Psittacosis or parrot fever

Psittacosis or parrot fever is an affliction that affects humans and Psittaciformes and is also known as ornithosis (in doves and poultry). The disease is caused by the Chlamydia psittaci bacteria. The illness has been recorded in over 465 bird species and is a zoonosis, which means it could be transferred to humans. Wageningen Bioveterinary Research (WBVR) studies this zoonosis.

What causes psittacosis?

Psittacosis is caused by the Chlamydia psittaci bacteria. This is a Gram-negative bacterium capable of multiplying in cells only in the reticular body. Outside of the cell, the bacteria survive in the elementary body, which is a more compact form of the bacteria, making it more resistant to environmental influences.

Genetic studies sub-categorise C. psittaci into various genotypes. This is relevant to source research because there is a connection between the genotypes and the different hosts. Type A is found primarily in Psittaciformes, while type B is found mostly in doves.

A number of new Chlamydia strains capable of causing clinical profiles in birds similar to that of C. psittaci have been recorded since 2014. These include Chlamydia avium in doves and Psittaciformes, Chlamydia buteonis in birds of prey and Chlamydia gallinacea in poultry. To better describe diseases caused by Chlamydia in birds, the term avian chlamydiosis is generally preferred to psittacosis or ornithosis.

How are animals impacted?

In birds, psittacosis occurs mostly in Psittaciformes and doves. The clinical pictures vary from mild symptoms to severe symptoms, including secretion from the eyes and nose, coupled with a lack of appetite and diarrhoea. Asymptomatic carriers are also found among birds. Stress or other factors may decrease a bird's immune response, causing them to fall ill and transfer bacteria, making them contagious for other birds and humans. The C.psittaci bacteria is mainly transferred through faeces and secretions from the eyes and nose. Avian psittacosis is a notifiable disease.

Infection in humans

Humans are infected by inhaling contaminated dried ocular fluid, nasal secretions or faeces. The disease may range from mild flu-like symptoms to severe pulmonary infection. Pulmonary infection is the most common expression of the disease in humans, sometimes necessitating admittance to a hospital. The disease is highly treatable with antibiotics, resulting in a mortality of <1%.

How does psittacosis proliferate?

Psittacosis occurs in birds, mainly affecting Psittaciformes and doves. Birds may be asymptomatic carriers, making it difficult to distinguish between contaminated and non-contaminated birds.  C. psittaci remains contagious in the bird's faeces, long after it has dried.

How is psittacosis managed?

In the Netherlands, psittacosis is a notifiable disease for birds that are kept domestically, with the exception of poultry. This means that birds suffering from the disease or showing symptoms must be reported to the Dutch Food and Consumer Goods Authority (Dutch acronym: NVWA). If psittacosis is established, the animal is treated with antibiotics. Subsequently, the bird is tested to ensure the disease has left the body. In humans, laboratory-confirmed cases must also be reported.

How does Wageningen Bioveterinary Research contribute?

Wageningen Bioveterinary Research runs diagnostics on samples submitted by the NVWA. These are samples from birds suspected of having the disease or to trace infections in humans. The diagnostics are run on faeces and swabs from the eyes, choanae or cloaca.

The bacterium's DNA is identified using a PCR test. First, a general PCR test identifying all types of Chlamydia is run, followed by a second PCR test to confirm that the bacterium is indeed C. psittaci. Further classification (ompA classification) may reveal the C. psittaci genotype.

WBVR does not have a test to show antibodies, but the bacteria can be cultivated. This is, however, far from easy and must be done under strict safety protocols (BSL3). Thus, cultivation is not routinely carried out.

WBVR collaborates on research on the epidemiology and fighting psittacosis with the RIVM, Utrecht University Veterinary Faculty and the NVWA. Moreover, we focus on the role of new Chlamydia strains such as C. avium and C. gallinacea and on Chlamydia types such as Chlamydia caviae, which was assumed to not affect humans until recently. 

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