The weather is getting cooler, this disease should not be ignored, diagnosis and treatment of swine dysentery and prevention measures

　　Swine dysentery (SD), also known as swine blood dysentery, is characterized by hemorrhagic diarrhea in its acute form, while the chronic and subacute forms mainly present with mucous diarrhea. This disease was first discovered in China in 1978, identified in breeding pigs imported from the United States. Through experimental examination and clinical observation, it was confirmed as swine dysentery.

　　1.1 Source of Infection and Pathogen

　　The pathogen of this disease is the swine dysentery spirochete, a strict anaerobic bacterium. It is very sensitive to environmental conditions, humidity, and dryness. The anaerobic bacteria in the colon and cecum of infected pigs help to expand the disease and spread the pathogen.

　　1.2 Epidemiology

　　The affected pigs generally weigh between 15 and 80 kg. Piglets in the nursing period and fully grown adult pigs are less commonly infected. Pigs can be infected with this disease throughout the year, with a long epidemic period and rapid transmission. The disease is mainly spread through the digestive tract of sick pigs. Additionally, dogs, rodents, and other animals can excrete the bacteria in feces after oral infection for 13 days and 8 hours respectively; flies can carry the bacteria for at least 4 hours, and mice for over 100 days. Various stress factors such as moldy feed, environmental changes, overcrowding, long-distance transport, and insufficient drinking water can promote the occurrence of this disease.

　　1.3 Clinical Symptoms

　　The incubation period of this disease can be short, about 2 days, or longer, up to one or two months. It mainly manifests as acute hemorrhagic diarrhea, chronic and subacute mucous diarrhea. A small number of infected pigs may die within hours of infection. Most infected pigs have a body temperature rising to about 40.4 ℃, with feces containing a large amount of mucus, yellowish-white in color, foul-smelling, and containing undigested feed residues. Due to continuous diarrhea, affected pigs become emaciated, dehydrated, and the diarrhea contains blood, eventually leading to death.

　　1.4 Pathological Features

　　Lesions are limited to the mucosa of the cecum and colon, showing catarrhal, hemorrhagic, and necrotizing inflammation, with multiple ulcers and blood exudation.

　　2.1 Microscopic Examination

　　Samples of the large intestine mucosa and mucus or fresh feces from sick pigs are taken for smear preparation, naturally dried, and stained with Giemsa, fuchsin, or crystal violet ammonium oxalate for 2 to 4 minutes. Under dark-field microscopy, 3 to 5 short spirochetes can be observed, allowing preliminary diagnosis of swine dysentery.

　　2.2 Serological Tests

　　Using enzyme-linked immunosorbent assay (ELISA), blood is collected from sick pigs and allowed to clot naturally. Serum is taken, and purified diagnostic antigen from naturally isolated swine dysentery spirochetes is used. Antibodies are added to the antigen wells, with positive and negative controls. The samples are incubated in a thermostat at 30 to 32 ℃ for 20 to 24 hours. A clear precipitation line between the antigen and test serum wells indicates a positive result, confirming swine dysentery.

　　Sick pigs can be treated with intramuscular injection or oral administration of dysentery agents at 5 mg per kg of body weight, orally twice daily. Additionally, intramuscular injection of doxycycline at 0.1 mL per kg of body weight is given twice daily for 5 consecutive days. Lincomycin 100 mg and florfenicol 250 g can be added per ton of feed and fed continuously for 21 days. For more severe cases, vitamin C and vitamin K3 supplementation is appropriate. Intramuscular injection of vitamin B1 can enhance resistance. Cardiac glycosides can be used for heart failure cases.

　　By analyzing and summarizing the etiology, transmission routes, and pathological changes of swine dysentery, key prevention and control points for large-scale pig farms are concluded: First, there is currently no vaccine available for swine dysentery, but with ongoing research, vaccine development is only a matter of time. Second, control mainly relies on integrated prevention and treatment measures. Pig farms should implement all-in-all-out management. Do not purchase pigs from infected farms; sick pigs should be separated from healthy ones with strict isolation measures. Third, the environment closely affects the occurrence of pig diseases. Farms should regularly disinfect according to procedures, strengthen feeding management, control rodents and flies, ensure ventilation and dryness indoors and outdoors, harmlessly treat feces, and add antibiotics and nutrients to feed and water to enhance pig resistance. Disinfectants containing chlorine should be added to the drinking water of sick pigs, and medications added to feed for treatment. Fourth, all pigs in infected farms should be culled, with thorough disinfection and cleaning. Pig houses should remain empty for 3 to 4 months before introducing healthy pigs. Fifth, recovered pigs develop immunity and antibodies, which can be used to produce inactivated vaccines for other pigs to improve resistance to swine dysentery. Combined with feces removal, disinfection, drying, and isolation measures, swine dysentery can be controlled or even eradicated from pig herds.

　　Swine dysentery is a contagious disease that long-term harms the health of piglets. It is highly infectious and spreads rapidly. Therefore, medication must be administered to the entire pig house with a sufficient course to achieve good results. Rodent, mosquito, and fly control, harmless treatment of feces, regular disinfection of pig houses, and integrated prevention and control are necessary to effectively control the disease.