The Fungi of Medical Importance

1. The Fungi of Medical Importance Chapter 22

2. Fungi as infectious agents • molds & yeasts are widely distributed in air, dust, fomites & normal flora • humans are relatively resistant • fungi are relatively nonpathogenic • of the 100,000 fungal species, only 300 have been linked to disease in animals • fungi are the most common plant pathogens • human mycoses are caused by both true pathogens and opportunistic pathogens

3. Mycoses (general statements on) • Most fungal pathogens do not require a host to complete their life cycles and infections are not communicable • Dermaphytes & Candida sp naturally inhabit human body & are transmissible • Dermaphytoses most prevalent fungal infection • Most cases go undiagnosed or misdiagnosed • Infections can be systemic, subcutaneous, cutaneous or superficial

4. Levels of invasion

5. Mycoses • immunity to fungal infections consist of nonspecific barriers, inflammation & cell mediated defenses • diagnosis & identification require microscopic examination of stained specimens, culturing in selective & enriched media & specific biochemical & serological tests • control with Antifungals such as amphotericin B, flucytosine, azoles & nystatin

6. Antifungal Therapies • Mycoses are among the most difficult diseases to heal • Fungi can often resist the oxidative damage of T cells during cell-mediated immune responses • Fungi are biochemically similar to human cells and antifungal drugs can harm human tissues • Fungi have ergosterol in their membranes rather than cholesterol and it is often a target for antifungal treatment • Side effects can still result, especially with long-term use

7. Systemic mycoses caused by true pathogens • Thermal dimorphism • Restricted to certain endemic regions of the world • Soil is normal habitat • Infection by inhalation of spores  Pulmonary infections • Histoplasma capsulatum • Coccidioides immitis • Blastomyces dermatitidis • Paracoccidioidomycosisbrasiliensis

8. Thermal Dimorphism 25 degrees - Hyphal state………………..37 degrees – Yeast state Thermal dimorphism is a property of true fungal pathogens but is uncommon for opportunistic pathogens

9. Distribution of True Fungal Pathogens

10. Histoplasmacapsulatum • causes histoplasmosis • typically dimorphic • distributed worldwide, most prevalent in eastern & central regions of US • grow in moist soil high in nitrogen content (bat and bird droppings) • Inhalation of organism produces primary pulmonary infection that may progress to systemic involvement of a variety of organs & chronic lung disease • amphotericin B, ketoconazole

11. Histoplasma capsulatum Areas with large amounts of bird droppings are esp. dangerous

12. Coccidioidesimmitis • causes coccidioidomycosis • dimorphic • lives in alkaline soils in semiarid, hot climates & is endemic to southwestern US • spores inhaled from dust leads to primary pulmonary infection which can progress to system body-wide disease • amphotericin B treatment

13. Coccidioides immitis

14. Coccidioides immitis Disseminated coccidiomycosis

15. Blastomycesdermatitidis • causes blastomycosis • dimorphic • free-living species distributed in soil of a large section of the midwestern and southeastern US • inhaled spores convert to yeasts & multiply in lungs • symptoms include cough & fever • chronic cutaneous, bone, & nervous system complications • amphotericin B

16. Blastomyces dermatitidis Hyphal state Yeast state

17. Blastomycesdermatitidis Cutaneous blastomycosis

18. Paracoccidioidomycosisbrasiliensis • Distributed in Central & South America • Infections of the lung or skin • Most infections are self-limiting, systemic disease is not common • Ketoconazole, amphotericin B, sulfa drugs Budding yeast

19. Subcutaneous mycoses • Invade traumatized skin, rarely become systemic but can cause destructive local lesions • lymphocutaneous sporotrichosis • chromoblastomycosis • mycetoma

20. Sporothrixschenckii • sporotrichosis (rose-gardener’s disease) • very common saprobic fungus that decomposes plant matter in soil • infects appendages & lungs • Lymphocutaneous variety occurs when contaminated plant matter penetrates the skin & the pathogen forms a nodule, then spreads to nearby lymph nodes

21. lymphocutaneous sprotrichosis Primary sore and series of secondary nodules along lymphatic chain in the arm

22. mycetoma • when soil microbes are accidentally implanted into the skin • progressive, tumorlike disease of the hand or foot due to chronic fungal infection; may lead to loss of body part • caused by Pseudallescheria or Madurella

24. Cutaneous mycoses • infections strictly confined to keratinized epidermis (skin, hair, nails) are called dermatophytoses-ringworm • 39 species in the genera Trichophyton, Microsporum, Epidermophyton • communicable among humans, animals, & soil • infection facilitated by moist, chafed skin

25. Ringworm of scalp (tinea capitis) affects scalp & hair-bearing regions of head; hair may be lost • Ringworm of body (tinea corporis) occurs as inflamed, red ring lesions anywhere on smooth skin • Ringworm of groin (tinea cruris) “jock itch” affects groin & scrotal regions • Ringworm or foot & hand (tinea pedis & tinea manuum) is spread by exposure to public surfaces; occurs between digits & on soles. (Athlete’s foot) • Ringworm of nails (tinea unguium) is a persistent colonization of the nails of the hands & feet that distorts the nail bed

26. Ringworm

27. Ringworm / Dermatophytosis

28. Ringworm treatment • ointments containing tolnaftate, miconazole or menthol & camphor • lamisil or griscofulvin 1-2 years

29. Superficial mycoses • Tineaversicolor causes mild scaling, mottling of skin • White piedra is whitish or colored masses on the long hairs of the body • Black piedra causes dark, hard concretions on scalp hairs • White & black piedra • Transmission is often mediated by shared hair brushes or combs • Several members of a family are usually infected at the same time • Infected areas must often be shaved to remove the fungi

30. Tinea versicolor

31. Black Piedra

32. White Piedra

33. Opportunistic Mycoses

34. Table

35. Candida albicans • widespread yeast • infections can be short-lived, superficial skin irritations to overwhelming, fatal systemic diseases • budding cells of varying size that my form both elongate pseudohyphae & true hyphae • forms off-white, pasty colony with a yeasty odor

36. Candida albicans • Normal flora of oral cavity, genitalia, large intestine or skin of 20% of humans • Account for 80% of nosocomial fungal infections • Account for 30% of deaths from nosocomial infections • Thrush – occurs as a thick, white, adherent growth on the mucous membranes of mouth & throat • Vulvovaginal yeast infection – painful inflammatory condition of the female genital region that causes ulceration & whitish discharge • Cutaneouscandidiasis– occurs in chronically moist areas of skin and burn patients

37. Candida albicans Thrush Candidal diaper rash Vaginitis

38. Cryptococcus neoformans • a widespread encapsulated yeast that inhabits soils around pigeon roosts • causes cryptococcosis • common infection of AIDS, cancer or diabetes patients • infection of lungs leads to cough, fever, & lung nodules • dissemination to meninges & brain can cause severe neurological disturbance & death

39. Cryptococcus neoformans

40. Pneumocystisjiroveci(P.carinii) • a small, unicellular fungus that causes pneumonia (PCP), the most prominent opportunistic infection in AIDS patients • this pneumonia forms secretions in the lungs that block breathing & can be rapidly fatal if not controlled with medication • pentamidine & cotrimoxazole

41. Aspergillus • very common airborne soil fungus • 600 species, 8 involved in human disease • inhalation of spores causes fungus balls in lungs and invasive disease in the eyes, heart, & brain • amphotericin B & nystatin

42. Aspergillus Invasive eye infection Conjunctival infection Brain abscesses (darkened areas)

43. zygomycosis • Zygomycota are extremely abundant saprobic fungi found in soil, water, organic debris, & food • Genera most often involved are Rhizopus, Absidia, & Mucor • usually harmless air contaminants invade the membranes of the nose, eyes, heart, & brain of people with diabetes, malnutrition with severe consequences

44. Hyphae and spores of zygomycosis-causing fungus

45. Fungal allergies & mycotoxicoses • Fungal spores are common sources of atopic allergies • asthma, often occurring in seasonal episodes • farmer’s lung, a chronic & sometimes fatal allergy of agricultural workers exposed to moldy grasses • teapicker’s lung • bagassosis, a condition caused by inhaling moldy dust from processed sugarcane debris • bark stripper’s disease caused by inhaling spores from logs • Fungal toxins lead to mycotoxicoses Some may be caused by eating poisonous or hallucinogenic mushrooms Ergot poisoning can occur from ingestion of moldy grain