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135 Cards in this Set

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What type of infection is the most prevalent among developing countires?
parasites; but also common in developed countries...
T/F Parasitic infection is distinct from parasitic disease
true, you can have the infection without having the disease symptoms.

parasite might live in host without causing symptoms..and at some pt. in time will start to cause symptoms.
How many people are infected by parasites?
Billions of pple
- most pple have been infected at least once in life
What is parasitic disease a consequence of?
prolonged, repeated or high burden of infection
Most Parasitic disease are RARELY FATAL - except what?
Plasmodium falciparum malaria - may be rapidly fatal (3-5 days)
infections in immunocompromised ind.
Most parasitic infections are caused by agents that infect animals aka:?
zoonosis
What is usually required for parasites to complete thier life cycle?
human and nonhuman hosts
- human are dead-end hosts for some parasites - infection occurs but no parasite developemental stage - (life cycle not completed)
What are the two parasite types?
Protozoa
Helminths
Which parasite is the one-celled eukaryotic organism?
Protozoa
Protozoa are different form helminths in that the disease is consequence of parasite replication to high numbers - can this occur in humans?
yes; only a small inoculum sized is requried to initiate infection
Where in the human can the protozoa reside and replicate?
Intracellularly (red blood cells, macrophages)
Extracellulary (lumen of GI tract)
What is the difference between Intravs. Extracellular protozoa (parasites)?
Intracellular are unable to withstand environmental dessication - thus they have no cysts, or spore-like structures)
Their life cycles do not include free environmental stage (go host-to-host) and are transmitted via arthropod vectors.
EXTRACELLULAR
Often transmitted oral-fecal route
LIfe cycle alternate between two forms:
Active trophozoite
Dormant cyst (unlike intra) - withstands environmental dessication
What parasite type is a multicellular animals (metazoa)?
Helminths (worms) - roundworms, flatworms
Where are helminths found within the human?
EXTRACELLULARLY - due to large size -
protected by cuticle,
larvae can develop into dormant cysts
Helminths have complex life cycles and can reproduce (sexually/asex)?
Sexually - some species (tapeworms) are hemphrodites.
IS the human a definitive or intermediate host for helminths?
it is a dead-end host (definitive) - do not typically complete life cycle in human - unlike insect vectors or animal reservoirs which are a intermediate host.
Most helminth cause chronic infections that are tolerated by the human host
Is the disease a consequence of parasitic replication?
disease is NOT A consequence of parasitic replication - unlike protozoans
What is the disease caused by with helminths?
parasitic burden due to number of parasites that host initially acquires from environment.
Does the host response eliminate the established infection that was created by the helminth?
NO, they spontaneously resolve when adult worms reach sensecence. (this is diff. than protozoans)
What are most parasite vectors?
Arthropods
ex: mosquitos
Are the parasite vectors essential steps in parasitic life cycle?
yes
What is the parsitic prevalence dependent on? and what does it favor?
dependent on: local conditions favoring arthropod breeding
- sometimes there is a 3rd vector required:
ex: mice -> ticks -> humans
If there weren't vectors, we wouldn't see in man.
What is the definition of a a parasite reservoir?
sources of parasites that do not participate directly (actively) in transmission
What are some examples of parasite reservoirs?
humans (dead-end)
Animals (pigs, cattle)
Environment (soil with parasitized feces)
Do parasite VECTORS actvely transmit the parasite from one host to antoher?
yes
What are the 3 ways that parasites enter humans?
oral ingestion (most prevalent)
Penetration of the skin (unbroken) - worms attach to feet
Arthropod-borne - bite wounds, very effective - once you have it you can share via blood transfusion
What are some examples of transmission contraints of parasites
Dependent on parasitic life cycle and presence or absence of intermediate hosts.
ex: Schistosomiasis - snails required to allow parasite to mature;
no snails in europe and north america so no schistosomiasis present
Anopheles mosquitoes are present in US and indigenous mosquito CAN be infected if someone with disease comes and is bitten by anopheles and it spreads.
T/F Disease manifestation dependent on size of inoculum.
True, especially for helminths - directly proportional to inoculum from environment - not actively replication to levels that cuase disease
For survival against the elicited antibody and cell-mediated immune responses how do parasites circumvent?
Camouflage -
host plasma protein coatings (blood flukes)
Surface antigen variation (trypanosomes)
Superoxide dismutase secretion - protection from host phagolysosome
What are the life cycles of the parasites living within the body determined by?
species and tissue tropisms
When speaking of parasite spread and multiplication explain some examples of temperature dependent species and their optimal temps for multiplication.
Leishmania donovani - replicates at 37 degrees C - Visceral leishmaniasis (bone marrow, liver, spleen)
Leishmania tropic - replicates at 25-30 degrees C - thus more skin infections
T/F The temperature changes also induce stage -specific transitions.
T
What damage from parasites shows a clinical manifestation?
Direct tissue damage by parasite
- cytolysis -> colonic ulcers, liver abscesses
Effecgts of host immune system
- deep tissue infections -> chornic inflammation
BOTH
What cells of the immune system neutralize helminth infections and are NOT characteristic of protozoan infections.
Eosiniophilia
Why do large numbers of eosinophils appear?
in response to helminth surface glycoproteins and polysacccharides
- also accompanied by increased levels of IgE and driven by increase IL-5 levels.
Most clinical complications occur ______ (min., hours, days, weeks, years) after initial infection
YEARS - remember subacute or chronic infections
What is an example of how clinical complications can occurs years later (hint: from kissing bug)
Chaga's Disease:
starts with trivial skin lesion -> asymptomatic or mildly symptomatic
chronic infections -> heart blockage, impaired swallowing, defecation due to colonic damage
Parasites are difficult to diagnose - what do you ID when looking for it?
ID of parasites or progeny (cysts, eggs, larvae)
- NEED to understand the life cycle - b/c of differential location and differential timing.
For Treatment and Prevention of Parasites: to eradicate the disease what are the 3 main ways
Chemoprophylaxis
Immunization
Field Control Measures
Will only one of these methods eradicate the disease?
no, only successfuly when more than one are employed
With chemoprophylaxis - is this abortive or preventatie?
Preventative drugs -
Chloroquine effective against all 4 species of Plasmodium (some becoming resistant)
Ivermectin for onchocerciases (river blindness) provided free by Merck
Why would immunization for parasites be so difficult?
b/c of complex life cycles
- Masquerade as Host cells - coating in host antigens
- some parasites (trypanosomes ) continually alter surface antigens
- different proteins/polysacharides displayed on surfaces at different stages
What does it mean to have field control measures for treatment and prevention?
Use insecticides
Sanitation - take away their environment
*What is the most important of all protozoan diseases?
Malaria
*What are the four plasmodium species that infect HUMANS and vary virulence due to red blood cell age preferance? (there are 156 Plasmodium species which infect various species of vertebrates)
P. falciparum - all ages of rbcs (greatest mortality)
P. vivax - reticulocytes and young rbcs
P. ovale - reticulocytes and young rbcs
P. malariae - older rbcs
Where does malaria generally occur?
in areas where conditions allow parasite muliplication in the vector - usually restricted to tropical/semitropical areas - distribution is enlarging because of global warming
What is the only reservoir for Plasmodia?
INfected Humans
What does it mean that transmission occurs 9-27 days after bite of infected femal Anopheles mosquitoes - symptoms develop 8-30 days later
mosquito takes blood meal form host with malaria parasite and it take 9-17 days to replicate in that mosquito and then when it bites the new host it will take 8-30 days to exhibit symptoms
What does it mean to have imported malaria?
endemic area infection - travelers import parasite to nonendemic areas during incubation
What gender of mosquito is an arthropod vector for malaria?
FEMALE ANOPHELES mosquitos
What does it mean to have INDUCED malaria?
transmission via blood transfusions or needles
How does the parasite exist in the mosquito?
as Sporozoites inhabiting the mosquitos SALIVARY glands
When a mosquito that has sporozoites bites a human what is the path that it take through the human; where does it end up?
travels through bloodstream and enters liver cells within 30 min. - multiplies and matures (hepatocellular cycle)
Once the sporozoites mature in the liver what do they end up as and what path do they take next?
release to blood as MEROZOITES - invade rbcs, divide and mature (erythrocytic cycle)
2-3 days: rbc burst and liberate more MEROZOITES that are then available for mosquitos to take up again.
How does parasite multiply in liver and rbcs?
ASEXUALLY (binary fission) -

Some plasmodia in blood may develop into gametocytes capable of sexual reproduction in mosquitoes.
What are the intracellular location consequences from Malaria and the RBC - what do P. falciparum infected cells do to RBC?
P. falciparum infected cells develop special "knobs" on surfaces that bind to receptors on venules and capillaries - impede blood flow
What do the "knobs" cause? (makes cells less deformable)
Spleen tries to clean it up - recognizes and removes, malaria cause spleen enlargement (splenomegaly) and thus needs to be removed.
What is typical paroxysm? in relation to malarial damage
Parasite (plasmodia) replication can by synchronous.
- simultaneous lysis of many rbcs and release of large number of merozoites and other parasitic molecule.
When speaking of Malaria and Human Genetics, how is the infection dependent or prescence of specific rbc surface molecules?
Glycophorin A (surface antigen)/Dufffy bloodgroup antigen is specifically required for infection of plasmodium -

African Americans are Duffy Negative and thus don't get malaria - but instead have sickle cell anemia.
How do you treat malaria and prevent it?
Natural Immunity imperfect.
Immune response - significant control, but
- sporozoite antibodies are not sufficient to protect from infection
- too many life cycles to control
Ultimately requires cell-mediated immunity - cell-mediated toxicity of infected liver cells may be involved for protective immunity
Chloroquine is effective for treating individuals with plasmodia - how?
targets parasites food vacuole where hemoglobin is degraded
- toxic heme detoxified usually by parasite
- Chloroquine blocks detoxificiation and kills parasite
P. falciparum is becoming resistant to Chloroquine, how?
it is altering the vaculolar membrane protein that pumps drug out of food vacuole - doesn't change surface structure or bind anything, just pumps it out.
T/F Chloroquine isn't effective again p.vivax/p. ovale
true
What is considered a 'close cousin' to malaria, is common in the US and also destroys rbcs?
Babesia
T/F Babesiosis is endemic in US and is COMMON in US?
TRUE
Babesia microti is unique in that it is similar to what other disease found in the same animal reservoir -
white footed mouse
transmitted by deer tick
same as Lyme disease
Babesia Merozoites are injected under skin by tick and directly targe RBCs (invaded by merozoites) - where do they go next? (hint: different than malaria)
NO intermediate liver stage

- Replication via binary fission

Lyse RBCs

Ticks feed on infected RBCs to keep cycle
Which disease has a simpler cycle?
Babesia or Malaria?
Babesiea - no intermediate liver stage
What Protozoa are Tissue Protozoa and what are are blood protozoa and Intestinal and Vaginal Protozoa?
Blood: Babesia and Plasmodium
Tissue: Toxoplasma, Leishmania, Trpanosoma cruzi
Intestinal and Vaginal: Giardia lamblia, Trichomonas vaginalis, Entamoeba histolytica, cryptosporidium, cyclospora, isospora, microsporidia (not true protozoa -like bacteria)
*What does Toxoplasma gondii causes?
toxoplasmosis
Is toxoplasmosis comon in humans?
the infection is common in humans but the disease is rare
-disease can be severe for immunocompromised pateients and developing fetuses
*What are the 3 symptoms for toxoplasmosis?
- mononucleosis -like
- Congenital infection (can kill fetus)
- *Brain/heart (immunocompromised)
*How are Tissue protozoa unqiue in their survival?
they can survive in macrophages - prevent acidification and phagolysosome fusion
*How is toxoplasma introduced to humans?
The introduction of the organism to the human host is through meats - inadequate cooked meat (tissue cysts) or food contaminated with cat feces (OOCYSTS)
-cats harbor sexual cycle (similar to mosquitoes in malaria)
*How does the toxoplasma get 'into the body'
The ingested toxoplasma cysts penetrate intestinal wall, enter bloodstream and disseminate
*Why are pregnant woman advised to not be around cats?
because they may contract toxoplasma through the cats feces (litter box) etc. and their embryo will suffer the consequences.
*Is the immune response to toxoplasmosis effective?
pretty effective, most pple's immune system can control,
but it can result in dormant tissue cysts that can reactivate later in life.
The second protozoan Dr. Dicken's talked about is a SMALL tissue protozoan (flagellates) and is transmitted via SANDFLIES - what is it?
Leishmania -
Where are Leshmania found in the world?
transmitted by SANDFLIES - thus is found in tropical/subtropical areas
Where is the Reservoirs for Leshmania?
Rodents, dogs, other animals, humans
There are several species of Leishmania - that have diff. tissue tropisms and clinical displays - what is unique about it's diff. temp. preferences (25-30 vs. 30)
L. donovani - replicates at 37 degrees - in visceral leishmaniasis (bone marrow, liver, spleen)
L. tropica - replicates at 25-30 degrees - results in SKIN infections
-temp change also induces stage-specific transitions
What is the life cycle of Leishmania and how is it spread? (hint: promastigote -> amastigote)
Promastigote (flagellated) binds to macrophages (then produces superoxide dismutase)
in the macrophage is converts to amastigote (no flagella) -> which is resistant to lysosomal enzymes and requires low pH for nutrient uptake (glucose and proline)
like Chloroquine for malaria - Antimony containing compuonds are useful for treatment of leishmania.
What does Trypanosoma cruzi cause and where is it found?
Chaga's Disease (american tryponsomiasis) in Latin America and southern US
*How is Trypanosomes transmitted?
reduviid (kissing) bug (grows in bugs intestine) - grows in intestine, bug deposits feces OUTSIDE SKIN (not in blood stream), *scratching introduces organism into bite...
(different than other transmissions
When does the Illness of trypanosomes occur?
mild illness, complication 10-20 yrs. later (prob because as age immune system dec.)
Nerve, GI, Heart damage
*What Trypanosome is known to cause African Sleeping Sickeness?
Trypanosma brucei
*How is Trypansoma brucei transmitted?
Tsetse flies in Africa - transmitted DIRECTLY by the bite, NOT the feces like the kissing bug for Chaga's Disease
How does African Sleeping Sickness exhibit in infected humans?
Systemic (fever and swollen lymph nodes) and chronic in bloodstream
*T/F Trypanosomes are notorious for having a dominant surface antigen (variable surface glycoprotein) that changes to avoid immune system.
TRUE - antigenic variation via genetic rearrangement (on expressed locus, multiple 'silent' loci that can recombine)
- months/year later - infects CNS, brain, spinal fluid.
Are free-living amebae present and do they cause disease?
There are free living Amebae out in the world causing many different types of diseases including - encephalitis and eye infections (with contact lenses and will target cornea)
What intestinal protozoa is a worldwide zoonosis?
Giardia lamblia and Giardiasis (disease)
and CRyptosporidium
Where is Giardia lamblia found?
in water contaminated with feces from animal carriers (with cysts)
- lakes, streams, ponds
*What are the giardia lamblia cysts highly resistant to?
Chlorine - waterborne outbreaks (can get into water treatment
Stomach acid - *stimulates cysts to transform to vegetative trophozoites. (likes acid) allows cyst to get into sm. intestine and grow
What does Giardia lamblia cause in the host it's infecting?
Mild, persistant diarrhea
- not bloody like Entamoeba
- Asymptomatic carriers can pass cysts for years.
- Daycare and mental institution epidemics are common
*How do the trophozoites attach to the sm. intestine (duodenum) and cause diarrhea?
using ventral sucking disk (african shield morphology), but do not invade
- inflammation leads to maladsorption of proteins and fat (greasy, foul smelling stools)
What does Entamoeba histolytica cause?
Amebiasis
What is Amebiasis?
Destruction of host tissue (colon) - =bloody diarrhea (unlike giardia)
-flask-shaped ulcers, can spread via - bloodstream and produce abscesses in liver, brain and other organs
How is Entamoeba histolytic transmitted?
fecal-oral route
-has vegetagtive trophozoite (like giardia)
- highly resistant cyst (like giardia)
WHat is the main differing characteristic between giardia and entameoba?
bloody diarrhea - ent.
mild, persistnat diarrhea - giardia
How do the entamoeba histolytica destroy the host tissue?
adhere to host cell receptors containing DIAGALACTOSE RESIDUES - attachment via lectin surface protein
Damage
- Attachment
- Contact killing - secretes Pore-forming proteins (amebapores) -which are analogous to toxins
- ingestion of killed host cell by ameba (as food)
What happens to Non-immune hosts and entamoeba histolytica?
Pathogenic amebas destroy host phagocytic cells (neutrophils, non-activated macrophages)
require other phagocytic cells to take over
*What is required to become immune to entamoeba histolytica?
- Cell-mediated immunity required
circulating antibodies not likely important because....
- *Amebas produce cysteine protease that digests IgA, IgG and other proteins. - THIS IS WHY AB aren't effective.
Another zoonosis that resembles toxoplasma. it is a intestinal protozoa is often in rural areas but can be spread person to person in crowded urban environments (day care centers)
- Out breaks with public water systems - found in most surface waters that utilites draw from.
- what is it?
Cryptosporidium
How does Cryptosporidium resemble toxoplasma?
Infectious oocysts produced in intestine and spread to other animals.
- highly resistant to chlorine (like giardia)
- expelled in huge numbers in watery stools
*T/F Cryptosporidium invades intestinal epithelial cells and disseminate
*FALSE; they DO NOT invade intestinal epithelial cells or disseminate , stay localized
- stay within microvilli of small intestine
- single episode of diarrhea that lasts </= 2 weeks
- common in great britain and US
What protozoa resembles cryptosporidium - produces acid-fast cysts, but the cysts are 2x LARGER.
Cyclospora cayetanensis
*T/F the Large cysts produced by Cyclospora cayetanenses are NOT infectious when excreted in human feces
TRUE -*must incubate (days/weeks) in environment at warm temp. and high humidity **(differs form cryptosporidium whose are immediately infectious - main diff.)
Where do the infections come from for Cyclospora cayetanensis?
from contaminated food or water by the incubated cysts -
thus, person-to person spread RARE
Which one has an initial life cycle in the environment?
cryptosporidium or cyclospora cayetanensis?
cyclospora cayetanensis
What intestinal parasite is a common *vaginal flagellate (15% or more of women)
-can occasionally cause vaginalis
*Trichomonas vaginalis
How is trichomonas vaginalis transmitted?
sexual contact
- *men are usually asymptomatic
What are the two other trichomonas that are less common, less pathogenic species and where are they found?
T. hominis - GI tract
T. tenax -Mouth
What is the most frequent infection (southern US) caused by (intestinal helminth)
Ascaris
Name the 3 Intestinal Helminth's we are responsible for?
Roundworms(Ascaris)

Pinworms(Enterobius)

Hookworms(Necator american, Ancylostoma duodenale)
Which of the 3 intestinal helminth's are nematodes?
roundworms
pinworms
hookworms
- ALL of them
What is the life cycle of Ascaris(roundworm - intestinal helminth)?
- eggs require several weeks in environment to mature to infective stage
- eggs are ingested
- hatch in small intestine and release larvae that penetrate mucosa
- travel to lung, then to trachea/pharynx and swallowed
- Mature in GI lumen and eggs released in stool

(occurs over and over again)
*How does Enterobius (pinworm) differ from round worms?
*Eggs DO NOT require maturation stage outside of body
How is Enterobius (pinworms) transmitted?
readily by fecal-oral route (ingestion)
- b/c eggs resist drying and can be transmitted from clothes or dust
- hatch in sm. intestine and larvae mature in large intestine
- females travel perianal skin, layeggs (perianal itching symptom, which facilitates spread)
What intestinal helminth is assoc. with an "itchy crack"?
Pinworms - enterobius
*Which intestinal helminth can penetrate through the skin?
called:fecal-cutaneous route.
*Hookworms as filariform larvae (unlike other helminths)
- soil contaminated with human, cat or dog stools and larvae
*Do not require ingestion
- *Fecal-cutaneous route
Once inside the skin where do the hookworms head?
move form skin to heart via blood or lymphatics an become trapped in lung
- difference btwn human vs. dog/cat hookworms is that in dog/cat the hookworms stay in the skin.
Once the hookworm breaks through the lung, what is the rest of it's life cycle?
coughed up, swallowed to GI tract - life cycle continues in sm. intestine and eggs release (10,000-20,000 eggs/day)
How come individuals with hookworms exhibit chronic anemia?
hookworms hang onto intestinal mucosa with teeth, secrete anticoagulatn, and suck host's blood
-severity proportion to worm burden
*How are tapeworms acquired?
*by eating raw or uncooked fish
Taenia saginata - beef
Taenia solium - pork
Diphyllobothrium latum (fish)
- all human infections correlate with consumption of undercooked or raw meat - cooking destoryed larvae -
What does the tapeworm life cycle depend on?
humans (definitive host) and animals (intermediate host)
*What is the life cycle of tapeworms?
cattle infected, enter bloodstream, lodge in tissues...eggs hatch, enter bloodstream, lodge in tissues
- **Humans infected by eating beef containing larvae -> (CYSTICERCI)
How long can tapeworms live in intestine and to what length do they grow?
can live in intestine for decades and grow up to 10 m in length
- fish tapeworm associated with B12 deficiency
*What Tissue and Blood Helminth is ingestion required and causes trichinosis?
Trichinella spiralis
T/F Most infections of trichinosis are asymptomatic.
true, but larvae hatch, cross mucosa, enter lymphatics and blood = diarrhea/pain
The trichinella spiralis larvae can become encysted, what does this cause?
can produce inflammation in striated/cardiac muscle
the cysts calcify, but worms can be viable for 30 yrs. = recurrent infection later on in life.
*What tissue and blood helminth is skin acquireed, and each species has unique geographic distribution, dependent on SNAIL intermediate host?
Schistosomes (blood flukes)
What is Schistosomiasis symptoms dependent on?
location of the adult worms and the type of eggs released.
**What Schistosome species are found in bladder, sm. int. and large int. - describe each one?
*S. haematobium - bladder (eggs released in urine
*S. mansoni - large intestine (eggs released in stools
*S. japonicum - small intestine (eggs released in stool)
What is the life cycle of Schistosomes?
Infective cercariae released form snails - burrow through skin of people in infected water, los tails and change to schistosomulae that enter blood -> pass to portal venous system to mature - > move in pairs (male/female) to smal/large intestine/bladder, sexually reproduce and eggs released.
T/F Schistosomiases eggs trapped in host tissues induce formation of granulomas that undergo fibrosis that can produce disease symptoms years later.
true