Causes and Prevention and Treatment Methods of Infectious Laryngotracheitis in White-Feathered Broiler Chickens

Infectious laryngotracheitis in chickens is an acute respiratory infectious disease caused by a herpesvirus. Infectious laryngotracheitis in chickens is characterized by difficulty breathing, coughing, and expectoration of exudate containing blood. On necropsy, swelling, hemorrhage, and erosion of the laryngeal and tracheal mucosa can be seen. In the early stage of the disease, intranuclear inclusion bodies can form in the cells of the affected area. This disease spreads quickly and has a high mortality rate, endangering the development of the chicken farming industry. This disease has already occurred and spread in some areas of our country.

1. Pathogen Infectious laryngotracheitis virus mainly exists in the tracheal tissue and exudate of sick chickens. This virus has very weak resistance to the external environment. When heated at 55C it survives for 10—15 minutes, at 37C it survives for 22—24 hours, and after the water is boiled it dies ·immediately. Disinfection with 3% Lysol or 1% caustic soda disinfectant solution can kill it in 1 minute.

2. Epidemiological characteristics Under natural conditions, infectious laryngotracheitis in chickens mainly affects chickens, and chickens of all ages and breeds can be infected, but the symptoms are most characteristic in adult chickens. Sick chickens and virus-carrying recovered chickens are the main sources of infection, generally transmitted through the respiratory tract and intraocular routes. Bedding, feed, drinking water, and equipment contaminated by respiratory organ and nasal secretions can become transmission vectors. The activities of humans and wild animals can also spread it mechanically. Hatching eggs may also transmit it. A small proportion of recovered chickens can carry the virus for as long as two years. Overcrowding of chickens, poor ventilation, poor feeding and management, lack of vitamins, and parasitic infections can all promote the occurrence and spread of this disease. Once the disease is introduced into a chicken flock, it spreads rapidly, and the infection rate can reach more than 90%. The mortality rate varies depending on feeding conditions and flock status, with the low being about 5%, and the high reaching 50% to 70%.

3. Clinical symptoms of infectious laryngotracheitis in chickens The incubation period for natural infection is 6—12 days, and for artificial tracheal inoculation it is 2—4 days. Sick white-feathered broiler chickens initially have nasal discharge, which is semi-transparent, with tearing and conjunctivitis, followed by characteristic respiratory symptoms, namely wet rales when breathing, coughing, and wheezing sounds. Sick chickens squat on the ground or on perches. Each time they inhale, the head and neck extend forward and upward, the mouth opens, showing a posture of trying hard to inhale, with wheezing calls. In severe cases, there is marked difficulty breathing, spasmodic coughing, and blood-streaked mucus may be expectorated. If the secretions cannot be expectorated and block the trachea, death by suffocation can occur. Sick chickens have reduced or lost appetite, rapidly lose weight, the comb turns purple, and sometimes greenish watery droppings are passed, and finally most die from exhaustion. In laying hens, egg production rapidly decreases or stops, and it can only recover 1 to 2 months after recovery. The course of the disease is 5—10 days or longer. Most of those that do not die recover after 8—10 days, and some may become virus-carrying chickens.

4. Pathological changes The main lesions are in the trachea and larynx. At the beginning of the disease, the mucosa is congested, swollen, and has mucus. The mucus then undergoes degeneration, hemorrhage, and necrosis, and the lumen narrows. After 2—3 days of the disease course, there is a yellowish-white fibrinous caseous pseudomembrane. Due to severe coughing and spasmodic breathing, the expectorated secretions are mixed with blood clots and shed epithelial tissue. In severe cases, the inflammation can also extend to the bronchi, lungs, and air sacs, and even ascend to the infraorbital sinus.

5. Diagnosis This disease often occurs suddenly, spreads quickly, and occurs most in adult chickens. The incidence rate is high, and the mortality rate varies greatly depending on conditions. The clinical symptoms are relatively typical: open-mouth breathing, wheezing with rales, and blood-streaked mucus can be expectorated when coughing. The trachea shows catarrhal and hemorrhagic inflammatory lesions. When symptoms are atypical, laboratory tests can be carried out.

6. Prevention and control measures At present, there is no effective therapeutic drug. When the disease occurs, symptomatic treatment can be used, and antibacterial drugs can be used to prevent secondary infection. Feeding and management equipment and chicken houses must be disinfected. Recovered chickens must not be raised mixed with susceptible chickens. In areas where infectious laryngotracheitis in chickens is epidemic, chickens can be immunized by eye-drop and intranasal inoculation with attenuated vaccine. The first immunization time is around 4 weeks of age, and the second immunization is carried out after 6 weeks.