Factors of Parasitic Virulence

Why do some parasites kill the host they depend upon while others coexist with their host? Two prime factors determine parasitic virulence: the manner in which the parasite is transmitted, and the evolutionary history of the parasite and its host. Parasites which have colonized a new host species tend to be more virulent than parasites which have coevolved with their hosts. Parasites which are transmitted horizontally tend to be more virulent than those transmitted vertically. …

…and Host Behaviour. Barnard, C. J. and Behnke, J. M. Eds. Taylor & Francis. London. Read, A. F. and Harvey, P. H. 1993. The evolution of virulence. Nature. 362:500-501. Toft, C. A. and Aeschlimann, A. 1991. Introduction: Coexistence or Conflict? pp. 1-12 In Parasite-Host Associations: Coexistence or Conflict? Oxford University Press. Oxford. Wise, L. A. (1990) Small Animal Medical Nursing pp. 226-261 In Clinical Textbook for Veterinary Technicians, Second Edition. McCurnin, D. M. Ed. W. B. Saunders Company. Philadelphia.