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Infectious bronchitis IB, Etiology, Econonimical Impact
- 2. An acute, highly contagious viral respiratory disease of chicken Tracheal rales, coughing, sneezing, Broiler-----hinder growth rate Layers-------effect reproductive tract--------decreased egg production with poor egg quality
- 3. ETIOLOGY Infectious bronchitis virus (IBV) Genus coronavirus of family coronaviridae killed rapidly by common disinfectants Inactivated after 15 minutes at 56°C and after 90 minutes at 45°C Electron micrograph of Infectious Bronchitis virus particles
- 4. EPIDEMIOLOGY Chicken is the only natural host Severe death in birds of 10-12 wks age Occurrence is more in winter Common in northern areas of Pakistan Very rapid transmission (within flock) Transmission occur through air borne route (b/t flocks) Contaminated feed and equipment Clothing, foot wear (attendants and visitors)
- 5. Economic impact mainly due to: Poor growth performance and mortality due to the respiratory disease in broilers Egg production losses in layers Losses caused by renal damage may be seen in broilers, layers.
- 6. CLINICAL SIGNS Appear within 36-48 hrs of infection Signs vary in different age groups Young chicks Highly susceptible Gasping Distressed breathing Tracheal rales, sneezing, cough (audible) Nasal discharge Open mouth breathing Depressed and huddle together or under heat source
- 8. CLINICAL SIGNS Morbidity---25-30%-----60% complicated Very young chicks----damage to oviduct Grow normal hen-----no eggs Course-----3-6d
- 9. CLINICAL SIGNS Growing chicks Intensity is less sever Respiratory signs----less sever-----unnoticed Distressed breathing, tracheal rales Significant retarded growth, poor FCR, low weight gain Permanent injury to developing oviduct Morbidity –5-10%, mortality----negligible Course---7-10d
- 11. Laying birds Respiratory signs less sever----may absent Drastic drop in egg production (60-90% to 5- 20% in 1-2 wks) Laying birds ----out of production-----up to one month after passing disease Slow recovery Recovered birds—seldom gain full production
- 12. CLINICAL SIGNS Inferior quality eggs (small, thin shelled, misshapen, have calcareous deposits)
- 13. Comparison of normal eggs (above, left) with shell-less eggs (above, right), rough-shelled egg (centre), and misshapen eggs (bottom) laid by hens during an outbreak of IB
- 14. POSTMORTEM LESIONS Catarrhal and Caseous exudates in upper respiratory tract Caseous plug may be found in the trachea Atrophied oviduct Abdominal air sacs may contain yellow caseous exudate-- Occasionally swollen and pale kidneys containing urolith deposits (uric acid crystals)
- 15. Trachea with excessive amount of mucus, chicken Gasping, coughing, and tracheal rales are due to an excessive amount of mucus in the trachea.
- 16. DIAGNOSIS CF PM lesions Virus isolation (9-10 day of age embryonated specific SPF eggs) PCR Serology (Antibody determination) Virus neutralization test (VNT) Haemagglutination Inhibition Test (HI) Enzyme linked Immunosorbent Assay (ELISA)
- 17. Diagnosis Testing serum samples at intervals (for example at the time of the clinical signs and 2 or 3 weeks later) provide the best basis for serological diagnosis. This is also applicable for monitoring vaccination results.
- 18. Comparison of a normal 18-day old chicken embryo (right) and two infected embryos of the same age, showing dwarfing
- 19. TREATMENT None Provide additional heat Antibiotic Control Vaccination
Editor's Notes
- The economic impact of Infectious bronchitis is mainly due to: Poor growth performance and mortality due to the respiratory disease in broilers Egg production losses in layers and breeders Losses caused by renal damage may be seen in broilers, layers and breeders
- Laboratory confirmation is required for diagnosis of respiratory forms because of similarities to mild forms of disease caused by agents such as Newcastle disease virus, avian metapneumovirus, infectious laryngotracheitis virus, mycoplasmas, A paragallinarum, and Ornithobacterium rhinotracheale. Demonstration of seroconversion or a rise in antibody titer against IBV by ELISA, or hemagglutination inhibition or virus neutralization tests can be used for diagnosis when there is a history of respiratory disease or reduced egg production. Definitive diagnosis is generally based on virus detection and identification. Virus can be isolated by inoculation of homogenates of tracheal, cecal tonsil, and/or kidney tissue into 9- to 11-day-old SPF chicken embryos, with growth of IBV indicated by embryo stunting and curling, and deposition of urates in the mesonephros, with variable mortality. Alternatively, IBV may be isolated in tracheal organ cultures, with growth of virus indicated by cessation of cilial motility. Several blind passages of the virus may be necessary for isolation of some field strains. More rapid diagnosis may be achieved using reverse transcriptase-polymerase chain reaction (RT-PCR) assays to detect viral RNA in nucleic acid extracts of tracheal, cecal tonsil, or kidney tissue. Typing viruses can help distinguish vaccine and field strains and may help diagnose outbreaks caused by serotypes distinct from those of the vaccines used in a flock. Serotypes have been identified using sera from SPF chickens inoculated with known serotypes in virus neutralization tests. However, because this is expensive and time consuming, it is not readily available. A restricted range of serotype-specific monoclonal antibodies (MAb) have been developed for serotyping, but direct detection viral antigen using these MAbs to immunohistochemically stain tissue sections from diseased birds is of limited value because of the low concentration of antigen in tissues. 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. Analyses of the products of RT-PCR assays are now commonly used to identify the virus serotype and to identify individual strains within serotypes. The S1 region of the spike glycoprotein gene determines the serotype, and RT-PCR products derived from this region can be subjected to restriction fragment length polymorphism analysis, analyzed by nucleotide sequencing, or compared with reference strains using high-resolution melting curve analysis. Genotype determination based on the S1 region can be complemented by analyzing other regions of the viral genome, including the nucleocapsid gene and the 5' untranslated region. These analyses can also aid in rapid detection of novel recombinant IBVs.
- No medication alters the course of IBV infection, although antimicrobial therapy may reduce mortalities caused by complicating bacterial infections. In cold weather, increasing the ambient temperature may reduce mortalities, and reducing the protein concentrations in feed and providing electrolytes in drinking water may assist in outbreaks caused by nephropathogenic strains. The attenuated vaccines used for immunization may produce mild respiratory signs. These vaccines are initially given to 1- to 14-day-old chicks by spray, drinking water, or eye drop, and birds are commonly revaccinated. Revaccination with a virus from a distinct serotype can induce broader protection. Attenuated or adjuvanted inactivated vaccines can be used in breeders and layers to prevent egg production losses. There are many distinct serotypes of IBV, and new or variant serotypes, which are not fully controlled by existing vaccines, are identified relatively frequently. Some variants may be derived from recombination between existing field strains and vaccine strains, whereas others result from point mutations in existing strains. Selection of vaccines should be based on knowledge of the most prevalent serotype(s) on the premises. The correlation between serotype and protection is imperfect, and definition of the most appropriate vaccine, or combination of vaccines, may require experimental assessment of several combinations of vaccines to identify the most effective regimen. The most commonly used live vaccines in the USA contain derivatives of the Massachusetts, Connecticut, and Arkansas strains, whereas in Australia, where the most prevalent serotypes are distinct from most other countries, vaccines are based on derivatives of the VicS and Armidale strains. In Europe, vaccines incorporating derivatives of the 4/91 strain and those derived from QX-like viruses are available. Vaccination with selected variant serotypes may be of use when these variants are the dominant strain in flocks, although regulatory authorities in some countries only permit use of vaccines derived from the Massachusetts strain.