Avian Chlamydiosis
Avian chlamydiosis can be an inapparent subclinical infection or
acute, subacute, or chronic disease of wild and domestic birds
characterized by respiratory, digestive, or systemic infection.
Infections occur worldwide and have been identified in at least 150
avian species, particularly colonial nesting birds (eg, egrets,
herons), ratites, caged birds (primarily psittacines), raptors, and
poultry. Among poultry, turkeys, ducks, and pigeons are most often
affected; infection of chickens is infrequent. The disease is a
significant cause of economic loss and human exposure in
European duck flocks. Longterm inapparent infections lasting for
months to years are common and considered the normal
chlamydia-host relationship; %30-10of surveyed avian populations
may be found positive. The same strain may cause mild disease or
asymptomatic infection in one species, but severe or fatal disease
in another species .
Avian chlamydiosis is a zoonotic disease that can affect people
following exposure to air- or dustborne organisms when infected
birds are in flocks or processed, or when organisms are shed from
the digestive or respiratory tracts of infected birds confined in
breeding aviaries, lofts, or wholesale or retail outlets. Human
disease most often results from exposure to psittacines or pigeons
and can occur even if there is only brief proximity to a single
infected bird. When workers are exposed to infected turkeys or
ducks at processing, increased absenteeism due to acute
respiratory disease often occurs ~ 1wk after a flock with a high
condemnation rate due to airsacculitis has been processed. Some
individuals, especially pregnant women and those with impaired
immunity, are more susceptible than others. The illness in people is
usually respiratory and characterized by abrupt onset of flu-like
symptoms; pneumonia, organ failure, and death can result if the
disease is severe or left untreated. Precautions should be taken
when examining a dead infected bird (eg, detergent disinfectant to
wet feathers, fan-exhausted examining hood, dust mask or plastic
face shield, and gloves) to avoid exposure .
Etiology and Epidemiology :
A recent taxonomic revision resulted in the causative organism
being renamed Chlamydophila psittaci (formerly Chlamydia psittaci
). The name of the disease resulting from infection with C psittaci
remains avian chlamydiosis. C psittaci is an obligate intracellular
bacterium. All strains of chlamydia share an identical genusspecific antigen in their lipopolysaccharide but often differ in the
composition of other cell-wall antigens, providing a basis for
serotypic identification. Currently, 8serotypes are recognized; 6(AF) infect avian species and are distinct from mammalian chlamydia
serotypes. Each avian serotype tends to be associated with certain
types of birds (Table: Associations Between Avian Serotypes of C
psittaci and Types of Birds). Serotype D is highly virulent for
turkeys and can cause mortality of %30or higher. Serotypes B and
E are most frequently recovered from wild birds. Avian serotypes
are capable of infecting people and other mammals .
Respiratory discharges or feces from infected birds contain
elementary bodies that are resistant to drying and can remain
infective for several months. Airborne particles and dust spread the
organism. After inhalation or ingestion, elementary bodies attach to
microvilli on mucosal epithelial cells and are internalized by
endocytosis. Elementary bodies within endosomes in the cell
cytoplasm differentiate into metabolically active, noninfectious
reticulate bodies that divide and multiply, eventually forming
numerous infectious, metabolically inactive elementary bodies.
Newly formed elementary bodies are released from the host cell by
lysis .
Possible sources of C psittaci include infected birds, asymptomatic
carriers, vertical transmission from infected hens, infected rodents,
and contaminated feed. Stressors and concurrent infections,
especially those causing immunosuppression, can initiate
shedding in latently infected birds and may cause recurrence of
clinical disease. Carriers often shed the organism intermittently for
extended periods. Persistence of C psittaci in the nasal glands of
chronically infected birds may be an important source of
organisms. Transmission is fecal-oral or by inhalation. The
incubation period typically is 10-3days but may be up to 2mo in
older birds or following low exposure .
Host and microbial factors, route and intensity of exposure, and
treatment determine clinical course .
Clinical Findings and Lesions :
Severity of clinical signs and lesions depends on the virulence of
the organism and susceptibilty of the bird; asymptomatic infections
are common. Nasal and ocular discharges, conjunctivitis, sinusitis,
green to yellow-green droppings, fever, inactivity, ruffled feathers,
weakness, inappetence, and weight loss can be seen in clinically
affected birds. Necropsy findings in acute infections include
serofibrinous polyserositis (airsacculitis, pericarditis, perihepatitis,
peritonitis), pneumonia, hepatomegaly, and splenomegaly. Multiple
pale foci and/or petechial hemorrhages can be seen in the liver and
spleen. Similar lesions are seen in other systemic bacterial
infections and are not specific for avian chlamydiosis. Multifocal
necrosis in the liver and spleen is associated with large, granular,
basophilic intracytoplasmic inclusions, occasional heterophils, and
increased mononuclear cells (macrophages, lymphocytes, plasma
cells) in hepatic sinusoids and splenic sinuses. Necrosis results
from direct cell lysis or vascular damage. The latter is also the
source of the generalized serofibrinous exudation. Enlargement
and discoloration of the spleen or liver characterize chronic
infections. Necrosis and inclusions are not seen, but the
mononuclear cell response is present in these birds. Lesions are
usually absent in latently infected birds, even though C psittaci is
often being shed .
Diagnosis :
Because of the variety of clinical presentations and common
occurrence of latently infected carriers, no single diagnostic test
can reliably determine infection. Procedures to detect the organism
or antibodies are used. In general, the more acute the disease, the
greater the number of infective organisms and the easier it is to
make a diagnosis. When birds are acutely ill, clinical findings,
including hematology, clinical chemistries, and radiology or typical
gross lesions, are adequate for a tentative diagnosis. The organism
can often be identified in impression smears of affected tissues
stained by Giemsa, Gimenez, or Macchiavello’s methods .
Antigen detection methods include immunohistochemistry
(immunofluorescence, immunoperoxidase), ELISA, and PCR.
Immunohistochemistry is accurate when done by a skilled person
and the number of organisms is sufficient for detection. ELISA kits
are available commercially and are relatively inexpensive, easy to
use, and have good specificity, but low sensitivity. They are most
useful when birds are clinically ill. PCR tests have been developed
but are not widely available and require further evaluation. Multiple
samples collected for 5-3days are recommended for detection of
intermittent shedding by asymptomatic birds .
Confirmation requires isolation and identification of C psittaci in
chick embryos or cell cultures (BGM, L929, Vero) at a qualified
laboratory. Cloacal, choanal, oropharyngeal, conjunctival, or fecal
swabs from live birds or tissues (eg, liver, spleen, serosal
membranes) from dead birds should be submitted. Sampling from
mutiple sites and over several days will increase detection of
intermittent shedding. Freezing, drying, improper handling, and
certain transport media can affect viability. Refrigeration; placing
specimens in sealed plastic bags or other containers; using a
special buffer prepared from sucrose, phosphate, and glutamase
(SPG buffer); and prompt delivery of fresh specimens are preferred.
The laboratory should be contacted for directions on submitting
samples before they are sent. Concurrent infections with other
more easily diagnosed diseases (eg, colibacillosis, pasteurellosis,
herpesvirus infections, mycotic diseases, etc) may mask
chlamydial infection. Laboratory and clinical findings should be
correlated with each other. Chlamydiosis must be distinguished
from other respiratory and systemic diseases of birds .
Antibodies may or may not be detectable depending on the test
used, degree and stage of infection, and treatment of the bird.
Interpretation of titers from single serum samples is difficult. A 4fold increase in titers between paired acute and convalescent
samples is diagnostic, and high titers in a majority of samples from
several birds in a population are sufficient for a presumptive
diagnosis. Serologic methods include direct and modified direct
complement fixation, latex agglutination, elementary body
agglutination, and direct and competitive ELISA. ELISA provides
the greatest sensitivity and specificity compared with culture. The
elementary body agglutination test detects IgM and is useful for
determining recent infection .
Prevention and Treatment :
Local governmental regulations should be followed wherever
applicable. No effective vaccine for use in birds is available.
Treatment will prevent mortality and shedding but cannot be relied
on to eliminate latent infection; shedding may recur. Tetracyclines
(chlortetracycline, oxytetracycline, doxycycline) are the antibiotics
of choice. Drug resistance to tetracyclines is rare, but reduced
sensitivity requiring higher dosages is becoming more common.
Tetracyclines are bacteriostatic and only effective against actively
multiplying organisms, making extended treatment times (from 6-2
wk, during which minimum-inhibitory concentrations in blood are
consistently maintained) necessary .
Outbreaks in poultry flocks are not common. Treating infected
flocks with chlortetracycline at 750-400g/ton for a minimum of 2wk
before processing has effectively eliminated potential risk of
infection for plant employees .
In companion birds, use of chlortetracycline-medicated feeds for 45
days is a standard recommendation for imported birds (see
chlamydiosis, Chlamydiosis). Difficulties in palatability of the feed
itself or high level of antibiotic necessary for adequate blood levels
have limited its use. Long-acting oxytetracycline at 100-50mg/kg,
IM, every 3-2days for 30days, provides adequate continuous blood
levels and results in elimination of shedding within 24hr. However,
muscle necrosis at injection sites may be extensive, which limits
the usefulness of this treatment. Doxycycline in a formulation for IM
use has been given at 100-75mg/kg as a series of 7injections over
a 6-wk period. Addition of doxycycline to feeds can also result in
adequate blood levels and has less effect on normal intestinal flora
than does chlortetracycline. Supportive care for acutely affected
birds also aids recovery .
Appropriate biosecurity practices are necessary for controlling the
introduction and spread of chlamydiae in an avian population.
Minimal standards include quarantine and examination of all new
birds, traffic control to minimize cross-contamination, isolation and
treatment of affected and contact birds, thorough cleaning and
disinfection of premises and equiment (preferably with small units
managed on an all-in/all-out basis), provision of uncontaminated
feed, maintenance of records on all bird movements, and continual
monitoring for presence of chlamydial infection .
The organism is susceptible to heat and most disinfectants (eg,
1:1,000quaternary ammonium chloride, 1:100bleach solution, %70
alcohol, etc), but is resistant to acid and alkali. A voluntary
cooperative improvement plan leading to certification of companion
birds derived from chlamydia-free breeders has been developed .