Chlamydiosis, a disease caused by the intracellular bacterium
Chlamydia psittaci, is commonly seem in wild and
pet birds. Between 1982 and 1991, 1,344 cases of human chlamydiosis
were reported to the Center for Disease Control. Of those
cases where the source of infection was known, 70% were
due to exposure to pet caged birds (Satalowich, et. al.,JAVMA
1993). Veterinarians should be aware of the zoonotic potential
of this disease.
The infectious particles of Chlamydia psittaci,
called elementary bodies, are shed in feather dust,feces,
and lacrimal and nasal secretions. Elementary bodies
are approximately 0.3 um in size and survive for long periods
outside the body. If aerosolized elementary bodies are inhaled
or ingested, they will attach to and penetrate host cells.
Once inside the cell, elementary bodies transform into non-infectious
reticulate bodies that grow and divide by binary fission.
Often micro-colonies will form and can be seen microscopically
as cellular inclusions, called LCL(Levinthal-Cole-Lillie)
bodies. As the reticulate bodies mature, they transform
into the infectious elementary bodies which are released
when the cell is lysed.
Clinical signs in birds range from inapparent infections
to severe disease and death. Young birds are most susceptible
and often appear sick, while adult birds tend only to show
clinical disease after periods of stress. Latent infections
are possible with clinically normal birds shedding the organism.
The clinical signs caused by Chlamydia psittaci
depend on the age, condition, and species of the bird combined
with the dose, strain, and virulence of the bacteria.
Respiratory and/or gastrointestinal signs are common along
with ocular and nasal discharge, conjunctivitis, sinusitis,
dyspnea, greenish diarrhea, and emaciation. Occasionally
neurological signs are seen: tremors, seizures, torticollis,
and/or opisthotonus. Hepatosplenomegaly may be observed
on radiographs. Clinical pathology data may reveal a leukocytosis
and elevated liver enzymes.
The gross lesions of chlamydiosis vary and are nonspecific.
Hepatomegaly, splenomegaly, and pneumonia are common
findings. Fibrinous air sacculitis, serofibrinouspericarditis,
and fibrinous peritonitis may be prominent. Histopathologic
lesions are also nonspecific, unless the causative agent
is seen. LCL bodies, which stain with Giemsa, Castaneda
and Machiavello stains, are pathognomonic if seen. Impression
smears of liver, spleen, or air sac can be stained to observe
LCL bodies. If LCL bodies are present, the diagnosis can
be made; but, further diagnostics are necessary if LCL bodies
are not observed.
Two diagnostic serology tests are currently available.
A Chlamydia-b\ocking antibody ELISA(BELISA) identifies
serum antibodies to the Chlamydia organism. The
antibodies deleted by this method are independent of the
bird's shedding status; however, the assay only detects
the patient's exposure to the organism, not necessarily
a current infection. False negative test results are frequent
in acute infections. An antigen ELISA test for Chlamydia
trachomatis of humans is used to detect Chlamydia
psittaci in birds. Cloacalswabs can be analyzed by
this test. False negatives are possible in samples that
contain low numbers of elementary bodies and in samples
from birds with latent infections or irregular shedding.
False positives are possible if high numbers of cross-reacting
bacteria, such as Staphylococcusaureus, are present.
Culture of the organism is the only direct means of identifying
Chlamydiapsittaci. Cloacal or fecal specimens can
be submitted for culture. Since shedding may be inconsistent,
a serial collection for three-five consecutive days is recommended.
Culture must be done in a cell line and may take one-two
weeks before results are seen. Post mortem specimens suitable
for culture include the liver and the spleen.
All confirmed or suspected cases of chlamydiosis should
be reported to the local and/or state health departments.
Professionals in these departments will oversee further
work-up and treatment. Any person who has been in contact
with infected birds should be warned of the zoonotic potential
and take appropriate precautions.
Gerlach,H. Chlamydia. In: Hamson and Hamson,
Clinical avian medicine and surgery,W.B.Saunders
Satalowich, FT; Barrett,L; Sinclair, C; Smith,
KA; Williams, LP."Compendium of chlamydiosis (psittacosis)
control, 1994.National Association of Public Health Veterinarians
Inc".Journal of the American Veterinary Medical
Timoney,JF;Gillespie,JH; Scott, FW; Barlough,JE.
Hagan and Bruner's Microbiology and Infectious Diseases
of Domestic Animals, 8th edition. Comstock Publishing
Van Buuren,CE;Dorrestein,GM; Van Dijk, JE. "Chlamydia
psittaci infections in birds:a review on the pathogenesis
and histopathological features". Veterinary Quarterly
1994, 16: 1, 38-41.
- TrinaDuncan, April 1995
- edited by Robert Porter