The incubation period for psittacosis is 1 to 4 weeks. The majority of infections cause symptoms in 5 to 14 days.

Symptoms

• Community-acquired pneumonia: influenza resembling symptoms, non-productive cough, dyspnea, soreness of the throat, nosebleed, pleuritic chest pain (rare), signs of systemic illness, fever, lethargy. It may follow a gradual, subtly evolving course or arise rapidly with acute sepsis and respiratory failure.
• Gastrointestinal symptoms: nausea, vomiting, abdominal cramps, diarrhoic phenomena and jaundice. These symptoms are not particularly common.
• Neurological symptoms (commonly observed): severe headache, photophobia, or extreme weakness.
• Dermatological symptoms: facial rash (Horder's spots), resembling the manifestations of the spots observed in typhoid fever.

Signs

Psittacosis often causes cardiac involvement, including bradycardia, pericarditis, endocarditis or myocarditis. Signs of pneumonic consolidation may arise, although a chest examination does not produce any characteristic results. Chest x-ray can also unveil the degree of pulmonary involvement. A less common feature observable by a physical examination is splenomegaly, which, if accompanied by  pneumonia, makes the diagnosis of psittacosis more likely. Dermatological signs include Horder's spots, erythema nodosum, or erythema multiforme.

A detailed medical history is vital for the direction of diagnostic tests towards a possible C. psittaci infection. Should the symptoms resemble those of psittacosis, a physician has to inquire about possible contact to birds, such as canaries and parrots, or other mammals. In many occasions, pets or domesticated birds and animals that are infected with the bacterium can simultaneously transmit it to the whole family; therefore, a family history of symptoms similar to the patients' should also raise suspicion of a potential psittacosis case.

A thorough physical exam should also be conducted in order to establish the existence of typical findings: fever, pharyngeal erythema, diffuse rales, hepatomegaly, splenomegaly and potentially, tachycardia [1], are all compatible with a respiratory psittacosis. More specifically, an erythema of the sclera is usually the one and only finding in cases of psittacosis strictly confined to the eye [11].

Blood tests are also useful in detecting markers of mild inflammation and serological markers. The white blood cell count will most likely be found normal or augmented with a left shift and sometimes eosinophilia is present. Liver enzymes are normal or slightly elevated. As far as serology is concerned, microimmunofluorescence (MIF) antibody is used to detect a C. psittaci infection. Cultured pleural fluid, sputum or blood may also produce a positive result, but the procedure should not be attempted by professionals without much clinical experience, since there is a significant danger of creating aerosolized particles and contaminating the laboratory grounds. Regarding imaging techniques, a chest x-ray may unveil the presence of cellular exudate in the pulmonary alveoli, a typical finding of pneumonia [1].

Sputum tested by means of a polymerase chain reaction (PCR) is a relatively new test for detecting a C. psittaci infection. Its use is currently limited and has primarily been applied to unveil the presence of C. psittaci in tissue harvested from animals [12].

First-line treatment of psittacosis includes tetracycline or doxycycline for 2-3 weeks to prevent the potential relapse [6]. In cases where the aforementioned treatment is not indicated, erythromycin may alternatively be administered. ICU or high-dependency treatment may be a necessity for patients with severe coexisting pathologies.

Patients with a C. psittaci infection greatly benefit from a therapeutic scheme including antibiotic agents. Symptoms usually subside within 24 hours, even though symptomatology can re-emerge in cases of persistent infection [1].

Patients with severe symptomatology are in risk of succumbing to potentially fatal complications, such as pulmonary and cardiac incidents [1], should proper IV drugs not be administered promptly. Antibiotic resistance has been reported by non-scientific data and concerns azithromycin [10].
Mortality can amount up to 20% in patients who do not receive any treatment [1].

Psittacosis is a result of an infection with chlamydia psittaci and is a disease known to the medical community for over a century [3]. People can contract the bacterium from direct contact with poultry, birds, mammals, or their secretions, excrement and tissue. Therefore, individuals whose profession involves close contact to potentially infected animals do run a higher risk of contracting C. psittaci [4]. Bacterial transmission from one person to another is a rare observation [5] [6].

Psittacosis' frequency has followed declining pattern, as far as the industrialized world is concerned, although it can be observed in any part of the world. Data indicates that from 1988 to 2003, the Center for Disease Control and Prevention (CDC) recorded 935 reports of psittacosis; the average incidence of the disease was 62 cases per year [7]. However, in the time period 2005 to 2009, only 66 additional cases reached the CDC, and so, averagely 16 human cases per year were recorded [8]. It is, however, believed, that in reality, the number of psittacosis-affected patients was larger and remained undiagnosed because the condition responds well to antibiotics administered empirically for cases of pneumonia.

Mortality rate used to amount to a staggering 15-20% in the past, due to lack of appropriate treatment. With the advent of antibiotics, the numbers have decreased to 1%. Psittacosis can affect people of all ages, ethnicities and genders. A slight increase of the number of people who contract C. psittaci in the industrialized world may be explained by the importation of exotic birds to these countries.

Psittacosis can affect all people irrespective of age, but is usually observed amongst people in their middle decades.

C. psittaci has a specific two-phased developmental cycle, featuring the contagious elementary body form (EB) and the reticulate body form (RB). While in the EB form, the bacterium latches on to the host cell and is endophagocytosed. It is then surrounded by an inclusion body, which assists the bacterium in its survival, as the lysosomes are unable to penetrate the structure. The EB then transforms into a replicating RB and produces the so-called intermediate bodies, where chromatin subsequently follows a condensation process, transforming into an EB. Cell lysis or exocytosis are the procedures responsible for EB's release from its host; the cell sustains no damage itself and the newly-produced EBs can further infect other cells in the vicinity, something which is expected to happen 36-48 hours after contagion [1]. 

C. psittaci can be cultured in various substrates, but protective measures and caution are advised, for fear of producing aerosolized particles. Aerosolized particles and contact with excrement, nasal secretions, or tissue are the ways a human can get infected. 7 known C. psittaci genotypes have been identified, all of which can be contracted by humans [9]. The length of its maturation cycle and its endurance are the factors that probably result in chronic infection, which cannot be eradicated with the usual antimicrobial medication. There are also bacterial types that are deemed more lethal. For a treatment scheme to be successful, a longer period of antibiotic administration is necessary; even in these cases, some patients may still have sustained difficult-to-eradicate infection.

One of the first measures one can take to prevent psittacosis is making sure that pet birds will not contract it themselves. Measures include: cleaning birdcages daily, taking good care of pet birds to prevent an infection, proper food and enough space, so they are not always close to one another in the cage. If there are more cages with birds, keeping the cages at a distance will prevent excrement and other biological substances from being transferred from one cage to another.

Any new bird expected to join the cage should be kept at separate surroundings and monitored for at least 30 days, before it can be placed together with other birds.

Psittacosis is an infectious disease caused by Chlamydia psittaci, an obligate, intracellular, gram-negative bacterium [1]. The primary hosts of C. psittaci are birds and mammals, with humans being only accidental hosts [1]. Humans can get infected irrespective of age; contracting the bacterium results in conjunctivitis and community-acquired pneumonia [1] [2]. Psittacosis also goes by the names parrot fever and ornithosis, and is sometimes reserved for the disease when it is carried by birds of the Psittacidae family; ornithosis is used when other birds are the disease carriers.

Psittacosis is a contagious disease caused by Chlamydophila psittaci. It is a type of organism (bacterium), which infects birds and mammals and can infect humans who come into contact with their excrement and secretions. People who run a higher risk for contracting C. psittaci are those who have direct contact to animals: veterinarians, bird owners, pet shop employees. The birds that are most frequently infected are parrots, parakeets, and budgerigars, although other birds and animals can also be affected by the disease and transmit it to humans. Typical symptoms include fever, chills, head and muscle aches, blood in one's sputum and malaise.

In order to diagnose the disease, a physician will carry out a detailed physical examination and will also ask for a detailed medical history. Other laboratory tests on sputum and blood, a chest CT scan or x-ray can also contribute to the successful diagnosis of a psittacosis infection. Patients are treated with antibiotics upon the diagnosis and are expected to have a full recovery, if they have no other diseases.

In order to prevent the disease, avoid exposure to birds that you suspect to be ill, such as imported parrots or unknown birds. Take good care of other conditions you might be affected by, so that your immune system is as strong as possible against all types of infection.

1. Schlossberg D. Chlamydophila (chlamydia) psittaci (psittacosis). In: Mandell GL, Bennett JE, Dolin R, eds. Principles and practice of infectious diseases, 6th ed. Philadelphia, PA: Churchill Livingston; 2005:2256-2258.
2. Dean D, Kandel RP, Adhikari HK, et al. Multiple Chlamydiaceae species in trachoma: implications for disease pathogenesis and control. PLoS Med. 2008;5:e14.
3. Harris RL, Williams TW Jr. "Contribution to the question of pneumotyphus": a discussion of the original article by J. Ritter in 1880. Rev Infect Dis. 1985;7:119-122.
4. Gaede W, Reckling KF, Dresenkamp B, et al. Chlamydia psittaci infections in humans during an outbreak of psittacosis from poultry in Germany. Zoonoses Public Health. 2008;55:184-188.
5. Harkinezhad T, Geens T, Vanrompay D. Chlamydia psittaci infections in birds: a review with emphasis on zoonotic consequences. Vet Microbiol. 2009;135:68-77.
6. Ito I, Ishida T, Mishima M, et al. Familial cases of psittacosis: possible person-to-person transmission. Intern Med. 2002;41:580-583.
7. Smith KA, Bradley KK, Stobierski MG, et al. Compendium of measures to control Chlamydophila psittaci (formerly Chlamydia psittaci) infection among humans (psittacosis) and pet birds, 2005. J Am Vet Med Assoc. 2005 Feb 15. 226(4):532-9.
8. Smith KA, Campbell CT, Murphy J, et al. Compendium of measures to control Chlamydophila psittaci infection among humans (psittacosis) and pet birds (avian chlamydiosis), 2010. J Exotic Pet Med. 2011 Jan. 20 (1):32-45.
9. Vanrompay D, Harkinezhad T, van de Walle M, et al. Chlamydia psittaci transmission from pet birds to humans. Emerg Infect Dis. 2007;13:1108-1110.
10. Binet R, Maurelli AT. Frequency of development and associated physiological cost of azithromycin resistance in Chlamydia psittaci 6BC and C. trachomatis L2. Antimicrob Agents Chemother. 2007;51:4267-4275.
11. Dean D. Pathogenesis of chlamydial ocular infections. In: Tasman W, Jaeger EA, eds. Duane's foundations of clinical ophthalmology. Philadelphia, PA. Lippincott Williams & Wilkins, 2010.
12. Sprague LD, Schubert E, Hotzel H, et al. The detection of Chlamydophila psittaci genotype C infection in dogs. Vet J. 2009;181:274-279.