There is no specific therapeutic drug for porcine pseudorabies, so comprehensive control measures must be taken. At ordinary times, it is necessary to strengthen feeding management, do a good job of sanitation and disinfection, and do a good job of killing mosquitoes, flies and rats. Cephalosporin combined with interferon has certain curative effect at the onset. Eliminating rodents in pasture is of great significance to prevent the disease. At the same time, it is necessary to strictly control the entry of dogs, cats, birds and other poultry into pig farms, strictly control personnel exchanges, and do a good job in disinfection and serological monitoring, which can also play a positive role in promoting the prevention and control of the disease.
Immunity of porcine pseudorabies
1. Reserve pigs should be vaccinated with pseudorabies vaccine at least twice before breeding, and attenuated vaccine with gene deletion can be used for both times.
2. According to the infection degree, the multiparous sows were immunized 1 ~ 2 times in the late pregnancy (20 ~ 40 days before delivery or 75 ~ 95 days after mating).
3. Inactivated vaccine or attenuated vaccine with gene deletion can be used for sow immunization, and at least 1 attenuated vaccine with gene deletion was used for two immunizations.
4. Pigs with no pseudorabies epidemic in and around this field can be vaccinated with 1 inactivated vaccine after 30 days.
5. Pigs with epidemic situation in or around the farm should be vaccinated with 1 attenuated vaccine at the age of 19 or 23-25 days.
6. Frequent piglets should be inoculated with attenuated vaccine with gene deletion by nasal drip at the age of 3 days. Piglets in epidemic areas or pig farms with serious epidemic situation should be immunized 1 time after the first immunization for 3 weeks.
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