Infectious Catarrh in Birds
The diagnosis "infectious catarrh" can often be established simply from the behavior of affected pigeons, the inflammatory changes in the head region and respiratory tract and the characteristic sounds of respiration (wheezing).
The door to infection is opened by mycoplasma and viruses, in addition to fungi und trichomonads. These lower the pigeons’ resistance and allow pathogenic bacteria - pasteurella, cocci und coli bacteria - to colonise and multiply. It is these secondary pathogens that engender the actual clinical picture of visible and audible catarrh (wheezing).
Catarrh is not always caused by pathogens. Very often, inadequate ventilation and waste-air extraction, drafts, a deficient supply of oxygen and high concentrations of noxious gases and dust in the loft reduce the pigeons’ resistance, making them extremely susceptible to infection.(thank you Chevita.com)
Pigeons suspected of infection that show mild infestation are not treated, in order not to disturb the host-pathogen equilibrium.