INTRODUCTION	Section 2 of 10
Author Information Introduction Clinical Differentials Workup Treatment Medication Follow-up Miscellaneous Bibliography

Background: Psittacosis is an infection caused by the obligatory intracellular bacterium Chlamydia psittaci. 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.

Pathophysiology: The primary route for infection is through the respiratory system. Infection develops after inhaling organisms from aerosolized dried avian excreta or respiratory secretions from sick birds. 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 is implicated in transmission. Transient exposure to infected birds may cause symptomatic infection, even in visitors to pet shops.

Frequency:

• In the US: 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 employed empirically for therapy of community-acquired pneumonia), and often is not reported.

  From 1988-2003, 935 human cases of psittacosis were reported to the CDC.

• Internationally: 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 prior to the advent of antimicrobial treatment was approximately 15-20%. The mortality rate is less than 1% with appropriate antibiotic therapy.

Breed: Certain strains of C psittaci infect sheep, goats, and cows and may cause chronic infection and abortion.

• 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.

Race: No race predilection is observed.

Sex: No sex predilection is observed.

Age: Psittacosis occurs in all age groups, including children. The infection is more common among individuals in the middle decades of life.

	CLINICAL	Section 3 of 10
Author Information Introduction Clinical Differentials Workup Treatment Medication Follow-up Miscellaneous Bibliography

History: The incubation period generally is 5-14 days. The longest observed incubation time was 54 days. The predominant presentation is respiratory tract infection with constitutional symptoms. Clinical findings are variable.

• Constitutional

• Fever (50-90%)

• Chills

• Malaise

• Respiratory

• Cough (50-90%), usually not productive

• Pleuritic chest pain (rare)

• Dyspnea

• Sore throat and mild pharyngitis (common)

• Epistaxis (common)

• Gastrointestinal

• Nausea and vomiting (uncommon)

• Abdominal pain (uncommon)

• Diarrhea (rare)

• Jaundice (rare)

• Neurological

• Severe headache (common)

• Photophobia (common)

• Agitation and lethargy

• Dermatological - Includes facial rash (Horder spots)

Physical: Disease may range from mild insidious presentations to severe pneumonia that requires mechanical ventilation.

• Respiratory

• Nonspecific auscultatory findings that often underestimate clinical and radiographic findings may develop.

• Patients may develop fatal pulmonary embolism and pulmonary infarction.

• Pleural effusion is rare.

• Cardiac

• Relative bradycardia is common.

• Physicians may observe pericarditis, culture-negative endocarditis, and myocarditis.

• Gastrointestinal

• Splenomegaly occurs in 10-70% of patients, depending on the study.

• When present, this sign suggests psittacosis in patients with pneumonia.

• Neurological

• Patients may develop meningitis, encephalitis, seizures, and Guillain-Barré syndrome, but these are rare.

• Cerebrospinal fluid (CSF) findings usually are normal.

• Dermatological

• Patients may develop Horder spots, which are macular rashes resembling the rose spots observed in typhoid fever but appearing on the face.

• Patients also may develop erythema multiforme and erythema nodosum.

• Hematological

• Patients may develop anemia secondary to hemolysis.

• Disseminated intravascular coagulation may occur in patients with overwhelming infections.

• Renal symptoms include acute glomerulonephritis and tubulointerstitial nephritis.

• Musculoskeletal symptoms include reactive arthritis that usually is polyarticular. Rarely, rhabdomyolysis has been observed.

• Stages of disease progression
  1. Flu-like syndromes without radiographic abnormalities

  2. Mild-to-moderate pneumonia

  3. Severe pneumonia

  4. Acute respiratory failure, sepsis, and septic shock

Causes: Psittacosis is an infectious disease caused by the obligatory intracellular bacterium, C psittaci.

• C psittaci is associated with psittacine birds and poultry.

• Psittacosis is an occupational disease of poultry farmers, pet shop workers, and veterinarians.

• Relapses may occur.

• Since the organism is a bacterium, it is unlikely that major protective immunity will develop after a single episode of disease. The exact risk of recurrence upon reexposure is unknown. It is reasonable to advise advoidance of infected birds.