ABSTRACT
Introduction ................................................................................................................................... 732 Global Dissemination of Parasites ...................................................................................... 733 Parasitism as a Form of Symbiosis ..................................................................................... 734
Adaptations FOR Parasitism as a Way of Life .............................................................................. 734 Characteristics of Parasites ................................................................................................. 734 Parasite Life Cycles: Denitions ........................................................................................ 736 Mechanisms of Pathogenesis .............................................................................................. 736 Parasite Genomes................................................................................................................ 736
Protists .................................................................................................................... 736 Helminths: Cestodes, Trematodes, and Nematodes................................................. 737
Host Factors ................................................................................................................................... 737 The Immune Response ....................................................................................................... 737
The Humoral Pathway ............................................................................................. 737 Cell-Mediated Immunity ......................................................................................... 737
Parasite Evasion of the Immune Response ......................................................................... 738 The Immunocompromised Host ......................................................................................... 738
Human Parasitic Diseases .............................................................................................................. 738 Protists ................................................................................................................................ 739
African Sleeping Sickness ....................................................................................... 739 Protist Infections ...................................................................................................... 745
Helminths: Cestodes ........................................................................................................... 747 Pork Tapeworm ........................................................................................................ 748 Cestode Infections.................................................................................................... 748
Helminths: Trematodes (Flukes) ........................................................................................ 748 Schistosomiasis ........................................................................................................ 749 Trematode Infections ............................................................................................... 750
Helminth Infections: Nematodes ........................................................................................ 750 Onchocerciasis ......................................................................................................... 750
Nematode Infections ...................................................................................................................... 750 Insects/Acarids .................................................................................................................... 753
Parasite Epidemiology ................................................................................................................... 753 Epidemiology: Ways that Parasites Spread ......................................................................... 753
Insect Transmission ................................................................................................. 753 Fecal-Oral Transmission .......................................................................................... 753 Direct Blood Transmission ...................................................................................... 753 Fomite Transmission ................................................................................................ 754 Zoonotic Transmission ............................................................................................. 754 Sexual Transmission ................................................................................................ 754
The focus of this chapter is on human parasites of both cellular and multicellular organization — and particularly those that have achieved a high degree of prominence for the diseases they cause. In size, they range from protists* of microscopic dimensions to tapeworms that can attain a length of 20 to 30 feet. Parasitology is a broad discipline lling many tomes dedicated solely to the topic, as well as focused chapters in medical and veterinary texts. The reader is encouraged to consult these more extensive treatments for a fuller understanding of the human-parasite associations. In many ways, human parasitology as a science was a benecent spin-off of colonialism, with imperialist nations founding institutes devoted to tropical medicine and seeking ways of protecting their nationals from diseases while serving abroad.
