They don't really get more, you just increase the risk. And it's a question of how much a risk you are willing to take. You don't necessarily pass diseases so to say, but you can pass mites, lice, and things like worms. Chickens in every flock build up their own immunities and resistances to the things found in their environment. Strong birds can be fine, and if you chose not to keep a closed flock that is fine. But trading bird around flock to flock to flock can be a risk factor. Not an end all don't do it. Just a risk factor.
Like when you go to foreign countries, you often have to get vaccinated for stuff, are warned not to drink tap water, only eat fully cooked foods, and so on. I'm sure there are a good number of people who went to city/country and the water gave them a stomach ache, while others can drink it by the gallon. The movement of any animal, chicken or not carries a risk of introducing a factor which is undesirable. That's why there are restrictions on wild animal trades, and the smuggling of exotic birds have brought various avian viruses across continents. Emerging and re emerging diseases in humans are often exasperated by the way people move, and is one of the reasons human infectious diseases are so carefully monitored. We as a society move a lot and spread our bugs all around. In general we are healthy, but even if we look fine, we carry billions of bacteria and other stuff that could make someone sick who has never been exposed. We can test as disease free, but you have to know what you are testing for, and even then doesn't mean we don't carry stuff on us that usually don't harm people.
Like fish owners, it can take just one cute little fish on sale you bring home and put in your community tank that has been the star of health for a decade, can collapse due to some disease you never saw.
Like when you go to foreign countries, you often have to get vaccinated for stuff, are warned not to drink tap water, only eat fully cooked foods, and so on. I'm sure there are a good number of people who went to city/country and the water gave them a stomach ache, while others can drink it by the gallon. The movement of any animal, chicken or not carries a risk of introducing a factor which is undesirable. That's why there are restrictions on wild animal trades, and the smuggling of exotic birds have brought various avian viruses across continents. Emerging and re emerging diseases in humans are often exasperated by the way people move, and is one of the reasons human infectious diseases are so carefully monitored. We as a society move a lot and spread our bugs all around. In general we are healthy, but even if we look fine, we carry billions of bacteria and other stuff that could make someone sick who has never been exposed. We can test as disease free, but you have to know what you are testing for, and even then doesn't mean we don't carry stuff on us that usually don't harm people.
Like fish owners, it can take just one cute little fish on sale you bring home and put in your community tank that has been the star of health for a decade, can collapse due to some disease you never saw.
