Prevention and treatment of Leptospirosis in Pig

Leptospirosis is a zoonotic and natural infectious disease caused by pathogenic Leptospira. The clinical symptoms of the disease are various. Porcine leptospirosis is generally a recessive infection and sometimes breaks out. Acute cases are characterized by fever, hemoglobinuria, anemia, edema, abortion, jaundice, hemorrhagic quality, skin and mucosal necrosis. The carrier rate and morbidity of pigs are high. The disease is distributed all over the world and occurs frequently in tropical and subtropical areas. The disease occurs and spreads in many provinces and cities in China, especially in the Yangtze River Basin and other parts of the south. In recent years, the occurrence and prevalence of porcine leptospirosis have increased, which has been reported in Fujian, Heilongjiang, * and other places.

Pathogen

The pathogen of leptospirosis belongs to Leptospira. Leptospira is pathogenic to humans, animals and wild animals. Leptospira has many serogroups and serotypes. at present, there are 25 serogroups and at least 190 different serotypes of pathogenic Leptospira in the world. The serogroups causing leptospirosis in pigs include Pomona group, febrile group, autumn fever group and jaundice hemorrhagic group, of which Pomona group is the most common.

Epidemiology

Pigs of all ages can be infected, but the incidence of piglets is more, especially suckling piglets and weaned piglets, the disease is generally mild in medium and large pigs, but not in sows. The main sources of infection are diseased pigs and infected pigs. Leptospira can pollute the environment in vitro with the urine, milk and saliva of infected pigs and diseased pigs. The amount of bacteria excreted by pigs is large, the period of excretion is long, and they have the most opportunities to come into contact with people, which will also pose a great threat to people. After infection, people can also carry bacteria and discharge bacteria. There is a complex cross-transmission between humans and animals, which is of great significance in epidemiology. Rodents and frogs are also important sources of infection, and they are the natural storage hosts of the bacteria. Rodents can carry bacteria all their lives and expel bacteria through urine, causing long-term environmental pollution. The main cause of borer is urination to pollute the water source.

Leptospirosis is transmitted directly or indirectly, mainly through the skin, followed by digestive tract, respiratory tract and reproductive tract mucosa. Blood-sucking insect bites, artificial insemination and mating can spread the disease. The occurrence of the disease is not seasonal, but the epidemic peak is in the rainy season of summer and autumn. The disease is often sporadic or endemic.

Clinical symptoms

Clinically, porcine leptospirosis can be divided into acute type, subacute type and chronic type.

1. Acute type is more common in piglets, especially in suckling piglets and nursing pigs. The incubation period was 1-2 weeks. The clinical symptoms were sudden onset, body temperature rising to 40: 41 ℃, missed for 3-5 days, depressed spirit, anorexia, diarrhea, dry skin, jaundice of skin and mucosa, nervous weakness and tremor in hindlimbs; in some cases, hemoglobinuria, urine color such as strong tea; feces green, foul smell, blood feces can be seen in the long course of the disease. The mortality rate can reach more than 50%.

2. Subacute and chronic types are mainly characterized by damage to the reproductive system. At the beginning of the disease, the body temperature increased in varying degrees, eye conjunctiva flushed, edema, some yellowing, some mandible, head, neck and systemic edema. Sows generally have no obvious clinical symptoms, and sometimes show fever and no milk. However, in sows with less than 4-5 weeks of pregnancy, miscarriage and stillbirth can occur 4-7 days after Leptospira infection, and the abortion rate can reach 20%-70%. The sows in the later stage of pregnancy can give birth to weak piglets after infection, and the piglets can not stand or suck milk, and die in 1-2 days.

Pathological changes

1. The acute type is mainly characterized by septicemia, systemic jaundice and extensive hemorrhage and necrosis of various organs and tissues. Yellow staining and varying degrees of bleeding in skin, subcutaneous tissue, serosa and visual mucosa, liver, kidney and bladder. Dry and necrotic skin. There is turbid yellow effusion in the pleural cavity and pericardium. Splenomegaly, congestion, and sometimes hemorrhagic infarction. The liver is enlarged, khaki or brown, brittle, gallbladder filling, congestion, bleeding can be seen under the capsule. Kidney enlargement, congestion, bleeding. Pulmonary congestion, edema, bleeding spots on the surface. The bladder has red or dark yellow urine. Intestinal and mesenteric congestion, mesenteric lymph nodes, inguinal lymph nodes, submandibular lymph nodes enlarged, gray-white.

2. Subacute and chronic type showed tissue edema in all parts of the body, especially in head and neck, abdomen, chest wall and limbs. The hemorrhage of kidney, lung, liver and epicardium was obvious. Excessive yellow fluid and fibrin are often seen in the serous cavity. The liver, spleen and kidney are enlarged. The kidney disease was the most obvious in the chronic cases of adult pigs.

Diagnosis and differentiation

Leptospirosis can only be diagnosed on the basis of clinical symptoms and pathological examination, combined with microbiological and immunological diagnosis.

1. Microbiological diagnosis of sick animals can collect blood and urine before death. Postmortem examination should be carried out within 1 hour, no later than 3 hours at the latest, otherwise most of the bacteria in the tissue will be dissolved. It can collect the liver of sick and dead pigs. Tissues such as kidney, spleen and brain should be treated immediately and examined directly under a dark field microscope or by immunofluorescence antibody method. The bacteria in pathological tissue can be examined by Giemsa's staining or silver plating staining. The disease material can be used for the isolation and culture of pathogens.

2. Serological diagnosis mainly includes agglutination lysis test, micro complement fixation test, enzyme-linked immunosorbent assay, carbon agglutination test, indirect hemagglutination test, indirect fluorescent antibody test and latex agglutination test.

3. In animal test, the diseased material (blood, urine, tissue suspension) can be inoculated intraperitoneally or subcutaneously into young guinea pigs. If Leptospira is virulent, typical symptoms such as fever, jaundice, non-eating and emaciation may occur in 3-5 days after inoculation, and finally die. When the body temperature rises, the heart blood can be taken for culture to detect pathogens.

4. Molecular biological diagnosis technology can be used to detect pathogens in disease materials by DNA probe technology and PCR technology.

5. Differential diagnosis of leptospirosis in pigs should be different from porcine eperythrozoonosis and hemolytic anemia in newborn piglets.

Prevention and control measures

1. Treatment methods

Pigs with ① should be isolated and treated in time, and the contaminated environment and appliances should be disinfected in time.

② can use 10% florosulfone mycin (0.2mL per kg body weight, intramuscular injection, once a day for 5 days), sulfonamides (sulfa-5-methoxypyrimidine, 0.07g per kg body weight, intramuscular injection, twice a day for 5 days) to treat sick pigs; seriously ill pigs can be treated with vitamins and glucose infusion; streptomycin, oxytetracycline and other tetracycline antibiotics also have a certain effect.

Pigs infected with ③ can be fed with oxytetracycline mixture (0.75~1.5g/kg) for 7 days to prevent and control the spread of the disease. Pregnant sows were continuously fed with oxytetracycline one month before delivery to prevent abortion.

2. Preventive measures

① does a good job in the environmental hygiene and disinfection of the pig house.

② detected, eliminated and disposed of infected pigs in time.

③ does a good job in rodent control to prevent water, feed and environmental pollution, and forbids raising dogs, chickens and ducks.

Pig herds can be immunized with inactivated vaccine in pig farms with this disease in ④.