Detailed Explanation of Diagnostic Methods and Prevention and Control Measures for Swine Dysentery

Swine dysentery, also known as bloody dysentery, is a serious intestinal infectious disease caused by Brachyspira hyodysenteriae. The main clinical symptom is severe mucohemorrhagic diarrhea; the acute form is dominated by hemorrhagic diarrhea, while the subacute and chronic forms are dominated by mucoid diarrhea. The pathological features on necropsy are catarrhal, hemorrhagic and necrotic inflammation of the large intestinal mucosa.

Key points for diagnosis

1. Disease characteristics Under natural conditions, only pigs are affected; pigs of all ages and breeds can be infected, but it mainly affects piglets aged 2-3 months; the morbidity and mortality rates of piglets are both higher than those of adult pigs; diseased pigs and carrier pigs are the main sources of infection, and the occurrence of this disease has no obvious seasonality; due to the presence of carrier pigs, the disease is often spread through the movement of pig herds and the buying and selling of pigs. Carrier pigs often do not develop the disease under normal feeding and management conditions, but when unfavorable factors that reduce the pig's resistance, insufficient feeding, vitamin deficiency and stress factors are present, they can promote the onset of the disease.

2. Clinical symptoms The most common symptom is diarrhea of varying severity. Generally, soft feces are passed first, gradually changing to yellow watery feces mixed with mucus or blood. When the condition is severe, the feces passed are red and pasty, containing large amounts of mucus, blood clots and purulent secretions. Some pass gray, brown or even green pasty feces, sometimes with many small gas bubbles and mixed with mucus and fibrinous pseudomembranes. Diseased pigs are listless, anorexic and drink water readily, arch their backs, become dehydrated, have a tucked-up abdomen, walk unsteadily, kick at the abdomen with the hind limbs, have rough and dull hair, rapidly become emaciated, and in the later stage have fecal incontinence. The area around the anus and the base of the tail are soiled with feces, they are unable to stand, and they die in extreme weakness. Most diseased pigs have a normal body temperature. In chronic cases, the symptoms are mild, the feces contain relatively large amounts of mucus and necrotic tissue fragments, the course is longer, and there is progressive emaciation and stunted growth.

3. Pathological necropsy The main lesions are confined to the large intestine (colon and cecum). In acute cases in pigs, there is mucoid and hemorrhagic inflammation of the large intestine, with swelling, congestion and hemorrhage of the mucosa, and the intestinal lumen is filled with mucus and blood; in cases of slightly longer duration, the main finding is necrotic colitis, with pinpoint, patchy or diffuse necrosis on the mucosa; the necrosis is often limited to the mucosal surface, and the intestine contains large amounts of mucus and necrotic tissue fragments. Other organs usually show no obvious changes.

4. Etiological diagnosis (1) Take fresh feces or large intestinal mucosa smears from diseased pigs, stain with Giemsa, ammonium oxalate crystal violet or compound red solution, and examine under a microscope; if 3 or more relatively large spirochetes with 3-4 curves are seen per field of view under high magnification, this disease can be suspected; (2) Isolation and culture; this must be carried out under anaerobic conditions.

5. Serological diagnosis includes agglutination test, immunofluorescence test, indirect hemagglutination test, enzyme-linked immunosorbent assay, etc. The agglutination test and enzyme-linked immunosorbent assay are relatively good and can serve as one indicator for combined judgment.

Prevention and control methods

1. Prevent the purchase of carrier breeding pigs from diseased farms; if they are introduced, the pigs must be isolated for observation and quarantine.

2. Treat diseased pigs promptly. Drug treatment is often somewhat effective, such as mequindox (MAQO, 3-methyl-acetyl-quinoxaline-1,4-dioxide) at 5 mg/kg, orally, twice daily, for 3 consecutive days as one course of treatment, or 0.5 ml/kg of 0.5% mequindox solution by intramuscular injection; various antibacterial drugs such as dimetridazole, neomycin sulfate, furazolidone, lincomycin and tetracycline antibiotics all have certain efficacy. It must be pointed out that this disease is prone to relapse after treatment, and only by adhering to the course of treatment and combining it with improved feeding and management can good results be achieved.

3. Do a good job of cleaning, sanitation and disinfection of pig houses and the environment; properly handle feces.

4. Diseased pigs are best culled.

5. Adhering to purification measures combining drugs, management and hygiene can achieve relatively good purification results.