from Hany M. Elsheikha and Naveed Ahmed Khan writing in Essentials of Veterinary Parasitology:
We tend to think of parasites as a nuisance, but they are in fact very serious disease-causing agents. Despite advances of veterinary medicine, parasitic diseases have remained a major cause of morbidity, mortality and economic losses, worldwide. With the increasing burden of parasites on human and animal suffering, study of "parasitology" has become an important and rapidly growing discipline of science. Veterinarians' awareness of parasitic diseases is undoubtedly more critical now than at any time in the history of veterinary medical practice. This chapter provides a short introduction to parasites and their unique properties.
Further reading: Essentials of Veterinary Parasitology