Background
Psittacosis, also known as parrot fever, is an infection caused by the obligatory intracellular bacterium Chlamydia psittaci. [1] The term psittacosis is derived from the Greek word for parrot, psittakos, and was first used by Morange in 1892.
This bacterium can infect parrots, parakeets, canaries, and other avian species (eg, turkeys, pigeons, ducks). Another term for this infection is ornithosis, which describes the infection caused by nonpsittacine birds.
The largest epidemic occurred in 1930 and affected 750-800 individuals. This epidemic led to the isolation of C psittaci in several laboratories in Europe and the United States.
Psittacosis is an occupational disease of zoo and pet-shop employees, poultry farmers, and ranchers. Human-to-human transmission is rare, but possible. These cases may cause more severe disease than avian-acquired psittacosis.
Psittacosis is probably underdiagnosed because patients with milder cases may not seek medical attention or may not be reported. [2]
Pathophysiology
The primary route for infection is through the respiratory system. [1] Infection develops after organisms from aerosolized dried avian excreta or respiratory secretions from sick birds are inhaled. C psittaci attaches to the respiratory epithelial cells. After the initial inoculation, the organism spreads via the blood stream to the reticuloendothelial system. Subsequently, secondary bacteremia causes lung infection.
Humans may acquire disease by handling sick birds. Mouth-to-beak resuscitation also has been implicated in transmission. Transient exposure to infected birds may cause symptomatic infection, even in visitors to pet shops.
Epidemiology
Frequency
United States
Reports show up to 200 cases of psittacosis annually. From 1988-97, the US Centers for Disease Control and Prevention (CDC) received 766 reports of psittacosis, which probably is an underestimate of the actual number of cases because psittacosis is difficult to diagnose, is covered by macrolide antimicrobials (which may be used empirically for therapy of community-acquired pneumonia), and often goes reported.
From 1988-2003, 935 human cases of psittacosis were reported to the CDC. [3] From 2005-2009, 66 human cases of psittacosis were reported (mean, 13; range, 8-21) to the CDC through the Nationally Notifiable Diseases Surveillance System. [2, 4]
International
Psittacosis is found worldwide. The incidence seems to be increasing in developed countries, which is correlated to the import of exotic birds.
Mortality/Morbidity
The mortality rate of psittacosis prior to the advent of antimicrobial treatment was approximately 15-20%. [4] The mortality rate is less than 1% with appropriate antibiotic therapy.
Race
Psittacosis has no observed racial predilection.
Sex
Psittacosis has no observed sexual predilection.
Age
Psittacosis occurs in all age groups, including children. The infection is more common among individuals in the middle decades of life.
Breed
Certain strains of C psittaci infect sheep, goats, and cows and may cause chronic infection and abortion. [5]
Wild birds such as falcons have caused disease through nasal or fecal secretions.
Mowing lawns without a grass catcher has been found to be a risk factor.
Most diseases resulted from exposure to infected pet birds, usually cockatiels, parakeets, parrots, and macaws.
Prognosis
With appropriate antibiotic therapy, the mortality rate of psittacosis is less than 1%. [1]
Hypoxemia and renal failure portend a poor prognosis.
Patient Education
Warn pet owners and pet-shop and poultry workers to be aware of possible respiratory symptoms and fever.
Tables
| Laboratory Findings | Association with Psittacosis |
|---|---|
| White blood cell counts | Normal to mildly decreased |
| Liver function test values | Usually mildly increased |
| Erythrocyte sedimentation rate (ESR) | May be elevated |
| Urinalysis | May show mild proteinuria (< 3500 mg/d) |
| Culturing of C psittaci | Possible but avoided due to hazards to laboratory personnel |
| Acute-phase serum and convalescent-phase serum | Test 2 weeks after onset to confirm a 4-fold or greater rise in titer |
| Complement fixation (CF) | Not specific and may cross-react with other chlamydial species |
| Microimmunofluorescence (MIF) and polymerase chain reaction (PCR) | Used by physicians to detect different chlamydial species; PCR is specific |
| Enzyme-linked immunosorbent assay (ELISA) and direct immunofluorescence (DIF) | Experimental but used in diagnosis of C psittaci infection |
| Serologic tests | Mainstay of diagnosis; delayed appearance of specific antibodies not helpful in emergent clinical management |
| Diagnosis | Established by clinical presentation and positive antibodies against C psittaci using MIF methods |
