How birds can quietly spread a severe form of pneumonia

Birds are everywhere. They perch on rooftops and windowsills and sometimes share our homes as pets. But they can also carry dangerous germs, even when they appear healthy.

In a recent case report published in Frontiers in Medicine, a 43-year-old man presented with a persistent fever of 104 degrees Fahrenheit (40 degrees Celsius), fatigue and muscle pain but few respiratory symptoms. Several courses of antibiotics failed to bring down his fever.

Doctors detected abnormal breath sounds, and a scan revealed a round blotch in his right lung—a sign of blood, pus, fluid or tissue—but tests for common pathogens came back negative. Suspecting a more unusual infection, they tested samples from his lungs and identified the culprit: Chlamydia psittaci, a bird-borne bacterium.

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The finding was key: the man switched antibiotics and recovered.

The likely source of the pathogen was a visit to a zoo, where the man had had direct contact with parrots about 10 days before his symptoms began. The infection, known as psittacosis, or parrot fever, can spread from many different birds, however, including poultry and pigeons.

Another case report describes a 16-year-old boy who developed pneumonia from a C. psittaci infection after he cleaned his dormitory, including by dusting windowsills and ventilation systems—despite the fact that he had no known direct contact with birds.

These cases show how everyday activities can expose people, sometimes unknowingly, to bird-borne diseases.

“Psittacosis is a respiratory disease mainly spread through inhaling the dust of bird droppings. You need to breathe in the bacteria to get infected,” says Brian Labus, an infectious disease epidemiologist at the University of Nevada, Las Vegas.

The U.S. Centers for Disease Control and Prevention states that there is no evidence that C. psittaci spreads through preparing or eating poultry products, though other case reports raise this possibility.

One, published in Case Reports in Infectious Diseases, described a chef who may have contracted psittacosis through handling poultry. Another, published in the International Journal of Infectious Diseases, involved a man who developed fever and severe diarrhea after eating undercooked pigeon meat. The same bacterial strain was detected in the patient and in pigeons from the source of the meat, raising the possibility of foodborne transmission. But the exact routes of transmission in these cases remains unclear.

Psittacosis can be difficult to recognize because its symptoms resemble those of other respiratory illnesses.

“There are no unique symptoms that can make you suspect psittacosis as the cause of a respiratory illness, and doctors can’t tell without laboratory testing,” Labus says. He recommends that people with symptoms tell their doctor about any bird-related exposures, including caring for pet birds or cleaning up after wild birds.

According to the CDC, fewer than 10 cases of parrot fever are typically reported in the U.S. each year. Psittacosis may be more common than reported figures suggest.

“Many infections probably go undiagnosed and are simply classified as community-acquired pneumonia without identifying the underlying causative pathogen,” says Daisy Vanrompay, a professor at Ghent University in Belgium. She directs the country’s national reference laboratory for human C. psittaci infections.

While some infections are mild, others can cause severe pneumonia and, in rare cases, damage to organs such as the heart, liver and brain.

Severity depends on the amount of bacteria that’s inhaled, the strain that’s involved and individual susceptibility, Vanrompay says. Labus adds that young children, older adults and people with weakened immune systems or underlying lung conditions may be at greater risk of severe illness.

To reduce exposure, both experts recommend wetting bird droppings before removal rather than dry sweeping or vacuuming them and wearing a well-fitting respirator when cleaning contaminated areas.