Gorgle
Gorgles are small, disease-laden bat-like creatures that dwell in dank dungeons and foul forests. They superficially resemble bats with a wingspan of perhaps 1' across, but on closer inspection they are not mammals at all, but some sort of glabrous, oozing amphibian-like creature. They are often kept as pets by troglodytes, froglings, and other such creatures.
AC 7 [12], HD 1 (4 hp), Att 1 x bite (1 + disease) THAC0 19 [+0], MV 30' (10') / 180' (60') flying, SV D14 W15 P16 B17 S18 (NH), ML 6, AL Neutral, XP 10, NA 1d20 (3d10), TT Nil
The bite of an individual gorgle is not deadly, but after each bite the target must roll their Constitution or lower on 3d6. Those failing contract gorgle fever. It has an onset of 1d4 days and affects the victim's eyesight. The victim beomes extremely sensitive to light, suffering a -1 penalty to all rolls made while in sunlight or equivalent. The victim may attempt a CON check for each day they suffer from the disease. Those rolling equal to or under their CON are able to throw off the disease. If the victim is under the care of a healer roll 2d6, if simply resting (ie no other activities) roll 3d6, and if active roll 4d6. A cure disease spell will also cure the victim.
If 11 or more gorgles are encountered one of them will be a 2 HD version with a much more virulent bite, doing 1d4 damage and requiring those to roll their CON or lower on 4d6 to avoid infection.