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Compendium of Psittacosis (Chlamydiosis) Control, 1997


Infection with Chlamydia psittaci, often referred to as avian chlamydiosis (AC), is an important cause of systemic illness in companion birds (i.e., birds kept by humans as pets) and poultry. Infection can be transmitted from infected birds to humans. In humans, infection caused by C. psittaci is referred to as psittacosis, which can result in fatal pneumonia. This compendium provides information on AC (also known as psittacosis, ornithosis, and parrot fever) and psittacosis (also known as parrot disease, parrot fever, and chlamydiosis) to public health officials, veterinarians, physicians, the companion-bird industry, and others concerned with control of the disease and protection of public health. These recommendations provide effective, standardized disease control procedures for AC in companion birds and will be reviewed and revised as necessary.


In this report, psittacosis (also known as parrot disease, parrot fever, and chlamydiosis) refers to any infection or disease in humans caused by Chlamydia psittaci. Avian chlamydiosis (AC) refers to any infection with or disease caused by C. psittaci in birds. This compendium provides information on AC and psittacosis to public health officials, veterinarians, physicians, the companion-bird industry, and others concerned with control of the disease and protection of public health. These recommendations provide effective, standardized disease control procedures for AC in companion birds and will be reviewed and revised as necessary.


AC is a zoonotic disease caused by the bacterium C. psittaci. This bacterium has been isolated from 129 avian species and is most commonly identified in psittacine birds (e.g., parakeets, parrots, macaws, and cockatiels). Among caged, nonpsittacine birds, infection with C. psittaci occurs most frequently in pigeons, doves, and mynah birds. The incidence of infection in canaries and finches is believed to be lower than in other psittacine birds.

The time between exposure to C. psittaci and the onset of illness in caged birds ranges from 3 days to several weeks. However, latent infections are common in birds, and active disease may appear years after exposure. Shipping, crowding, chilling, breeding, and other stress factors may activate shedding of the infectious agent among birds with latent infection. Birds may appear healthy but may be carriers of C. psittaci and may shed the organism intermittently. When shedding occurs, the organism is excreted in the feces and nasal discharges of infected birds, is resistant to drying, and can remain infective for several months.

Clinical Signs of Chlamydial Infection in Birds

Chlamydial infection in birds may be asymptomatic, or it may become an acute, a subacute, or a chronic clinical disease. Signs depend on the species of bird, virulence of the strain, stresses on the bird, and route of exposure.

Birds with symptomatic AC typically have manifestations (e.g., lethargy, anorexia, and ruffled feathers) consistent with those of other systemic illnesses. Other signs associated with AC include serous or mucopurulent ocular or nasal discharge, diarrhea, and excretion of green to yellow-green urates. Anorectic birds may produce sparse, dark-green droppings. Birds may die soon after onset of illness or, as the disease progresses, may become emaciated and dehydrated before death. Mortality depends on stress factors, virulence of strain, species and age of bird, and extent of treatment or prophylaxis.

Case Classification for Avian Chlamydiosis

A confirmed case of AC is defined as infection by C. psittaci based on at least one of the following confirmatory laboratory results: a) isolation of C. psittaci from a clinical specimen, b) identification of Chlamydia antigen by immunofluorescence (fluorescent antibody {FA}) or enzyme-linked immunosorbent assay (ELISA) of the bird's tissues, c) a greater than fourfold change in serologic titer in two specimens from the bird obtained at least 2 weeks apart and assayed in parallel at the same laboratory, or d) identification of Chlamydia organisms within macrophages in smears stained with Gimenez or Machiavelo stain or sections of the bird's tissues.

A probable case of AC is defined as infection by C. psittaci in a bird that has clinical illness compatible with AC and at least one of the following confirmatory laboratory results: a) one high serologic titer in one or more specimens obtained after the onset of signs or b) the presence of C. psittaci antigen (identified by ELISA or FA) in feces, a cloacal swab, or respiratory or ocular exudates.

A suspected case of avian chlamydiosis is defined as a) clinical illness compatible with AC that is epidemiologically linked to another case in a human or bird but that is not laboratory confirmed; b) an asymptomatic infection in a bird for which laboratory results are equivocal (e.g., a single serologic titer of greater than or equal to 1:64); c) illness in a bird that has positive results for infection based on a nonstandardized test or a new investigational test; or d) a clinical illness compatible with chlamydiosis that is responsive to appropriate therapy. Several diagnostic methods are available for identifying AC in birds (Appendix A).

General Recommendations for Treatment of Infected Birds

All birds that have confirmed or probable AC should be placed in isolation and treated, preferably under the supervision of a veterinarian. Birds that have suspected cases or birds that have been exposed to AC should be isolated and retested or treated. Because treated birds can be reinfected by C. psittaci after treatment, such birds should be isolated from untreated birds or other potential sources of infection. To prevent reinfection from environmental sources, aviaries should be thoroughly cleaned and sanitized. No vaccine against chlamydiosis in birds is currently available.

The following general recommendations should be followed by bird owners and dealers in treating birds that have confirmed, probable, or suspected cases of AC:

  • Protect birds from undue stress (e.g., chilling or shipping), poor husbandry, or malnutrition. These problems reduce the effectiveness of treatment and promote the development of secondary infections with other bacteria or yeast.

  • Observe the birds daily, and weigh them every 3-7 days to confirm maintenance of body weight.

  • Do not administer antibiotics to birds through drinking water, and avoid the use of high dietary concentrations of calcium or other divalent cations.

  • Isolate birds that are to be treated in clean, uncrowded cages, segregated by sex.

  • Clean up all spilled food promptly; wash water and food containers daily.

  • Provide fresh water and appropriate vitamins daily. Treatment options for companion birds that have AC are provided (Appendix B).

Recommended Control Measures

The following control measures are recommended for veterinarians, physicians, and the companion-bird industry to prevent the transmission of C. psittaci infection to persons or other birds.

  • Maintain accurate records of all bird-related transactions to aid in identifying sources of infected birds and potentially exposed persons. Records should include the date of purchase, species of bird(s) purchased, source of birds, and any identified illnesses or deaths among birds. In addition, when birds are sold by a store, the seller should record the name, address, and telephone number of the customer; the date of purchase; the species of bird(s) purchased; and the band numbers, if applicable.

  • Do not purchase or sell birds that have signs compatible with AC (e.g., ocular or nasal discharge, diarrhea, or low body weight).

  • Quarantine newly acquired birds for 14-30 days and test or prophylactically treat them before adding them to a group. If birds are boarded or sold on consignment, they should be kept in an area with separate air-handling equipment. Birds should be tested for AC before they are accepted for boarding or consignment.

  • Practice preventive husbandry. Cages should be positioned so that fecal matter, feathers, food, and other materials from one cage cannot enter another cage. Cages should not be stacked, and solid-sided cages or barriers should be used if cages are adjoining. All cages and all food and water bowls should be cleaned daily. Soiled bowls should be emptied, cleaned with soap and water, rinsed, placed in a disinfectant solution, and rinsed again before reuse. Between occupancies by different birds, cages should be thoroughly scrubbed with soap and water, disinfected, and rinsed in clean, running water. Exhaust ventilation should be sufficient to prevent accumulation of aerosols.

  • Avoid reinfection of birds by using proven prevention measures. If AC is confirmed, probable, or suspected, birds requiring treatment should be held in isolation. Rooms and cages where infected birds were housed should be cleaned immediately and disinfected. The bottom of the cage should be made of wire mesh, and litter that will not produce dust (e.g., newspapers) should be placed underneath the mesh. When the cage is being cleaned, the bird should be transferred into a clean cage, and the soiled cage should be a) thoroughly scrubbed with a detergent to remove all fecal debris, b) rinsed, c) disinfected (allowing at least 5 minutes of contact with the disinfectant), and d) rerinsed to remove the disinfectant. The cages and the room where the bird was housed -- as well as the room's air-handling system -- should be thoroughly disinfected to eliminate chlamydial organisms from the environment. All items that cannot be adequately disinfected (e.g., wooden perches, nest material, and litter) should be discarded. During treatment, precautions should be taken to minimize circulation of feathers and dust (e.g., by wet-mopping the floor frequently with disinfectants, making liberal use of oil-impregnated sweeping compounds when sweeping between moppings, and preventing air currents and drafts within the area). Contamination from dust can be reduced by spraying the floor with a disinfectant or with water before sweeping it. To prevent aerosolization of particles, the use of vacuum cleaners is strongly discouraged. Waste material should be removed frequently from the cage (after moistening the material). This waste should be burned or double-bagged for disposal. When possible, healthy birds should be cared for before isolated birds are handled.

  • Use disinfection measures. Because C. psittaci has a high lipid content, it is susceptible to most disinfectants and detergents. In the clinic or laboratory, a 1:1,000 dilution of quarternary ammonium compounds (alkyldimethylbenzylammonium chloride {e.g., Roccal{registered} or Zephiran{registered}}) is effective, as is 70% isopropyl alcohol, 1% Lysol{registered}, 1:100 dilution of household bleach (i.e., 2.5 tablespoons per gallon {10 mL/L}), or chlorophenols. (C. psittaci is susceptible to heat but is resistant to acid and alkali.) Many disinfectants are respiratory irritants and should be used in a well-ventilated area. Avoid mixing disinfectants with any other product.

  • Take measures to protect persons at high risk from becoming infected. All persons in contact with infected birds should be informed about the nature of the disease. If respiratory illness develops in an exposed person, a physician should initiate early and specific treatment for psittacosis. Persons at risk should be instructed to wear protective clothing, gloves, and a paper surgical cap and respirator with at least an N95 rating (or a dust-mist mask if an N95 or higher-efficiency respirator is not available) when cleaning cages or handling infected birds. Surgical masks may not be effective in preventing transmission. When necropsies are performed on birds that are potentially infected, additional precautions should be taken, including a) wetting the carcass with detergent and water to prevent aerosolization of infectious particles and b) working under an examining hood that has an exhaust fan.

Responsibilities of Veterinarians

Veterinarians should be aware that AC is not a rare disease in pet birds. The disease should be considered in any lethargic bird that has nonspecific signs of illness, especially if the bird was recently purchased. If AC is suspected, appropriate laboratory specimens should be submitted to a veterinary diagnostic laboratory to confirm the diagnosis. Both laboratories and attending veterinarians should follow local and state regulations or guidelines regarding the reporting of cases.

Veterinarians should work closely with authorities who conduct investigations in their jurisdictions. When appropriate, veterinarians should inform their clients that infected birds should be isolated and treated. In addition, clients should be informed of a) the public health hazard posed by AC, b) appropriate precautions that should be taken to avoid the risk for transmission to persons and other companion birds, and c) the need to seek medical attention if persons exposed to the bird develop influenza-like symptoms or other respiratory illness.


The appropriate state animal and/or public health authorities may issue a quarantine for all affected and susceptible birds on a premises where infection has been identified. The purpose of imposing a quarantine is not to discourage disease reporting but to prevent further disease transmission (1). Because of the severe economic impact of quarantines, reasonable economic options should be made available to the owners and operators of pet stores. With the approval of state authorities, the owner of quarantined birds may choose one of two options: a) remove the birds from the premises and treat them in a separate quarantine area or b) euthanize the birds. After completion of the treatment or removal of the birds, a quarantine may be lifted when the infected premises are thoroughly cleaned and disinfected. The area can then be restocked with birds.

Importation of Birds and Import Regulations

The Veterinary Services of the Animal and Plant Health Inspection Service, U.S. Department of Agriculture (USDA), regulates the importation of pet birds to ensure that exotic poultry diseases are not introduced into the United States. These regulations are set forth in the Code of Federal Regulations (CFR), Title 9, Chapter 1 (1). Because of the possibility of smuggled pet birds, these import measures do not guarantee that avian chlamydiosis cannot enter the United States. In general, current USDA regulations regarding the importation of birds require --

  • that the importer obtain, in advance of shipping, an import permit from the USDA and a health certificate issued and/or endorsed by a veterinarian of the national government of the exporting country;

  • a USDA veterinary inspection at the first port of entry in the United States and quarantine for a minimum of 30 days at a USDA-approved facility, to determine if the birds are free of evidence of communicable diseases of poultry. In addition, the birds must be tested to ensure they are free of exotic Newcastle disease and pathogenic avian influenza; and

  • that, during U.S. quarantine, psittacine birds receive a balanced, medicated feed ration containing greater than or equal to 1% chlortetracycline (CTC) with less than or equal to 0.7% calcium for the entire quarantine period as a precautionary measure against avian chlamydiosis. The USDA recommends that importers continue CTC prophylactic treatment of psittacine birds for an additional 15 days (i.e., for 45 continuous days).


Because several diseases affecting humans can be caused by other species of Chlamydia, the disease resulting from the infection of humans with C. psittaci is frequently referred to as psittacosis. Most C. psittaci infections in humans result from exposure to psittacine birds.

During 1985-1995, a total of 1,132 cases of psittacosis in humans was reported to CDC (2). Because the diagnosis of psittacosis can be difficult, these 1,132 cases probably represent an underestimation of the actual number of cases. During the 1980s, public health surveillance indicated that exposure to caged pet birds accounted for 70% of the psittacosis cases for which the source of infection was known; of these, owners of companion birds or bird fanciers were the largest group of affected persons (43%). Pet-shop employees accounted for an additional 10% of cases. Other persons at risk include pigeon fanciers and persons whose occupation places them at risk of exposure (e.g., employees in poultry-slaughtering/processing plants, veterinarians, veterinary technicians, laboratory workers, workers in avian quarantine stations, farmers, and zoo workers). Because human infection can result from transient exposure to infected birds or their contaminated droppings, persons with no identified avocational or occupational risk may become infected.

Clinical Signs

Human infection with C. psittaci usually occurs through the inhalation of the organism aerosolized from urine, respiratory secretions, or dried feces of infected birds. Other sources of exposure can include bird bites, mouth-to-beak contact, and handling the plumage and tissues of infected birds. Transient exposures may be adequate to induce infection. The incubation period is 5-14 days, and the severity of disease resulting from infection ranges from inapparent to severe systemic disease accompanied by pneumonia.

Cases of symptomatic infection typically are characterized by abrupt onset of fever, chills, headache, malaise, and myalgia. A nonproductive cough usually develops, and a pulse-temperature dissociation sometimes occurs. Auscultatory findings may underestimate the extent of pulmonary involvement. Radiographic findings may include lobar or interstitial infiltrates.

The differential diagnosis of psittacosis-related pneumonia may include infection by Coxiella burnetii, Mycoplasma pneumoniae spp., Chlamydia pneumoniae, Legionella spp., and viruses (e.g., influenza). Psittacosis may result in endocarditis, myocarditis, hepatitis, arthritis, keratoconjunctivitis, and encephalitis. Death occurs in less than 1% of properly treated patients.

Case Definition

A patient is considered to have a confirmed case of psittacosis if a) C. psittaci is cultured from clinical specimens or b) clinical illness is compatible with chlamydiosis and the antibody titer is increased by greater than fourfold (i.e., to greater than or equal to 32) as demonstrated by a complement-fixation (CF) or microimmunofluorescence (MIF) test for C. psittaci by either paired sera obtained at least 2 weeks apart or detection of IgM antibody (i.e., greater than or equal to 16) by MIF against C. psittaci. A patient is considered to have a probable case of psittacosis if there is a) a clinically compatible illness that is epidemiologically linked to a confirmed case or b) a single antibody titer greater than or equal to 32 by MIF or CF is present in at least one serum specimen obtained after onset of symptoms.

These case definitions were established by CDC and the Council of State and Territorial Epidemiologists for epidemiologic purposes (3). They should not be used as sole criteria for establishing clinical diagnoses.


Diagnosis almost always is established by using serologic methods in which paired sera are tested for Chlamydia antibodies by CF test. However, because Chlamydia CF antibody is not species specific, high CF titers also may result from C. pneumoniae and Chlamydia trachomatis infection. Acute- and convalescent-phase serum specimens should be obtained as soon as possible after onset of symptoms and greater than or equal to 2 weeks after onset of symptoms, respectively. Because treatment with tetracycline may delay or diminish the antibody response, a third serum sample may help confirm the diagnosis. All sera should be tested simultaneously at the same laboratory. If indicated by epidemiologic and clinical history, MIF assays can be used to distinguish C. psittaci infection from infection with other chlamydial species. Information about laboratory testing is often available at state laboratories. In humans, the infective agent can be isolated from sputum, pleural fluid, or clotted blood during acute illness before treatment with antibiotic.


Tetracyclines are the drugs of choice for treating psittacosis in humans; most persons respond to oral therapy (100 mg of doxycycline administered twice a day or 500 mg of tetracycline hydrochloride administered four times a day). For severely ill patients, tetracycline hydrochloride may be administered intravenously at a dosage of 10-15 mg/kg of body weight/day. Remission of symptoms usually is evident within 48-72 hours. However, relapse may occur, and treatment must continue for at least 10-14 days after fever abates. Although its in-vivo efficacy has not been determined, erythromycin is probably the best alternative agent for persons for whom tetracycline is contraindicated (e.g., children aged less than 9 years and pregnant women).

Reinfection can occur. Person-to-person transmission occurs only rarely; therefore, patient isolation and prophylaxis of contacts are not indicated.

Responsibilities of Physicians

Most states require physicians to report cases of psittacosis in humans to the appropriate health authorities. Timely diagnosis and reporting may aid in identifying the source of the infection and in controlling the spread of disease. Because single-serum titers are both insensitive and nonspecific for diagnosis of psittacosis, confirmation with paired acute- and convalescent-phase sera is recommended.

Birds that are suspected sources of human infection should be referred to veterinarians for evaluation and treatment. Local and state authorities may conduct epidemiologic investigations and institute additional disease-control measures.

Epidemiologic Investigations

Epidemiologic investigations may be necessary to assist in controlling the transmission of C. psittaci in birds and humans. An epidemiologic investigation should be initiated if: a) a bird that has confirmed AC was procured from a pet store, breeder, or dealer within 60 days of the onset of its signs or b) a bird has come in contact with a human who has confirmed psittacosis.

Humans or birds infected with or suspected of being infected with C. psittaci should be investigated at the discretion of the appropriate local or state public or animal health authorities. Investigations involving recently purchased birds should include a visit to the site where the infected bird is located and identification of the location where the bird was originally procured (e.g., pet shops, dealers, breeders, and quarantine stations). In conducting investigations, important considerations may include documenting the number and type(s) of birds involved, the health status of potentially affected persons and birds, locations of facilities where birds were housed, relevant ventilation-related factors, the treatment protocol, and the source of medicated feed, if such treatment is initiated. To facilitate identification of multistate outbreaks of C. psittaci infection, local and state authorities should report suspected outbreaks to the Childhood and Respiratory Diseases Branch, Division of Bacterial and Mycotic Diseases, National Center for Infectious Diseases, CDC; telephone (404) 639-2215.


  1. US Department of Agriculture, Animal and Plant Health Inspection Service. Importation of certain animals, birds, and poultry and certain animal, bird, and poultry products: requirements for means of conveyance and shipping containers. CFR Title 9 Part 92. 101-7, Jan. 1, 1997.

  2. CDC. Summary of notifiable diseases, United States, 1995. MMWR 1995;44(53):74-7.

  3. CDC. Case definitions for infectious conditions under public health surveillance. MMWR 1997;46(No. RR-10):27.

Bibliography Fudge AM. Avian chlamydiosis. In: Rosskopf WJ, Woerpel RW, eds. Diseases of cage and aviary birds. Baltimore: Williams & Wilkins, 1996:572-85. Gelach H. Chlamydia. In: Ritchie BW, Harrison GJ, Harrison LR, eds. Avian medicine, principles and applications. Lake Worth, FL: Wingers Publishing, 1994:984-96. Reports from the symposium on avian chlamydiosis. J Am Vet Med Assoc 1989;195:1501-76. Schlossberg D. Chlamydia psittaci (psittacosis). In: Mandell GL, Bennett JE, Dolin R, eds. Principles and practice of infectious disease, 4th ed. New York: Churchill Livingstone, 1995:1693-6. Schaffner W. Birds of a feather -- do they flock together? Infect Control Hosp Epidemiol 1997;18:162-4.

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