"I lived in Cambodia for 7 years. The average Cambodian street or neighborhood is far more a risk in many ways than any dog park in the USA. Both my dogs lived there and one is from there and they were healthy and happy. Dog immune systems are amazing things and designed to deal with most of the day to day challenges they face. The average US dog park is a far safer place for your dog than the day to day living areas most dogs deal with all over the world. The fact is we are just spoiled. And we project our fear of germs and disease onto our pets when in fact their immune systems would be better served if they had MORE exposure to the things they need to deal with."
Gee, that shows a real thorough knowledge of immune systems. So, if Cambodian children live in filth, and drink contaminated water-should you send your kids to live in the same conditions to toughen them up? I guess these all of these dog diseases are just a scam that veterinarians invented to make their boat payments? I think the OP should learn to deal with the real world, rather than postulating how people and animals, 'should' act.