Infectious Bronchitis (Gasping Disease)

Infectious Bronchitis (Gasping Disease) also known as Blind layer disease in animals.

Infectious Bronchitis (IB) or Gasping Disease is an acute, highly contagious viral disease of commercial chicken flocks throughout the world.

Infectious Bronchitis (Gasping Disease) is usually characterized by respiratory signs (coughing, sneezing, tracheal rales with accumulation of mucus in the bronchi) decreased egg production and poor egg quality in breeders and layers, interstitial nephritis in association with myopathy and proventriculitis, particularly in chicks.

Etiology

• Infectious bronchitis virus (IBV), genus Coronavirus is a member of the family Coronaviridae. It is a positive stranded linear ssRNA virus.
• The severity of disease are influenced by the strain of the virus, age and immune status of host and concurrent infection with Mycoplasma gallisepticum, Mycoplasma synoviae, Escherichia coli, and/or Avibacterium paragallinarum can exacerbate disease, diet of the chickens and cold stress.

Epidemiology

• This disease is worldwide in distribution.
• In recent years, a novel IBV genotype, the QX strain, has become increasingly common in Asia and Europe.
• Chicken is the only bird that is usually infected by IBV, although some other birds may be subclinically infected.
• All age group of birds are susceptible, but the disease is most severe in baby chicks.
• Morbidity is commonly close to 100%  and mortality rate is 5%.

Source of infection

• Infected chickens  shed the IBV in respiratory discharges and faeces.
• Naturally infected chickens and those vaccinated with live IBV may shed virus intermittently for up to 20 wk after infection.

Transmission

• Inhalation of aerosol.
• Ingestion of contaminated feed and water, and contact with contaminated equipment and clothing.

Clinical manifestation

• The incubation period of IB is 18-36 hour depending on the route of inoculation.
• The characteristic respiratory signs of IB in chicks are gasping, coughing, sneezing and have a tracheal rales and nasal discharges for 10-14 days.
• Wet eyes may be observed and occasional swollen sinuses.
• The chicks appear depressed, huddled under heat source. The feed consumption and weight gain are significantly reduced.
• In chickens over 6 weeks of age and in adult birds the signs are similar to those in chicks, but nasal discharge does not occur as frequently and the disease may go unnoticed unless the flock is examined carefully by handling the birds or listening to them at night when the birds are normally quiet.
• Infection with nephropathogenic strains can cause initial respiratory signs, then later depression, ruffled feathers, wet droppings, increased water intake, and death.
• Nephropathogenic strains can induce interstitial nephritis with high mortality (up to 60%) in young chicks.
• In laying flocks there is drop in egg production upto 70% and misshapen eggs with thin, soft, rough or pale shell with watery albumin are seen in addition to respiratory signs.
• The  egg albumin may be thin and watery without definite demarcation between the thick and thin albumen.
• In most cases, egg production and egg quality return to normal, but this may take up to 8 wks.
• Infection of young chicks may cause permanent damage to the oviduct, resulting in layers or breeders that never reach normal levels of production. These birds are called as blind layers.

Necropsy Findings

• Infected chickens have serous, catarrhal or caseous exudates in the trachea, nasal passages and sinuses.
• Airsacs may appear cloudy or contain yellow caseous exudates.
• A caseous plug may be found in the lower trachea or bronchi of the chicks.
• When birds infected at very young age may have cystic oviducts, whereas those infected while in lay have an oviduct of reduced weight and length and regressed ovaries.
• In affected layer birds fluid yolk material may be found in the abdominal cavity.
• Infection with nephropathogenic strains results in swollen, pale kidneys and distension of the tubules and ureters with urate crystals.

Sample collection

• Paired sera sample, tracheal swab, trachea, caecal tonsils and kidney tissue.

Diagnosis

• Based on clinical history and lesions.
• Isolation of virus by inoculation of homogenates of tracheal, cecal tonsil, and/or kidney tissue into 9- to 11-day-old SPF chicken embryos. The growth of IBV indicated by embryo stunting and curling, and deposition of urates in the mesonephrons with variable mortality.
• Alternatively, isolation of virus by tracheal organ cultures, the growth of virus indicated by cessation of cilial motility.
• The MAbs have been best used after propagation in chicken embryos, to detect viral antigen in the chorioallantoic membranes by immunofluorescence or immunoperoxidase staining, or in the allantoic fluid by ELISA.
• Rapid detection of viral antigen by RT-PCR, and detection of specific serotype and strain by restriction fragment length polymorphism analysis, analyzed by nucleotide sequencing.
• The S1 region of the spike glycoprotein gene determines the serotype of virus.
• Typing of viruses can help to distinguish vaccine strain from field strains and may help to diagnose outbreaks caused by serotypes distinct from those of the vaccines used in the flock.
• Antibodies in serum is diagnosed by HI test.

Differential diagnosis

• New castle disease
• Infectious laryngiotracheitis

Management procedures

• No medication alters the course of IBV infection.
• Antimicrobial therapy may be used to reduce caused by secondary bacterial infection.
• In cold weather, increasing the ambient temperature may reduce mortalities.
• Reduce protein concentration in feed and provide electrolytes in drinking water,  when outbreaks caused by nephropathogenic strains.

Vaccination

• Both live and inactivated virus vaccines used for IB immunization.
• Live vaccines are used in broilers and for initial vaccination of breeders and layers.
• Inactivated oil emulsion vaccines are used primarily at point of lay in breeders and layers.
• Live vaccine administered individually by eye drop, intra tracheal or intranasal route.
• Mass application methods include administration of vaccine as coarse spray, aerosol and drinking water.
• Inactivated vaccines require injection of individual birds. These vaccines are usually given after priming with live virus and are administered a few weeks before production commences.
• The most commonly used live vaccines in the USA contain derivatives of the Massachusetts, Connecticut, and Arkansas strains.
•  In Australia- VicS and Armidale strains.
•  In Europe- 4/91 strain and those derived from QX-like viruses.

Time of vaccination

• Two weeks (14 days) of age is frequently used as the time for initial immunization.
• Booster doses administered at 28 days and 16-18 weeks of age.

Control measures

• Strict isolation and repopulation with only day old chicks, following the cleaning and disinfection of the poultry house.