Why did he call 'Puppy Love' a disease in 'Where the Red Fern Grows'?

"Where the Red Fern Grows"

by Wilson Rawl

"I suppose there's a time in practically every young boy's life when he's affected by that wonderful disease of puppy love." Billy Coleman

The book is about a young boy love of coon huntin' and his first dog.

Billy, the main character in the book, called puppy love a disease, because it is "catchy" and you get infected with this disease from your first dog. But it is said that it is a wonderful disease. He is speaking of "puppy love" in it's truest sense, a boys love of his first dog.