The present invention relates to novel protease inhibitor proteins that have been identified in ticks. These proteins may be used as components of vaccines, as inhibitors of mast cell tryptase, in detection of mast cells and in the isolation and purification of mast cell tryptase. The invention also relates to the control of diseases and injury caused by parasites in animals and humans and to the use of the proteins of the invention in the treatment of certain diseases and allergies.
