Birds are among the most popular pets in the United States, ranking fourth behind dogs, cats, and fish. According to a commercial survey,1 6.4 million US households own at least one pet bird—and are therefore at risk of a number of bacterial, protozoal, fungal, viral, or parasitic zoonoses (infectious diseases of animals that are communicable to humans).2
This review focuses on the most common pet bird-associated diseases, with implications for bird-keepers’ health. Unless specifically stated otherwise, these diseases are not routinely transmissible from human to human.
NO NEED TO AVOID OWNING A BIRD
Although one can indeed acquire an infection from a pet bird, this possibility need not discourage people from owning birds.3,4
The ability of a microorganism to make a person sick varies with the virulence of the organism, the dose to which a person is exposed, and the route of infection. For a bird owner, prevention often involves simple hygiene, handwashing, sanitation, and regular veterinary care for the bird.3 Many of these diseases are transmitted by ingestion of food contaminated by avian fecal matter or inhalation of contaminated dust. Therefore, bird owners should take steps to minimize dander in the environment. Furthermore, wearing a mask during cage cleaning is suggested.5 Obtaining pet birds from reputable domestic sources decreases the risk of acquiring a bird with an infectious disease.4,6
These hygienic measures are especially important for people who are more susceptible to infection, eg, the very young or very old, those in poor health to begin with, and those with compromised immunity.
Most of the illnesses one can acquire from birds are asymptomatic or self-limited in humans, but they should be considered if a bird-keeper has persistent or unusual symptoms of infection or if the pet bird was recently acquired or has been ill or died.
DISEASES PRESENTING WITH FLU-LIKE OR PULMONARY SYMPTOMS
Psittacosis (ornithosis, parrot fever, chlamydiosis)
Psittacosis is caused by Chlamydophila (formerly Chlamydia) psittaci. The organism has been reported to be present in 40% of birds.4,7 Humans are considered incidental hosts.
Transmission of C psittaci is usually via inhalation of aerosolized particles contaminated with infected bird excreta, nasal secretions, tissue, or feathers. Beak-to-mouth transmission and transmission via bird bites have been reported.8 Unlike Chlamydophila pneumoniae, C psittaci has not conclusively been reported to be transmitted from human to human.
Many infected pet birds show no signs of the disease, but others may have conjunctivitis, liver disease, or generalized signs of severe infection such as ruffled feathers, loss of appetite, diarrhea, or lime-green urates (R. Stevenson, personal communication, 2007).2,5,9,10
Recognizing that the patient has been exposed to birds is clinically useful, as in one study 90% of patients with psittacosis had been exposed to birds as pets or in their occupations.11
Atypical pneumonia is the most common presentation of psittacosis in humans. The symptoms typically begin 7 to 14 days after exposure, with fever, chills, prominent headache, photophobia, and cough. Hepatosplenomegaly is clinically detectable in 10% to 70% of patients. Serious but uncommon presentations include pericarditis, myocarditis, bacterial culture-negative endocarditis, mental status changes, and thrombophlebitis. The combination of pneumonitis and hepatosplenomegaly should prompt consideration of psittacosis.11
All known subtypes of influenza A virus can infect birds (influenza B virus cannot). However, there are substantial genetic differences between the subtypes of influenza A that typically infect both people and birds.12
Avian influenza viruses affecting birds and humans (H5N1, H7N7, H9N2, and others), commonly called “bird flu,” emerged in 1997 in association with poultry.13,14 Highly pathogenic H5N1 viral infections have attracted particular attention, as they have killed millions of birds and infected several hundred humans, half of whom have died.13 Various avian influenza viruses that can affect humans have been isolated from captive birds such as parrots, canaries, and poultry and from wild waterfowl and migrating birds.15 To our knowledge, pet birds have not been implicated in transmission, but they are a potential source of infection if they have been in contact with infected birds.
Transmission from bird to human has usually been via inhaled droplets and, less likely, from contaminated environmental sources. According to the US Centers for Disease Control and Prevention, family clusters of H5N1 infection have been observed,16 but person-to-person transmission has been very rare, limited, and unsustained.13
Signs of influenza in birds can range from none to respiratory tract infection, decreased egg production, systemic illness, and death.15
Avian influenza should be suspected in people with flu symptoms who have been exposed to sick poultry or wild birds, have travelled to an endemic area, or have had direct contact with a person known or suspected to be infected with avian influenza.17 Information about areas of the world in which avian influenza is endemic or is breaking out is available at the World Health Organization Epidemic and Pandemic Alert and Response Web page (www.who.int/csr/disease/avian_influenza/updates/en/index.html).
Signs and symptoms of avian influenza in humans include fever, upper respiratory tract infection, cough, and gastrointestinal symptoms. With highly pathogenic viruses such as H5N1, the disease can progress very rapidly from onset to death. Less-pathogenic viruses such as H9N2 cause milder symptoms.16