Chapter 34: Eukaryotic Pathogens: Fungi, Protozoa, and Helminths

Eukaryotic Pathogens: Fungi, Protozoa, and Helminths parasites establish complex relationships with their hosts, often involving specialized life cycles that require intermediate hosts, vectors, or environmental stages before infecting humans. Important helminth infections include trichinosis caused by Trichinella species, which is transmitted through consumption of contaminated meat and leads to larvae encysting in muscle tissue, producing symptoms such as fever, muscle pain, facial swelling, and potentially severe complications including cardiac or neurological damage. Diagnosis often relies on immunological assays and muscle biopsy, while treatment commonly involves benzimidazole class antihelminthic drugs. Other parasitic infections discussed include schistosomiasis, a disease caused by parasitic trematodes that differ from many other pathogens because they infect humans through direct penetration of the skin by larval stages present in contaminated water. The chapter also addresses vector transmitted protozoan diseases such as malaria, trypanosomiasis, and leishmaniasis, which involve complex life cycles and are spread by insect vectors such as mosquitoes, tsetse flies, or sandflies. Additional pathogens covered include Onchocerca volvulus, the nematode responsible for river blindness, as well as intestinal parasites that cause dysentery and systemic infections affecting multiple organ systems. Fungal infections, collectively known as mycoses, are also considered and include superficial, subcutaneous, and systemic mycoses that vary in severity depending on host immune status. Through these examples the chapter highlights the biological diversity of parasitic pathogens, the mechanisms by which they invade host tissues, and the diagnostic and therapeutic approaches used to control parasitic diseases that remain major global health concerns.