Swine necrotic dermatitis requires focused prevention and control in summer and autumn

I had never seen swine necrotic dermatitis before, and thought it was an old disease that might have already disappeared in our area. Unexpectedly, in July last year, it occurred at a small-scale @#@227@#@ farm in our county. The diagnosis and treatment are summarized below to remind farmers to pay attention to the prevention and control of this disease.

1 Disease situation

The normal inventory of this pig farm was 70-80 head. Because the pig market was poor at the time, the farm owner brought in more pigs, reaching 100 head. By July, when the pigs reached about 60 kg, it was found that some pigs on the farm had broken skin, itching, and scabs, mainly on the buttocks, neck, and sides of the body. At that time, the author suspected it was caused by external parasites or mosquito bites, so Chulailing (main ingredient phoxim) was diluted with water and sprayed on the whole herd. After 2 d, 1 pig was found dead. The farm owner suspected Chulailing poisoning. When the author arrived at the pig farm, the dead pig had already been buried. Another 2 pigs were already seriously ill, and some other pigs in the same pen had infection in individual areas. The 2 severely affected pigs had hair loss on the neck, buttocks, and sides of the body, and some skin had already ulcerated, discharging grayish-yellow, and in some cases grayish-brown, foul-smelling exudate. The ulcerated wounds varied in size, generally about the size of a 1-yuan coin, and the wound base was uneven. The 2 severely affected pigs had more than 10 such necrotic foci on their bodies, while mildly infected pigs had 4-5.

2 Preliminary diagnosis and treatment

Based on the symptoms, the site of the lesions, and the characteristic pus and odor, a preliminary diagnosis was made as swine necrotic dermatitis, caused by Fusobacterium necrophorum. It was recommended to immediately provide cardiac support, fluid replacement, and detoxification for the 2 severely affected pigs. For local treatment, wash the necrotic foci on the body surface of the affected pigs with warm water, use a bristle brush to open the necrotic foci, then use a syringe to draw medical hydrogen peroxide (commonly sold in pharmacies) and spray it onto the necrotic lesions, remove necrotic tissue, and then apply erythromycin ointment. Because the affected pigs were itchy, they did not resist during treatment. For symptomatic treatment, oxytetracycline hydrochloride injection, analgin injection, etc. were given intramuscularly for 3 d. Then 10% sulfadiazine sodium was used according to the size of the pigs, 5-30 mL each time, intramuscularly, 3 times daily, for 3 d. For the herd, the affected pigs were immediately isolated, the whole herd was disinfected with Quanfu (main ingredients including dual-chain quaternary ammonium salts, iodine complexes, etc.), and oxytetracycline tablets were mixed into feed for prevention, for 5 d.

3 Laboratory examination

Samples were collected from the junction between necrotic areas and healthy areas for smears, stained with methylene blue, and examined under a microscope. Slender bacilli with uneven staining could be seen, leading to a further diagnosis of necrobacillosis.

4 Causes

Because the pig farm normally had only 70-80 head in inventory but suddenly increased to 100 head, the pigs' activity area was too crowded; in addition, the pig farm was located in the field, with two artificial fish ponds nearby and too many mosquitoes; furthermore, the pigs were introduced from another province and may have carried pathogens; in addition, when these pigs were brought together into the herd, they fought each other to establish an orderly hierarchy; and it was also the rainy season, with a stuffy, hot, humid, and filthy environment and other factors; all of these can reduce the resistance of the pigs and cause disease in the herd.

5 Symptoms

The symptoms of necrotic dermatitis that occurred on this pig farm were very obvious, mainly on the buttocks, neck, and sides of the body. The characteristic lesions were necrosis and ulceration of the body surface skin and subcutaneous tissue. In the early stage of the disease, because of local itching, it was confused with external parasitic diseases. After careful examination, dry scabbed nodules were seen, which were hard and swollen to the touch but without heat or pain. As the tissue under the scabs became necrotic, necrotic foci rapidly formed. Grayish-yellow or grayish-brown foul-smelling liquid flowed from the necrotic foci; the wounds of the necrotic foci varied in size, with irregular edges and uneven bases. In individual affected pigs, the ears or tails would become dry and necrotic, and some affected pigs had the body surface covered like armor, which finally peeled off and fell away gradually from the edges. Severely affected pigs would eat little or not at all, and their body temperature would rise, leading to death.

6 Prevention

The herd should avoid overcrowding, prevent biting and fighting among pigs, and avoid damage to the skin and mucous membranes. If trauma is found, it should be treated promptly. When introducing piglets, attention should be paid to whether necrobacillosis has occurred in the local area. Keep the livestock housing, environment, and equipment clean and dry. Use correct feed formulation and scientific feeding. Clean up manure and filth from the site in a timely manner. When disease occurs in the herd, attention should be paid to inspection, isolation, and timely treatment of sick animals; contaminated sites should be disinfected promptly. The treatment of this disease mainly involves improving feeding and sanitary conditions, eliminating predisposing factors, and combining this with drug therapy, so as to stop the outbreak and increase the cure rate.

7 Note the differentiation from sarcoptic mange

Swine sarcoptic mange mostly occurs in pigs under 5 months of age, starting from the head, then affecting the ears and eyes; due to rubbing and itching, there is bleeding, scabbing, and severe hair loss, the epidermis turns white and has deep cracks; collecting diseased material and finding the mites can confirm the diagnosis. It is a parasitic disease.

Because the diagnosis was correct and treatment was timely, the condition was quickly brought under control, and no pigs died. Here I remind colleagues not to assume that an old disease that has not occurred for more than ten years will not occur again. We must always be alert to old diseases re-emerging. The porcine reproductive and respiratory syndrome that spread nationwide last year has already given us a warning shot. As veterinary workers, we should keep our responsibilities firmly in mind.