Fungi and Parasites 8/27/25

Vocabulary flashcards covering key concepts in fungal biology, antifungal drugs, pathogenic fungi, dimorphic fungi, common mycoses, protozoa, helminths, and ectoparasites from the lecture.

Mycosis

An infection caused by a fungus.

Mycology

The study of fungi

Eukaryotes with their own kingdom, ergosterol in membranes, cell wall has chitin/Bglucans/mannoproteins

Molds (filamentous, sex/asex repro) and yeast (round,unicellular, binary fission/budding)

Ergosterol

Sterol in fungal cell membranes; target of many antifungal meds; not present in human cholesterol.

Chitin

A polysaccharide component of fungal cell walls.

Recognized by TLR2

melanin

found near the fungal membrane, can block phagocytosis

Beta-glucan

Polysaccharide in fungal cell walls; target of antifungal meds that inhibit glucan synthesis.

Mannoprotein

Proteins in the fungal cell wall surface rich in mannose.

Sabouraud dextrose agar

Culture medium commonly used to grow fungi.

Polyenes

Antifungal target: interact w/ ergosterol, disrupts plasma membrane, cell bursts.

Amphotericin B - May bind to our cholesterol and cause toxicity :(

Amphotericin B

Polyene antifungal that binds ergosterol and disrupts fungal membranes.

Azoles

Antifungal class that inhibits ergosterol synthesis by interfering w/ yeast enzymes (ex: fluconazole).

Fluconazole

Azole antifungal commonly used to treat Candida and Cryptococcus infections.

Allylamines

Antifungal class that inhibits ergosterol synthesis (squalene epoxidase) (e.g., terbinafine).

Different MOA than azoles

Terbinafine

Allylamine antifungal; inhibits squalene epoxidase in ergosterol synthesis.

Echinocandin

Antifungal class that inhibits glucan synthesis, weakening the fungal cell wall (e.g., caspofungin).

Caspofungin

An echinocandin antifungal used against Candida and Aspergillus species.

Challenges of antifungal development

• Fungi cells are very similar to ours = similar targets (Fewer unique drug targets)

• Not all fungi rely on their “unique” structures (Chitin, etc)

• Ergosterol targeting = cross-reactivity to cholesterol (Toxicity big issue, Ampho”terrible” B)

• Fungi grow slowly in lab, difficulties in studying

• Many fungal infections are in immunocompromised, prolonged infections, toxic treatments

Candida albicans

Yeast; normal flora of mucosal surfaces (colon, vagina, oral); opportunistic pathogen causing thrush and other infections (usually immunocompromised overgrowth, normal flora disruption, vulnerable pt age)

Microscope: KOH prep and look for budding yeast and pseudohyphae

Treatment: oral/topical fluconazole to inhibit ergosterol synthesis

KOH prep

destroys human cells within lab sample

oral candidiasis

thrush: white patches, pseudomembrane that can wipe off leaving red area. common w/ chronic illness and babies

esophagitis: difficult/painful swallowing, AIDS defining infection

Cryptococcus neoformans/gattii

Only encapsulated yeast; opportunistic and neurotropic (likes to infect CNS); causes cryptococcal (fungal) meningitis, especially in the immunocompromised (HIV/AIDS very susceptible if low CD4).

Inhaled from bird droppings, soil.

Diagnose: india ink stain, capsular antigen test

Treat: amphotericin B and fluconazole (could be prophylactic)

Not related!

mycosis and mycolic acid are NOT related at all

sabouraud dextrose agar

used for growing yeast

opportunistic infections

• Immunocompromised or debilitated patient

• Break in skin or mucous membranes

• Normal microbiota OR environmental fungi

primary pathogen infections

• Healthy people

• Environmental fungus

• Soil, inhaled

• Pneumonia is usually primary manifestation

superficial / cutaneous mycoses

• Hair, skin, nails

• Most common – Dermatophytes, Malassezia

subcutaneous mycoses

• Beneath skin, but doesn’t disseminate to organs etc

• Rare

• Sporothrix

systemic mycoses

• Deep within body; internal organs

• Endemic mycoses (Histoplasma, Coccidioides)

• Immunocompromised

superficial transmission

• Person-to-person

• Animal-to-human (dogs, cats)

• Examples: dermatophytes (ringworm)

subcutaneous transmission

skin penetration (cut, wound)

deep/systemic transmission

• Opportunistic growth in immunocompromised or primary pathogen

• Candida in oral cavity, vagina, esophagus

• Primary entry – respiratory tract

major reservoir transmission

• Soil

• Decaying plant matter

• Own normal flora

• Bat/bird droppings

yeast

single celled eukaryotes

round/oval

asymmetrical, asexual reproduction(budding)

candida & malassezia can be overgrown normal flora

cryptococcus = bird droppings

blastoconidia

yeast buds

failure to detach will cause chain (pseudohyphae) formation.

common w/ candida

Capsule

Polysaccharide capsule cell; key virulence factor.

Only yeast/fungus with capsule is cryptococcus neoformans!!

India ink stain

A lab stain used to visualize the capsule of Cryptococcus in CSF.

Malassezia furfur

Yeast causing pityriasis (tinea) versicolor

shows yellow fluorescence with Wood lamp; ‘spaghetti and meatballs’ hyphae/yeast in KOH prep.

Overgrowth of normal flora, very common.

Noninvasive, stays in stratum corneum but prefers sebaceous glands

damages melanocytes - hypo/hyperpigmentation, pink patches

treat: ketoconazole, topical azoles. can prevent with selenium sulfide lotion

molds

• A single hyphae will grow from a spore

• Hyphae – branching cylindrical tubules (Grow from tips, Multinucleated, Will grow like this inside/on the host)

• Aerial (vertical) growth - spores for dissemination (Transmission of spores = infection route) Aerosols, inhalation, Inoculation in wounds/skin break

Hyphae

can be septate or nonseptate (coenocytic)

conidia

individual spores

sporangia

individual spores enclosed in sac-like membrane

Tinea versicolor

Superficial fungal infection of the skin caused by Malassezia species.

Spaghetti and meatballs

A descriptive microscopic appearance of Malassezia hyphae (spaghetti) with yeast cells (meatballs) on KOH prep.

Aspergillus fumigatus

Opportunistic mold with septate hyphae that invades tissues; inhaled conidia; can cause invasive pulmonary/ sinus infections, especially in neutropenic patients.

spores inhaled from soil, compost

infections:sinusitis, rhinosinusitis, acute pulmonary aspergillosus, cerebral aspergillosis

treatment: varies

dimorphic fungi

shape shifters!

can be fungi or yeast depending on temperature

cold = mold (infectious), warm (body temp) = yeast w/ diagnostic morphology

blastomyces, coccidiodes, histoplasma, sporothrix

Septate hyphae

Hyphae with cross-walls (septa); characteristic of many molds including Aspergillus.

Mucor/Rhizopus

Zygomycete molds; causes mucormycosis; non-septate hyphae; rapid, angioinvasive disease.

Dermatophytes

Fungi that invade keratinized tissues (hair, skin, nails); examples include Microsporum, Trichophyton, Epidermophyton.

Dimorphic fungi

Fungi that are mold in the environment and yeast in the human host, depending on temperature.

Blastomyces dermatitidis

Dimorphic fungus; causes blastomycosis; environmental mold forming yeast in tissue.

Coccidioides immitis

Dimorphic fungus causing coccidioidomycosis; environment form is mold arthroconidia; tissue forms yeast spherules with endospores in humans.

Airborne within dry dirt, dust, desert (valley fever)

diagnose: cxr/ct, microscopy/biopsy, antigen testing

treat: fluconazole, maybe amphotericin B

can cause acute pneumonia

Spherules

Large tissue yeast forms of Coccidioides that contain endospores.

Histoplasma capsulatum

Dimorphic fungus; histoplasmosis; yeast inside macrophages; associated with inhalation of soil enriched with bird/bat droppings.

Most common endemic systemic mycoses in USA

Diagnose: cxr/ct, micro/biopsy w/ silver stain. antigen detection

treatment: itraconazole, maybe amphoterican B

Microconidia

Small asexual spores produced by Histoplasma in mold form; infectious form in environment.

Sporothrix schenckii

Dimorphic fungus; “rose-handler’s disease” (sporotrichosis); lymphocutaneous infection.

direct inoculation of spores into skin (wound, etc), found in soil, decomposing plants

diagnose: culture, direct microscopy for oval/cigar shape yeast

treatment: months of itraconazole or terbinfine

Rose-handler’s disease

Sporotrichosis; cutaneous/lymphatic spread after traumatic inoculation with Sporothrix conidia.

pathogenic mechanisms of fungi

Adhesion to cells: Candida and epithelia

Biofilm formation: Catheters, prosthetics

Host tissue invasion

• Hyphal extension, angioinvasive (Aspergillus)

• Protease, lipases (Malassezia)

• Keratinase (dermatophytes)

Immune evasion

• Antiphagocytic capsule (Cryptococcus only)

• Melanin

• Antigenic variation

• Intracellular survival (Histoplasma in macrophages)

clue for fungi and parasite infections

eosinophilia

parasite overview

no vaccines for any of them

tropical or sub-tropical usually

giardiasis most common

70% of world population is infected with worms

parasitic pathogenesis overview

Parasitism – parasites benefits while the host is harmed

• Deprive host of nourishment

• Suppress or trick immune system

No vaccines

Exogenous source: Insects, non-human animals etc.

Diseases symptoms

• Some produce toxins, hydrolytic enzymes

• Some physically obstruct and damage organs due to size and number

Disease manifestations can be due to immune response

• Anaphylaxis, Immune complexes, Granulomas

Adhesion – not as tissue specific

• Some tissue tropism (preference)

• Adhesins – sucking disks – mouthparts

Most protozoans replicate intra- or extra-cellularly in the human host

• Stages of life-cycle general for each group

• Portal of entry does not always = final location!

Wide range of pathogenic mechanisms

• Subacute, chronic – MOST don’t tend to be acute and life-threatening IMMEDIATELY

• Can have asymptomatic infections

Many immune evasion strategies

Severity of disease relates to infectious dose and # organisms acquired over time

• Chronic, repeat exposures, increased burden

• Life cycle inside host?

Tissue migratory parasite: eosinophilia

protozoan

unicellular eukaryote

most have locomotion method

various shapes/sizes/locations that can be diagnostic

usually binary fission

common in developing countries, usually tropical/subtropical areas

helminth

• Worm, multicellular eukaryotes

• Tapeworm (cestode/thorny-headed) - hermaphrodites

• Roundworm (nematode) – male and female

• Fluke (trematode/flat worm) – male and female ; hermaphrodites

ectoparasites

• Parasite that lives on the external surface of a host’s body (skin, hair, or outer body structures)

• E.g., Lice, fleas, ticks, and mites

definitive host

• Host in which sexual reproduction occurs

• Not all will have one

intermediate host

supports one or more developmental cycles

dead end host

• Intermediate host that does not allow transmission to definite host

• Prevents parasite from completing development

Fecal-oral route

contaminated food/water

giardia lamblia - giardiasis

vector borne transmission

plasmodium spp. - malaria via Anopheles mosquito

wucheria bancrofti - lymphatic filiarasis nematode via mosquito

direct inoculation/contact

naegleria fowleri - direct inoculation of water with cysts deep into sinuses

sexual transmission

trichomonas vaginalis - trichomoniasis

ingestions of eggs or larvae (fecal-oral)

enterobius vermicularis (pinworm) - ingestion of eggs from contaminated surfaces

ingestion of undercooked or raw meat/fish

diphyllobothrium latum - fish tapeworm

skin penetration be larvae

hookworms (necator americanus, ancylostoma duodenale) - larve penetrate bare skin from contaminated soil

Giardia lamblia

Flagellated protozoan; causes giardiasis; acquired via ingestion of cysts in warm water, fecal contamination, etc.; leads to diarrhea and malabsorption (trophozoites attach to intestines).

very infectious - only need a couple to cause disease

hiking, camping, drinking from river, etc

diagnose: microscopy, stool antigen test

treatment: metronidazole (not a fungal -azole!)

Trophozoite

Active, feeding stage of many protozoa, including Giardia and Entamoeba.

Cyst

Dormant, hardy form of protozoa like Giardia; typically transmitted via oral ingestion.

Plasmodium species

Apicomplexan protozoa that cause malaria by infecting RBCs; transmitted by Anopheles mosquitoes to humans only; cycles (paroxysms) of fever.

Found mainly in tropics, africa, etc.

sporozoites get injected by mosquitoes → become merozoites that infect RBCs → fever and chills caused by burst RBCs every 2-3 days

diagnose: peripheral blood smears to look at RBCs

treatments: chloroquine, primaquine, prophylaxis before/during/after travel

Anopheles mosquito

Mosquito genus that transmits Plasmodium species causing malaria.

Sporozoite

Infectious stage of Plasmodium injected by the mosquito; travels to liver to initiate infection.

Merozoite

Plasmodium stage that invades red blood cells after liver stage.

Naegleria fowleri

Amoeboflagellate protozoan (ameba AND flagellated trophozoite) causing primary amoebic meningoencephalitis (PAM); typically inhaled via contaminated warm freshwater (summertime). Not communicable. Very rare but 97% fatal.

PAM first resembles bacterial meningitis. Altered taste/smell senses, brain tissue destruction. 3-7 days to death

diagnose: PCR the CSF, see trophozoites in autopsy

unsure of existing treatment

Primary amoebic meningoencephalitis (PAM)

Rapidly fatal CNS infection caused by Naegleria fowleri after nasal inoculation.

helminths

parasitic worms

multicellular eukaryotes

infections usually in warmer countries

cestodes

tapeworms.

Reproductive organs (male and female) within each segment of the worm

Proglottid – each segment

• Gravid proglottid – those containing fertilized eggs (Terminal ones are released and pass through feces)

Eggs develop into larvae: Larvae must go through at least 1 intermediate host before it can be infective again

Scolex, suckers – attachment to intestinal wall

Adult tapeworms are acquired by eating undercooked or raw meat containing larval stages

Adult tapeworms are relatively harmless despite their potential for reaching a large size

platyhelminths

• Flattened bodies with muscular suckers and / or hooks for attachment to the host

• Most are hermaphrodites, except Schistosoma

nematodes

Long cylindrical bodies and generally lack specialized attachment organs.

separate sexes. most species liberate fertilized egg from host

development from egg → larvae → adult can directly occur in 1 host

can be human specific or zoonotic

some need warm soil for ferilization

helminth transmission routes

swallowing infective eggs/larvae, active skin penetration by larvae, bite from blood sucking insect vector

Hookworm (Necator americanus)

Nematode (roundworm) that directly penetrates skin; causes iron-deficiency anemia with heavy infection.

Human only host. Usually in tropics by human fecal soil contamination, requires heavy infection of 500-1000 worms

cutaneous larvae migrans → pulmonary phase (larvae in lungs cause dry cough, wheezing, SOB) → GI phase (abd pain, lost appetite, N/V/D, iron deficiency anemia)

diagnose: eosinophilia, iron deficient anemia, eggs in stool

treament: albendazole paralyzes the worms (not fungal -azole)

Diphyllobothrium latum

Fish tapeworm; cestode; proglottids wider than long; causes B12 deficiency; acquired from undercooked fish.

Definitive host = humans, intermediate host = freshwater fish

Northern hemisphere: Scandinavia, russia, japan, canada, some USA

Human ingest raw fish containing larvae → larvae mature in small intestine and release eggs → eggs enter fresh water to embryonate (2-3 intermediate hosts: crustaceans, fish, etc)

diagnose: proglottids, eggs in stool. low B12 in serum

treatment: praziquantel (paralyzes parasite by increasing calcium permeability and it dies)

diphyllobothriasis

Disease from fish tapeworm

Most asymptomatic - Might have abdominal discomfort, diarrhea

Vitamin B12 deficiency - The tapeworm competes and causes Megaloblastic anemia

Mechanical obstruction of intestines

Malabsorption, weight loss

Proglottid

Segment of a tapeworm containing reproductive organs; shed in feces.

Praziquantel

Anthelmintic used to treat cestode and trematode infections by increasing parasite cell membrane permeability.

trematodes

flukes

humans always definitive hosts

sexual reproduction. eggs in body fluids

eggs develop into larvae in environment.

must pass through at least 1 intermediate host, must be a freshwater snail. will infect 1 human and adult fluke will be in intestine, lungs, liver, blood vessels

Schistosoma species

Blood fluke; trematode; male and female worms joined together. life cycle involves snails and cercariae, eggs gets excreted from urine or stool; causes schistosomiasis.

Acute: swimmers itch on legs/feet (were cercariae entered skin), fever, cough, eosinophilia, ebd pain

Chronic: intestine: abd pain, low appetite, blood diarrhea. urinary: abd pain, urinary frequency/urgency, can cause bladder cancer

diagnose: visualize eggs in excretions, ELISA

treatment: praziquantel (same as fish tapeworm)

parasitic immune evasion strategies

• Antigenic variation: Plasmodium, Schistosoma

• Cover surface in “self ” antigens = molecular mimicry: Schistosoma larvae

• Intracellular survival: Plasmodium, Toxoplasma, Trypanosoma

• Suppress or alter immunity

diagnostic studies for protozoa and helminth infections

• Clinical signs and symptoms, travel history, vector contact etc.

• Microscopy – Gold standard for many

— Stool (ova and parasite) – Giardia (cysts and trophozoites), Schistosoma (eggs), Diphyllobothrium

(proglottids), Hookworms (Necator)

— Peripheral blood smears –Plasmodium

—CSF/brain tissue – Naegleria fowleri

• ELISA, antigen testing

—Stool – Giardia

• Serology for antibodies

—IgM, IgG

ectoparasites

• Arthropods found either on the skin or only in the

superficial layers of the skin

• Insects (six-legged arthropods) and arachnids (eight-

legged arthropods) — Lice, flies, bedbugs, mites, ticks, spiders

• Not vectors of disease, but the cause themselves

Louse / lice

• Nits are eggs —Found attached to hair shaft:White, seen with naked eye

• Transmission: fomites - hats, combs, towels, sheets

—Common in kids

• Adult lice bite and feed on blood – puritis

botfly

• Myiasis - caused by the larvae (maggots) —Inflammatory response causes symptoms

• Usually in tropical areas

• Transmission: Adult fly deposits egg in a wound; egg hatches to produce larva. → Fly deposits the egg in nostrils, in conjunctiva, lips → Fly deposits the egg on unbroken skin and larva invades skin

• Painful, pruritic lesions that resemble furuncles (boils) → Some patients feel movement in the lesion

bedbugs

• Mattresses, crevices of wooden beds

• At night, emerge for blood meal

• Pruritic wheel – hypersensitivity to bug saliva