Symptoms and Prevention and Control Methods of Pseudomonas aeruginosa Infection in Chickens

Etiology

Pseudomonas aeruginosa belongs to the genus Pseudomonas and is Gram-negative. It is a short, small bacillus with rounded ends, motile, with a single flagellum at one end of the cell. The bacterium measures 1.5-3.0μm×0.5-0.8μm, occurring singly or in pairs, occasionally in short chains.

Epidemiology

This disease mainly affects chicks, with onset mostly at 1-35 days of age. The morbidity and mortality rates vary, sometimes reaching as high as 50%. There is no obvious seasonality. According to Liu Shanggao et al. (1987), the prevalent Pseudomonas aeruginosa in chickens in China is mainly serotype IV, belonging to IATS9 type.

Pseudomonas aeruginosa is widely distributed in soil, water and air, and can be found in the intestines and skin of normal humans and livestock. This bacterium is usually seen mostly in wound infections, so the occurrence of this disease has a certain relationship with environmental contamination and vaccine injection.

Symptoms

Sick chickens mainly show reduced food intake and listlessness; diarrhea of varying degrees, with watery feces that are pale yellow-green, and severely affected chickens have blood in the feces; abdominal distension, soft when pressed by hand, and sick chickens in the later stage show abdominal breathing; some sick chickens develop edema of varying degrees around the eyes, and the swollen areas rupture and discharge fluid, forming scabs, with the eyes fully closed or half closed, and lacrimation; subcutaneous edema of the neck. Severely affected chickens also show subcutaneous edema on the inner sides of both legs.

Pathological Changes

The subcutaneous tissue of the neck and umbilical region of sick chickens shows yellow-green gelatinous infiltration, and the muscles have hemorrhagic spots or hemorrhagic patches. Internal organs show congestion and hemorrhage of varying degrees. The liver is brittle and enlarged, earthy yellow in color, with pale grayish-yellow small necrotic foci. The gallbladder is distended. The kidneys are enlarged, with scattered small hemorrhagic spots on the surface. The lungs are congested, with hemorrhagic spots in some cases, and inflammatory lesions of the pulmonary lobules, showing purplish-red or marbled changes. There is hemorrhage of the coronary fat, with gelatinous infiltration, and hemorrhagic spots on the endocardium and epicardium. The glandular stomach mucosa sloughs off, and the muscular stomach mucosa has hemorrhagic patches that are easily peeled off, and the intestinal mucosa shows severe congestion and hemorrhage. The spleen is enlarged, with small hemorrhagic spots. The air sacs are cloudy and thickened.

The lesions in chickens artificially infected with the disease are green cellulitis at the injection site, atrophy of lymphoid tissue in immune organs, and depletion of lymphocytes. Fibrinoid degeneration around the splenic sheathed arteries, with purulent meningoencephalitis seen in most chickens, focal hepatic necrosis and interstitial myocarditis in a few, and hemorrhagic necrotizing inflammation of the pulmonary lobules in individual chickens.

Diagnosis

For the diagnosis of this disease, in addition to considering the epidemiological characteristics, clinical symptoms and pathological changes, it mainly relies on the collection of specimens for isolation and identification of the pathogen.

1. Collection of specimens and isolation and culture Take heart blood, liver, spleen, lung and subcutaneous edema fluid from the chest and abdomen of dead chickens, and inoculate them respectively onto culture media suitable for isolation of this bacterium, such as ordinary broth, ordinary agar plates, blood agar plates, MacConkey agar plates, SS agar plates, and culture in a 37℃ constant-temperature incubator for 18-24h, and observe the characteristics and color of the colonies. If the colonies are blue-green, a preliminary diagnosis of Pseudomonas aeruginosa can be made.

2. Laboratory diagnosis

(1) Morphological observation: Take pure culture to make smears, and perform Gram staining for microscopic examination. The morphological characteristics of this bacterium are described in the pathogen section.

(2) Examination of cultural characteristics and biochemical characteristics: same as described in the pathogen section.

(3) Animal test: Take 24h broth culture fluid and inoculate healthy chicks intraperitoneally, 0.2ml per bird (2×109CFU/m1). Set up controls at the same time. If Pseudomonas aeruginosa can be re-isolated from the heart, liver, spleen, kidney and other organs of the dead test chickens, the diagnosis can be confirmed.

Prevention and Control Measures

1. Strengthen feeding management and carry out hygiene and disinfection work well.

2. Use antibiotics for treatment, and select drugs according to the results of drug sensitivity tests. Most reports believe that Pseudomonas aeruginosa is sensitive to gentamicin, polymyxin, carbenicillin and sulfadiazine, which are effective for treating this disease.

3. Pseudomonas aeruginosa is very prone to developing drug resistance to most antibacterial drugs, so it is necessary to develop biological products. However, so far there have been no reports of using hyperimmune serum or vaccines to prevent and control this disease. Nevertheless, the typing of the main serotypes of Pseudomonas aeruginosa prevalent in China provides a scientific basis for the future production of hyperimmune serum or the development of vaccines.