Chlamydia psittaci exists in two forms – an Elementary Body and a Reticulate Body. The Elementary Body is the form that is infective and exists outside the bird. Ebs are shed in ocular and respiratory secretions as well as in the droppings. Once the EB invades a bird’s cells it is transformed into a Reticulate Body. RDs are metabolically active and undergo cell division (multiplication) resulting in the production of many progeny. These progeny are transformed back into Ebs. Within 48 hours after cells have been invaded, numerous EBs are released, ready to invade new cells and be shed by the newly infected bird.Chlamydia is transmitted by Elementary Bodies that are aerosolized in feather dust and dried feces. Birds become infected when they ingest or inhale these Ebs. Transmission through the egg is also thought to occur in certain speciessuch as budgies, ducks, seagulls and turkeys. It is likely that this type of transmission may occur in other psittacines as well.
Infected birds shed large numbers of infective EBs in their oral cavity, nasal discharges, ocular secretions, crop milk, urine and feces.
Shedding of Ebs can be intermittent rather than continuous. This makes detection of chlamydia very difficult at times.
Some birds are subclinical carriers, meaning they appear normal and do not shed the organism until they are stressed. Stress can be a nutritional deficiency, a second illness, breeding, a new mate or a new location.
Young birds are most susceptible to Chlamydia and may develop a rapidly fatal illness. Adults may become infected, yet remain asymptomatic.
Different strains of Chlamydia exist which vary in their virulence. Young birds exposed to virulent strains may develop anorexia (appetite loss), conjunctivitis, dyspnea, sinusitis, tremors, biliverdinuria (green urates), emaciation, dehydration and diet within several days.
Less virulent strains can produce a subacute or protracted disese with with more subtle signs.
The next article will discuss diagnosis and treatment of Psittacosis (Parrot Fever).