19/09/2024
Infectious bronchitis is a highly contagious, acute infection of chickens characterized by nasal discharge, coughing, and rales. In layers, it causes a marked reduction in egg production and quality.
Infectious bronchitis is caused by an avian coronavirus, an enveloped single-stranded RNA virus with characteristic spike-like projections on the surface of its envelope. Variation in the viral spike protein gives rise to multiple strains of the virus, which may vary regionally. The virus transmits rapidly through the flock, causing respiratory distress. Mortality is usually low in uncomplicated infections;
CLINICAL SIGNS
Conjunctivitis and nasal discharge are commonly observed. After a few days post-infection, most of the flock will show coughing and respiratory distress due to increased mucus in the trachea. In uncomplicated cases, clinical signs subside after one week. However, coinfection with opportunistic bacteria can complicate the disease.
Infected chicks can appear listless and huddle together for warmth. Feed consumption and weight gain are decreased. Infection with nephropathogenic strains can lead initially to respiratory signs, then later to lethargy, ruffled feathers, wet droppings, polydipsia, and death
In layers, a significant drop in egg production is often observed, and there may be an increase in the production of thin, wrinkled egg shells for several weeks.
And also layers with infectious bronchitis, egg production can drop by up to 70%, and eggs are often misshapen, with thin, soft, , rough, and/or pale shells. Eggs can also be smaller and have watery albumen.
TRANSMISSIONS
The virus is transmitted to the upper respiratory tract by either direct bird-to-bird contact or exposure to fomites. Once an animal is infected, viral replication occurs in the respiratory tract and digestive tract.
The virus is not transmitted through the egg. Clinical signs can be observed after a short incubation period (~24-48 hrs). Infected birds shed virus in their respiratory secretions and droppings.
PREVENTION
Vaccines are available commercially. The vaccine must be of the same serotype as the field strain to generate protective immunity. In general, live vaccines are used in young animals either by spray or drinking water applications.
Because many backyard flocks are unvaccinated, biosecurity plays a fundamental role in the prevention of infectious bronchitis. Stringent biosecurity practices, covering all aspects of the operation, are needed to keep flocks healthy. Before the arrival of new birds, the poultry house and equipment must be disinfected.
TREATMENT AND CONTROL OF INFECTIOUS n BRONCHITIS IN CHICKEN
Antimicrobials for secondary infections
Supportive care (eg, adjusting ambient temperature, decreasing protein content in feed, adding electrolytes to water)
Attenuated live or killed (inactivated) vaccines
No medication alters the course of IBV infection; however, antimicrobial treatment can lower the mortality rate exacerbated by complicating bacterial infections. In cold weather, increasing the ambient temperature also can decrease the mortality rate. In addition, decreasing the protein concentrations in feed and providing electrolytes in drinking water can assist in outbreaks that are due to nephropathogenic strains.
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