In the calm space of our homes, the melodic chirping of birds conveys a sense of community and happiness. However, beneath those vibrant feathers and entrancing sounds is an unspeaking threat known as psittacosis. This infectious disease mainly spread by birds can cause serious respiratory illness in humans. Albeit the friendship we have with our feathered companion is valuable, it requires attentiveness and awareness. Read on to discover the involvements of psittacosis and respiratory infection and the vital precautions we must take to safeguard ourselves and our plumed friends.

Introduction

What is psittacosis?

Psittacosis (pronounced “sit-ah-COH-sis”) also known as parrot fever or ornithosis is an uncommon animal-borne disease caused by a bacteria called Chlamydia psittaci. This disease is rare because of limited data on human cases. For instance, according to the Centers for Disease Control and Prevention (CDC), only 58 human cases have been recorded from 2006 to 2012 in the United States. Birds are the identified primary host of the bacteria. Psittacosis is transmitted by contact with infected birds. It presents with respiratory symptoms like fever, chills, headache, and dry cough. It mostly affects people who keep birds for pets, farmers, and workers at pet stores, avian quarantine stations, zoos, and laboratories.¹

What is respiratory infection?

Respiratory infections are diseases associated with the upper and lower respiratory tracts. It can be caused by viruses, bacteria, fungi, or a parasite. These infections include influenza, common cold, bronchiolitis, otitis media, and pneumonia.^{2, 3}

Overview of psittacosis

Causes and pathogenesis

Causative agent

The causative agent of psittacosis is an intracellular bacterium (only exists or stays alive inside a host cell)  called  Chlamydia psittaci.^{1, 4}

Route of transmission

Psittacosis can be transmitted in two ways:

• Direct transmission: This occurs when humans come in contact with birds infected with the causative agent. In this case, when the infected bird bits or when there is a beak-to-mouth contact, direct transmission is possible. It is important to mention that psittacosis can not be transmitted from person to person¹
• Indirect transmission: Some birds infected with the bacteria are asymptomatic (show no sign of the disease). Contact with the infected carrier bird faeces, respiratory fluids, and urine can transmit the infection. These fluid-like secretions dry, releasing the bacteria as airborne particles and are inhaled by humans¹

Pathogenesis

The pathogenesis of psittacosis is uncertain. After transmission of the bacteria to humans, Chlamydia psittaci propagates using the host cell components. Chlamydia psittaci infects the lungs via the blood causing the associated respiratory symptoms.^{5, 6}

Clinical manifestations

Incubation period

The incubation period of Chlamydia psittaci inside the intracellular host is between 1 to 4 weeks and a majority of infected persons begin to manifest symptoms after 10 days.⁶ 

What are the symptoms of psittacosis?

In infected humans, psittacosis often presents with respiratory symptoms in addition to some non-respiratory symptoms. These symptoms include:

• Fever
• Non-productive cough 
• Chills   
• Headache 
• Muscle ache 
• Nausea 
• Vomiting  
• Diarrhoea  
• Neck stiffness 
• Sore throat 

What are the complications associated with psittacosis? 

Psittacosis spreads to other organs of the body resulting in complications like:

• Respiratory system complication:      Community-acquired pneumonia (CAP) , septic shock, acute respiratory distress syndrome acute respiratory (ARDS)
• Cardiac complications: Myocarditis, endocarditis
• Rheumatic manifestations: Arthritis
• Complications associated with the central nervous system: Encephalitis, cerebella ataxia
• Hepatitis 
• Acute renal failure  

What are the birds associated with psittacosis?

 As there are many types of avian in the world, Chlamydia psittaci can infect all types of birds, especially the following:

• Pet birds like parakeets, parrots, cockatiels, cockatoos, canaries
• Domesticated or farm birds like turkeys, ducks, chickens, and geese 
• Other birds like pigeons⁷

Who is at risk of psittacosis?

Individuals who work in an environment that places them in close contact with birds are at risk of psittacosis. They include:

• Pet shop employees
• Veterinary clinic workers
• Poultry workers
• Bird dealers 
• People who have birds as pets

How can psittacosis be diagnosed?

The diagnostic examination for the detection of psittacosis includes a range of laboratory tests and diagnostic imaging.

Laboratory test

Laboratory detection of C. psittaci infection involves the collection of samples from the patient’s respiratory fluid.

Serological test

Serology is the mainstay for the detection of psittacosis. Serological tests for C. psittaci include:

• Complement fixation (CF) testing: This is a serum test which is based on the reactivity of antibody to the chlamydial antigen¹
• Micro-immunofluorescent (MIF) antibody testing: This is a confirmatory test for serological diagnosis of  C. psittaci infection. The representative strain of C. psittaci and serovar-specific antibody responses are detected using this method. The accuracy of the result depends on the personnel's level of experience and antigen preparation¹

Polymerase chain reaction (PCR)

PCR is a very sensitive, and specific tool for molecular diagnosis of psittacosis. It has a shorter turnaround time when compared to serological tests. The challenge with this method is the unavailability of the diagnostic tool .¹

Imaging (chest X-ray)

Chest computed tomography (CT) is used to detect the presence of C. psittaci infection. A positive test does not rule out psittacosis.¹ 

Treatment and management

Antibiotics treatment

Antibiotics are often prescribed by medical professionals for the treatment of psittacosis. Antibiotics include:¹ 

• Doxycycline: This is the first-line antibiotic used for the treatment of psittacosis
• Tetracycline: This is in the same class as doxycycline and is also used for the treatment of psittacosis. It is contraindicated in pregnant women and children¹
• Minocycline: This is administered via oral and intravenous route with the dosage of 100mg twice daily⁸
• Macrolides: While tetracycline is contraindicated in pregnant women and children, macrolides, specifically azithromycin and erythromycin are used to treat the infection in these groups.¹
• Fluoroquinolones¹
• Corticosteroids¹

Supportive care

People with psittacosis should get enough rest. Adequate fluid intake is recommended to reduce dehydration resulting from vomiting and diarrhoea, which are among the symptoms of psittacosis.

What is the chance of recovering from psittacosis infection?

When treated well and the right protocol of treatment is followed, people with psittacosis recover fully within 6 to 8 weeks. Nevertheless, the rate of recovery also depends on the early detection and treatment, underlying health conditions of the patient, and disease progression.⁸

How can psittacosis be prevented and controlled?

Control measures have been set to reduce the spread and occurrence of psittacosis among humans and birds. Some of the preventive measures are:

• Creating awareness about psittacosis amongst persons at risk and healthcare providers 
• Reduce the risk of human infection when taking care of infected birds by proper cleaning of birds and their cages, good handwashing techniques, and proper disposal of bird droppings
• Do not buy or sell birds that show signs of C. psittaci infection
• Isolation of ill birds and quarantine of exposed and newly purchased birds
• Birds from different sources should not be mingled together
• Birds should be tested for C. psittaci before they are sold
• Records of all bird transactions should be kept to aid in easy identification of the source of infected birds and likely exposed persons.⁹

Differential diagnosis of psittacosis concerning respiratory infection 

Chlamydia psittaci infection presents with clinical symptoms that are the same as some respiratory infections.

1. Mycoplasma pneumonia infection: Mycoplasma pneumonia is a bacteria that causes pneumonia, basically, community-acquired pneumonia (CAP) and upper respiratory tract infection. Unlike psittacosis, CAP is transmitted from human to human through respiratory fluid droplets. Pneumonia presents with symptoms close to psittacosis. Some of the symptoms are cough, fever, chills, nausea, and vomiting, others include anorexia, tachypnea, and dyspnea^{10, 11}
2. Q fever (Coxiella burnetii): Q fever is a disease caused by a bacteria known as Coxiella: burnetii. It has flu-like symptoms like that of psittacosis. These include chills, fever, muscle aches, nausea, vomiting, tiredness, cough, chest pain, and headaches¹²
3. Influenza: Influenza also known as flu is a viral infection of the upper respiratory system caused by an influenza virus. It manifests clinically as fever, cough, sore throat, vomiting, diarrhoea, nasal congestion, headache, and myalgia¹³
4. Bacterial pneumonia: This is pneumonia caused by bacteria, affecting the lower respiratory tract. It is characterised by symptoms such as cough, fever, headache, myalgia, and tiredness¹⁴

Summary

Psittacosis is an animal-originated (zoonotic) infection caused by Chlamydia psittaci. It is most common in people who breed birds, work in poultry farms, have birds as pets, and work in zoos or veterinary clinics. The symptoms of psittacosis resemble that other of respiratory infections. Therefore, healthcare providers are encouraged to consider differential diagnosis when trying to detect C. psittaci infection. Psittacosis can be treated using prescribed antibiotics, and most infected humans recover after treatment with antibiotics.

FAQs

Is there any vaccine for immunisation against psittacosis?

Currently, there is no available vaccine for psittacosis.

Can psittacosis cause pneumonia?

When the causative agent invades the lungs, psittacosis can cause pneumonia.

Is psittacosis communicable?

No, psittacosis can not be transmitted from human to human.

Can dogs get psittacosis?

Dogs can be infected with psittacosis when they come in contact with the feces of infected birds