Doneley, Bob

University of Queensland eSpace

Exotics — Avian 
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AN APPROACH TO DIAGNOSING 
CHLAMYDIOSIS 
 
Bob Doneley, BVSc, FACVSc (Avian Health) 
West Toowoomba Vet Surgery 
Toowoomba, Queensland, Australia 
 
 Chlamydiosis is an important zoonotic disease of 
birds caused by Chlamydophila psittaci (Order 
Chlamydiales, Family Chlamydiaceae; genus 
Chlamydophila), an obligate intracellular gram-negative 
bacteria. It has been estimated that up to 50% of the 
world’s captive bird population is infected. From 1985 to 
1995, 1,332 cases of human psittacosis were reported to 
CDC in the United States alone, making it a significant 
problem in pet avian practice. Although this disease is 
most frequently reported in psittacines, turkeys, and 
pigeons, it can occur in any and all bird species. In most 
countries it is a notifiable disease, with clinicians 
required to report diagnosed cases to relevant heath 
authorities. 
 Chlamydophila can be highly contagious, spreading 
through feces, respiratory secretions, aerosolized 
feather or fecal dust, lacrimal fluid, nasal discharge, and 
“crop milk.” Carrier states are believed to exist, with 
latent infections activated by stress and/or concurrent 
illness. Once the organism has entered the host body, 
there are five steps in its replication: 
 
1. Attachment to, and penetration of, the host cell 
(usually epithelial cells of respiratory and digestive 
tracts) by the infectious but non-propagating 
elementary bodies. The organism is incorporated 
into an endosome, which protects it from host-
derived lysozymes. 
 
2. Transition of elementary bodies into the larger, 
metabolically active reticulate body. Reticulate 
bodies resemble L-form bacteria (which have 
defective cells walls) and can persist despite 
circulating antibodies.  
 
3. Growth and binary fission of reticulate bodies forming 
multiple micro-colonies and subsequent inclusion 
bodies.  
 
4. Maturation of reticulate bodies back into elementary 
bodies.  
 
5. Newly formed elementary bodies are released when 
Chlamydophila’s glycolysis system destroys the 
integrity of host cell, releasing elementary bodies 
 
 The outcome of infection in the individual bird is 
determined by the virulence of Chlamydophila strain 
involved, the dose of infectious agent taken in by the 
bird, and the bird’s immune system. High doses of 
virulent Chlamydophila cause a toxic effect on cell 
membranes, resulting in illness. Low doses of virulent 
Chlamydophila induce an adequate immune reaction 
and the agent is inactivated. A low dose of a non-virulent 
 
strain, combined with an inadequate response by 
macrophages, transforms these macrophages into long-
lived epithelioid cells, effectively creating a carrier state. 
The incubation period for this disease can be as short as 
3 days or as long as 1 to 2 years 
 
CLINICAL SIGNS 
 As mentioned above, the virulence and dose of the 
strain involved determines the clinical course of the 
disease. Clinical signs range from inapparent infections 
to severe septicemia and acute death. Commonly seen 
signs include poor feathering, listlessness, depression, 
anorexia, weight loss, conjunctivitis, nasal discharge, 
dyspnea, diarrhea, and green or yellow stained urates. 
Less common signs include torticollis, tremors, 
convulsions, and polyuria.  
 
DIAGNOSING CHLAMYDIOSIS 
 It is obvious from reviewing the clinical signs 
described above that the diagnosis of chlamydiosis 
cannot be made on clinical signs alone. While a detailed 
history is vital for determining the likelihood of exposure, 
and a thorough physical examination is essential to 
determine what is actually happening to the patient, 
laboratory tests are needed to specifically diagnose this 
disease. The zoonotic aspects of chlamydiosis make an 
accurate diagnosis more than just desirable.   
 Laboratory diagnosis is, however, difficult, as there is 
no single “best test.”  Clinicians need to gather as much 
information as possible to analyse and finally diagnose 
this disease. This information can be broadly 
categorized into three groups: 
 
1. The detection of the Chlamydophila antigen; 
2. Determining the body’s immune (humoral) response 
to the antigen; and 
3. Evaluating the body’s overall response to infection.  
 
Detection of the Chlamydophila Antigen 
 Several tests exist to detect Chlamydophila itself in an 
affected patient. Isolation through cell culture is the gold 
standard, but is time consuming, expensive, and rarely 
practical in clinical practice. Cytology of serosal 
membranes, liver, spleen and affected air sacs using 
Giemsa, Gimenez, or Macchiavellos’ stains to reveal 
intracytoplasmic inclusions is commonly used in 
necropsy samples. Negative staining does not, however, 
rule out Chlamydophila. Immunofluorescence antibody 
testing is available through some labs, but it may give 
false positive results through cross-reactions with 
Mycobacterium avium.  
 ELISA and latex agglutination tests are available. 
However, false-positive results are common due to 
cross-reaction with bacterial cell walls. False-negative 
results can also occur because of the intermittent 
shedding of the organism.  
 The most commonly employed antigen detection test 
in practice is the PCR. However, clinicians need to be 
aware of false-negative results caused by the presence 
of inhibitors of PCR reaction such as blood, serum, 
urine, feces, sputum, hair shafts, lab reagents and 
The North American Veterinary Conference — 2006 
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specifically hematin, DMSO, NaCl, phosphate-buffered 
saline, melanin, heparin, detergents, and glove powder. 
False-positive results also occur because the test cannot 
distinguish between live and dead organisms (which 
may be contaminants). 
 
The Humoral Response 
 Several serologic tests are available to detect either 
IgM (acute infection), IgG (infections longer than            
2 weeks), or both. These tests include latex agglutination 
for IgM, ELISA, and BELISA tests.  Direct complement 
fixation tests, measuring IgG, are commonly used in 
people, but are only useful if paired serum samples are 
tested. They are not used in birds because they produce 
mainly non-CF antibodies with Chlamydophila infection. 
 Serologic tests are not perfect, and many false- 
positive and false-negative results are reported. 
 
The Overall Response of the Body 
 Nonspecific findings in the clinical evaluation of an 
affected patient include anemia, leukocytosis, 
monocytosis, and elevated bile acids, AST, CK, and 
LDH. Radiology may reveal hepatomegaly, 
splenomegaly, and air saculitis. Protein electrophoresis 
may show elevations in total globulins, (especially beta 
and gamma globulins) and a decrease in albumin. 
 
PUTTING IT ALL TOGETHER 
 It can be seen by this discussion that it is difficult, if 
not impossible, to have a single test confirm a diagnosis 
of chlamydiosis. The Centers for Disease Control has 
 
issued a classification system for the diagnosis of this 
disease:  
 
1. Confirmed Case:  C. psittaci confirmed by isolation, 
FA of affected tissue, >4x increase in serologic titer 
in paired samples collected 2 weeks apart and 
processed by same lab, or demonstration of the 
organism in macrophages via Macchiavellos’ or 
Gimenez stain 
 
2. Probable Case: Clinical infection consistent with 
Chlamydophila combined with one of the following: 
single high titer obtained after onset of illness; 
Chlamydophila antigen demonstrated by FA or 
ELISA in feces, exudates, or cloacal swab 
 
3. Suspect Case: Clinical signs consistent with 
Chlamydophila in a bird epidemiologically linked to 
another case in a bird or human, but not lab 
confirmed; or an asymptomatic bird with a single 
high titer or antigen detected; or illness in a bird 
confirmed with a non-standardized test; or clinical 
illness that is responsive to appropriate treatment 
 
 The diagnosis of Chlamydophila infection therefore 
relies on a combination of history, physical examination 
to evaluate clinical signs, and the use of antigen 
detection tests, serology and ancillary testing in 
combination. Given its zoonotic potential and legal 
liabilities associated with a diagnosis, clinicians should 
be wary of diagnosing or ruling out this disease on the 
basis of single or inadequate tests. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 


An approach to diagnosing chlamydiosis

http://espace.library.uq.edu.au/view/UQ:229680/chlamydia.pdf

An approach to diagnosing chlamydiosis

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