Infectious Bronchitis (IB) is an acute, viral, highly contagious disease of poultry characterized by rales, coughing and sneezing. Young birds may have nasal discharge and in laying flocks there is drop in egg production and poor quality of eggs. In young chicks there may be mortality and loss in weight gain and feed efficiency.
Distribution
Infectious Bronchitis was first reported in the USA in 1931. It is now distributed worldwide. In USA, several serotypes of Infectious Bronchitis virus were identified in the beginning of 1950.
The disease was first reported from India by Verma in 1964 on the basis of serology and isolation of virus. Sharma and Singh (1968) and Mohanty (1974) found characteristic lesions in the oviducts of 30.9 and 24.29% birds respectively. An outbreak of Infectious Bronchitis in laying birds was reported from Andhra Pradesh. All India co-ordinated project on respiratory diseases of poultry revealed the serological existence of this disease in almost all the states of this country.
Aetiology
Infectious Bronchitis virus is a member of coronaviridae family and is single stranded RNA virus and measuring 80-200 micrometre. Virus has got as many as 24 strains. They are grouped into Massachusetts or Connecticut strains. There are reports that other serotypes like Beaudelt’s strain also occur. These serotypes are determined by virus neutralization and haemagglutination inhibition test. The virus is sensitive to ether and other lipid solvents. Newly isolated strains are inactivated at 56° C within 15-30 minutes but chicken ebryo adapted strains are stable upto 3 hours at this temperature. The virus can survive upto 12 days in spring and about 56 days in winter. However, virus is destroyed readily in summer under direct sunlight. Infectious Bronchitis virus grows well in developing chick embryo. Infectious Bronchitis virus – Beaudette strain can also replicate in turkey embryos. Infectious Bronchitis virus can also grow well in chick embryo kidney cells and CK cells. The Massachusetts strain of virus is used for immunization purpose and is found to be useful in endemic areas.
Susceptible Hosts
Chicken is naturally infected, through susceptibility varies among breeds and strains of chicken. Infectious Bronchitis virus has also been isolated from pheasants causing respiratory signs and decreased egg production. Severity of the disease is inversely related to age. Respiration form is most severe in young chicks and nephritic form is predominantly seen in birds under 10 weeks of age. Experimentally, this virus can produce disease in Turkeys, Ring-necked pheasants and suckling mice.
Mode of Transmission
This is very contagious type of disease and susceptible birds develop clinical signs within 48 hours, if kept in a room along with infected birds and whole flock may be infected within a week. Nasal discharge containing virus particles spread by aerosol and circumstantial evidence of IBC transmission over a distance of 1200 yd was reported. The virus may be transmitted through contaminated feed and equipment. Clothing, foot wear etc. of the attendants and visitors may also spread the infection. Actively infected and recovered birds can transmit the virus for approximately one month. Once the birds are immune, they do not remain as carrier. Spread is mainly by horizontal way.
Pathogenesis
Birds of all ages are susceptible, but chicks of 1-4 weeks of age are most severely affected. The disease condition is most severe in younger birds, where mortality is between 20-90% with secondary infection with Mycoplasma or septicaemic E.coli. Incubation period varies from 18-30 hours.
After invasion virus localise in the respiratory system following which a viraemia occurs and the virus is distributed in the body and affect the reproductive and urinary system and replicates upto 1-8 days post infection. Urogenital tract infection results in nephritis with tubular damage and interstitial infiltration of lymphoid cells. The laying flocks have lowered egg production and egg may be misshaped, rough, soft shelled and poor in internal quality.
Clinical Findings
The clinical signs may appear within 36-48 hours of infection. The clinical manifestation may vary in different age group of birds.
(i) Signs in young chicks upto 6 weeks of age: The birds below 6 weeks of age are highly susceptible. There is gasping and distressed breathing. Beaks are kept open and extend upward in each expiration. Tracheal rales, sneezing and hoarse cough are prominently audible. Nasal discharge and open mouth breathing are evident. Eyes remain wet. There is general malaise with depression and retarded growth and birds huddle together. Mortality may range from 25-60%.
(ii) Signs in growing chicks: The intensity of manifestation is less severe in this age group. The signs comprise of distressed breathing and tracheal rales. The respiratory noise can be heard very distinctly during night. Nephritic form of the disease affects growing chicks of 3-6 weeks of age shows signs of depression, ruffled feather, wet droppings and increased drinking. Urolithiasis is also associated with Infectious Bronchitis in layer flocks.
(iii) Signs in laying birds: The principal complain in layers is drop in egg production. In majority of cases egg production may go up to 50%. The quality of eggs are grossly deteriorated ‘belted eggs’. Egg shells become soft and misshaped, lack in symmetry or show corrugations on outline. The cell may be depigmented and have calcareous deposits. Loss in the viscosity of albumin. broken chalaza and the yolk floats freely. Eggs, after incubation, give rise to embryonic defect and mortality. The embryo shows poor stunted growth and dwarfness. Respiratory signs are less obvious in nature and nasal discharge is usually absent.
Lesions
Trachea, nasal passages and sinuses contain serous, catarrhal or caseous exudate, air sacs appear cloudy or contain a yellow caseous exudate. Small areas of pneumonia may be observed around large bronchi. In nephritic form, kidneys are pale an swollen with tubules and ureters are often distended with white urates. Functional oviduct results in regression in size, metaplasia of epithelium and glandular dilatation. There may be complete absence of duct or vestiges which are non-potent or cystic.
Diagnosis
The diagnosis is made based on the following considerations:
- Clinical signs in different age groups of birds.
- Post-mortem an histopathological changes. Catarrhal and caseous exudates in the upper respiratory tract. There is hyperplasia of the epithelial lining of the bronchi and trachea. Changes in the reproductive tract of laying birds and ruptured yolk sac. In non-layers, atrophy of the oviduct, ovary non-functional degenerative changes in ovary and there is mucopurulent exudate. Kidneys are inflamed.
- Isolation of virus in chick embryo and characteristic histopathological changes.
- Lung tissue suspension or tracheal exudate is inoculated. After third passage, it will produce stunted growth and death of embryo. Whole embryo may have ball like appearance.
- Serological tests: Serum neutralization test, Agar gel precipitation test, Complement fixation test, Fluorescence antibody test, Serum agglutination test, Enzyme linked immunosorbent assay, Immunoperoxidise technique.
Treatment
There is no specific treatment for Infectious Bronchitis. Provision of additional heat, avoidance of over crowding. Treatment with antibiotics is recommended to prevent air sacculitis. Electrolyte replaces are recommended to compensate for the acute loss of sodium and potassium and thereby reduce losses from nephritis.
Control
Management procedures are strictly to be followed:
(a) Strict isolation and repopulation with only day old chicks following the clearing and disinfection of the poultry house.
(b) Air borne spread can be prevented by ventilating houses with filtered air under positive pressure.
(c) Birds of different age groups should be raised separately.
(d) Vaccination programme: vaccine is given through eye drop, nasal instillation or aerosol spray. This is also be given through drinking water. But before giving into drinking water, following factors are to be considered:
- Birds should be deprived of water for at least two hours.
- Vaccine should be diluted with clean water and kept in clean container.
- Skim milk powder may be used in the drinking water @ 16 gm per 10 litre of water.
Commercial available vaccine
(A) Avian Infectious Bronchitis Vaccine (living) Freeze dried B.P.
Recommended Schedule
Primary: 21 days, 1 drop in each eye/nostril
Booster: 6th week and then 14th week in drinking water.
(B) Avian Infectious Bronchitis Vaccine Living Mars type strain
Recommended Schedule
Broiler: 4-5 weeks of age; Inra ocular or beak dripping
Layer: 2 weeks of age, intra ocular or beak dripping. Booster at 10-12 weeks of age, drinking water method
