What are the clinical symptoms of swine Japanese encephalitis? Detailed explanation of prevention and treatment methods
Swine Japanese encephalitis, abbreviated as JE, is a zoonotic infectious disease caused by the Japanese encephalitis virus. The disease was first discovered in Japan, so it is also called Japanese B encephalitis.
Pathogen
The JE virus has weak resistance to the external environment. It can be inactivated after 30 minutes at 56°C or after 2 minutes at 100°C, but it can survive for several years at minus 70°C. When the pH value is less than 7 or greater than 10, its activity declines rapidly. Disinfectants such as 2% caustic soda solution and 3% Lysol water are effective against it.
Epidemiological characteristics
The JE virus must rely on blood-sucking female mosquitoes as vectors for transmission, and the epidemic cycle is pig-mosquito-pig. The JE virus can multiply and overwinter in mosquitoes and can be passed to the next generation through eggs. The JE virus can vertically infect fetuses through the placenta. Pigs, humans, horses, cattle, sheep, and others all have a certain susceptibility. Pigs of all ages, breeds, and sexes are susceptible to this disease, but those under 6 months of age are more susceptible, and there is no recurrence after recovery. This disease has obvious seasonality, occurring mainly in July to August.
Clinical symptoms
Sick pigs mostly show high fever, mental depression, or neurological symptoms, reduced appetite, and some develop hindlimb paralysis, decreased vision, head swinging, and random collisions. Pregnant sows suddenly abort and give birth to stillborn fetuses, weak fetuses, and mummified fetuses. Boars often develop orchitis, mostly unilateral, with swelling and a hot, painful sensation in the early stage. After several days, the inflammation subsides, the testicles atrophy and harden, libido decreases, semen carries the virus, and they lose breeding ability.
Pathological changes
In aborting sows, the endometrium is congested and covered with viscous secretions, with a few having hemorrhagic spots. In sows with high fever or stillbirth, the submucosal tissue of the uterus is edematous, and the placenta shows an inflammatory reaction. In sick pigs with neurological symptoms, congestion of the meninges and spinal meninges can be seen.
Diagnosis
Based on the epidemiological characteristics with obvious seasonality, combined with manifestations such as sow abortion, premature birth, mummified fetuses, and boar orchitis, a diagnosis is not difficult to make, but confirmation depends on laboratory diagnosis.
Prevention and control measures
Pig farms should retain more spring-born piglets as breeding pigs and avoid having first-parity sows become pregnant and give birth during the peak mosquito season. Repel mosquitoes and eliminate flies, do a good job of isolation and disinfection, and cut off transmission routes. For immunization, use the swine Japanese encephalitis attenuated vaccine according to the number of doses indicated on the bottle label. Add 1 milliliter of the dedicated diluent to each dose. After it is completely dissolved, inject 1 milliliter intramuscularly into each pig. The immune protection period is 12 months. For replacement gilts and breeding boars on positive farms, the immunization can be boosted once 20 to 30 days before mating. Vaccination can also be carried out about 45 days before the mosquito and fly season arrives.