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Avian Chlamydiosis

Other Names: Chlamydiosis, Parrot Fever, Psittacosis, Chlamydia, Ornithosis

Avian chlamydiosis (AC) is a zoonotic disease primarily caused by the Gram-negative bacterium Chlamydia psittaci. This pathogen is found worldwide in more than 500 species of domestic and wild birds. In addition to birds, mammals such as cattle, sheep, and horses can serve as reservoirs. Humans may become infected through contact with infected birds or reservoir species, as well as exposure to their droppings.

There are at least 15 known genotypes of C. psittaci, each with varying host preferences. In recent years, five additional Chlamydia species have been identified in birds: C. avium, C. gallinacea, C. buteonis, C. ibidis, and C. abortus. Co-infection with more than one Chlamydia species has also been reported.

Clinical Signs

Clinical signs in chickens are often nonspecific and can vary widely depending on factors such as age, immune status, and the bacterial strain involved.

Avian chlamydiosis may present in acute, subacute, or chronic forms.

Chronically infected birds may appear healthy but develop symptoms during times of stress, including molting, environmental or seasonal changes, or other conditions that weaken the immune system.

Common clinical signs include:

Reduced appetite
Ocular or nasal discharge
Conjunctivitis
Diarrhea
Lethargy
Poor feather quality
Discolored urates

In severe cases, birds may produce scant, dark green droppings, followed by weight loss, dehydration, and eventual death.

Transmission

Chlamydia is transmitted through direct contact with infected animals or via inhalation of contaminated dust from feces, feathers, or respiratory secretions. Both clinically ill and subclinically infected animals can act as reservoirs, intermittently shedding the organism depending on their immune status and the strain involved.

Incubation period

The incubation period typically ranges from 2 to 14 days.

Diagnosis

Diagnosis is most commonly confirmed through polymerase chain reaction (PCR) testing. Samples are collected from oropharyngeal or cloacal swabs, or from feces. Because shedding can be intermittent, repeated sampling over several consecutive days may be necessary.

Bloodwork may reveal elevated white blood cell counts, often with heterophilia, lymphopenia, and toxic changes. Increased total protein levels, particularly beta- and gamma-globulins, may also be observed.

Postmortem (necropsy) findings may include:

Enlargement of the spleen and liver with pulmonary congestion
Necrotizing splenitis
Hepatitis
Interstitial pneumonia
Nephritis

Treatment

Avian chlamydiosis is treated with antibiotics, with doxycycline considered the drug of choice. Successful treatment typically requires a prolonged course. Calcium supplementation should be avoided during treatment, as it can interfere with the effectiveness of doxycycline.

Clinical Signs

Greenish diarrhea

Ruffled feathers

Lethargy

Sneezing

Conjunctivitis

Nasal/ocular discharge

Poor appetite

Weight loss

Depression

Diagnosis

History
Clinical signs
Radiographs
Endoscopy
Cytology
Sinus flush and culture

Reported Cases

Case 1: Chlamydiosis in a Finch In May 2018, avian chlamydiosis was diagnosed in a 1-year-old male Gouldian finch at the Turlock Branch of the California Animal Health and Food Safety Laboratory System. The bird belonged to an outdoor aviary with mixed avian species, including Gouldian finches, doves, and psittacines. Severe respiratory distress and mortality were noted among the finches. Gross and histopathologic lesions were concentrated in the liver and spleen, with a mild involvement of the upper respiratory tract. Chlamydia spp. were detected in the spleen and kidney by real-time PCR and were further confirmed by immunohistochemistry. Subsequently, Chlamydia psittaci was isolated from the liver and spleen and characterized as a CP3-like strain (genotype B). In addition, viral particles compatible with circovirus were identified in the liver by direct electron microscopy. Ref

Case 2: Avian chlamydiosis in a Parrot A two-year-old Congo African grey parrot was examined since the bird had shown clinical signs of anorexia, depression, diarrhea, and mild dyspnea and based on biochemical and hemathological analysis the bird was diagnosed as having anemia, leukocytosis, heterophilia, lymphopenia and monocytosis. With regards to clinical and paraclinical findings, the case was diagnosed to be carrying Chlamydiophila spp. In addition, choanal cleft and cloaca swabs were positive for Chlamydiophila spp. in a diagnostic polymerase chain reaction (PCR) (600 bp amplicon). Polymerase chain reaction products were typed by ompA gene-based PCR, using CTU/CTL primers (1050 bp amplicon). The PCR product sequence was compared with the sequences obtained from GenBank. The phylogenetic tree has revealed 100% identity with genotype B obtained from previous studies. The bird was hospitalized and treated with doxycycline regimen for 45 days, with a weekly sampling process to trace the presence of C. psittaci DNA in faecal and choanal swabs, this process continued to the point where the specimens turned negative after two weeks. Laboratory and radiology results were within normal limits after the treatment. Genotype B is predominantly isolated from Columbidae and there have not been any reports regarding the clinically affected African gray parrot with this genotype. Ref

Case 3: Avian chlamydiosis in a Turkeys Chlamydiosis affecting only the nasal glands was observed in less than 1% of 24-week old turkey hens in a flock of 5,000 birds. The disease was clinically manifested by mild to moderate swelling above the eyes and was diagnosed based on FAT, PCR and immunohistochemistry. They killed the birds to prevent it from spreading. Ref

Case 4: Avian chlamydiosis in a Turkeys Ornithosis caused swelling over the eyes in 13-week-old, female turkeys. Ten percent of 36,000 birds were affected. Histologically, there was nasal gland inflammation and chlamydia was detected only in the nasal gland by immunohistochemistry and fluorescent antibody (FA) testing. The birds were otherwise healthy. Testing of wild pigeons on a neighboring farm confirmed the presence of chlamydia by FA. Ref

Case 5: Avian chlamydiosis in a Penguin An outbreak of Chlamydophila psittaci occurred in an outdoor colony of 63 Magellanic penguins at the San Francisco Zoo. Affected penguins presented with inappetence, lethargy, and light green urates. Hematologic and serum biochemical findings were consistent with chronic inflammation. Penguins did not respond to initial supportive and antimicrobial therapy, and 3 died. Necropsy results of the 3 birds revealed hepatomegaly and splenomegaly, and histologic lesions included necrotizing hepatitis, splenitis, and vasculitis. Chlamydophila psittaci infection was confirmed by results of Gimenez staining, immunohistochemistry, and tissue polymerase chain reaction assay. As additional birds continued to present with similar clinical signs, the entire colony of penguins was prophylactically treated with a 30-day minimum course of doxycycline, administered orally or intramuscularly or as a combination of both. Despite treatment, 9 additional penguins died during a 3-month period. Pathologic results from these birds revealed renal and visceral gout (n = 4), cardiac insufficiency (n = 2), sepsis from a suspected esophageal perforation (n = 2), and no gross lesions (n = 1). During the outbreak, 4 birds presented with seizures, 5 developed dermatitis, and nearly 90% of birds in the colony showed severe keratoconjunctivitis, believed to be related to drug therapy with doxycycline. We report the clinical and pathologic features of Chlamydophila psittaci infection in an outdoor colony of penguins and the associated challenges of treatment. Ref

Case 6: Conjunctivitis and rhinitis in a Duck Chlamydia psittaci was isolated from the eyes of domestic ducks with conjunctivitis and rhinitis. Ref

Treatment

Name	Summary
Supportive care	Isolate the bird from the flock and place in a safe, comfortable, warm location (your own chicken "intensive care unit") with easy access to water and food. Limit stress. Call your veterinarian.
Antibiotics	Doxycycline or Oxytetracycline