Here is information about PLN:
http://www.vimpva.com/articles/Prote...0in%20Dogs.pdf
The reason I believe both girls are doing well is that it was picked up before there were symptoms. One of the most important things to do is minimum yearly blood work on pups...and every 6 months for older ones.
It also is why I constantly preach about taking pups to a vet at the first signs of illness because often people wait and wait and it is too late to turn the pup around. Not that anything is guaranteed .. but I think you are more apt to be successful if you opt to do a bit of prevention.