Detailed Explanation of the Symptoms and Prevention and Control Measures of Classical Swine Fever

Classical swine fever, commonly known as “rotten intestine fever”, is an acute, febrile, contact-transmitted infectious disease caused by the classical swine fever virus of the genus Pestivirus in the family Flaviviridae. It is highly contagious and lethal.

Types of Classical Swine Fever

Generally 5—7 days; according to clinical symptoms it can be divided into four types: peracute, acute, chronic and mild.

1. Acute type of classical swine fever

① Sick pigs often show no obvious symptoms and die suddenly, generally appearing in newly affected areas and the early stage of an outbreak.

② Sick pigs are lethargic, febrile, with body temperature between 40—42℃, showing continuous fever, preferring to lie down, arching the back, shivering and staggering when walking. Appetite is reduced or completely lost, they drink water frequently, and some vomit. Conjunctivitis with purulent discharge glues the upper and lower eyelids together so they cannot open, and purulent nasal discharge flows from the nose. In the early stage there is constipation, with dry hard fecal pellets whose surface is covered with a large amount of white intestinal mucus; in the later stage there is diarrhea, with foul-smelling feces containing mucus or blood. On the skin of the snout, behind the ears, abdomen and inner sides of the limbs, as well as the mucous membranes of the gums, inner lips and anus, pinhead-sized hemorrhagic spots appear that do not fade under pressure, and the inguinal lymph nodes are enlarged. In boars the prepuce becomes inflamed, the preputial sheath accumulates urine, and when squeezed by hand a foul-smelling turbid liquid is ejected. Piglets may show neurological symptoms, manifesting as teeth grinding, backing up, circling, rigidity, lying on the side and swimming movements, and even coma.

[Symptoms]There are hemorrhages of varying degrees in the skin, serous membranes, mucous membranes and internal organs throughout the body. The lymph nodes throughout the body are swollen,

juicy, congested, hemorrhagic, appearing purple-black on the surface, with a marbled appearance on the cut surface; the kidneys are pale in color, with pinhead- to millet-sized hemorrhagic spots on the cortex; the spleen has infarcts, mostly at the edges, appearing as small black-purple patches; the laryngeal mucosa and tonsils are hemorrhagic. Scattered hemorrhagic spots are present on the bladder mucosa. The gastric and intestinal mucosa shows catarrhal inflammation. Button-shaped ulcers form at the ileocecal valve of the large intestine.

2. Chronic type of classical swine fever

It mostly develops from the acute type, with body temperature rising and falling, poor appetite, alternating constipation and diarrhea, gradual emaciation, anemia, weakness, rough coat, and when walking the two hind limbs are weak and unsteady. In some sick pigs the ear tips, tail tip and lower parts of the limbs become blue-purple or necrotic and drop off; the course of disease can last more than one month, ending in weakness and death, with an extremely high mortality rate.

[Symptoms]It mainly manifests as necrotic enteritis, with no obvious systemic hemorrhagic changes; due to disturbance of calcium and phosphorus metabolism,

in weaned sick pigs, at the junction of the rib ends and cartilage tissue, yellow ossification lines formed by ossification disorders can be seen.

3. Mild type of classical swine fever

Also called atypical, it mainly occurs more often in weaned piglets and feeder pigs, with mild and atypical symptoms, a mild course, and inconspicuous pathological changes; the course is relatively long, with body temperature remaining around 40℃, no small hemorrhagic spots on the skin, but there is congestion and necrosis, appetite fluctuating between good and bad, and feces alternating between dry and loose. The sick pigs are very emaciated, and the mortality rate is relatively high. Some survive, but their growth and development are severely stunted.

Prevention and Control Measures for Classical Swine Fever

[Prevention]

1. Immunization.

2. Carry out immune monitoring, using methods such as enzyme-linked immunosorbent assay or forward indirect hemagglutination test to monitor immune antibodies.

3. Promptly cull latently infected virus-carrying breeding pigs.

4. Adhere to the breeding management system of self-breeding and self-raising, and all-in-all-out.

5. Do a good job in isolation, hygiene, disinfection and pest control of pig farms and pig houses to reduce the invasion of classical swine fever virus.

Epidemic Handling Measures

1. Report immediately and diagnose promptly.

2. Delineate the epidemic point.

3. Blockade the epidemic point and epidemic area.

4. Handle sick pigs and carry out harmless treatment.

5. Emergency preventive vaccination. Presumed healthy pigs in the epidemic area and live pigs in threatened areas should be vaccinated with attenuated classical swine fever vaccine.

6. Disinfection: carefully disinfect contaminated sites, pens, utensils, etc.; pile up feces for fermentation and harmless treatment of classical swine fever.