What is psittacosis?
Psittacosis is an infectious disease caused by the bacterium, Chlamydophila psittaci, that is transmitted from birds to humans. The bacteria used to be previously known as Chlamydia psittaci. It is not a commonly seen infection in the general population and bird handlers are at the greatest risk of contracting psittacosis. Human-to-human transmission has not as yet been reported. Psittacosis can be very effectively treated with antibiotics and complications are unlikely with early diagnosis and the appropriate treatment.
How common is psittacosis?
Psittacosis is a rare infectious disease. It occurs globally but antibiotic therapy has greatly reduced the chances of complications and death. The true incidence may be unclear as the infection is often misdiagnosed but still effectively treated with antibiotics. There is between 100 to 200 cases of psittacosis reported each year in the United States. It can affect all age groups but middle-aged adults are more commonly affected.
How does psittacosis infect humans?
The bacteria is transmitted when bird feces or secretions are inhaled by humans. Therefore people in close contact with the sick birds are more likely to be affected especially when working with the beddings in closed spaces. Not all birds contract the disease but it is often the bird species that have relatively close contact with humans that are often affected. Once the psittacosis bacteria, Chlamydophila psittaci, gain entry into the airways, it attaches to the respiratory epithelial cells. However, it does not always cause an infection immediately.
Instead the bacteria enter the blood stream and get taken up in the reticuloendothelial system. This is the part of the immune system ‘manned’ by immune cells that ‘consume’ any invading microbes or debris in the body (phagocytes). The main parts of the reticuloendothelial system is the spleen and the lymph nodes. However, the bacteria may not be destroyed at this point especially in a person with a weakened immune system. Therefore HIV/AIDS patients and the elderly are among those who at a higher risk of contracting the psittacosis even with short term exposure. People who have very frequent contact with psittacine birds (all parrot species, turkeys) are obviously at a greater risk as well due to prolonged exposure.
It is important to note that not every person infected with the bacteria will develop the disease. Some may experience only mild symptoms and only a minority of people experience severe, or even life threatening symptoms. This is mainly as a result of the bacteria being able to disperse through the blood stream to various organs (bacteremia). The lungs are more commonly affected as pneumonia is a prominent manifestation of psittacosis. However, other organs may also be affected and depending on the severity of the infection and access to medical care, psittacosis can lead to fatal complications.
What are the symptoms of psittacosis?
The incubation period of psittacosis varies between 5 to 14 days which means that a person does not exhibit any symptoms during this time after contracting the infection. In some rare instances the incubation period can be as long as 50 days. Often there is just generalized symptoms that closely resembles the flu. The symptoms may pass in a short while and there are no further complications. Sometimes there are lung symptoms in the event of pneumonia and in rare cases there may be bowel, skin and central nervous system symptoms.
- Joint aches
- Muscle pain
- Headaches (mild)
- Dry cough (initially)
- Blood-tinged sputum (later)
- Shortness of breath
- Bloody nose (epistaxis)
- Sore throat
- Abnormal breathing sounds
- Chest pain when breathing (uncommon)
Other symptoms are present as a result of involvement of the gastrointestinal tract, skin and central nervous system. These complications are, however, uncommon.
- Severe headaches
- Light sensitivity
- Skin rash on the face (Horder spots)
- Nausea and sometimes vomiting
- Abdominal pain
What are the complications of psittacosis?
Although psittacosis is treatable, death is seen in about 1% of cases. Patients with respiratory failure or kidney failure are at the highest risk of death. However, there are several other possible complications such as heart infections (endocarditis, myocarditis or pericarditis), hepatitis (liver), pancreatitis (pancreas), meningitis (lining of brain and spinal cord) or encephalitis (brain). Reactive arthritis which is an autoimmune response to the infection leading to joint inflammation may also be seen.
What causes psittacosis?
Psittacosis is caused by inhaling dried bird droppings and secretions or contaminated soil containing the bacterium Chlamydophila psittaci. Infected birds may not always display obvious signs of being ill. The birds that are typically infected are parrots, canaries, parakeets, cockatiels, macaws and budgerigars. These are psittacine birds therefore the term psittacosis. Ducks, pigeons and turkeys may also be infected. Some strains of Chlamydophila psittaci can also infect livestock (cows, goats and sheep). However, the infection is not transmitted from these animals to humans. It is also possible for non-psittacine birds to be infected with Chlamydophila psittaci in which case the infection is referred to as ornithosis.
Who is at risk of psittacosis?
People who are at a greater risk of contracting the infection tend to have repeated exposure to the infected birds. This may include :
- Bird owners
- Pet store workers
- Poultry farmers
- Zoo workers
Naturally these people are at a higher risk since they have frequent exposure to the infected birds and the airborne feces, dried secretions and contaminated dust. These contaminants can remain airborne for long periods of time in a closed room. An immunocompromised person is more likely to be at risk of developing psittacosis even with short term exposure to the contaminants. This includes people living with HIV/AIDS, undergoing chemotherapy, using anti-rejection drugs after an organ transplant and the elderly.
How is psittacosis diagnosed?
The symptoms of psittacosis are non-specific for Chlamydophila psittaci infection and given that it is a rare disease, it is often misdiagnosed. It should be suspected among high risk people who present with pneumonia. Various diagnostic investigations are needed to confirm the diagnosis.
- Blood tests to confirm the presence of antibodies against Chlamydophila psittaci.
- Sputum culture confirming the presence of Chlamydophila psittaci. Blood cultures are often avoided.
- Other blood and urine tests and imaging studies like a chest X-ray are useful for assessing the effects associated with Chlamydophila psittaci infection but are not specific for confirming the presence of the bacteria.
What is the treatment for psittacosis?
Psittacosis can be effectively treated with antibiotics. In order to prevent a recurrence of the infection, antibiotic use extends for 2 to 3 weeks. For adolescents and adults, the treatment of choice is doxycycline and tetracycline. Hospitalization and intravenous administration of doxycycline may be needed in severe infections. Chloramphenicol is another antibiotic that may be considered as a first option. Pregnant women and children need to use erythromycin. Alternative antibiotics may include azithromycin, moxiflacin and rifampin. Most patients report an improvement within 48 to 72 hours and full recovery can be expected if the patient adheres to the treatment for the entire duration.