Going to respond to each paragraph, went back and numbered yours in quote:1.) My concern about chicken illness is also the result of having chicks die that I bought as chicks instead of hatching them myself. They were in an outdoor brooder while my chicks are indoors but since this person has spent over $500 for a breeding pair of chickens I trusted his flock was healthy. These were chicks that were hatched in a professional incubator and hatcher while I use Little Giant incubators to hatch my own (with great results but some people don't get them to work well for them and go with more expensice incubators). I had two chicks that looked weak when I got home and they both died. They were older chicks mixed in with younger chicks that needed more heat so I thought I overheated them on the way home. Then I have lost two more that were trampled when I found them so I did not know what hapened to them. A few days ago I had another older chick down that was getting trampled so I pulled it out and noticed that it seemed to be having tremors when I held it on its back. It was keeping both legs stretched out in front of it so I was trying to figure out if there was something wrong with its legs. Looked up symptoms online and came up with a possible diagnosis of AE (Avian Encephalomyelitis) but the chick is older than three weeks so I am not sure if it is accurate. All the chicks that died are older than three weeks but less than 6 weeks old. According to what I read, if they survive they are immune but I don't know if they are carriers. It will be awhile before these chicks go outside but now I am wondering if my flock will be infected if that is what is causing chicks to die. I am also worried that my own chicks that I am hatching could be infected. I use plastic tubs for brooders with chicks of different ages in each tub so only one tub has had deaths but a second tub has chicks from the same breeder and could be infected as well. It sounds like symptoms in adults are not serious if they were to get it but it can be transmitted to their eggs (although a symptom of AEV is decreased egg production for two weeks). I may have infected my own Orpington and Silkie chicks with these other chicks but then they would basically be vaccinated from exposure, if I am understanding the virus exposure creating resistance theory correctly. Would this mean that I have nothing to worry about besides a handful of dead chicks or do I have a serious epidemic to contend with? Do I need to destroy all the exposed chicks or will they benefit from the exposure if that is what I am dealing with? Should I figure out how to test for it is any more die (only one death seems like it could be AEV at this point and that is based on my suspicion, not conclusive testing) or do I just take the losses and hope it is nothing serious?
2.) I made the mistake of buying a trio from an unethical woman in Auburn and both hens from that trio died shortly after I got them (one a day or two after I brought her home and the other about a month after I brought her home). They both died suddenly without symptoms and nothing else has died so I am hopefully it was just the stress she put them through by separating them when she kept one of them to sit on eggs for her. The rooster they were with was fine but I still do not trust buying anything from this woman again. Chances are the hens were spent before she sold them to me and that is why she was selling them (they were supposed to be laying but neither one did, although the second one that she held did not have much of a chance because it died so soon after I got her home.
3.) My hope with having a flock that is routinely tested for NPIP is that they would catch any diseases and diagnose them for me so I would know how to keep my flock disease free. Is that realistic or will all flocks have some sort of diseases that birds build antibodies to so they don't get sick. I know stress makes birds more prone to disease so adding new birds can cause stress for the new birds and the established birds as well. I want to keep a closed flock and only add chicks I have hatched and raised since that is what I have always done in the past and my chickens were always healthy but now I am afraid that adding chicks from someone else may have posed a threat to my flock. Also, what if I sell healthy birds that have been exposed to something they have a resistance against but the flock they are going to has not already been exposed? Would I risk getting someone else's flock sick by selling them my birds?
4.) I had an older chick get into the duck water this summer and when I pulled it out of the water it was sneezing. I thought that was good to get any water out of its lungs so I did not think to treat it with antibiotics. A friend wanted the chick and I told her about the sneezing when I delivered it with another chick she wanted. She had another bird that was sneezing so she put the chick from me with her young rooster to treat both with antibiotics. Her rooster recovered while the chick I sold her did not recover and died 6 to 8 weeks later. Then the other bird she got from me died suddenly 5 to 6 months after she got her. Nothing else seems to have been effected on my property or on her property so we don't know what happened. The not knowing scares me the most, though, because I don't know how to solve a problem until I can identify the problem.
5.) I have hatched and raised hundreds of chicks this summer without problems so having so many losses from the chicks I bought from someone else concerns me. I am going to stick with no more birds coming in but what about birds here and birds going out? How can I be certain none of my birds are diseased when I have had five chicks die from a batch of 18 chicks?
1) Just because someone paid a lot of money for their birds doesn't assume they're a safe source, or a good poultry person, just that they spent a lot of money I'm sorry you had to learn that particular lesson. It sucks the birds got sick and you lost them, but as you said the survivors shouldn't have an issue with it. They will pass on their superior immune systems to their offspring. Most things that are dangers to younger birds are not for older birds, so I wouldn't worry about integrating them into your flock as they age. Sometimes I'll put some vitamin/electrolyte powder in the birds water when I'm doing introductions just to give a boost to the birds. Personal anecdote, especially not knowing other breeders methods for dealing with sickness sometimes the first year, maybe two you have higher than normal mortality, but if you stick strongly to the survival of the fittest, and aren't "helping" them they will get stronger and you won't even get a hint of illness.
2) Sounds like they were very frail, and stress may have done them in (perhaps they were much older than you were told too which would make them more fragile as well?). I'd tend to agree with your thinking here and just not do business with that person any longer and make sure to tell other people if they ask your opinion.
3. NPIP only tests for PT and AI. Nothing else. It is a false security blanket. There are people that are NPIP certified that I know their stock and would never buy a bird from them, there are non-NPIP members that I trust implicitly to have healthy vigorous stock. It's worth mentioning that a small breeder may not have a choice in the matter since WA's minimum birds to get tested is 30, a lot of breeders who specialize in one breed might not even have 30 birds that would qualify. It is always possible, but unlikely, that your flock may carry a strain of something that creates a problem elsewhere, but this is remote and neither you nor the buyer has any way of knowing this beforehand. I have never had this happen on either side of the transaction and I have been breeding, showing and trading for over 20 years. I will add that dealing with longtime breeders and show breeders will drastically reduce your risks. The truth is most birds if they appear healthy and vigorous and in good condition...are.
4.) I would imagine her bird was sick, your bird was weakened due to the experience with the getting soaked and almost drowning, caught the illness from her bird and couldn't fight it off. It's the most plausible scenario so Occam likes it. The bird that died suddenly after 5 or 6 months, if it arrived ill would have been infected before that, even if your flock was susceptible to something her flock carried. Sometimes birds die. It's just the way things go. It could have gotten sick from picking something up from a wild bird, it could have eaten something toxic, it could have had a heart attack. The large time difference (and no issues in your flock) tells us it's super highly unlikely that it was anything from your flock causing the issue. You can't worry about small isolated incidents, especially in animals as fragile as chickens. It takes time and a hard-nosed stance on breeding for hardiness to overcome.
5.) It would concern me too, but I wouldn't worry about it spreading to my birds because A) It's entirely possible their genetic line is just weak and the birds just don't thrive, I had this happen a few times with different breeds, the more rare and exotic the more likely this is (I have a theory on why that may surprise some but won't put it here, ask if you want) and B) If my bird's aren't strong enough to resist it I probably don't really want to breed from them anyway, no sense passing on weak immune systems.
To recap...don't overthink the room. If your birds are healthy and vigorous, good, keep it that way (by breeding from the most vigorous, and removing birds that get sick from the breeding program, seriously I know guys that if they see a bird sneeze period they chop it's head off, I'm not and don't advocate being that extreme.) You'll only have what you tolerate, if you tolerate birds that get sick, that require constant medication or vaccination then that's all you'll ever have.
When acquiring stock from a breeder, make sure it's someone that values vigor in their breeding, inspect the birds, or if they're young inspect the parent stock if possible. Ask other breeders about people. If it's a weaker line it will take time to breed them up, know you'll have higher than normal losses, plan accordingly and hatch extras, maybe don't sell chicks (under about 4-5 months since that's when most diseases that are harsher on young birds hit) from them for a couple years.
Hopefully some of that helps put your mind at ease. I know it sounds trite to say just don't worry, but honestly that's the best policy. I went through that phase of poultry keeping, my mentor tried and tried to get me to relax, it took a while to sink in.