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Infectious Disease and Microbiology – Psittacosis
Psittacosis, also called parrot fever or ornithosis, is a systemic zoonotic infection caused by Chlamydophila psittaci. It is transmitted from infected birds to humans and most often affects the lungs, producing an atypical pneumonia. Although the name comes from the Greek word for parrot, almost any bird can act as a source of infection.
The disease is uncommon in the United States, with only a small number of reported cases each year, but it is likely underdiagnosed because many infections are mild or self-limited. C. psittaci is estimated to cause a small percentage of community-acquired pneumonia cases. People at higher risk include bird owners, pet shop workers, poultry workers, veterinarians, pigeon fanciers, taxidermists, zoo workers, and people who handle birds or bird tissues.
Transmission occurs mainly through inhalation of contaminated bird secretions, dried feces, feathers, or tissues. Infected birds may appear healthy or may show signs such as ruffled feathers, respiratory symptoms, conjunctivitis, or diarrhea. Shedding increases when birds are stressed. Prevention includes proper bird quarantine, treatment of infected birds by veterinarians, protective clothing, gloves, eye protection, and fitted respirators when handling potentially infected birds or cleaning cages.
After an incubation period of about 5–21 days, psittacosis usually begins suddenly with fever, chills, headache, muscle aches, sweating, and a dry cough. Respiratory symptoms may be mild early in illness. Severe headache is common, and some patients develop confusion, agitation, lethargy, or meningoencephalitis. Gastrointestinal symptoms such as nausea, vomiting, abdominal pain, and diarrhea may occur. Rarely, psittacosis can involve the heart, kidneys, liver, eyes, joints, blood, or central nervous system. Severe cases can progress to respiratory failure, septic shock, kidney failure, liver failure, disseminated intravascular coagulation, or hemophagocytic syndrome.
On examination, patients may have fever, pharyngitis, hepatomegaly, and abnormal lung findings such as fine rales, rhonchi, egophony, or bronchial breath sounds. Neck stiffness, photophobia, altered mental status, and splenomegaly may occur in some cases.
Diagnosis can be difficult because laboratory findings are nonspecific. Testing may include complete blood count, electrolytes, kidney and liver function tests, coagulation studies, urinalysis, blood cultures, and specific testing for psittacosis. White blood cell counts may be low, normal, or elevated, and inflammatory markers may rise. Mild liver enzyme elevation is common. Diagnosis is usually made by serology, showing a fourfold rise in IgG titers between acute and convalescent samples. PCR testing of respiratory specimens may also help, although culture is rarely performed because it requires specialized facilities.
Chest radiographs are abnormal in most patients and may show interstitial infiltrates, nodules, a miliary pattern, or lobar consolidation. Radiographic findings may appear more severe than the physical examination suggests. Bronchoscopy with bronchoalveolar lavage may be useful when PCR testing is needed.
The differential diagnosis includes other causes of atypical or community-acquired pneumonia, such as Chlamydia pneumoniae, Mycoplasma pneumoniae, Coxiella burnetii, Legionella pneumophila, viral pneumonia, influenza, histoplasmosis, coccidioidomycosis, and obstructive lung cancer.
Doxycycline is the first-line treatment. Mild to moderate disease is treated with doxycycline 100 mg orally twice daily, while severe cases may require intravenous doxycycline. Tetracycline is an alternative. Symptoms and fever usually improve within 24–48 hours after treatment begins. Therapy should continue for at least 10 days and generally for 10–14 days after fever resolves. Macrolides such as azithromycin or erythromycin may be used in children, pregnancy, or patients unable to tolerate doxycycline.
Severe cases may require hospitalization, respiratory support, and intensive care. Patients with altered mental status, hypoxemia, cardiac dysfunction, or kidney impairment should be admitted. Droplet precautions and standard infection control practices should be used.
Follow-up includes completion of antimicrobial therapy and public health reporting. Health departments may investigate possible bird sources and additional cases. Patients should be educated about symptoms in birds and humans, transmission routes, and prevention strategies.
With appropriate doxycycline therapy, prognosis is usually excellent and death is rare. Complications can include fulminant multisystem disease, hepatitis, anemia, reactive arthritis, meningoencephalitis, keratoconjunctivitis, myocarditis, pericarditis, nephritis, thrombophlebitis, and pulmonary infarction.
Psittacosis, also called parrot fever or ornithosis, is a systemic zoonotic infection caused by Chlamydophila psittaci. It is transmitted from infected birds to humans and most often affects the lungs, producing an atypical pneumonia. Although the name comes from the Greek word for parrot, almost any bird can act as a source of infection.
The disease is uncommon in the United States, with only a small number of reported cases each year, but it is likely underdiagnosed because many infections are mild or self-limited. C. psittaci is estimated to cause a small percentage of community-acquired pneumonia cases. People at higher risk include bird owners, pet shop workers, poultry workers, veterinarians, pigeon fanciers, taxidermists, zoo workers, and people who handle birds or bird tissues.
Transmission occurs mainly through inhalation of contaminated bird secretions, dried feces, feathers, or tissues. Infected birds may appear healthy or may show signs such as ruffled feathers, respiratory symptoms, conjunctivitis, or diarrhea. Shedding increases when birds are stressed. Prevention includes proper bird quarantine, treatment of infected birds by veterinarians, protective clothing, gloves, eye protection, and fitted respirators when handling potentially infected birds or cleaning cages.
After an incubation period of about 5–21 days, psittacosis usually begins suddenly with fever, chills, headache, muscle aches, sweating, and a dry cough. Respiratory symptoms may be mild early in illness. Severe headache is common, and some patients develop confusion, agitation, lethargy, or meningoencephalitis. Gastrointestinal symptoms such as nausea, vomiting, abdominal pain, and diarrhea may occur. Rarely, psittacosis can involve the heart, kidneys, liver, eyes, joints, blood, or central nervous system. Severe cases can progress to respiratory failure, septic shock, kidney failure, liver failure, disseminated intravascular coagulation, or hemophagocytic syndrome.
On examination, patients may have fever, pharyngitis, hepatomegaly, and abnormal lung findings such as fine rales, rhonchi, egophony, or bronchial breath sounds. Neck stiffness, photophobia, altered mental status, and splenomegaly may occur in some cases.
Diagnosis can be difficult because laboratory findings are nonspecific. Testing may include complete blood count, electrolytes, kidney and liver function tests, coagulation studies, urinalysis, blood cultures, and specific testing for psittacosis. White blood cell counts may be low, normal, or elevated, and inflammatory markers may rise. Mild liver enzyme elevation is common. Diagnosis is usually made by serology, showing a fourfold rise in IgG titers between acute and convalescent samples. PCR testing of respiratory specimens may also help, although culture is rarely performed because it requires specialized facilities.
Chest radiographs are abnormal in most patients and may show interstitial infiltrates, nodules, a miliary pattern, or lobar consolidation. Radiographic findings may appear more severe than the physical examination suggests. Bronchoscopy with bronchoalveolar lavage may be useful when PCR testing is needed.
The differential diagnosis includes other causes of atypical or community-acquired pneumonia, such as Chlamydia pneumoniae, Mycoplasma pneumoniae, Coxiella burnetii, Legionella pneumophila, viral pneumonia, influenza, histoplasmosis, coccidioidomycosis, and obstructive lung cancer.
Doxycycline is the first-line treatment. Mild to moderate disease is treated with doxycycline 100 mg orally twice daily, while severe cases may require intravenous doxycycline. Tetracycline is an alternative. Symptoms and fever usually improve within 24–48 hours after treatment begins. Therapy should continue for at least 10 days and generally for 10–14 days after fever resolves. Macrolides such as azithromycin or erythromycin may be used in children, pregnancy, or patients unable to tolerate doxycycline.
Severe cases may require hospitalization, respiratory support, and intensive care. Patients with altered mental status, hypoxemia, cardiac dysfunction, or kidney impairment should be admitted. Droplet precautions and standard infection control practices should be used.
Follow-up includes completion of antimicrobial therapy and public health reporting. Health departments may investigate possible bird sources and additional cases. Patients should be educated about symptoms in birds and humans, transmission routes, and prevention strategies.
With appropriate doxycycline therapy, prognosis is usually excellent and death is rare. Complications can include fulminant multisystem disease, hepatitis, anemia, reactive arthritis, meningoencephalitis, keratoconjunctivitis, myocarditis, pericarditis, nephritis, thrombophlebitis, and pulmonary infarction.
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