Psittacosis, also known as Parrot Fever or Ornithosis, is an infectious disease caused by the bacterium Chlamydia psitacci which can prove fatal in birds and humans. The bacterium is most commonly found in members of the Psittacidae genus such as parrots and parakeets, but it can infect any species of bird, as well as many mammals and even some amphibians.

The link between the avian and human forms of the disease was first established in 1879, but it wasn't until 1930 that any significant research was undertaken. At that time a psittacosis pandemic occurred due to bulk shipment of Amazonian parrots worldwide which led to restrictions and outright bans on psittacine imports in many countries.

C psittaci is a highly resilient bacterium which can live outside of the body for several months in ideal conditions and is excreted in faeces and mucus. The most common route of infection is by inhaling airborne particles of dried bird faeces, but the disease can also be spread by sneezing or feather dust, and any direct contact with an infected bird can lead to infection.

The form of the disease that affects birds is usually referred to as Avian Chlamydiosis, and typical symptoms include lethargy, diarrhoea, ruffled feathers and nasal discharge. In severe cases death can result, but this is much less common in the wild than in captivity. However, birds can also harbour the disease without being contagious or showing any symptoms for several years, with the disease only appearing when the bird is placed under stress. Thus, although Avian Chlamydiosis is relatively rare in the wild, it becomes much more common in imported birds as the stress and crowding involved in their transportation facilitates the spread of the disease.

In an effort to stop psittacosis at the border, many countries require imported birds to be quarantined and treated with antibiotics. Diagnosis and treatment can be carried out thus: Faeces collected over a three to five-day period can be cultured for the bacterium combined with a blood test which can be taken by an avian specialist vet that will measure the antibody and antigen levels with results in less than seven days. Treatment is best administered in vet hospital (due to reasons mentioned above) by crop feeding the antibiotic with additional multivitamin injections and fluid therapy (ie, a bird equivalent of an intravenous drip) if needed, due to the malnutrition and dehydration that is usually present by the time sick birds get presented for treatment. At least three weeks treatment is needed.

It is not that hard now to diagnose it in birds due to the recent improvement in tests available and providing you combine all three tests - faeces culture, antibody and antigen levels. Consequently it is advisable to follow basic hygiene procedures such as cleaning birdcages daily and washing after contact with birds.

While the disease can occasionally have no symptoms in humans, usually it's much more serious than in birds. Groups most at risk from infection are small children, the elderly, pregnant women, and people with pre-existing respiratory conditions (such as asthma) or impaired immunity (such as HIV). After an incubation period of up to two weeks, typical early symptoms include fever, lethargy, muscular pain and a dry cough. Unfortunately, while psittacosis is relatively easy to test for, doctors almost never check for it unless they know that the patient has been in contact with birds or until serious symptoms develop. Pneumonia often occurs in untreated cases, and infections of the heart, liver and spleen can also result.

About 300 cases of psittacosis are diagnosed annually in the UK, and about 100 cases in the USA, but it is estimated that the true number of cases is at least four times higher, as the disease is often misdiagnosed. The mortality rate is around 20% if the disease is untreated, but falls to less than 1% if the patient receives a course of antibiotics such as tetracyclines.