Infectious Bronchitis – Silent Killer which is often escaped ignored: Clinical Signs of IB (Infectious Bronchitis)
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| Pullets with dyspnea and conjunctivitis. Mature chicken with mucopurulent ocular and nasal discharge associated with conjunctivitis. |
- The incubation period of IB is dose-dependent and can be as short as 18 hours for intratracheal inoculation and up to 36 hours for ocular application.
- The nonspecific respiratory signs of IB in susceptible chicks are gasping, coughing, sneezing, tracheal rales, and nasal discharge.
- Watery eyes may be observed, and an occasional chick may have swollen sinuses (face swelling seldom seen in non-complicated IB cases).
- The chicks appear depressed and may be seen huddled under a heat source.
- Feed consumption and weight gain are significantly reduced.
- In chickens older than 6 weeks of age, the signs are usually less clear, and the disease may even go unnoticed unless the flock is examined carefully by handling the birds or listening to them at night when the birds are normally quiet.
- The severity of the respiratory signs is influenced by the quality of the climate, housing, kind of bird, strain involved, IB vaccination the program, and presence of co-infections including secondary infections.
- Chickens that have IB or a severe reaction to IB vaccination may develop airsacculitis, due to an increased susceptibility to secondary infectious agents (especially Escherichia coli or Mycoplasma gallisepticum).
- Broiler chickens infected with a nephropathogenic virus may appear to recover from the respiratory phase and then show signs of depression, ruffled feathers, wet droppings, increased water intake, and mortality.
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| The internal quality of eggs may also suffer. In this photograph the light is being reflected from the outer ring of a watery egg white and there is no internal ring of albumen like in the normal egg (right). “False layers” infected by IB with watery cysts may present a “penguin posture” like in cases of ascites. |
- Cold stress, breed of chicken, and high-protein diets containing animal byproducts as the protein source are predisposing factors for the development of clinical signs during an infection with a nephropathogenic strain.
- In laying flocks, declines in egg production and quality are seen in addition to respiratory signs. The respiratory signs also can be absent or very mild, even in cases of clear production drops and the production of eggs with pale, unpigmented shells.
- The severity of the production decline may vary from slight up to 70% and depends on factors such as the causative virus strain and level of immunity against that strain, the timing of infection within the period of lay, and by co-infections
- A co-infection of IBV increased the percentage of eggshell apex abnormalities caused by Mycoplasma synoviae
- Following IBV infection at the onset of production a more severe drop in total production of normally shelled eggs, an increase in the number of abnormally shelled eggs, and more lasting adverse effects on egg weight and internal egg quality were observed, in comparison with infection after peak production.
- With mild drops in production, a normal level of production can be restored in 1 or 2 weeks. With severe drops of production, 6–8 weeks may elapse before production returns to the pre-infection level, but in some cases this is never attained.
- In addition to production declines, IBV infections can cause a range of effects on the egg quality varying from loss of shell pigment, shell quality (misshapen, thin, soft-shelled and rough-shelled, thin to watery albumen in a fresh egg, and decreased hatchability.
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| Eggs are more or less discoloured, dirty and bloodstained. Eggs are discoloured, small, deformed and “ringed”; altered eggshell tends to break easily. From top to bottom: control eggs, bloodstained eggs, smaller eggs, altered eggshell (soft and easily broken), deformed eggs. |
- The D388 strain was isolated from 19-day old breeders with respiratory signs and nephritis. This flock had a peak in egg production of 36%. An infection of day-old SPF birds resulted in 30% mortality due to nephritis, and the survivors had 81% incidence of cystic oviducts
- Chickens that had IB or a severe reaction to IB vaccine when less than 2 weeks of age may suffer permanent damage to the oviduct resulting in poor-to-no egg-laying capacity.
- All birds in the flock become infected (Morbidity is virtually 100%, although severity of signs varies), but mortality is variable depending on virulence and pathotype of the infecting strain; age of infection; status of immunity, either maternal or active; and stresses such as cold or secondary bacterial infections. The highest mortality is usually seen with infections of nephropathogenic strains in young birds. Mortality in young chicks is usually negligible unless the disease is complicated by other infectious agents.
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