Black Fang by Susan Blexrud (The Fang Series Book 5)
Blurb: Someone is deliberately infecting bats with a deadly fungus. The flying mammals are dying by the thousands, and along with them, a significant number of vampires in bat form have also succumbed. Enter John and Lauren Wright. The vampire couple has conquered evil enemies in the past, but the perpetrator behind the bat deaths is more cunning than any they’ve encountered. Though John initially suspects that werewolves are the culprits, he discovers he is up against a colony of Unseelie faeries. The intoxicating scent of the faeries has been known to deceive vampires, pitting friend against friend—and wife against husband.