Ornithosis (psittacosis) in humans is a flu-type illness, featuring fever, hedaches and chills. Many birds carry this infection, which is often transmitted in the dust from dried bird faeces. Exotic caged birds are a particular risk.
Ornithosis is an infection communicable by animals to man (zoonosis), caused by an organism belonging to the Chlamydia group. As carriers, parrots were first recognized; later, procellarians, pigeons, song birds and poultry (ducks, chickens, turkeys) were also incriminated. However, neither from the microbiological nor from the clinical standpoint is it possible to differentiate between the carriers. Consequently today it is no longer justifiable to distinguish between psittacosis (the disease communicated by psittacine birds) and ornithoses (infections communicated by other birds). As a particular form of ornithosis, psittacosis is now largely of historical interest only.
The infection is communicated to man either by direct contact with infected birds or indirectly by inhaling dry dust from the plumage or excrement of such birds. Infection can in principle be passed from man to man, but this results in a considerable decline in virulence. Most infections occur in persons having close contact with birds - breeders, handlers, fanciers, pet owners and so on. Amongst pet birds, cockatiels have the highest incidence of psittacosis. Ducks, turkeys and pigeons are also major sources of the disease in man. Infection from these sources has been reported among farmers, poultry processors and rendering-plant workers, some of whom have been severely infected more than once. Several outbreaks of an endemic nature have been reported in workers at poultry slaughterhouses, particularly in persons working in air containing plumage dust. Agents prevalent in birds are highly contagious and virulent for man. The fact that there are, in animals and man, serologically related strains of Chlamydia which show relatively low virulence may explain why, in spite of a very high incidence of Chlamydia infection in the population (30-40%), only relatively few cases of actual disease occur.