Swine pasteurellosis occurs frequently in autumn and winter when temperatures alternate between cold and warm with large differences, so timely prevention and treatment are needed
Swine pasteurellosis occurs frequently in autumn and winter when temperatures alternate between cold and warm with large differences, so timely prevention and treatment are needed
Pasteurella multocida is generally considered a conditional pathogen that can infect multiple animal species. Based on differences in antigenic composition among strains, the bacterium can be divided into several serotypes. Porcine Pasteurella multocida is mainly types 5:A and 6:B. The bacterium exists in all tissues, body fluids, secretions and excretions of diseased pigs, and in a few cases exists within lung lesions of diseased pigs. Healthy pigs may also carry the bacterium in some cases, and it can be isolated from the nasal cavity, larynx and other sites. When carrier pigs are in poor environments, such as cold, stuffy heat, dampness, fatigue, malnutrition, poor ventilation, long-distance transport, etc., the body's resistance declines, and the pathogen proliferates massively and causes disease.
Pasteurella multocida has weak resistance to the external environment. It can survive 7-8 days in surface soil, 4 days in pig manure at room temperature, and 2-4 months in the carcasses of pigs that died in winter, and dies quickly under direct sunlight. Common disinfectants can easily kill the bacterium within a few minutes.
Disease manifestations
The incubation period of swine pasteurellosis is 1-5 days. According to the length of the disease course, it can be divided into the peracute type, acute type and chronic type.
1. Peracute type
Infected pigs show no obvious symptoms and suddenly develop the disease and die. This is commonly seen in the early stage of an outbreak. In cases with a slightly longer course, the body temperature rises to 41°C-42°C, appetite is completely lost, the animal is depressed, breathing is difficult, and the heartbeat is accelerated. The visible mucous membranes are purplish red; the throat and neck are hot, red and swollen, and hard; and purplish red patches appear on the skin of the neck, abdomen and other areas. Diseased pigs often assume a dog-sitting posture and make wheezing sounds. In severe cases, white foam flows from the mouth and nose, the condition deteriorates rapidly, and death finally occurs from suffocation. The disease course is 1-2 days, and the mortality rate is extremely high.
The characteristic pathological changes in diseased pigs are hemorrhage of the systemic serosa and subcutaneous tissue, and a large amount of gelatinous pale yellow or grayish-blue fibrinous serous fluid in the subcutaneous tissue of the neck. Lymph nodes are enlarged with red cut surfaces; the lungs show edema, emphysema and hemorrhage, with marble-like patterns on cut surfaces. There are hemorrhagic spots on the epicardium and pericardium, with effusion in the thoracic cavity and pericardium, along with fibrin. The spleen has hemorrhages but is not enlarged. The skin has hemorrhagic patches. There is hemorrhagic inflammation of the gastrointestinal mucosa. There are hemorrhagic patches or spots on the epicardium and kidneys.
2. Acute type
This is the most common type. Diseased pigs mainly show pneumonia symptoms, with body temperature rising to 40°C-41°C, reduced or completely lost appetite, difficult breathing, and white foam flowing from the mouth and nose, sometimes containing blood. There is first a dry short cough, which later becomes a wet painful cough. The conjunctiva is cyanotic, and later red patches appear on the skin, with constipation changing to diarrhea. As the disease progresses, breathing becomes more difficult, a dog-sitting posture appears, and in the later stage the animal becomes weak and unable to stand, finally dying from suffocation. The disease course is 4-7 days. Acutely affected pigs that do not die eventually turn into chronic cases.
Necropsy of pigs with acute swine pasteurellosis shows edema and widening of the interlobular interstitium of the lungs, a large amount of foamy mucus in the trachea and bronchi, serous infiltration of the pulmonary lobules, and a marble-like appearance on lung cut surfaces, with hepatized areas of different colors such as dark red and grayish yellow. Caseous necrosis is often present in the center of the hepatized areas. The pleura is mixed with yellowish-white fibrin, and in cases with a long course, the pleura adheres to the pericardium.
3. Chronic type
It mainly manifests as pneumonia and chronic gastroenteritis, with persistent coughing and difficult breathing at times, poor appetite, listlessness, swollen joints, and extreme emaciation. Eczema occurs on the skin, and finally diarrhea develops. The disease course is more than 2 weeks. If there is concurrent infection ortreatmentis inappropriate, death usually occurs 2-3 weeks after onset.
In chronic cases, most of the lung tissue becomes carnified, the lungs have hepatized areas, and there are yellow or gray necrotic foci, with connective tissue on the outside and caseous material inside; some form cavities that connect with the bronchi. The pleura adheres to surrounding tissues.
Diseaseprevention and treatment
1. Prevention
The occurrence of this disease is related to environment and stress. Poor environmental factors, such as a pig house that is too cold, too hot, damp, or crowded, and long-distance transport of pigs, can reduce the body's resistance and thereby induce the disease. In ordinary times, feeding management should be strengthened and the pig house environment improved. Introduced pigs should be isolated for more than 1 month and only mixed into the herd after being confirmed healthy. Pigs already diagnosed with the disease should be isolated immediatelytreatment, and the contaminated pig house should be thoroughly disinfected. For pigs in the same pen, serum or vaccine should be used for emergency prevention.
Vaccination can be carried out for the pig herd. Swine pasteurellosis EQ-630 attenuated vaccine is injected intramuscularly or subcutaneously at 1 ml, with an immunity period of 6 months. Piglets are vaccinated once at 40-50 days of age,breeding pigsare injected 2 times a year. Other vaccines such as swine pasteurellosis inactivated bacterin, swine pasteurellosis Inner Mongolia strain attenuated bacterin, swine pasteurellosis ta53 live bacterin, and swine pasteurellosis c20 live bacterin can be used according to specific circumstances.
2.treatment
Swine pasteurellosis is an acute septicemic infectious disease with great harm and rapid onset. When this disease is found in large-scale pig farms, it is not advisable totreat; it is recommended to cull immediately and disinfect promptly. Iftreatmentis necessary, consideration can be given to combining antibiotics with sulfonamides, such as tetracycline + sulfadimidine, while tylosin + sulfadimidine has even better efficacy. Alternatively, gentamicin can be used at 1-2 mg per kg body weight, or 10% sulfadimidine injection at 0.07 g per kg body weight, injected intramuscularly twice daily. Because diseased pigs often show difficult breathing, it is not advisable to administer drugs by drenching; subcutaneous or intramuscular injection is generally preferable.
Pasteurella multocida readily develops drug resistance, so when using antibacterial drugs, drug sensitivity testing should be performed, and several drugs should be selected for alternating use and continuous administration. Swine pasteurellosis hyperimmune serum can be used together with medication to enhance the effect.