Respiratory infections in chickens are seen worldwide, but especially in temperate poultry-producing areas in winter months. A number of respiratory viruses, bacteria, mycoplasma & fungi may be involved. Dust, ammonia and other factors associated with poor ventilation, may act as predisposing factors. Live vaccines can also contribute to respiratory diseases in poultry. Morbidity is typically 10 - 20% and mortality 5 - 10%.
Figure 1 : Swollen head & conjunctivitis
Figure 2 : Discharge from the eye
Respiratory diseases caused by viruses
Figure 3 : Pox lesions on the skin
Figure 4 : Wet pox in the trachea
These viruses cause respiratory signs in broilers, breeders and layers. Viral infections can also cause other signs in breeder & layer birds such as a drop in egg production and/or egg shell abnormalities and/or a drop in hatchability in breeder birds. Viral diseases are mainly spread through the air with dust and feathers, but also through contact with infected droppings and bedding material. People, equipment and vehicles can also transmit the viruses between farms. The pox virus is spread through mosquito bites.
Figure 5 : White eggs, abnormal shapes, thin shells
Respiratory diseases caused by bacteria & mycoplasma
Bacteria & Mycoplasma cause respiratory signs in broilers, breeders and layers. It can also result in a drop in egg production in breeders and layers. Egg shells are usually not affected, but breeders can experience a drop in hatchability. Bacteria and Mycoplasma are transmitted in the same way as viruses.
Respiratory disease caused by fungi
Chicks are infected with Aspergillus when they breathe in spores during the incubation process in the hatchers. Chicks can also be infected on the farm from the environment, through inhaling spores from contaminated bedding material or feed. Chickens usually die within the first week of life, although mortalities can occur later in life. The most significant sign is gasping chicks. Dead birds have purple beaks and toes. On post mortem examination the yellow nodules (1 – 2mm) are usually visible in the air sacs and/or lungs.
Figure 6 : Aspergillus resulting in a gasping chicken
Figure 7 : Yellow Aspergillus nodules in the air sac sacs
Respiratory problems can be caused by a single pathogen, but it is often a combination of more than one pathogen present in the bird at the same time. Poor environmental conditions (e.g. high ammonia levels) and vaccination with life vaccines (e.g. NCD, IB, and ILT) can play an important contributing role in causing respiratory disease. A primary viral infection is often complicated by a secondary E.coli infection that causes colisepticemia and an increase in mortality.
Post mortem examinations have to be done and samples taken for laboratory analysis to determine which pathogen/s are responsible for the respiratory signs observed.
Antimicrobial treatment for specific bacterial & mycoplasma infections can be considered.
Maintaining proper chicken house environmental conditions and carefully applied appropriate viral, bacterial & mycoplasma vaccines forms the corner stone of preventing respiratory diseases in chickens.