Psittacosis is a bacterial infection in birds, caused by the Chlamydia bacteris. it is like pneumonia and it can be transmitted between species and to humans.

It is very contageous it is often know as the Parrot desease although can spread across many species and is common in Pigeons and Doves.

In medicine (pulmonology), psittacosis — also known as parrot disease, parrot fever, and ornithosis — is a zoonotic infectious disease caused by a bacterium called Chlamydophila psittaci (formerly Chlamydia psittaci) and contracted not only from parrots, such as macaws, cockatiels and budgerigars, but also from pigeons, sparrows, ducks, hens, sea gulls and many other species of bird. The incidence of infection in canaries and finches is believed to be lower than in psittacine birds.

http://en.wikipedia.org/wiki/Psittacosis

Also known as parrot fever, it is a very infectious disease of parrots and related species. It is caused by a bacterium (Chlamydia psittaci) which may infect humans. A human with psittacosis may suffer from high fever, severe headache, and symptoms like those of pneumonia.

It's a really terrible disease her in the US. When it shows it's ugly head, we go under tighter quarantine. If one bird shows up with it, they will come in an kill all of your birds, no questions or pleas or anything. They are trying to protect the chicken and turkey industry as they are very susceptible to the disease, too. I remember back in the 80s they were doing raids on bird owners homes looking for smuggled birds. It was scary!