• The key to successful management of psittacosis is to consider this diagnosis, particularly in cases of community-acquired pneumonia (CAP), especially given a history of bird contact.
• The typical clinical pictures are of CAP, influenza-like illness, or fever of unknown origin. Onset is usually sudden with fever, chills and a prominent headache. Consider this diagnosis in a patient with CAP unresponsive to β-lactam antibiotics.
• Investigation will typically reveal a normal or slightly elevated white blood cell count with a left shift or toxic changes, increase in C-reactive protein (CRP) or erythrocyte sedimentation rate (ESR), mildly abnormal liver function tests, hyponatremia, and mild renal impairment. Chest x-ray may be more abnormal than examination alone would predict.
• Diagnosis can be confirmed with (ideally) paired serum samples: using either the complement fixation test (widely used but unable to differentiate between Chamydophila species), or the microimmunofuorescence test, which is specific for individual Chamydophila species. Either a single high titer or a fourfold rise in titer using samples collected at least 14 days apart are interpreted as positive. More recently, real-time polymerase chain reaction (rt- PCR) tests are used to detect specific DNA. These can provide a more rapid diagnosis as well as sub-specific genotype.
• Therapy should commence when the diagnosis is suspected on clinical presentation and initial investigation.
• Tetracyclines are the drugs of choice; for example, doxycycline (Vibramycin) 100 mg bid for 10 to 14 days.
• Macrolides are suitable (but probably less effective) alternatives in those intolerant of tetracyclines (e.g., children and pregnant women).
• Notification to health authorities facilitates public health investigation and interventions to reduce transmission and control outbreaks.
Psittacosis is caused by infection with the bacterium Chlamydophila psittaci (formerly Chlamydia psittaci). It is twice as common in men than in women, and mainly affects adults typically aged 40 to 50 years. The main reservoir for psittacosis is birds, particularly psittacine birds (parrots, parakeets, budgerigars and cockatoos), but other bird species and mammals can be infected.
The most common etiological factor is exposure to infected birds— especially a new, sick, or dead one—typically a pet or via occupational exposure (e.g., work as a veterinarian, zoo keeper, or poultry-worker). Most cases are sporadic, but outbreaks have occurred associated with pet shops, aviaries, and poultry-processing plants and with mowing lawns in areas with large numbers of psittacine birds. Person-to- person transmission is rare. Ingestion of poultry products is not a risk factor.
C. psittaci infection is via the respiratory tract, and is typically thought to be by inhalation of an aerosol of dried feces or other avian secretion. It then either travels via the blood to the liver and spleen (where it replicates, causing a secondary bacteremia) or directly infects respiratory epithelial cells.
Prevention is aimed at controlling disease and/or colonization in susceptible host species: usually birds. This is facilitated by import restrictions including quarantine and treatment of suspected infections with tetracycline-impregnated feeds. Notification of health authorities is important for initiating public health investigations and interventions to reduce transmission and control of outbreaks.
The incubation period varies from 4 to 14 or more days. The typical presentation of psittacosis is of an influenza-like illness with sudden onset of fever, chills, and prominent headache, with or without rigors. A more gradual onset is also seen. A typically mild, dry cough usually starts later. There may also be diarrhea, pharyngitis, altered mental state, or shortness of breath. Chest examination is usually abnormal, but the findings are often minimal and less prominent than symptoms or x-ray findings would suggest. Pleural effusion is rare.
Patients might present with a fever of unknown origin without obvious respiratory involvement, or the disease can be misdiagnosed as meningitis due to prominent headache, sometimes with photophobia.
The white cell count is usually normal or slightly raised, but there is often a left shift or toxic changes. Increases in the C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR) are common. Mildly abnormal liver function tests, hyponatraemia, and mild renal impairment are also common. The cerebrospinal fluid sometimes contains a few mononuclear cells but is otherwise normal. The chest x- ray usually shows more (nonspecific) abnormality than examination findings might predict. The most common finding is lobar consolidation, but bilateral consolidation and interstitial opacities are also common.
Confirmation of diagnosis is more commonly performed using serology. The complement fixation (CF) test is widely used, but cannot differentiate between Chlamydophila species. A fourfold rise in titer, using samples collected at least 14 days apart, or a single titer of 1:128 or higher, is interpreted as positive, but this test is not widely available. Culture of C. psittaci is difficult and hazardous. Polymerase chain reaction (PCR) assays have been developed, but are not yet widely available for routine clinical use.
Diagnosis is facilitated by eliciting a history of recent bird contact from a patient with a compatible clinical syndrome, most commonly an influenza-like presentation, community acquired pneumonia (CAP), or a fever of unknown origin. The diagnosis should be considered in a patient with CAP and prominent headache, splenomegaly, or failure to respond to β-lactam antibiotics.
Differential diagnosis of an atypical CAP, includes infection with Legionella species, Mycoplasma pneumoniae, or Chlamydophila pneumoniae.
When the diagnosis is suspected on clinical presentation and initial investigations, empiric therapy should be commenced. Tetracyclines are the drugs of choice, for example doxycycline (Vibramycin) 100 mg bid for 10 to 14 days. Tetracycline treatment usually leads to improvement in symptoms (including fever) within 24 to 48 hours.
Macrolides are usually recommended for pregnant women, children, and other patients intolerant of tetracyclines. However, erythromycin (Erythrocin)1 has been shown to fail in situations where a tetracycline was effective, and there are few clinical data on the efficacy of the other agents in this class. Some data suggest that quinolones may be effective. Tetracycline hydrochloride2 or doxycycline (4.4 mg/kg/d divided into two infusions) may be given intravenously for critically ill patients.
Symptomatic improvement usually occurs within 24 to 48 hours of starting a tetracycline; typically including reduction of fever.
The degree of illness varies from asymptomatic to life threatening. Given appropriate antimicrobial therapy, subsequent case-fatality is less than 1%. Elderly persons and pregnant women are susceptible to more severe illness. Neurologic consequences (e.g., meningo- encephalitis) are recognized but rare. Other less-common sequellae include hemoptysis, proteinuria, hepatosplenomegaly, and encephalitis. Cardiac manifestations include relative bradycardia and, rarely, myocarditis, culture-negative endocarditis, and pericarditis.
Erythema nodosum and other skin manifestations have also been described. C. psittaci has been demonstrated by PCR to be present in ocular adnexal lymphoma (OAL) in parts of Eurasia. Up to one half of such cases respond to antibiotic treatment. However, studies elsewhere suggest that this organism might not commonly play a role in OAL. Recovery with minimal residual deficit is normal.
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5. National Association of State Public Health Veterinarians. Compendium of measures to control Chlamydophila psittaci infection among humans (psittacosis) and pet birds (avian chlamydiosis), 2010. Available at: http://www.nasphv.org/Documents/Psittacosis.pdf [accessed July 9, 2015].
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1 Not FDA approved for this indication.
2 Not available in the United States.