Murthy

Question 1

Heterotrophic or saprobes

Answer 1

Organisms that live on dead or decaying matter

Question 2

symbionts

Answer 2

Organisms that live together and in which the association is of mutual advantage

Question 3

commensals

Answer 3

Organisms living in a close relationship in which one benefits from the relationship and the other neither benefits nor is harmed

Question 4

parasites

Answer 4

Organisms that live on or within a host from which they derive benefits without making any useful contribution in return; in the case of pathogens, the relationship is harmful to the host

Question 5

Two major differences from human cells:

Answer 5

Cell walls composed of chitin, mannans and glucans
Stain with calcofluor-white fluorescent stain
Whitening agent in paper industry – binds to cellulose and chitin (fluoresces upon UV exposure)
Cell membranes contain ergosterol (not cholesterol)
Imidazoles and amphotericin B bind to ergosterol to disrupt membrane integrity

Question 6

Fungal Classification

Answer 6

Based on morphologies:
Mold and hyphae (filamentous cells)
Yeast (ovoid cells)

Many have sexual (hyphal) and asexual (yeasts) life stages

Source of antibiotics and food products

Disease due to tissue invasion and destruction (few toxins…mushrooms) and damage from inflammatory immune response

Question 7

Fungal Morphology

Answer 7

Some fungi exist as single cells and are known as yeasts
However, most species are multicellular composed of hypha (pl., hyphae) – a slender filament of cytoplasm and nuclei enclosed by a cell wall
A mass of these hyphae make up an individual organism, and is collectively called a mycelium
A mycelium can permeate soil, water, or living tissue
Many of the parasitic fungi have modified hyphae called haustoria, which are thin extensions of the hyphae that penetrate living cells and absorb nutrients
Hyphae of some species of fungi have cross walls called septa that separate cytoplasm and nuclei into cells
Hyphae of other species have incomplete or no septa (i.e., are aseptate) and therefore are coenocytic (multinucleate)

Question 8

Asexual Reproduction (anamorph

Answer 8

Mitotic production of diploid vegetative cells 
Conidia, Endospores
Spores in sporangia
Conidia on conidiophores 
Budding
Blastoconidia
Mitosis with an uneven distribution of cytoplasm (common in yeasts)
Cell with less cytoplasm detaches and matures
Fragmentation 
Arthroconidia (Arthrospores)
Breaking of an organism into one or 
	more pieces  each can 
	develop into a new 
	individual

Question 9

Sexual Reproduction

Answer 9

Hyphae of two genetically different individuals of the same species interact
Nuclei of a fungal mycelium are haploid during most of the life cycle

Union of the cytoplasm of two parent mycelia is known as plasmogamy
Union of two haploid nuclei contributed by two parents is known as karyogamy

Meiosis quickly follows formation of the zygote (only haploid stage)

Haploid cells produced by meiosis are not gametes; rather they are spores that grow into a mature haploid organism (mycelia)

Question 10

Culture

Sabouraud’s agar (SDA)

Answer 10

Antibiotics added to inhibit bacterial growth
Grows most fungi (mold and yeast)
Can perform IF or gene probing on clinical isolates

Question 11

Microscopy

Skin scrapings

Answer 11

Dissolve in KOH to see morphology

Question 12

Microscopy

Calcofluor white stain

Answer 12

Binds to fungal cell wall (fluorescence

Question 13

Microscopy

Silver stain

Answer 13

Stains fungi and basement membrane

silver to black-brown

Question 14

Microscopy

Periodic acid Schiff (PAS) stain

Answer 14

Stains fungi pink color

Question 15

Microscopy

India ink

Answer 15

Highlights capsule of C. neoformans

Question 16

Antibody / Antigen Detection

Answer 16

ELISA/gene probes used to detect patient Ig or fungal Ags in body fluids

Question 17

Superficial mycoses

Answer 17

Surface of the skin and hair

Discoloration or depigmentation and scaling of skin

Question 18

Cutaneous mycoses

Answer 18

Keratinized layer of skin, hair and nails

Itching, scaling, broken hairs, ring-like patches of the skin, and thickened, discolored nails

Question 19

Subcutaneous mycoses

Answer 19

Deeper layers of the skin, including the cornea, muscle, and connective tissue
Abscess formation, non-healing ulcers, and draining sinus tracts

Question 20

Endemic or systemic mycoses

Answer 20

Caused by the classic dimorphic fungal pathogens (exist as yeasts or spherules at 37° C and molds at 25° C)

Question 21

Opportunistic mycosis

Answer 21

Immunocompromised individuals

Normal human commensals or the environment

Question 22

: Malassezia furfur

Answer 22

Superficial – Pityriasis (Tinea) Versicolor
Causative Agent: Malassezia furfur

Transmission:
Direct or indirect transfer of infected keratinous material from person to person

Characteristics
Oval or spherical yeasts show bud formation with a “lip” (colarette) around bud initiation

Clinical Syndrome
Small, hypopigmented or hyperpigmented spots on chest, back, arms, shoulders, face and/or neck
Interferes with melanin production
Also indicated in seborrhoeic dermatitis and dandruff
Complication: infections of hair 
	(folliculitis, dermal abscess)
Diagnostics
Microscopy of fungus from epidermal 
	scales in 10% KOH (H&E or PAS)
Fluorescence upon exposure to Wood’s 
	lamp (UV light)
Growth on SDA or Dixon agar
Cream-yellow smooth colonies

Treatment
Generally chronic and persistent
Topical Azoles or Selenium sulfide shampoo

Severe infection / Relapse
Ketoconazole
Itraconazole

Question 23

Hortaea werneckii

Answer 23

Superficial – Tinea Nigra
Causative Agent: Hortaea werneckii

Transmission:
Traumatic inoculation of the fungus into the superficial layers of the epidermis

Characteristics
Branched or septate hyphae and arthroconidia
Inhabitant of soil, compost, found on wood
Halophilic (has been isolated from saltwater fish)

Clinical Syndrome
Solitary irregular pigmented (brown to
black) macule on palms of hands or
plantar of feet
No scaling or invasion of hair follicles
Diagnostics
Microscopy of fungus from skin scrapings in 10% KOH (or Calcofluor white)
Growth on SDA (+10% NaCl and antibiotics)
Initially mucoid then shiny brown-black mycelia growth
Lesions resemble malignant melanoma – skin scrapings/culture to rule out

Treatment
Topical azoles
Whitfield’s ointment (benzoic acid compound)
Terbinafine

Question 24

(White Piedra): Trichosporon beigelii

Answer 24

Superficial
Characteristics
Hyphae
Arthroconidia
All forms growing on hair shaft
Clinical Syndrome
Soft greyish-white nodules along hair shaft
Common – hair of scalp, axilla, groin
Transmission: Poor hygiene
Diagnostics
Microscopy of fungus from hair (10% KOH, Calcofluor white, H&E)
Growth on SDA (add hair fragments)
Trichosporon – white-yellow smooth, wrinkled, velvety colonies
Piedra – brown-black velvety colonies (2-3wks to appear)

Treatment
Haircut-shave, proper hygiene and topical azoles (if needed)
Black Piedra may require terbinafine to clear

Question 25

Agent (Black Piedra): Piedra hortae

Answer 25

Superficial 
Characteristics
Hyphae (brown-red mold) develops 
	into hard mycelium with arthroconidia 
	surrounding the hair shaft
Clinical Syndrome
Hard black nodules along hair shaft
Common – hair of scalp, beard, mustache, groin
Transmission: Poor hygiene

Diagnostics
Microscopy of fungus from hair (10% KOH, Calcofluor white, H&E)
Growth on SDA (add hair fragments)
Trichosporon – white-yellow smooth, wrinkled, velvety colonies
Piedra – brown-black velvety colonies (2-3wks to appear)

Treatment
Haircut-shave, proper hygiene and topical azoles (if needed)
Black Piedra may require terbinafine to clear

Question 26

Candida species

Answer 26

Superficial – Diaper Rash (Diaper Dermatitis)
Characteristics
Blastoconidia
Pseudohyphae or true hyphae 
All forms seen in disease 
Most common infectious cause of diaper rash 
Also causes:
“Yeast infections” (vaginitis)
Candidiasis of groin area
Oral thrush
Interdigital candidiasis
Onychomycosis

Clinical Syndrome
Red rash (due to skin irritation) in 
	patches or large regions which  
	may develop in areas around the 
	groin (can 	include all regions covered by a diaper)
Transmission: Poor hygiene

Diagnostics
Classical appearance of rash upon examination
Microscopy of fungus from skin scrapings
in 10% KOH (H&E stains)

Treatment
Topical agents (barriers; oils)
Persistent rash – ketoconazole

Question 27

Trichophyton, Microsporum and Epidermophyton species (Dermatophytes)

Answer 27

Cutaneous – Dermatophytoses
Characteristics
aka Tinea or ringworm
Produce keratinase to utilize keratin as a 
	nutrient source
Do not invade living tissues but colonize the 
	stratum corneum of skin, nails, hair
Presence/metabolism induces allergic/
	inflammatory response (disease)
In culture:
Microconidia and/or macroconidia
Skin samples:
Septate hyphae and/or arthroconidia
Clinical Syndrome
Tinea capitis (lesions on scalp)
Tinea barbae (lesions of beard area)
Tinea corporis (lesions on body)
Tinea cruris (lesions of groin) – “Jock itch”
Tinea pedis (lesion of foot) – “Athlete’s foot”
Tinea unguium (lesions of nail)

Diagnostics
Microscopy of fungal hyphae from skin, hair or nail samples [10% KOH, Parker’s ink (blue), Calcofluor white]
Fluorescence upon exposure to Wood’s lamp (some species)
Growth on SDA (+cycloheximide)

Treatment
Tinea unguium and nonresponsive tineas
 Terbinafine (Lamisil)
Tinea pedis
Tolnaftate, an azole (Tinactin)
All others
Griseofulvin

Question 28

Sporothrix schenckii

Answer 28

Subcutaneous – lymphocutaneous Sporotrichosis
Characteristics
Found in soil and decaying vegetation
Dimorphic fungus:
Mold (soil)
Tan-black growth; septate hyphae
“Daisy petal” conidia formation on conidiophores
Yeast (patient)
“Cigar-shaped” blastoconidia
Transmission:
Direct contact with soil and decaying vegetation; appears to be some zoonotic infections reported (cats)

Clinical Syndrome
Nodular lesions along lymphatics draining the site of inoculation
May ulcerate with pus (2wks)
If inhaled can spread to other tissues via lungs (pulmonary disease)  bloodstream (few cases can spread from lymphatics as well)
Can lead to meningitis, retinitis, GI infections
Diagnostics
Microscopy of fungal hyphae (mold culture on SDA at 25C) or yeast (yeast culture on SDA at 35C) from skin tissue or pus in 10% KOH (PAS, Silver stain, Gram stain)
May resemble squamous cell carcinoma and mycobacterial infections

Treatment (cutaneous disease)
Oral potassium iodide
Itraconazole or terbinafine is best

Question 29

Cladosporium and Exphiala

Answer 29

Subcutaneous – Chromoblastomycosis
Characteristics
Chronic infection
Dimorphic fungus:
Septate Mold (wood & soil)
Conidia bearing cells  called anelids
Yeast (patient)

Transmission
Due to occupational hazard (body parts exposed such as walking bare foot)
No reports on person to person transmission
Clinical Syndrome
chronic, pruritic, progressive, indolent, and resistant to treatment
Early lesions are small, warty papules
Established infections appear as multiple, large, warty, “cauliflower-like” growths that are usually clustered within the same region
Secondary bacterial infection may lead to elephantiasis

Diagnostics
H&E staining: Chestnut-brown muriform cells
Scaring of warty lesions and mounted on 10% KOH
No serological tests

Treatment (cutaneous disease)
Ineffective during advanced stage
Itraconazole or terbinafine and posaconazole being used in early stages

Question 30

Conidiobollus coronatus and Basidiobolus ranarum

Answer 30

Subcutaneous – Zygomycosis (entomophthoromycosis)
Characteristics
Sporadic – traumatic implantation
Proximal limbs in children and facial area in adults
Dimorphic fungus:
Septate Mold (leaf and plant debris)
Conidia bearing cells called anelids

Transmission
Inhalation of spores, then invade the tissues such as nasal, paranasal and facial
Clinical Syndrome
infected with B. ranarum have disk-shaped, rubbery, movable masses that may be quite large and are localized to the shoulder, pelvis, hips, and thighs
C. coronatus infection is confined to the rhinofacial area
The swelling is firm and painless and may progress slowly to involve the nasal bridge and the upper and lower face

Diagnostics
Require biopsy for H&E staining: focal clusters of eosinophil’s around hyphae
Can be grown on SDA plates

Treatment (cutaneous disease)
Oral pottasium iodide
Itraconazole

Question 31

Endemic

Answer 31

Localized to specific geographical regions (infections only occur in these areas)
Residents take in spores, CMI can control
Fungal persistence can lead to new infections upon reactivation (immunosuppression)

Question 32

Dimorphic

Answer 32

Fungi that exist in two morphological forms (mold or yeast) based upon environment exposure
Mold form found growing in environment while yeast isolated from patient sources

Question 33

Blastomyces dermatitidis

Answer 33

Endemic Dimorphic – Blastomycosis
Characteristics
Natural habitat unclear (can isolate
	from soil esp. leaf litter)
Hyphae produce conidia
Yeast cells reproduce by budding (blastoconidia) in tissues
Clinical Syndrome
Inhalation of conidia
Two stages of disease:
Pulmonary blastomycosis 
Asymptomatic or mild flu-like (fever, cough, chills, myalgia) to severe pneumonia (severe chest pain)
2-12 wk recovery (immunity generated)
Cutaneous blastomycosis 
Dissemination from lung to skin (and/or bone); lesions may be papular, pustular, ulcerative on face, scalp, neck and hands
Occurs in 70% of patients
Untreated lesions can continue to grow in size unless patient receives treatment (result of inadequate immunity)
If spreads to bone, arthritis develops
Transmission
occupational/recreational contact with soil (conidia) – inhalation of conidia
Diagnostics
Microscopy of blastoconidia from skin scrapings, sputum or bronchial lavage in 10% KOH (Giemsa-Silver (GMS) stain, Calcofluor white)
Growth on SDA for dimorphism
Gene probe or ELISA
Treatment
Mild to moderate pulmonary/disseminated
Itraconazole 
Moderate to severe pulmonary
Amphotericin B 
Itraconazole 
Moderate to severe disseminated (also for immunosuppressed patients)
Amphotericin B 
Itraconazole 
CNS dissemination
Amphotericin B 
Oral azole

Question 34

Coccidioides immitis (C. posadasii)

Answer 34

Endemic Dimorphic – Coccidioidomycosis
Characteristics
Soil resident (growth enhanced by bat and rodent droppings)
Hyphae produce arthroconidia (spores; resistant to phagocytosis)
Endospore-containing spherule forms in human tissues
Clinical Syndrome- Most virulent
Inhalation of arthroconidia (only few required) convert to spherule produce endospores release new spherules
Pulmonary Coccidioidomycosis
Asymptomatic (60% of cases)
Mild flu-like (40% of cases; incubation ~2 wks)
May develop rash on trunk and limbs
Upon recovery 5-10% have pulmonary nodules or cavities that develop and persists for yrs (may harbor viable fungus)
~5% develop disseminated disease (within wks to mo after flu-like illness onset)
Disseminated Coccidioidomycosis
Spread to meninges, bones, joints and subcutaneous/cutaneous tissues
Untreated CNS infections have less than 10% survival
Patients frequently develop a Th2 response rather than Th1
Urease produced to cause tissue damage
Transmission
inhalation of arthroconidia
Diagnostics
Microscopy of spherules from skin scrapings, sputum or bronchial lavage in 10% KOH (Parker ink or Calcofluor white, PAS, GMS)
Young spherules have clear centers
Growth on SDA
Suede-like downy, greyish-white colony
Tan-brown reverse coloration
Gene probe for DNA
Treatment
Fungal/bacterial infections in cavities
Azoles and antibacterials (cavities usually remain)
Resection of localized cavities
Disseminated coccidioidomycosis
Itraconazole (other areas) or Fluconazole (CNS)
If lesions worsen…Amphotericin B
Fluconazole prophylactic for AIDS patients living in endemic area

Question 35

Histoplasma capsulatum

Answer 35

Endemic Dimorphic – Histoplasmosis
Characteristics
Soil resident (growth enhanced by chicken, bat
	and droppings: High Nitrogen contents)
Hyphae produce conidia (microconidia)
Yeast within reside in phagolysosome ( pH)
Clinical Syndrome
Inhalation of conidia convert to yeast within phagocytes granulomas form in lung (may calcify) organisms viable reactivation upon immune suppression (all patients)
80% of endemic population – positive skin test
Asymptomatic (~95% of cases)
~5% of cases:
Chronic Pulmonary Histoplasmosis
Prolonged mild to severe flu-like illness (or pneumonia)
Chronic Cutaneous Histoplasmosis
Recurrent oropharyngeal ulcers or other cutaneous lesions
Disseminated Histoplasmosis
Usually only seen in immunosuppressed patients
Systemic spread resulting in development of oral ulcers, ocular lesions, hepatosplenomegaly, meningitis and growth in bone 
Untreated nearly 100% fatal within 2 yrs
Transmission
Inhalation of conidia 
Diagnostics
Microscopy of yeast in phagocytes (mø, PMN) from skin scrapings, sputum, bronchial lavage and biopsy in 10% KOH (Parker ink, GMS, PAS, Calcofluor white)
Growth on SDA 
White suede-like colony
Pale yellow-brown reverse coloration
Detection of Ag (serum, urine) and/or Ab
Treatment
Mild Chronic Pulmonary (symptoms >4 wks)
Itraconazole 
Severe Chronic Pulmonary
Amphotericin B
Itraconazole 
Disseminated 
Amphotericin B 
Itraconazole

Question 36

: Candida albicans

Answer 36

Opportunistic – Candidiasis
Characteristics
Part of normal flora of nasopharynx, skin, vagina (also found in the air, water and soil)
Fourth most common nosocomial bloodstream infection (most common fungal opportunist)
Morphology (can modulate between each in tissues):
Hyphae and pseudohyphae
Blastoconidia
Capacity to adhere to a variety of surfaces
Hyphae can “feel” their way through tissues 
	(invasiveness)
Disease a result of predisposing factors:
Antibiotic therapy
Chemotherapy
Tumor development
Catheter insertion
Neutropenia
Surgery or burns
Assisted ventilation
ICU patients
Hemodialysis patients
Malnutrition
HIV infection (AIDS)
Neonates / Elderly
Clinical Syndrome
Oral Candidiasis
Mucocutaneous Candidiasis
Interdigital Candidiasis (hands and feet)
Cutaneous Candidiasis
Vaginal Candidiasis (vulvovaginitis)
Candidiasis of the Penis
Onychomycosis (Nail Candidiasis)
Diaper Dermatitis
Neonatal / Congenital Candidiasis
Superficial
Generalized
Ocular Candidiasis
Candidiasis of the Scalp
Esophagitis
GI Candidiasis
Pulmonary Candidiasis
Endocarditis / Myocarditis / Pericarditis
Hepatic Candidiasis
UTI
Meningitis
Transmission
Endogenous: autoinfection (immunosuppression) 
Exogenous: contaminated fluids into patient; person to person (nosocomial) 
Diagnostics
Microscopy of fungus from various clinical samples in 10% KOH (Parker ink, Calcofluor white, Gram stain, PAS)
Growth on SDA
Cream colored, smooth, waxy colonies
Treatment
Mucosal / cutaneous
Topical azoles; Nystatin for oral thrush
Most others
Fluconazole (or echinocandin) 
CNS / bone / ocular 
Amphotericin B (6 wks) then…
Fluconazole (echinocandin) 
Cardiovascular 
Amphotericin B, fluconazole or echinocandin
Fluconazole prophylaxis for high risk patients prior 
	to procedures such as surgery

Question 37

Cryptococcus neoformans

Answer 37

Characteristics
Isolated from bird guano (esp pigeon), rotting vegetables, fruits, juices, wood, dairy products and soil
Encapsulated yeast (blastoconidia)
Capsule and cell wall melanin protect from phagocytosis
Commonly affects immunocompromised hosts
~10% of AIDS patients are affected
AIDS-associated cryptococcosis accounts for 50% of all cryptococcal infections (meningitis most common)
Clinical Syndrome
Pulmonary Cryptococcosis
Asymptomatic (isolation of fungus from sputum) to self-limiting mild pneumonia (cough, fever, chest pain)
Unresolved infections can lead to chronic pneumonia with granuloma formation ( risk for dissemination)
Disseminated Cryptococcosis
Meningitis (~75% of cases)
Most common cause of fungal meningitis
Slow symptom development (over many months) including:
Also meningoencephalitis (tissue invasion) or expanding cryptococcoma (tumor-like masses of fungus)
Cutaneous (~15% of cases)
Small papules that ulcerate or cellulitis
Can disseminate to CNS
Often found on head and neck
Other Sites (~10% of cases)
Bone (lytic lesions causing joint pain)
Ocular (optic disc swelling leading to intracranial pressure)
Nephritis
Prostatitis
Transmission
High risk: AIDS patients
inhalation of yeast cells
Diagnostics
Microscopy of encapsulated yeast from tissues, blood, CSF (India Ink)
Growth on SDA (blood, CSF)
Cream colored smooth mucoid yeast-like colonies
Growth on Niger Bird Seed Agar
Dark brown colored smooth colonies (agar brown pigment absorbed by fungi)
Serological detection of capsular Ags in CSF
Treatment
Pulmonary Cryptococcosis
Mild – Fluconazole (6-12 mo)
Chronic – Amphotericin B + Flucytosine (4 wks) then…Fluconazole (8 wks)
Cryptococcal Meningitis
HIV patient
Amphotericin B + Flucytosine then…Fluconazole (8 wks) then…Fluconazole (> 1 yr based upon CD4 T cell numbers; CD4 T cells > 100 cells/ml for 6 mo)
nonHIV patient
Same as HIV patient exc. second Fluconazole (6-12 mo)

Itraconazole can be used to replace fluconazole in all cases

Question 38

Pneumocystis jiroveci

Answer 38

Opportunistic – Pneumocystis Pneumonia
Characteristics
Most common opportunistic infection of AIDS patients accounting for 50% of AIDS patient deaths (also important cause of disease in transplantation and chemotherapy patients)
Originally thought a life cycle form of T. cruzi by Carolos Chagas (1909) and Antonio Carinii (1910)…named P. carinii (1912)
Thought to be a protozoan based upon:
Ineffectiveness of antifungal drugs (effectivenss of antiprotozoal drugs such as pentamidine)
Absence of fungal features such as ergosterol (although possesses b-1,3-glucans as component of cell wall)
Similarity to other protozoans (two life cycle forms – troph and cyst)
Classified as fungus in 1988 by DNA comparisons
Unique Pneumocystis species discovered for virtually every mammal with differing genetics to conform to host specificity – thus no cross-species infections
Renamed from P. carinii to P. jiroveci after the Jirovec who first reported the organism in humans (not uniformly accepted)
Unknown environmental reservoir
Nearly all have Ig to Pneumocystis Ag by age of 2
Lack of data to support reactivation of latent infection (outbreaks occur suggesting it is transmitted)
Trophozoite (asexual haploid forms)
Cyst (diploids which divide into haploids)
Cannot propagate the organism in culture (all studies derived from infected animal models and fresh tissues)
Transient culture on media with lung epithelial cells
Life Cycle
Asexual Reproduction
Trophic form undergo binary fission
Sexual Reproduction
Haploid trophic forms unite to form diploid cyst which mature and rupture releasing new haploid trophic forms
Clinical Syndrome
Pneumocystis pneumonia (PCP)
P. jiroveci attaches to lung alveolar epithelial cells by gpA

Organism coated with host fibronectin/vitronectin which binds to alveolar epithelial cell integrins strengthening adherence

Organism adherence prevents repair to damaged epithelia

Damage mediated by immune response
Organism activates macrophages to produce TNFa, IL-1, IL-6, IL-8, IP-10 to recruit PMN and Th1/Tc T cells
Host inflammatory response needed to clear the fungal infection but induce damage as well

Symptoms:
Dyspnea, nonproductive cough, fever, cyanosis
Organism presence and inflammatory infiltration induce diffuse alveolar damage impairing gas exchange  respiratory failure
Transmission
High risk: AIDS patients
Studies suggest inhalation of cysts; person-to-person (immunocompetent) spread could serve as reservoir for outbreaks

Diagnostics
Microscopy of trophozoites or cysts from tissues, sputum or bronchial lavage (GMS, Giemsa, PAS, Parkers ink)
Chest radiography / CT scan

Treatment
Trimethoprim-Sulfamethoxazole
Alternate: 
Primaquine / Clindamycin
Pentamidine
Trimetrexate
Caspofungin

Question 39

Parasitic infections

Answer 39

Parasite is an organism that requires coexistence with another organism for survival

Depends on host for their life cycle, without 	benefitting the host

Some need dual environment to complete 	their life cycles

Question 40

Protozoa

Answer 40

Single-celled eukaryotes

 Found as ubiquitous free-living organisms in the environment

Classification:   Sporozoa (intracellular parasites)
	       Flagellates (tail-like structures for movement)
	       Amoeba (cell body projections called pseudopods)
	       Ciliates (hair-like structures called cilia)

Mode of infection:  Through ingestion of cysts (the dormant life stage)
	            Sexual transmission, insect vectors. 

Common infections: Malaria, Amebiasis, Trypanosomiasis, Leishmaniasis

Question 41

Amoebas of Medical Importance

Answer 41

Naegleria fowleri
Free-living amoeba
Highly fatal neurological infections
Occurs worldwide, including US
Acanthamoeba sp.
Free-living amoeba
Highly fatal neurological infections; ocular infections in contact lens wearers
Occurs worldwide, including US
Entamoeba histolytica
True parasite
Highly pathogenic, potentially invasive disease
Begins in intestine and can spread to liver and brain
Occurs worldwide, including US

Question 42

Flagellates of Medical Importance

Answer 42

Leishmania tropica
Transmitted by sandflies; cause of cutaneous leishmaniasis
Leishmania donovani
Transmitted by sandflies; cause of visceral leishmaniasis
Trypanosoma bruceii
Transmitted by tsetse flies; cause of African sleeping sickness
Trypanosoma cruzi
Transmitted by reduviid bugs, cause of Chagas’ disease
Giardia lamblia
Transmitted by ingestion of fecal conatminated water or person to person by fecal/oral route; cause of diarrhea
Trychomonas vaginalis
Transmitted by sexual contact; causes genital irritation and discharge

Question 43

Sporozoa of Medical Importance

Answer 43

Plasmodium sp
Transmitted by Anopheline mosquitoes; cause of malaria
Toxoplasma gondii
Transmitted by ingestion of tissue cysts or oocytes; cause of toxoplasmosis
Occurs worldwide including US
Cryptosporidium sp
Transmitted by ingestion of oocytes; cause of diarrhea
Occurs worldwide including US