psittacosis

[sit-uh-koh-sis]

psittacosis or parrot fever, infectious disease caused by the species of Chlamydia psittaci and transmitted to people by birds, particularly parrots, parakeets, and lovebirds. In birds the disease takes the form of an intestinal infection, but in people the illness runs the course of a virus pneumonia; infection follows inhalation of dust from feathers or cage contents or the bite of an infected bird. Human psittacosis, which can be transmitted to others by cough droplets and sputum, is treated the same as pneumonia. The mortality rate may run as high as 30%. Restrictions on bird importation and attention to infected flocks of pigeons have been used to control the disease. Treatment with tetracycline antibiotic is usually effective.

The Columbia Electronic Encyclopedia Copyright © 2004.
Licensed from Columbia University Press

Psittacosis

In medicine (pulmonology), psittacosis — also known as parrot disease, parrot fever, and ornithosis — is a zoonotic infectious disease caused by a bacterium called Chlamydophila psittaci (formerly Chlamydia psittaci) and contracted not only from parrots, such as macaws, cockatiels and budgerigars, but also from pigeons, sparrows, ducks, hens, gulls and many other species of bird. The incidence of infection in canaries and finches is believed to be lower than in psittacine birds.

The word "ornithosis" is only a synonym for "psittacosis" in certain contexts : more generally the term is applied to any infection that is spread by birds.

In birds

In birds, Chlamydophila psittaci infection is referred to as avian chlamydiosis (AC). Infected birds shed the bacteria through feces and nasal discharges, which can remain infectious for several months. Many strains remain quiescent in birds until activated under stress. Birds are excellent, highly mobile vectors for the distribution of chlamydial infection because they feed on, and have access to, the detritus of infected animals of all sorts.

Symptoms

C. psittaci in birds is often systemic and infections can be inapparent, severe, acute or chronic with intermittent shedding. Symptoms in birds include "inflamed eyes, difficulty in breathing, watery droppings and green urates."

Diagnosis

Initial diagnosis may be via symptoms, but is usually confirmed via an antigen and antibody test. A PCR-based test is also available. Although any of these tests can confirm psittacosis, false negatives are possible and so a combination of clinical and lab tests is recommended before giving the bird a clean bill of health.

Epidemiology

Infection is usually via the droppings of another infected bird, though it can also be transmitted via feathers and eggs, and are typically either inhaled or ingested.

C. psittaci strains in birds infect mucosal epithelial cells and macrophages of the respiratory tract. Septicaemia eventually develops and the bacteria become localized in epithelial cells and macrophages of most organs, conjunctiva, and gastrointestinal tract. It can also be passed in the eggs. Stress will commonly trigger onset of severe symptoms, resulting in rapid deterioration and death. C. psittaci strains are similar in virulence, grow readily in cell culture, have 16S-rRNA genes that differ by <0.8%, and belong to eight known serovars. All should be considered to be readily transmissible to humans.

C. psittaci serovar A is endemic among psittacine birds and has caused sporadic zoonotic disease in humans, other mammals and tortoises. Serovar B is endemic among pigeons, has been isolated from turkeys, and has also been identified as the cause of abortion in a dairy herd. Serovars C and D are occupational hazards for slaughterhouse workers and for people in contact with birds. Serovar E isolates (known as Cal-10, MP or MN) have been obtained from a variety of avian hosts worldwide and, although they were associated with the 1920s–1930s outbreak in humans, a specific reservoir for serovar E has not been identified. The M56 and WC serovars were isolated during outbreaks in mammals.

Treatment

Treatment is usually via antibiotics, such as doxycycline or tetracycline, and can be administered via drops in the water, or injections. Many strains of C. psittaci are susceptible to bacteriophage.

In humans

Symptoms

In humans, after incubation period of 5-14 days, the symptoms of the disease range from inapparent illness to systemic illness with severe pneumonia. It presents chiefly as an atypical pneumonia. In the first week of psittacosis the symptoms mimic typhoid fever: prostrating high fevers, arthralgias, diarrhoea, conjunctivitis, epistaxis and leukopenia. Rose spots can appear and these are called Horder's spots. Splenomegaly is frequent toward the end of first week. Diagnosis can be suspected in case of respiratory infection associated with splenomegaly and/or epistaxis. Headache can be so severe that suggests meningitis and some nuchal rigidity is not unusual. Towards the end of first week stupor or even coma can result in severe cases.

The second week is more akin of acute bacteraemic pneumococcal pneumonia with continuous high fevers, cough and dyspnoea. X rays show patchy infiltrates or a diffuse whiteout of lung fields.

Bloodwork shows leukopenia, thrombocytopenia and moderately elevated liver enzymes.

Differential diagnosis must be made with typhus, typhoid and atypical pneumonia by Mycoplasma, Legionella or Q fever. Exposure history is paramount to diagnosis.

Complications in the form of endocarditis, hepatitis, myocarditis, arthritis, keratoconjunctivitis, and neurologic complications (encephalitis) may occasionally occur. Severe pneumonia requiring intensive-care support may also occur. Fatal cases have been reported (less than 1% of cases).

Diagnosis

Diagnosis involves microbiological cultures from respiratory secretions of patients or serologically with a fourfold or greater increase in antibody titers against C. psittaci in blood samples combined with the probable course of the disease. Typical inclusions called "Leventhal-Cole-Lillie bodies" can be seen within macrophages in BAL fluid. Culture of Chlamydia psittaci is hazardous and should only be carried out in biosafety laboratories.

Epidemiology

Since 1996, fewer than 50 confirmed cases were reported in the United States each year. Many more cases may occur that are not correctly diagnosed or reported.

Bird owners, pet shop employees, and veterinarians are at risk of the infection. Some outbreaks of psittacosis in poultry processing plants have been reported.

Treatment

The infection is treated with antibiotics. Tetracyclines and chloramphenicol are the drugs of choice for treating patients with psittacosis. Most persons respond to oral therapy (100 mg of doxycycline administered twice a day , 500 mg of tetracycline hydrochloride administered four times a day) or 500 mg of chloramphenicol palmitate orally every 6 hours. For initial treatment of severely ill patients, doxycycline hyclate may be administered intravenously at a dosage of 4.4 mg/kg (2 mg/lb) body weight per day divided into two infusions per day (up to 100 mg per dose). In past years, tetracycline hydrochloride has been administered to patients intravenously (10-15 mg/kg body weight per day divided into four doses per day). Remission of symptoms usually is evident within 48-72 hours. However, relapse can occur, and treatment must continue for at least 10-14 days after fever abates. Although its in vivo efficacy has not been determined, erythromycin probably is the best alternative agent for persons for whom tetracycline is contraindicated (e.g., children aged less than 9 years and pregnant women).