Viruses are generally species specific, with few exceptions. Aside from the bird flu (get to the hospital and avoid contact with anyone) your bird cant catch a cold or flu virus from you. Your bird can catch a few parasites and bacterial infections however, and can likewise transmit these to you. Guinea pigs can catch a couple of rare respiratory infections, but it is highly unlikely that you are even carrying them. You should avoid allowing your bird having contact with any mucus membranes or body fluids to avoid bacterial transfer. This is pretty easy, we are talking saliva, urine, feces etc, the same precautions you should take with other people. Even if you are sick, washing your hands with normal soap and water should be sufficient to prevent any bacterial transfer. Keep in mind that most organisms you carry are completely harmless. If you have an illness that is transferable to an animal, you are very sick indeed and will need hospital attention. These are usually the scariest of pathogens and are called zoonoses. They usually only transmit across very specific species (ie HIV (non human primates), ebola (fruit bat), H1N1 (swine), bird flu (avian)). Parasites are more of an issue, and if you have a parasite odds are you will know it. Again they are almost always species specific with very few exceptions. Bed bugs prefer birds, but they arent picky feeders. Some ticks will munch on you and your birds, but they are usually one-time feeders so even if you have a tick it isnt likely to leave you for your bird. Lice and fleas are pretty picky, cat fleas will bite people but they are usually very specific. Again, if you have something moving from one species to another usually has serious medical complications.
