Prevention and treatment of Avian Cholera

Avian cholera is a contact disease that affects poultry and wild birds, also known as avian pasteurellosis and avian hemorrhagic septicemia. The disease often shows septic symptoms, with high morbidity and mortality, but it also often has a chronic or benign process.

Induced pathogen

Pasteurella multocida is a short bacillus with obtusely round ends and slightly convex center, long 1~1.5um, wide 0.3~0.6um, no spores and no movement. Ordinary dyes can be stained, and gram staining is negative. Microscopic examination of diseased tissue or body fluid smears with Wright's, Giemsa's method or methylene blue staining shows that most of the bacteria are oval, with deep staining at both ends, and the central part is lighter, much like two parallel cocci, so it is also called bipolar bacilli. The bipolar staining of the smears made with the culture is not so obvious. When dyeing with dyes such as Indian ink, a clear capsule can be seen. The capsule of the newly isolated bacteria is wide and thick, and the capsule of the weakly virulent bacteria that has been artificially cultured is narrow and incomplete.

Epidemiology

The disease is susceptible to all kinds of poultry, such as chickens, ducks, geese and turkeys, but geese are less susceptible, and all kinds of wild birds are also susceptible. The death loss of chickens caused by avian cholera usually occurs in laying hens, because chickens of this age are more susceptible than young chickens. Chickens under 16 weeks of age generally have strong resistance. However, chicken flocks with 10-day onset have also been found in clinic. The mortality rate of naturally infected chickens is usually 0-20% or higher, with frequent egg drop and persistent local infection. Cutting off feed, cutting off water or suddenly changing feed can increase the susceptibility of chickens to avian cholera.

How avian cholera spreads to chickens is often uncertain. Chronic infection of poultry is considered to be the main source of infection. The transmission of bacteria through eggs rarely occurs. Most farm animals may be carriers of Pasteurella multocida, and contaminated cages and grooves may spread pathogens. The transmission of Pasteurella multocida in poultry is mainly through the oral, nasal and conjunctival secretions of diseased birds, which pollute the environment, especially feed and drinking water. Feces rarely contain live Pasteurella multocida.

Clinical symptoms

The incubation period of natural infection is generally 2-9 days, and sometimes cases break out within 48 hours after the introduction of diseased chickens. Artificial infection usually occurs at 24 to 48 hours. Due to the difference between the body resistance of poultry and the pathogenicity of bacteria, the symptoms are also different. It is generally divided into the most acute, acute and chronic three types of disease.

1. The most acute type: it is common in the early stage of the epidemic, and the chickens with high egg production are the most common. The sick chicken had no prodromal symptoms, everything was normal at night, ate well, and died in the henhouse the next day.

2. Acute type: this type is the most common. The main manifestations of diseased chickens are depression, loose feathers, neck and eyes, head under wings, unwilling to walk, standing apart from the group. Diseased chickens often have diarrhea and discharge thin yellow, grayish-white or green feces. Body temperature rises to 43-44 ℃, diet is reduced or no food is eaten, thirst increases. Dyspnea, increased oral and nasal secretions. The chicken crown and meat beard turn bluish purple, and some diseased chicken beards are swollen and have a sense of heat pain. Laying hens stop laying eggs. Finally, there was exhaustion, coma and death, with a short course of about half a day and a long period of 1-3 days.

3. Chronic type: it changes from acute immortality, which is more common in the later stage of epidemic. Chronic pneumonia, chronic respiratory tract inflammation and chronic gastroenteritis are more common. In diseased chickens, viscous secretions flow out of nostrils, sinuses are enlarged, and secretions accumulate in the throat, which affect respiration. I often have diarrhea. The sick chicken is thin, listless and pale. In some diseased chickens, one or both sides of the beard is significantly enlarged, followed by purulent cheese-like substances, or dry knot, necrosis, and shedding. Some sick chickens have arthritis, often limited to the foot or wing joint and tendon sheath, characterized by joint swelling, pain, toe paralysis, resulting in claudication. The course of the disease can be delayed for more than a month, but the growth and development and egg laying can not be restored for a long time.

Pathological changes

The most acute type of dead chickens had no special lesions, and sometimes only a few bleeding spots in the epicardium could be seen.

The pathological changes of acute cases were characterized by small spot bleeding in peritoneum, subcutaneous tissue and abdominal fat of diseased chickens. The pericardium became thicker and there were a large amount of opaque yellowish fluid in the pericardium, some of which contained cellulose flocculent fluid, especially epicardial and coronal fat bleeding. There are congestion or bleeding spots in the lungs. The lesion of the liver is characteristic, the liver is slightly swollen, the quality becomes brittle, brown or yellowish brown. There are many gray-white, needle-sized necrotic spots scattered on the surface of the liver. The spleen generally has no obvious change, or slightly enlarged, the texture is softer. Myogastric bleeding is significant, the intestinal tract, especially the duodenum, shows catarrhal and hemorrhagic enteritis, and the intestinal contents contain blood.

The chronic type varies according to the organs invaded. When respiratory symptoms are dominant, a large amount of viscous secretions are seen in the nasal cavity and paranasal sinuses, and pulmonary sclerosis is seen in some cases. Limited to arthritis and tenosynovitis cases, mainly joint swelling and deformation, inflammatory exudates and caseous necrosis. The rooster's beard is swollen with cheese-like exudates, and the hen's ovaries are obviously bleeding, and sometimes the follicles are deformed, like semi-cooked.

The pathological changes of ducks were basically similar to those of chickens. Ducks who died of avian cholera were filled with transparent orange exudates in their pericardium and hemorrhagic spots in pericardium and coronal fat. The lungs show multiple pneumonia with emphysema and bleeding. Nasal mucous membrane congestion or bleeding. The liver is slightly enlarged, showing needle-like bleeding spots and gray-white necrotic spots. The intestinal mucosa congestion and bleeding in the anterior segment of the small intestine and large intestine were the most serious, while the posterior segment of the small intestine and the cecum were mild. Ducklings are polyarthritis with rough articular surface and yellow cheese-like substance or red granulation tissue. The joint capsule is thickened and contains red serous or grayish-yellow, turbid viscous fluid. Steatosis and local necrosis occur in the liver.

Diagnostic method

According to the epidemiology, autopsy characteristics and clinical symptoms of diseased chickens, the preliminary diagnosis can be made, and the diagnosis must be diagnosed by laboratory. Smears of diseased chicken blood and liver and spleen contact smears are stained with Meilan, Wright's or Giemsa. If you see a large number of bacilli strongly stained at both poles, it is helpful to the diagnosis. Further diagnosis depends on the isolation and culture of bacteria and biochemical reaction.

Prevention and cure measures

It is entirely possible to strengthen the feeding and management of chicken flocks, strictly implement veterinary health and epidemic prevention measures in chicken farms, and adopt a full-in-all-out feeding system in Dongshou as a unit to prevent the occurrence of this disease. Generally speaking, chicken farms where the disease has never occurred are not vaccinated. The disease of chicken flocks should be treated immediately, and effective drugs should be given to the whole group through drug sensitivity test where possible. Sulfonamides, chloramphenicol, erythromycin, gentamicin, ciprofloxacin, enrofloxacin and olaquindox are all effective. In the course of treatment, the dose should be sufficient and the course of treatment should be reasonable. when the death of chickens decreased significantly, they should continue to be administered for 2 or 3 days to consolidate the curative effect and prevent recurrence.

In frequent areas or chicken farms, the effect of drug treatment is decreasing day by day, and it is difficult to control the disease effectively. Vaccine can be considered for prevention. Because the vaccine immunization period is short, the prevention and treatment effect is not very ideal. The bacteria can be isolated in this field where there are conditions. after the identification, the inactivated vaccine is made and the chickens are injected regularly. It is proved by practice that the disease can be effectively controlled through 1 ~ 2 years of immunization. At present, there is a better inactivated vaccine of propolis in China, which is safe and reliable, can be stored at 0 ℃ for two years, is easy to be injected, does not affect egg production, has no toxic side effects, and can effectively prevent and control the disease.