Chapter 40: Fungal & Protist Diseases in Humans

Fungal infections are classified into five clinical groups: superficial, cutaneous, subcutaneous, systemic, and opportunistic. The systemic mycoses, such as blastomycosis, coccidioidomycosis (valley fever), and histoplasmosis, are typically caused by dimorphic fungi and are acquired when a susceptible host inhales spores from contaminated soil in specific endemic areas. A significant portion of the chapter focuses on formidable protozoal diseases transmitted by arthropod vectors, including malaria, caused by Plasmodium species injected by the Anopheles mosquito, which exhibits a complex life cycle involving liver and red blood cells, resulting in characteristic paroxysms. Other vector-borne diseases reviewed include leishmaniasis, spread by sand flies and classified as cutaneous, mucocutaneous, or visceral, and trypanosomiasis, which encompasses African sleeping sickness (tsetse fly vector) and American Chagas disease (triatomine bug vector). Direct contact routes transmit dermatophytes that cause common cutaneous infections known as tineas (e.g., ringworm, athlete’s foot) and subcutaneous mycoses like sporotrichosis, as well as the sexually transmitted protozoan infection trichomoniasis. Critical food and waterborne protozoal diseases, such as amebiasis, giardiasis, and chlorine-resistant cryptosporidiosis, are detailed, alongside toxoplasmosis, a zoonotic illness often linked to felines and consumption of undercooked meat. Finally, the text explores opportunistic fungal pathogens, including Aspergillus, Candida, and Cryptococcus, which exploit compromised host immunity—due to factors like HIV or chemotherapy—to cause severe, disseminated, and often fatal infections like Pneumocystis pneumonia (PCP).