Introduction

Psittacosis, also commonly known as Parrot fever, is an infectious disease generally spread from birds belonging to the psittacine family. The Psittacine family consists of parrots, macaws, cockatiels, and other similar birds found in the wild as well as at home as pets. Some other birds, such as pigeons, which belong to the psittacine family, have also been reported to spread the disease. The bacterium Chlamydia psittaci, which often infects birds, is the cause of the infection.^1,2 

Psittacosis is currently in the news as a widespread infection, primarily in parrots and similar birds, and subsequently in humans in Europe. This highlights the importance of everyone being familiar with the disease.²

Pathogen and pathogenesis of Psittacosis

The disease, Psittacosis, was first described in the literature in the late 1870s, but it took more than 50 years to identify the pathogen. The bacterium C. psittaci belongs to the family Chlamydiaceae, along with two other highly infectious bacteria that also cause disease in humans. This gram-negative pathogen generally infects wild and domesticated birds, as well as other primates, and in rare cases, humans, leading to psittacosis.¹

Although we don't fully understand how the infectious cycle works yet, recent studies show that when the bacteria C. psittaci gets into the body, it first infects the cells lining the air sacs in the lungs. This sets off a response from the body's defence system, with lots of neutrophils, a type of white blood cells rushing to those cells. This defensive response is triggered by certain chemicals released by the infected cells as a signal for inflammation.³,⁴

All these activities cause damage to the lung tissue and make it easier for the bacteria to spread through the blood which makes it harder for oxygen to get into the blood, leading to low oxygen levels in the body. This can make breathing difficult and reduce the ability of the lungs to expand properly.³,⁴

Sources of transmission

Directly from the birds: The transmission is possible directly from the birds as well as from the excreta of the birds. In direct transmission, the birds shed the bacteria through the respiratory droplets and infect another bird. This type of transmission is generally significant in premises where a lot of birds are kept in captive conditions inside a single confined space such as poultry. In the case of other birds that prefer to roam in flocks, the disease transmission may also take place directly such as pigeons. From the respiratory droplets of these birds, the bacteria may enter the human body.⁵

Contaminated dust or faeces: But most often the disease transmission takes place through this route. The birds shed bacteria through the excreta as well and from the dried secretion of birds, the bacteria may enter the human body.⁵

Other ways of disease transmission are there such as bites but these methods are very rare. Human-to-human transmission is possible only in extremely rare situations.⁵

High-risk groups

Occupational exposure: People engaged in animal husbandry, specifically in poultry farming, are at greater risk than others. This risk extends from the care of poultry to the transportation of birds from one location to another. Other occupational groups at risk include pet shop owners and those who work with parrots and similar birds. Additionally, zookeepers and veterinarians are also exposed to this risk.^3,4,5

Pet ownership: People who own pets, especially birds like parrots, are also at risk. This includes not only the care of the pets at home but also activities like cleaning cages or handling birds. So, anyone who has pet birds should be aware of the potential risk of getting infected with Psittacosis.^3,4,5

Epidemiology: Though exact data isn't available, evidence from surveys conducted in the 1980s in countries like the United States provides some insight into who constituted the most at-risk groups at that time. The survey found that pet owners formed the largest group, followed by pet shop owners. Since then, the pattern of disease spread may have changed, but due to underreporting, data are mostly unavailable.³

A study conducted in China in 2022 looked at severe cases of pneumonia acquired in the community. The study found that Chlamydia psittaci, a type of bacteria, was responsible for 6.8% (15 out of 222) of the cases they looked at.³

Symptoms

Common symptoms: The symptoms of psittacosis vary a lot and can take a severe course in no time. The onset of the disease is also abrupt in nature. It may be possible that there are no symptoms as well. But typical symptoms along with upper respiratory tract infection are fever, headache, muscle pain, and coughing with no production of sputum.⁴

Fever can be moderate to high in nature generally up to 40 degrees Celsius within 2 days of the onset of clinical symptoms. After 1-2 weeks from the onset of the disease pneumonia may occur. Fever may last up to 2 weeks and the cough gets worse over time. Coughing with no or a little sputum has generally been reported. In rare cases, bloody sputum has also been recorded. Sometimes, the disease might engage the liver and spleen, which could get bigger and could cause jaundice, where the skin and eyes turn yellow. Digestive symptoms like loss of appetite, stomach aches, and diarrhoea might happen to some people.⁴

Severe symptoms: In cases of severe psittacosis, multiple organs are affected. If left untreated or if the disease is not detected promptly due to various reasons like failure to recognize the symptoms, it can lead to death.⁴

Severe symptoms can include meningitis, which is inflammation of the layers covering the brain, inflammation of the heart muscles, circulatory failure, fluid buildup in the lungs (pulmonary edema), kidney failure, and coma.⁴

Diagnosis of Psittacosis

Clinical evaluation: In this situation, knowing the person's medical history is really crucial. We need to understand how often they cough, what their cough sounds like, and if they have any specific fever patterns. A percussion test, where the doctor taps on the chest, can be done to see if there are any abnormal sounds. The sign of moist rales is evaluated, which could indicate how the disease is progressing. The doctor will also palpate the person's liver to check its condition. But to be sure about what's going on, more tests will likely be needed.^4,5

Laboratory tests: Laboratory tests are required for an exact diagnosis of psittacosis. Though culturing this bacteria is extremely problematic because it needs a living cell to complete its replication, there are other methods available that might indicate the condition.⁶

A blood test to evaluate white blood cell count is done, A NAAT (Nucleic Acid Amplification Test) is extremely important for the rapid detection of the bacteria, and specific serological tests are done to evaluate the antibody formed against the bacteria.⁶

Radiographic evaluation: X-ray radiology and CT scanning are commonly used for diagnosing and differentiating psittacosis pneumonia. Abnormalities are seen in 80–95% of cases on X-ray. The abnormalities seen on X-ray may include patchy shadowing in certain parts of the lungs, along with fan-shaped shadows spreading out from these areas. Sometimes, there are wedge-shaped shadows at the lung's outer lining. These shadows are often found in the lower part of the lungs and may vary in how dense they appear. Other signs may include signs of inflammation in the airways and lung tissue. In some cases, there may be small, round nodules and areas where lung tissue has become denser. In severe cases, the whole section of the lung may be affected.⁴

Treatment

Tetracycline antibiotics are the drug of choice. Doxycycline is especially recommended for all of the cases if not contraindicated. The preferred regimen for psittacosis is doxycycline 100 mg orally or intravenously every 12 hours for 7 to 10 days. Beta-lactam antibiotics are not effective against psittacosis.^4,6

In cases where doxycycline cannot be used, such as during pregnancy, or if it's contraindicated, macrolide antibiotics like azithromycin or erythromycin are preferred. Macrolides are considered as the second-line medicines. For children with mild to moderate infection, macrolides are the preferred choice. Tetracycline is contraindicated in pregnancy as well due to its teratogenic effect. If these sensitive patients do not show any sign of improvement after the administration of the alternative antibiotics only then tetracycline is used despite contraindication.^4,6

Fluoroquinolones are considered third-line antibiotics and are also given in some cases. Fluoroquinolones are less effective compared to tetracyclines and macrolides.⁴

Prevention strategies

Prevention is not entirely possible as there are no vaccines available for psittacosis. The only measures that can be taken involve keeping the cages of the birds clean, regularly using disinfectants, maintaining proper bird husbandry practices, and avoiding overcrowding in cages. Since human-to-human transmission is extremely rare, isolation is not recommended.^{5, 6}

Summary

In conclusion, Psittacosis, or Parrot fever, spreads primarily from birds like parrots and macaws. Caused by Chlamydia psittaci, its exact transmission is still being studied. Untreated, it affects multiple organs, emphasising early diagnosis. High-risk groups, like bird handlers and pet owners, must remain vigilant. While prevention focuses on hygiene, there's no vaccine. Treatment involves antibiotics, highlighting the need for awareness and management.