BIO205H5 Chapter 15: Parasitism and Infectious Diseases
Document Summary
Ectoparasites live on host organisms whereas endoparasites live in host organisms. As a group, parasites include a wide range of species that include plants, fungi, protozoa, helminths, bacteria, viruses, and prions. Among parasites that cause diseases known as pathogens those that have recently become abundant are called emerging infectious diseases. Parasite and host dynamics are determined by the parasite"s ability to infect the host. The transmission of parasites can be horizontal either through direct transmission or transmission by a vector or vertical from parent to offspring. The ability to infect a host also depends on the parasite"s mode of entering the host, its ability to infect reservoir species, its ability to jump to new host species, and its ability to avoid the host"s immune system. These fluctuations occur because transmission increases with host density but decreases as an increased proportion of the host population develops immunity. These fluctuations can be modeled using the s-i-r model.
