How does the protozoa respond to environmental changes?
secretes a protective coat and shrink into a round armoured form (cyst), which is infective when ingested by humans; then can convert back to its motile form (trophozoite)
5 intestinal protozoa that cause diarrhea
1. Entamoeba histolytica--bloody diarrhea
2. Giardia lamblia--non-bloody diarrhea
3. Cyclospora cayetanensis--non-bloody diarrhea
4. Cryptosporidium--severe diarrhea in AIDS pts
4. Isospora belli--severe diarrhea in AIDS pts
What are chromotoid bodies?
ribosomal aggregates in precyst form of Entamoeba histolytica
3 dz associated with Entamoeba histolytica
1. bloody diarrhea with ulceration
2. liver abscesses
3. pulmonary abscesses-->death
How to distinguish active dz with Entamoeba histolytica versus asymptomatic carrier
active dz: stool has trophozites with RBC's in cytoplasm
asymptomatic carrier: stool has cysts or trophozites without internalized RBCs
Giardia lamblia has two forms
cyst and mature motile trophozoite
Where does Giardia lamblia infect?
small intestine-->prevents fat absorption so stools are smealy and fatty
Does NOT invade epithelial cells so no bloody diarrhea (unlike Entamoeba histolytica)
How is Cryptosporidium ingested?
as a round oocyst
How are Isospora and Cyclospora transmitted and dx? What other protozoa is dx in the same way?
acid-fast stain; Cryptosporidium
Trichomonas vaginalis infects
female vagina and male urethra
2 ways to dx Trichomonas vaginalis
1. wet prep vag d/c--highly motile parasite (flagellated)
2. examine urine
3 free-living amoebas causing meningitis and encephalitis
1. Naegleria fowleri--acute meningoencephalitis
2. Acanthamoeba--chronic granulomatous meningoencephalitis in immunocompromised
3. Balamuthia mandrillaris--chronic meningoencephalitis in normal and immunocompromised hosts
What is found in brain tissue in Naegleria infections?
mature amoeba only--no cysts
Corneal infection found in what amoebael infection
acanthamoeba (contact lenses)
Granulomatous skin lesions found in what amoebal infection
In what two amoebal infections are cysts AND mature amoeba found in brain tissue
Acanthamoeba and Balamuthia mandrillaris
Where are two ways to get exposure to Toxoplasma gondii?
1. ingestion of cysts in undercooked meats or food contaminated cat feces and kitty litter boxes (inhaled)
2. immunocompromised and transplacental (TORCHES)
Most common CNS infection in AIDS patients
Toxoplasma gondii encephalitis
Common organs affected by Toxooplasma gondii in AIDS patients
fever, lymph node, liver, spleen enlargement, pneumonia, chorioretinitis
Defects associated with congenital Toxoplasma gondii
MR, blindness, seizures, chorioretinitis, microcephaly, encephalitis
Can cause stillbirth
What is Pneumocystis carinii and what dz does it cause?
flying-saucer appearing fungus, fungus; opportunistic pneumonia in immunocompromised patients-->severe interstitial pneumonia (PCP); the most common opportunistic infection in AIDS pts
Dx Pneumocystis carinii
silver-staining or immunoflourescent staining of alveolar lung secretions
4 protozoa causing malaria
Plasmodium falciparum, Plasmodium viva, Plasmodium ovale, and Plasmodium malariae
Name of the form of Plasmodium that leaves the mosquito's sucker and into the human bloodstream
sporozoites (thin, motile, spindle-shaped)
What marks the beginning of the pre-erythrocytic cyle in malarial infections?
sporozoite burrowing into a liver cell
After infecting a liver cell, what does the sporozoite become?
a trophozoite--a round-up ball that can undergo nuclear division
After undergoing many rounds of nuclear division, what does the trophozoite become?
What are merozoites?
new small bodies of Plasmodium that burst open the liver cell and go into the blood stream
Infecting the liver and replicating is called the ---- cycle
What is the erythrocytic cycle?
Similar to the exo-erythrocytic cycle, except it occurs in the RBC; merozoite rounds up to form a trophozoite; then a multinucleated schizont forms, leading to lysis of RBC and release of merozoites
What species can lie dormant forms in the liver, leaping to relapsing malaria years later? What form of the organism lies in the liver?
P. viva and P. ovale
What events occur in the mosquito?
sexual reproduction: gametocytes sucked into stomach of mosquito, male and female gametocytes fuse and become an oocyst
oocyst divides into sporozoites which wiggle to the salivary gland to be injected into the human for asexual reproduction
Dz caused by Babesia microti and divergens
fever and RBC hemolysis; similar to malaria
How is Babesia different from Plasmodium?
spread by tick bites, and do not affect liver cells; no ex-erythrocytic phase
only mild hemolysis except in asplenic pts
Two blood-borne protozoa
Leishmania (sandfly) and Trypanosoma (tsetse fly and reduviid bug)
How does Leishmania infect the body?
Promastigotes form invades macrophages-->transforms into the immotile amastigotes-->multiples in the macrophages in lymph nodes, spleen, liver, and bone marrow
3 clinical forms of Leishmaniasis
1. Cutaneous leishmaniasis: simple ulcer leaving a depigmented scar (delayed hypersensitivity reaction) or a chronic diffuse nodular lesions in defective cell-mediated immunity
2. Mucocutaneous leishmaniasis: ulcers in nose and moth, leading to erosion of nasal septum, soft palate, lips and death by secondary bacterial infection
3. Visceral leishmaniasis: hepatosplenomegaly, fever, anorexia, and weight loss
Trypanosoma brucei gambiense responsible for what dz
West African sleeping sickness: slowly progressing intermittent fevers, wasting, and CNS changes including drowsiness, slurred speech, gait changes, and coma, death
Trypanosoma brucei rhodesiense responsible for what dz
East African sleeping sickness: more severe and rapid
How is Trypanosoma brucei similar to Borrelia recurrentis?
Variable surface glycoproteins and antigenic variation causing relapsing fever
Dz caused by Trypanosoma cruzi and its three phases
acute: choagoma (hardened red area)-->systemic sx, tachy and EKG changes, meningoencephalitis
Intermediate: no sx for many years
chronic: arrhythmias, dilated cardiomyopathy, megacolon and megadz of esophagus
How is Trypanosoma cruzi transmitted?
via reduviid bug (kissing bug) which feeds on humans and defecates--protoza is in the poop!
Immune response in a helminth infection
elevated eosinophils in response to dead worms or eggs, not usually to living worms
Ascaris lumbricoides: route of infection
1. ingestion of eggs
2. larvae in small intestine penetrate intestinal wall
3. go up to alveoli, where they are coughed up and swallowed
4. go back to small intestine where they mature into adult worms
5. eggs excreted in feces
Ascaris lumbricoides: type of helminth
intestinal nematode (roundworm)
Clinical findings with Ascaris lumbricoides infection
abd cramping, dry cough and fever, malnutrition as worms compete for food
Necator americanus: route of infection
1. larval form in soil transforms into filariform larva
2. filariform larva penetrates between toes
3. travels directly to lungs, coughed up and swallowed
4. small intestine and suck blood
5. copulate and release fertilized eggs
Necator americanus: type of helminth
intestinal nematode (hookworm)
Clinical findings with Necator americanus infection
abd pain, diarrhea, weight loss, iron deficiency anemia, cough, CXR infiltrate
What is Ancyclostoma duodenale?
a hookworm, similar to Necator americanus
Strongyloides stercoralis: route of infection
1. filariform larvae in soil penetrates human skin and travels to lung
2. coughed up and swallowed; reach small intestine
3. develop into adult worms and produce larvae
What 3 things can happen to the filariform larvae of Strongyloides stercoralis once it reaches the small intestine?
1. Autoinfection: penetrate intestine directly, go to lung, continue cycle
2. Direct cycle: filariform larvae pass into feces, survive in soil, and penetrate a next host
3. Indirect cycle: sexual cycle; larvae are passed into soil where they develop into male and female adults which mate in the soil and produced fertilized eggs that can hatch and reinfect a human
Clinical findings with Strongyloides stercoralis infection (normal vs immune-compromised)
abd bloating, n/v/d, anemia, weight loss, prurititic rash, cough, eosinophilia
immune-suppressed: severe autoinfection--pneumonia, ARDS, and multi-organ failure
Description of Trichuris trichiura egg and adult form
egg: football with polar bumps on each end
adult: whip-shaped (whipworm)
Enterobius vermicularis: route of infection
1. ingestion of eggs
2. mature in cecum and ascending large intestine
3. female migrates to perianal area to lay eggs
4. scratching perianal area will cause reinfection of himself and others
Dx enterobius vermicularis
scotch tape test
No eosinophilia since no tissue invasion
How are blood and tissue nematodes spread?
by bite of an arthropod
Filariae live in lymphatic tissue, giving birth to prelarval forms called microfilariae (they do not lay eggs) which are picked up by bloodsucking arthropods
Wuchereria bancrofti and Brugia malayi: route of infection
1. mosquito: transmit microfilariae
2. microfilariae mature into adults within lymph nodes/vessels of genitals and BLE; they mate
3. microfilariae enter nearby blood vessels
Wuchereria bancrofti and Brugia malayi: clinical features
LAD, febrile illness (filarial fever)
repeated exposures: fibrous tissue plugs up lymphatics-->edema-->thick scaly skin-->elephantiasis
tropical pulmonary eosinophilia: hypersensitivity rxn causing wheezing and coughing, associated with hypereosinophilia
What is cutaneous larva migrans?
larvae of dog and cat tapeworms; usually Ancylostoma braziliense (dog hookworm)
Clinical manifestation of cutaneous larva migrans infection
allergic response in skin--raised, red, itchy rash
What roundworm is responsible for visceral larva migrans?
ingestion of Toxocara canis (dog roundworm) eggs
Clinical manifestation of visceral larva migrans infection
toxocariasis: fever, diarrhea, wheezing, hepatitis, and chorioretinitis
2 groups of platyhelminthes
1. trematodes: aka flukes; include schistosomes
2. cestodes: aka tapeworms
Intermediate host of schistosomes
water snail species
Schistosomas: route of infection
1. found in freshwater: mature cercariae (larvae)
2. penetrate exposed skin
3. invade venous system in intestine or bladder
4. mate, lay eggs, but eggs cannot hatch (require freshwater snails) so excreted in urine or feces
What stimulates the immune system in schistomsoma infections?
cercariae (mature larvae) and eggs
The adult worms can live for years (molecular mimicry)
What species of Schistosoma is found in Eastern Asia, resides in intestinal tract veins, and deposits eggs in the feces?
What species of Schistosoma is found in South America and Africa, resides in intestinal tract veins, and deposits eggs in the feces?
What species of Schistosoma is found in Africa, resides in bladder veins, and deposits eggs in the urine?
3 major dz syndromes occurring sequentially in Schistosoma infections
1. dermatitis during cercariae penetration
2. katayama fever as the adults lay eggs (fever, hives, H/A, cough, weight loss; LAD, HSM, eosinophilia)
Complications of Schistosoma infection
When eggs deposit in the lung, liver, or brain, immune system forms granulomas, causing inflammation, ulceration-->hematuria, GI polyps, brain/spinal cord injury, or pulmonary artery HTN
Cestodes: one thing they lack, and one thing they have extra ; )
lack a true digestive tract but have both male and female organs (hermaphroditic, so a single tapeworm can produce an offspring
What are proglottids?
chain of boxlike segments making up a tapeworm "body", including its sex organs and container for fertilized eggs
What is a scolex?
The "head" of a tapeworm; has suckers and hooks
Taenia solium: route of asymptomatic infection
1. ingestion of undercooked pork with larvae
2. hooks attach to intestinal mucosa
3. eggs released into human feces
4. pigs eat egg-infested human feces-->become intermediate host
5. deposit in pig's muscle and develop into cysticercus (another larval form)
6. human eats undercooked pork muscle with cysticercus, becomes adult tapeworm in intestine
Taenia solium: route of cysticercosis
1. human ingests eggs (instead of encysted larvae)
2. eggs hatch in small intestine
3. larvae migrate throughout the body
4. form cysticerci in brain and skeletal muscles
Symptoms of neurocysticercosis
2. obstructive hydrocephalus
3. focal neuro deficits
What causes enhanced symptoms in neurocysticercosis?
Once the cysts begin to die and leak their fluid contents, causing local inflammation in the brain
Taenia saginata: route of infection
same as Taenia solium, except when humans ingest eggs, they do not develop cysticerci-->therefore relatively benign
1. ingestion of larval cysticerci in undercooked beef muscle
2. tapeworm matures and adult beef tapeworm attaches to intestinal mucosa
2 symptoms of Taenia saginata infection
weight loss and malnutrition
Diphyllobothrium latum: route of infection
1. human ingests larvae in raw freshwater fish
2. adult fish tapeworm in intestine deposits proglottids with eggs which end up in the water
3. once in water, convert to motile larval form
4. motile larval form ingested by a crustacean
5. crustacean is ingested by a freshwater fish
6. freshwater fish is ingested by a human
Diphyllobothrium latum: clinical symptoms of infection
nonspecific abd sx, vitamin B12 deficiency (megaloblastic anemia)
Echinococcus granulosus and multilocularis: route of infection
1. humans ingest fertilized eggs perpetuated by dogs and sheep
2. hatch in intestine and develop into larvae
3. larvae penetrate intestinal wall and disseminate
4. concentrate in liver; may also infect brain, lungs, kidney
What causes sx in Echinococcus granulosus and multilocularis?
larva form "hydatid" cysts that can undergo asexual budding, which can compress organs around it. Also, fluid in the cysts produce extreme allergic responses
6 characteristics common to prions
1. long incubation time
2. gradual increase in severity
3. no host immune response so no inflammatory processes
4. death within months of onset
5. macroscopic findings of CNS normal
6. microscopic findings of CNS show spongiform changes, neuronal loss, and amyloid plaques with accumulation of prion protein (PrP)
What is the difference between PrP^c and PrP^Sc
c = normal cellular isoform of the prion protein
sc = scrapie; dz associated isoform of the prior protein
chain reaction of post-translational modification
3 different etiologies related to the nature of prion dz
1. inherited: mutations in PrP gene favors spontaneous conformational change to PrP^Sc (autosomal dominant pattern)
2. infectious: exogenous PrP^Sc induces conformational change of host PrP^C into PrP^Sc
3. sporadic: sponatenous conversion or rare de novo mutation in PrP gene
3 examples of prion dz
Bovine spongeform encephalopathy aka new variant CJD
Fatal familial insomnia
5 clinical features common to all prion dz
1. rapid dementia
2. psych sx
3. cerebellar sx
4. involuntary movements
5. ultimately fatal
Onchocerca volvulus: vector and dz
black flies; causes "river blindness" and intraepithelial granulomas
Complication associated with Schistosoma haematobium
squamous cell carcinoma of bladder