Psittacosis: causes, symptoms, diagnosis, treatment, and prognosis

Psittacosis, also known as parrot fever, ornithosis, or avian chlamydiosis, is a contagious disease caused by Chlamydia psittaci, and is mainly characterized by conjunctivitis, rhinitis, and diarrhea.


Causes

This disease is caused by Chlamydia psittaci that is present mainly in the gastrointestinal and respiratory tract of diseased birds and can produce a hemagglutinin that can agglutinate erythrocytes in mice and chickens. Chlamydia psittaci has a weak resistance and can be inactivated at 60 °C for 10 minutes or 37 °C for 48 hours, in 0.1% formaldehyde or 0.5% phenol for 24 hours or ether for 30 minutes, or in ultraviolet irradiation, but is resistant to low temperatures and remains infectious at -70 °C for many years. Multiple Chlamydia inclusion bodies can be seen in the infected cells.

Mode of transmission

The source of infection is the diseased birds and carriers with Chlamydia psittaci. More than 140 species of birds can infect and carry this pathogen, including pigeons, fowls, ducks, and seabirds.

Route of transmission

Respiratory tract infection is the most common, mostly the droplets and dusts contaminated by excrement. Human infection is usually caused by the inhalation of the feathers or dusts contaminated by excrement of the infected birds. Human-to-human transmission may be associated with highly virulent strains. Bird-to-bird transmission is mainly through the digestive tract, and serious contamination of the feedstuffs can cause epidemics in birds.


Signs and Symptoms

The incubation period is 1 - 2 weeks, maximally up to 45 days. The clinical manifestations of the disease are diverse. The disease can occur and develop slowly, and the body temperature gradually rises within 3 - 4 days or longer. However, rapid onset is more common, and high fever, chills, relative bradycardia, general malaise, exhaustion, and anorexia are often present. Severe headaches and generalized myalgia are the common chief complaints. Myalgia in the extremities and trunk can prevent patients from standing up. Due to the spasms and stiffness of the back and neck muscles, the disease may be misdiagnosed as meningitis. Some patients have nosebleeds or rashes. Cough and serous or bloody sputum can occur about 1 week after onset. Severe patients may have dyspnea, cyanosis, irritability, convulsions, catalepsis, and coma. Some patients have gastrointestinal symptoms such as nausea, vomiting, and diarrhea. If jaundice occurs, the liver is involved.

Thrombophlebitis can occur during the recovery period. Sometimes pulmonary infarction in the late stage can cause death. In addition, complications such as endocarditis, myocarditis, pericarditis, icterohepatitis, suppurative otitis media, and acute bronchitis may occur, but are less common.

Mild patients have only pharyngeal congestion and focal pulmonary fine moist rales. In severe patients, lung consolidation may be present, and the liver, spleen, and superficial lymph nodes may be swollen.


Diagnosis

If there are high fever, relative bradycardia, severe headache, myalgia, pneumonia, and a history of exposures to birds, the disease should be considered. The pathogen found in the blood or bronchial secretions, or 4-fold elevation in titer of two complement fixing antibody tests, a definitive diagnosis can be provided.


Treatment

The disease can be treated with antibiotics such as tetracycline and doxycycline. The treatment regimen is tetracycline 0.5g orally 4 times a day or doxycycline 100mg orally twice a day for 10 - 14 days. In order to prevent recurrence, the duration of medications can be up to 21 days. If oral administration is inappropriate, tetracycline 0.5g diluted with 200ml of glucose solution intravenously can be used. Penicillin G 2,000,000U a day intramuscularly or intravenously can also be used. Erythromycin can be given to children. Symptomatic therapy should also be appreciated, and for patients with eating problems, rehydration should be performed. Oxygen therapy or mechanical ventilation should be given to patients with respiratory embarrassment.


Prognosis

If untreated, the disease can be life threatening, but most patients can recover in 10 - 21 days. Death may occur in few patients with severe pneumonia, myocarditis, jaundice, and encephalitis. The recurrence rate is about 21%. The number of reinfections ranges from 2 to 5 times, but repeated episodes within 8 - 12 years have been reported. The mortality rate was 20% - 40% before antibiotic application, and is less than 2% currently.