Infectious bronchitis is a highly contagious viral disease in chickens that cause death in young birds and chicks and production problems in older birds and broilers. Infectious bronchitis cause significant losses in the chickens industry and is found the world over.
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Infectious bronchitis can be prevented by vaccine and good husbandry but there are no direct treatments. It is a highly contagious disease of chickens characterised by respiratory signs and high mortality in young chicks and decreased egg production and deterioration of egg quality in laying birds.
Some strains of the infectious bronchitis virus cause severe kidney damage and may be associated with high mortality.
About Infectious bronchitis in chickens:
The disease was first described in 1931 in a flock of young chickens in the USA. Since that time, the disease has been identified in broilers, layers, and breeder chickens throughout the world.
Infectious bronchitis (IB) virus a member of the genus corona virus. Chickens and possibly pheasants are considered the only susceptible hosts.
- Chickens are the only natural host.
- Pheasants are susceptible experimentally.
- Waterfowl and other poultry are not affected and are not considered as reservoirs of the infectious bronchitis virus.
- Incubation Period varies between 3-10 days.
- The infection lasts 3-6 days in young chicks, 7-10 days in growers and 10-14 days in fully grown chickens.
- Infection is resolved within 10-14 days with a rise in antibody titres.
Infectious bronchitis is an enveloped, single stranded RNA virus, about 20000 bases in length, around 150 nm in size. It has a lipid membrane or envelop which is derived from the endoplasmic reticulum of the host cell.
Survival of infectious bronchitis virus outside the host:
- Infectious bronchitis virus persists in contaminated chicken houses for approximately four weeks.
- The virus rapidly killed by common disinfectants (killed in 3 minutes by 1% formalin).
- Infectious bronchitis is easily destroyed by heat and sunlight.
- The virus remains active for years when stored at -25 C.
Downtime between flocks and thorough cleaning is essential in combating the virus.
Transmission of infectious bronchitis occurs both between flocks and within flocks and from adult to young but not via the egg. It is likely that every chicken in the flock will contract the virus.
- Though the mixing of birds. Some chickens become carriers and shed the virus through secretion and discharges for many months after the infection.
- By air borne transmission in the direction of prevailing wind. The virus has been known to travel approximately 1200 yards on the wind.
- Mechanical transfer by visitors, service personnel, feed trucks, etc.
Within a flock:
- The virus is coughed up in air and infection occur through inhalation.
- Ingestion of faeces or contaminated feed or water. Spread is very rapid. The entire house become infected within 24-48 hours. Clinical sign will develop in contact chicks within 36 h and in nearby sheds within 1 to 2 days.
- Infection may persist in a flock for many months and may cycle from bird to bird.
- Recovered birds may shed the infectious bronchitis virus for about 4-9 weeks. The shedding of virus post infection lessens with time. Reinfection may lead to latency and shedding of the virus for longer periods.
Factors influencing the rate of transmission and the number of susceptible birds in the flock:
Age of the birds at the time of exposure. The disease occurs more frequently and causes severe death losses in chicks less than 10-12 weeks and the resistance of chickens to fatal infection increases with age.
Climatic stress, the occurrence somewhat higher in winter than in summer and latent or concurrent infections make the condition much worse.
Infectious bronchitis virus can predispose chickens, especially broilers, to infection by certain strains of E. coli.
Veterinarians can diagnose IB through a combination of clinical signs, laboratory tests, and PCR (polymerase chain reaction) assays to detect the virus's genetic material.
Heavy breeds and male birds are more prone to severe uraemic form of the disease.
The clinical signs and symptoms of infectious bronchitis in chickens:
Respiratory signs are seen in birds of all ages, although their severity may vary with age.
Sneezing, gasping, shortness of breath, coughing, nasal discharge, frothy pus in the eyes and abdominal respiratory sounds or rales are common symptoms of Infectious bronchitis regardless of the age of the infected chickens.
Young chicks, less than 3 weeks old, there is generally severe respiratory symptoms and in very young chicks with no maternal antibodies, damage may be done to oviducts that may cause false layers. These birds may grow up like normal hens but produce no eggs.
The morbidity or infection rate is very high, up to 100%. Chicks are depressed and huddle under the heat source.
Mortality may be up to 25-30 % when uncomplicated. May reach to 60% when super-imposed with E. coli.
Below: Bubble sin the eyes with no swelling is a sign of infectious bronchitis.
In growing and older birds respiratory signs are mild and may go unnoticed with the main symptom being poor feed conversion and reduce weight gain in broilers. There may be permanent damage to the developing oviduct and as many as 20% of the affected birds become “false layers”.
In fully grown adult birds respiratory symptoms are less severe, unapparent, or even absent.
Drastic drops in egg production, from 60-90% to 5-20% within 1-2 weeks. Laying birds stay out of production for about one month after the active disease has passed.
Recovery is slow and affected birds seldom regain full production since some birds are permanently damaged. It takes about 8-10 weeks to reach 50 % of the former level. Young pullets respond better than older birds.
Within two weeks, flocks lose condition, and many birds start to moult before time.
Inferior egg quality across the flock. Eggs are small, thin-shelled, soft-shelled, misshapen, rough-shelled or have calcareous deposits.
Loss of pigment in brown-shelled eggs is common.
Internal eggs quality is poor with the albumin become watery and yolk broken.
Increased number of un-settable of hatching eggs.
Reduced fertility and hatchability with 10-30 % embryo mortality and reduced chick quality.
Treatment, prevention and control of infectious bronchitis in chickens:
Prevention of infectious bronchitis is by vaccination and good flock management.
Vaccinate only healthy birds.
Many of the live vaccines induce a mild respiratory infection. IB virus loses its infective ability easily under adverse condition, therefore vaccines should be handled carefully.
Chickens that experience a severe vaccination reaction following IB vaccination or field infection during the first two weeks of life may have permanent damage in the oviduct, resulting in hens with poor production.
There is no direct treatment for infectious bronchitis in chickens and only supportive medications are given.
Antibiotics are given to control secondary infections. Pain killers and other supportive medications can be given.
Infectious bronchitis can not affect humans. There have been no reports of human infection with IB virus.
A carcass showing acute signs of clinical disease accompanied with emaciation on after slaughter inspection is condemned and would never get into the human food supply chain.
Chickens with infectious bronchitis will likely stop laying eggs as it affects food conversion and egg production. Infectious bronchitis is not passed through the egg and they are safe to eat.
Infectious bronchitis may cause secondary infections in chickens which can affect the eggs as well as the meat.