Fungi and Protozoans

Dermatophytoses (Ringworm / Tinea infections)

Dermatophytoses are skin diseases caused by dermatophyte fungi that invade keratinized tissues of the epidermis, hair, and nails, leading to dermatomycoses known as ringworm. These contagious infections include Tinea corporis (body), Tinea cruris (groin), Tinea capitis (scalp), Tinea unguium (nails), and Tinea pedis (feet). Infection occurs through contact with contaminated environments or fomites. Treatment requires antifungal drugs for many weeks, and Tinea pedis may lead to a secondary bacterial infection.

Candidiasis

Organism: Candida albicans. Candidiasis is an opportunistic fungal infection caused by Candida albicans, which is part of the normal human flora. It can cause thrush, vaginitis, tissue infections, and is the most common nosocomial fungal infection. In immunocompromised individuals, the organism may spread systemically and become life-threatening.

Candida auris

Organism: Candida auris. Candida auris is an emerging opportunistic fungal infection of major global concern. It primarily affects hospitalized patients and often enters the bloodstream, spreading throughout the body. The organism is highly resistant to antifungal drugs and requires special laboratory methods for identification.

Vulvovaginal Candidiasis

Organism: Candida albicans. Vulvovaginal candidiasis is a reproductive system opportunistic infection caused by Candida albicans. It commonly occurs with uncontrolled diabetes, changes in vaginal pH, hormonal changes, or long-term antibiotic therapy.

Trichomoniasis

Organism: Trichomonas vaginalis. Trichomoniasis is a sexually transmitted protozoan infection of the urogenital tract in both males and females. Many infections are asymptomatic; females are more likely to have symptoms, while males rarely do. Trichomonas hominis and Trichomonas tenax are normal commensals.

Coccidioidomycosis (Valley Fever)

Organism: Coccidioides immitis. Coccidioidomycosis is a respiratory fungal disease acquired by inhalation of spores, commonly in the southwestern United States. Infection is often mild or asymptomatic. In tissues, the organism forms thick-walled spherules filled with spores used for diagnosis. Complications include spread to the meninges or bones.

Histoplasmosis

Organism: Histoplasma capsulatum. Histoplasmosis is a respiratory and systemic fungal disease caused by inhalation of soil spores that mature into yeast-like cells in the lungs. The organism survives and multiplies inside macrophages, allowing dissemination throughout the body. It is usually mild but can cause pneumonia and infections of the spleen, liver, and lymph nodes.

Pneumocystis Pneumonia (PCP)

Organism: Pneumocystis jirovecii. PCP is an opportunistic respiratory fungal infection that invades lung cells. Healthy individuals usually have few or no symptoms, but immunocompromised patients, especially those with AIDS, can develop severe pneumonia. The disease has a high fatality rate if untreated and may spread to other organs.

Blastomycosis

Organism: Blastomyces dermatitidis. Blastomycosis is a respiratory and systemic fungal disease acquired through inhalation of endospores or entry through wounds. The spores mature into yeast cells and are transported by macrophages through the circulation, leading to systemic infection and extensive tissue damage.

Aspergillosis

Organism: Aspergillus fumigatus. Aspergillosis is an opportunistic respiratory fungal disease caused by inhalation of spores found in decaying vegetation. The organism infects the lungs and can become invasive, leading to asphyxiation, particularly in individuals with AIDS or weakened immune systems.

Giardiasis

Organism: Giardia duodenalis (also called G. intestinalis or G. lamblia). Giardiasis is a digestive system protozoan infection acquired by ingestion of cysts that mature into trophozoites in the small intestine. The trophozoites attach using an adhesive disk, causing severe diarrhea, dehydration, and impaired absorption. The cysts are not killed by chlorination.

Amebiasis (Amebic Dysentery)

Organism: Entamoeba histolytica. Amebiasis is a digestive system protozoan disease that may be acute or chronic. Infection occurs when cysts are ingested and mature into trophozoites in the colon. The organism can invade the intestinal lining and bloodstream, causing tissue damage and potentially peritonitis. Some individuals are asymptomatic carriers, and cysts resist normal chlorine levels.

Cyclosporiasis

Organism: Cyclospora cayetanensis. Cyclosporiasis is a digestive system protozoan infection caused by ingestion of oocysts in contaminated water or food such as berries. The disease results in watery diarrhea and is caused by a relatively recently identified protozoan.

Cryptosporidiosis

Organism: Cryptosporidium hominis and Cryptosporidium parvum. Cryptosporidiosis is a digestive system protozoan infection acquired by ingestion of oocysts that mature into sporozoites in the small intestine. It can cause life-threatening diarrhea in immunodeficient individuals, and contaminated water is the usual source.

Visceral Leishmaniasis

Organism: Leishmania donovani. Visceral leishmaniasis is a cardiovascular and lymphatic protozoan disease transmitted by sand fly bites. The organism survives and multiplies within macrophages and can cause extensive damage to the liver, spleen, and kidneys if untreated. It is increasingly recognized as an opportunistic infection in HIV patients.

Malaria

Organism: Plasmodium species. Malaria is a cardiovascular protozoan disease transmitted by the bite of an infected female mosquito. Sporozoites enter the bloodstream, travel to the liver, and develop into merozoites that infect red blood cells as trophozoites. Periodic RBC rupture causes fever spikes. Sickle cell trait provides protection. Plasmodium falciparum causes the most severe disease and shows chloroquine resistance. Control includes mosquito management and the Mosquirix vaccine, which provides limited protection in children.

Chagas’ Disease (American Trypanosomiasis)

Organism: Trypanosoma cruzi. Chagas’ disease is a cardiovascular and lymphatic protozoan disease transmitted by the reduviid bug and seen sporadically in the southern United States. Early symptoms include fever and swollen glands, with progression to chronic disease causing nerve damage to the heart, skeletal muscles, and colon. Congenital transmission can occur, and treatment is difficult in the chronic stage due to intracellular replication.

Toxoplasmosis

Organism: Toxoplasma gondii. Toxoplasmosis is an opportunistic protozoan infection acquired from cat feces or undercooked meat. Oocysts mature into trophozoites within host cells. The infection is usually mild and self-limiting but can cause congenital defects if transmitted across the placenta and severe disease in individuals with AIDS. Research is investigating a possible link to schizophrenia.

Cryptococcosis

Organism: Cryptococcus neoformans. Cryptococcosis is an opportunistic nervous system fungal disease caused by a budding yeast carried by birds. Infection occurs through inhalation or ingestion and often becomes systemic, spreading to the central nervous system. It is a common cause of meningitis in people with AIDS.

African Trypanosomiasis (Sleeping Sickness)

Organism: Trypanosoma brucei (T. b. rhodesiense and T. b. gambiense). African sleeping sickness is a nervous system protozoan disease transmitted by the tsetse fly. The organism infects multiple organs and progressively damages the central nervous system, leading to death if untreated. Vaccine development is unsuccessful due to antigenic variation.