NOTE: Dr Mike must answer questions here FIRST. Then others may continue the thread. I removed a members post here for that reason and Dr Mike is answering that members and Monas post together. Jerry
Hi, here comes my take:
First, Streptococcus is a genus of bacteria – NOT virus. There are a number of species of Streptococcus. The one that we commonly get as an infection in our tonsils and throat is, indeed, capable of infecting birds. So are several others that are not as common and are mainly found in agricultural animals, causing mastitis in cows, and pneumonia in pigs.
In general, there are three reasons a bacteria is able to cause infection:
1). Some species are just extremely virulent and are able to attack a strong, healthy system. the strep infections people get are one - the Jack-in-the-box strain of E. Coli is another. This mode of infection is quite rare, compared to the other two
2). Overwhelming or large-dose exposure to opportunistic bacteria. Good sanitation usually prevents this.
3). The most common is infection by opportunistic bacteria because of reduced immune response. This can happen in times of stress, poor nutrition, or concurrent disease conditions. Make no mistake, many of our birds are experiencing a good deal of stress at least some of the time. Of the several times I have been infected with psittacosis, for example, only once did it really make me very sick. This was a time in my life when I was under tremendous stress and the infection nearly killed me.
When we get a “cold”, this disease in us is caused by a virus. This virus does not, itself, readily infect our birds. Their body temperature is too high (106 degrees) for it to do well. This is, in fact why we get a fever when infected by viruses – it is one of our body's ways to fight them.
However, we do harbor a number of bacteria – normally found in our mouths, sinuses, and eyes, that can infect birds, if given the chance (Number 2 or 3 above). These bacteria I speak of include, but are not limited to, other species of Streptococcus than the one that infects us that we carry around all the time that don't bother us a bit, but can infect birds.
When we have a cold, we tend to cough and sneeze a lot. This liberates large numbers of these bacteria, which are opportunists to the bird, into the air. We end up contaminating our faces, hands, clothes, as well as their feathers, food and water dishes, cages, etc.
They are then more likely to become exposed to them when they come into contact with any of these surfaces.
Sometimes, conditions (like french-kissing your bird - yuk) are ideal for these bacteria to get into the bird by inhalation or ingestion and cause infection.
Their trachea does communicate with their sinuses when their mouth is closed. It connects and seals to the choana. The upper respiratory (sinus) infections they get do usually manifest with sneezing and runny nose.
The symptoms of tail-bobbing and increased effort in breathing are usually attributed to either middle airway (trachea) or lower airway (lungs or airsac) disease.
Birds with even quite severe upper (sinus) airway disease rarely show much difficulty in getting air in and out of the airsacs and through the lungs. They also don't usually show systemic signs of illness until and unless the infection extends down into the middle or lower parts of the respiratory system. They do often sound wet and gurgly, but only when their mouth is closed.
Its as “simple” as that.
BTW, one of my Amazons can rival the sound of a sneeze with the best of them - whenever anyone sneezes or coughs, she chimes in with her version - it is SOOO cute, a very dramatic ahhhhhhhhhh - CHEEEW!