01 Streptococcal encephalitis
① Streptococcus suis is a Gram-positive coccus arranged in chains. It has no flagella, is non-motile, does not form spores, but has a capsule. It is a facultative anaerobe. Streptococcal disease can be classified into septicemic, meningitis, lymph node abscess, and arthritis forms. This post mainly explains the encephalitic form of streptococcal disease:
② Disease course: 1–2 d. The main pathogens are Group C and Group R streptococci. It mainly occurs in weaned piglets and nursery pigs around 20–35 days of age, and primarily presents with neurological symptoms. At the onset of the disease, affected pigs have a slightly elevated body temperature, reduced appetite, nasal discharge, and constipation. They then develop neurological symptoms, such as circling, chewing motions, teeth grinding, lying on their backs, and eventually hindquarter paralysis. They lie on their sides and ultimately fall into a coma and die.
③ Characteristics: The symptoms are similar to those of pseudorabies. The arched-back posture and paddling legs resemble rowing, but the difference is that pseudorabies symptoms are intermittent, whereas in encephalitis the paddling is continuous and lasts a long time. If not treated promptly, the mortality rate is also high.
④ Medication: Penicillin-class drugs are the first choice and kill quickly, but penicillin cannot cross the blood-brain barrier. Therefore, sodium sulfadiazine, which can cross the blood-brain barrier, needs to be used in combination to achieve the desired therapeutic effect!
In addition, depending on the severity of the pig’s condition, ear vein bloodletting for decompression and medications such as glycerol and furosemide can be used to reduce cerebral edema, improve the treatment rate, and lower the mortality rate.
02 Japanese encephalitis
① This disease is mainly transmitted through mosquito and fly bites. The virus can reproduce inside mosquitoes, overwinter, and be passed on through eggs, making them a source of infection for animals the following year. Since it is transmitted by mosquitoes, its prevalence is closely related to mosquito breeding and activity, and is distinctly seasonal. 80% of cases occur during the three months of 7, 8, and 9.
② Characteristics: The age at which pigs develop the disease is related to sexual maturity. Most develop the disease at around 6 months of age. The infection rate is high, the morbidity rate is low (20%-30%), and the mortality rate is low. In newly affected areas, the morbidity rate is high and the disease is severe; it diminishes year by year, and eventually most pigs become asymptomatic carriers of the virus. The main features are high fever, abortion, stillbirth, and orchitis in boars. The reason is that the virus usually cannot cross the blood-brain barrier and enter the brain, so clinical signs generally do not appear. Infection is therefore usually subclinical, and cases with clinical signs of encephalitis are rare.
Nursery piglets may develop the disease suddenly, with their body temperature rising to 40-41 degrees Celsius. They have a sustained fever, appear depressed, eat less or stop eating, and pass dry, pellet-like feces with grayish-white mucus on the surface. Some pigs have mild paralysis of the hind limbs, an unsteady gait, swollen joints, and lameness; some have impaired vision. They eventually die of paralysis.
Pregnant sows may suddenly abort, delivering stillborn, mummified, and weak fetuses. The sow shows no obvious abnormalities, and live-born piglets may also be present in the same litter.
In addition to general symptoms, boars often develop unilateral testicular swelling. The scrotal folds over the affected testicle disappear, and the area becomes shiny, warm, and painful. The swelling subsides after about 3-5 days. In some cases, the testicle becomes smaller and harder, and the boar loses its ability to mate and reproduce.
② Prevention and control methods: Mainly control and eliminate mosquitoes according to seasonal epidemic patterns, and pay attention to eliminating overwintering mosquitoes. In pig farms in endemic areas, before mosquitoes become active, administer a preventive injection of the Japanese encephalitis attenuated live vaccine to boars and sows aged over 4 months and up to two years, 1-2 months beforehand. Give one booster immunization the following year. The immunity period can last 3 years, providing good preventive results.
As it is a viral disease, antibiotics generally are not very effective in treating it, so prevention and control measures should focus primarily on the preventive interventions mentioned above!
03 Pseudorabies
The clinical signs of pseudorabies virus infection depend mainly on the virulence and amount of the infecting virus, as well as the age of the infected pigs. Of these factors, the age of the infected pigs is the most important; the disease is most severe in young pigs infected with pseudorabies virus.
① Presentation: Pseudorabies virus infection in newborn piglets causes a high number of deaths. Clinically, newborn piglets appear normal on day 1, begin to show signs of illness from day 2, and deaths peak within 3–5 days; sometimes an entire litter dies. Affected piglets also show obvious neurological symptoms, drowsiness, squealing, vomiting, and diarrhea. Once symptoms appear, they die within 1–2 days. At necropsy, the kidneys are mainly found to be covered with pinpoint hemorrhages; pulmonary edema and congestion and hemorrhage on the surface of the meninges are sometimes observed. However, laboratory serological testing is required for a definitive diagnosis.
② Symptoms:
Piglets: Sudden onset, with body temperature rising to above 41℃. They become extremely lethargic, tremble, show uncoordinated movement and convulsions, and may vomit and have diarrhea; very few recover. In weaned piglets infected with pseudorabies virus, the morbidity rate is approximately 20%–40%, and the mortality rate is approximately 10%–20%. The main signs are neurological symptoms, diarrhea, and vomiting. Adult pigs are generally subclinically infected; if symptoms occur, they are also very mild and recovery is easy. The main signs are fever and depression. Some sick pigs vomit and cough, and generally recover completely within 4–8 days.
Pregnant sows: Abortion, mummified fetuses, or stillbirths may occur, with stillbirths being the most common. Both gilts and sows that have farrowed before can be affected. The disease has no strict seasonal pattern but occurs more often in cold seasons, particularly from late winter to early spring. Another feature of pseudorabies is infertility in breeding pigs. Sows may repeatedly fail to conceive, with a return-to-estrus rate as high as 90%; some fail to conceive despite repeated mating several times.
③ Control measures:
Production mode requires batch production, with different pigs not housed together;
Complete vaccine immunization: administer pseudorabies vaccine intranasally to piglets on the day of birth, then give a second immunization at 70 days of age during the nursery stage;
The replacement gilts should be vaccinated again at 130 days of age;
The foundation sow herd is vaccinated 1 times each quarter (1 month, 4 month, 7 month, 10 month);
Other: Serum samples need to be collected from the pig herd after immunization to test antibody levels and evaluate the immunization effect!
04 Escherichia coli edema disease
① Escherichia coli is Gram-negative. In addition to causing yellow and white diarrhea in pigs, it can also cause edema disease in pigs and encephalitis-like symptoms. This post will mainly discuss porcine edema disease with encephalitis symptoms caused by Escherichia coli:
② Pathogenesis:
Secreted endotoxin: Escherichia coli endotoxin is a lipopolysaccharide found in the outer membrane of Escherichia coli and released when the bacterial cells break down. Its lipid A component has the biological activity of an endotoxin and is a virulence factor, with a particularly pronounced role in sepsis.
Secretion of exotoxins: Escherichia coli exotoxins fall into two major categories: the first is heat-labile enterotoxin (LT) and heat-stable enterotoxin (ST). LT can activate adenylate cyclase in intestinal capillary epithelial cells, increasing the production of cyclic adenosine monophosphate (cAMP), causing intestinal mucosal cells to hypersecrete and resulting in diarrhea and dehydration. ST can activate particulate guanylate cyclase on the brush border of ileal epithelial cells, increasing the production of cGMP and likewise causing secretory diarrhea.
③ Characteristics of porcine edema disease: A disease caused by hemolytic Escherichia coli toxins, characterized mainly by edema of the eyelids or other parts of the body and neurological symptoms in weaned piglets.
The disease mostly occurs in piglets 1–2 weeks after weaning, with an incidence rate of approximately 5%–30% and a mortality rate of over 90%. In recent years, the disease has also shown new epidemiological characteristics: first, the age at onset has continued to increase; second, pigs that eat more and grow stronger have higher incidence and mortality rates;
Neurological symptoms: sudden onset; depression and complete loss of appetite; muscle tremors while lying still, aimless walking or circling, ataxia, frothing at the mouth, hoarse calls, followed by falling down and convulsions, with all four limbs moving as if swimming; progressive paralysis of the hindquarters, inability to rise, and death while comatose; body temperature may rise at the onset, then quickly return to normal or fall below normal; the course of the disease is 1-3 days, progressing relatively rapidly, with a high mortality rate; characteristic signs are swelling of the face and eyelids.