Parasites/Fungi Flashcards
protozoal infection stages
- trophozoite: feeding “ph-eeding” form; infectious
- cyst: hardy, excreted in feces, ingested and able to survive GI tract
Protozoa types
Amoebae:
- Entamoeba histolytica: diarrhea
Flagellates:
- Giardia intestinalis: diarrhea, malabsorption syndrome
- Trichomonas vaginalis: urogenital tract infections, vaginitis
Sporozoa:
- Cryptosporidium spp: GI disease
Entamoeba histolytica
- ingested cyst
- asymptomatic carriage
- intestinal amebiasis: large intestine tissue destruction
- extraintestinal amebiasis: liver abscesses, fever, leukocytosis, rigors, brain/heart/lung abcesses
Giardia intestinalis
- ingestion of cysts ==> infection of trophozoites in duodenum & jejunum
- wilderness streams, lakes, mountain resorts; reservoir animals
- asymptomatic carriage
- foul smelling watery diarrhea, fatty stools (“Ghiradelli chocolates”)
- malabsorption syndrome/chronic diarrhea in IgA deficient patients
Diagnosis: microscopic examination of stools, fecal antigen test
Treatment: Metronidazole
Prevention: boiling water, filtering water (resistant to chlorine)
Cryptosporidium spp
- intracellular parasite in brush border of intestinal epithelial cells
- waterborne infection: resistant to chlorination and ozone
- asymptomatic carriage
- mild, self-limiting diarrhea
- severe disease with massive fluid loss in immunocompromised patients (AIDS)
Trichomonas vaginalis
- exists only as trophozoite
- found in urethra, vagina, prostate glands
- urogenital infections: mostly symptomatic in females (green watery vaginal discharge, vaginitis)
- transmitted via sexual intercourse
Diagnosis: microscopic examination of discharge, elevated vaginal pH, fluorescent antibodies
Prevention: Metronidazole, safe sex
Protozoa of blood & tissue infections
Plasmodium spp: malaria, thru mosquitoes
- P. vivax
- P. ovale
- P. malariae
- P. falciparum
Babesia spp: babesiosis, thru ticks
- B. microti
Toxoplasma gondii: toxoplasmosis, thru oocyst consumption
Lesihmania spp: leishmaniasis, thru sand flies
- L. donovani
- L. tropica
- L. brailiensis
Trypanosomes: sleeping sickness & Chagas’ disease, thru Tsetse flies & kissing bugs
- T. brucei
- T. cruzii
Plasmodium spp
Malaria
- P. falciparum
- Chloroquine-resistant P. falciparum are present in all endemic regions except Central America & Carribean
- fever pattern: malignant tertian malaria
- shortest incubation period (7-10 days), most severe fever attacks
Diagnosis: blood smears (thick and thin), look for RBC infection
- Giemsa or Wright stain
Treatment: Chloroquine
Babesia
- transmitted by Ixodes tick
- invades RBCs and causes lysis
- does not infect liver
Diagnosis: Maltese cross in blood smear
Treatment: Clindamycin, quinine
Toxoplasma gondii
- CNS toxoplasmosis = brain abscesses
- AIDS-defining illness
- CT: multiple ring-enhancing lesions
- causes clinical symptoms when CD4 count < 100, due to reactivation of previously asymptomatic infection
- mental status changes, headaches, fevers, focal neurologic deficits, seizures (30%)
- transmission through cat feces
Prophylaxis: Trimethoprim-Sulfamethoxazole
Leishmania spp
- female sand flies
- cutaneous, mucocutaneous, visceral diseases
Diagnosis: amastigotes (tissue stage of parasite) in macrophages
Trypanosoma spp
T. brucei
- tsetse fly
- African trypanosomiasis (sleeping sickness): CNS, Winterbottom sign (cervical lymph node swelling)
T. cruzi
- kissing bug
- Chagas’ disease: chagoma, rash, Romana’s sign; chronic disease has myocarditis, megacolon
Helminths
- nematodes: round worms
- platyhelminths: flat worms
Nematodes
“you EAT these” = spread thru ingestion
E - Enterobius
A - Ascaris
T - Trichinella
“from the SANd” = spread thru cutaneous penetration
S - Strongyloides
A - Ancylystoma
N - Necator
Enterobius vermicularis (pinworm)
- most common helminth infection in U.S. children
- eggs deposited at night in perianal folds
- itching at night
Ascaris lumbricoidis (roundworm)
- large worms
- larvae develop in lung alveoli ==> swallowed and returned to small intestine
- intestinal obstruction
- pneumonia/asthma (Loeffler’s syndrome)
Strongyloides stercoralis (threadworm)
- larvae penetrate skin
- undergoes entire life cycle in human host
- larvae in sputum and duodenal aspirates
Taenia solium (pork tapeworm)
- ingestion of undercooked pork
- neurocysticercosis (NCC): seizures, headache
- NCC can be gotten from living in close proximity to someone w tapeworms and ingesting the eggs
dimorphic fungi
both saprobic (mold, outside body) & parasitic (yeast, inside body, pathogenic) forms:
- histoplasma
- blastomycoses
- coccidioides
- sporothrix
- penicllium (Candida)
all are agents of respiratory infections, none are obligate parasites
true pathogenic fungal infections
- superficial infection: Malasezzia furfur
- cutaneous infection: dermatophytes
- subcutaneous: sporotrichosis
- deep/systemic: histoplasmosis
Superficial mycoses
Pityriasis (Tinea) versicolor:
- superficial infection of epidermis
- caused by Malassezia furfur
- hypopigminted skin
- diagnosis: skin scraping => KOH
- fungal elements with spaghetti and meatballs (hyphae and yeast cells)
Cutaneous mycoses
Dermatophytosis or Tinea (ringworm):
- caused by dermpatophytes: Microsporum spp, Trichophyton spp, Epidermophyton spp
- only mold form with hyphae (branching septate)
- erythematous outer ring ==> crusting healing center
- jock itch, athlete’s foot, scalp
- diagnosis: Wood’s lamp (UV), Sabourauds agar
- treatment: topical antifungals
Onychomycosis (Tinea unguium):
- fungal infection under nails
Subcutaneous mycoses
Sporotrichosis
- Sporothrix schenckii
- due to traumatic introduction into subcutaneous tissues
- rose gardener’s disease
- found in soil
- stains like flowers
Opportunistic fungal pathogens
(systemic mycoses)
- Candida sp.
- Aspergillus fumigatus
- Mucormycosis
- Cryptococcus neoformans
- Pneumocystis jirovecii
Susceptible populations to opportunistic/primary mycoses
- HIV
- transplant patients
- cancer patients
- rheumatologic conditions => chronic immunosuppression
- chronic diseases and comorbidities
Candida spp
- normal flora in GI/GU tracts
- dimorphic
- Candida albicans: causes disease in otherwise healthy patients
- Mucocutaneous cadidiasis: overgrowth of normal flora after taking antibiotics; superficial infection on mouth (oral thrush, scrapable), groin, armpit, vagina
- Disseminated candidiasis: contaminated indwelling catheters ==> organism invades tissue; bloodstream infection ==> endocarditis
Aspergillius fumigatus
- saprophytic mold
- treelike pattern with acute angle branching (45˚) and septations
- colonizing aspergillosis: fungus ball in perinasal sinuses or cavitary lung lesions
- cause of invasive aspergillosis thru inhalation in immunocompromised patients (innate immunity): pneumonia
Treatment: Voriconazole
Mucormycosis (aka Zygomycosis)
- broad nonseptate hyphae
- invasive infections in those with uncontrolled diabetes
- high mortality rate
- rinocerebral/craniofacial mucormycosis: infection of paranasal sinuses with extension into orbit/frontal lobe
Cryptococcus neoformans
- yeast-like fungus
- virulence factor: thick polysaccharide capsule
- stain with India Ink and Mucicarmine
- found in bird excreta (pigeon droppings)
- AIDS-defining illness for those CD4 count < 100
- entry into lungs ==> pneumonia ==> meningoencephalitis
Diagnosis:
- blood/CSF antigen testing: latex agglutination test
- microscopic examination: India Ink, Mucicarmine stain showing encapsulated yeast
- NO ring-enhancing lesions on CT
Treatment: Amphotericin B + Flucytosine
Pneumocystis carinii (jiroveci)
- cyst and trophozoite forms
- infection in debilitated/ immunosuppressed patients
- most common opportunistic infection in patients with AIDS - AIDS defining condition
- pneumonia
- stain: crushed ping pong balls
- lung CT: ground glass opacities
Treatment and prophylaxis: Trimethoprim-Sulfamethoxazole
Primary (systemic) fungal pathogens
- Blastomyces dermatitidis
- Histoplasma capsulatum
- Coccidioides immitis
- Paracoccidioides brasiliensis
Blastomyces dermatitidis
- dimorphic
- “Chicago fever”; endemic to Mississippi & Ohio river basins
- decaying organic matter
- large Broad-Based Budding yeast in tissue
- cutaneous blastomycosis: papular, pustular, indolent ulcerative-necrotizing and verrucous lesions
- systemic blastomycosis: can be confined to lung or disseminate hematogenously
Treatment: Amphotericin B for severe blastomycosis with CNS involvement
Histoplasma capsulatum
- dimorphic: mold in environment, yeast in tissue
- endemic to Ohio & Mississippi river valleys, Central/South America
- bat guano (caves)
- most cases are asymptomatic
- clinical forms: acute pulmonary, disseminated, chronic pulmonary
- stain: halo formed due to retraction of cytoplasm in alveolar macrophages
Coccidioides immitis
- dimorphic
- Southwestern US, found in soil/dust (increased rainfall, dust storms, earthquakes)
- cough, fever, chest pain, night sweats, joint pain
- stain: spherule with endospores
Paracoccidioides brasiliensis
- dimorphic
- Central/South America
- stain: pilot’s wheel (several budding cells attached to parent cell)
- paracoccicoidomycosis: disseminated disease often causes ulcerative lesions of buccal, nasal, GI mucosa
“Paracoccidio parasails with the captain’s wheel all the way to Latin America”
