Immunopathology of Pneumonia in Animals

The lungs are continuously exposed to diverse array of microbes, organic and inorganic particulate materials. Pulmonary immunity determines the outcome of infections and failure of immune defenses may lead to development of pneumonia. Predisposing factors weaken the lung defenses and lead to infection with any pathogens including viruses, bacteria, parasites, and fungi. Pneumonia is an inflammation of the lungs that can cause mild to severe illness in animals of all ages. Pneumonia is one of the leading causes of death due to infection in animals in younger ages worldwide. Very young, older animals and animals with underlying health problems or immunosuppression were at high risk for pneumonia. Pathogens could interfere with different respiratory defenses, allowing two or more bacteria to colonize the lungs. Inhalants like microbes and environmental particles need to be eliminated quickly by the immune system, as failure to do so can lead to inflammatory responses that result in swelling that closes the airways results in increased incidence of infections. Most viruses and bacteria cause ciliary dysfunction and alteration of the mucosal surfaces that predisposes the bacterial and/or viral pneumonia. Further, virus and bacterial infections cause alteration of alveolar macrophage function, suppression of lymphocyte proliferation, induces apoptosis, and modified cytokine and other inflammatory mediator release resulted in modification of innate and adaptive immune responses. Viscosity of the mucus interferes with clearance, leading to airway obstruction, colonization with bacteria, and impaired migration and bactericidal activity of neutrophils. Elevated ammonia levels are associated with overcrowding and reduced ventilation results in ciliary dysfunction, degeneration and inflammation of the nasal epithelium, and increased susceptibility to pneumonia.