Parasitic Infections I - Protozoa Flashcards
symbiosis
when two species live together
mutualism
symbiosis that brings benefit to both species
commensalism
symbiosis where one species receives all the benefit, while the othe ris neithe rbenefited nor harmed
parasitism
when one species lives at the expense of the other and often inflicts injury or damage on the other
Name the five types of infectious agents from most to least numerous on Earth.
bacteria
viruses
fungi
parasites
prions
general fatures of parasites
majority are free-living, ecologically significant, do not infect humans
minority are obligate parasites, dependent on hosts for survival
complex life cycles
level of adaptation determines clinical consequence of infection
parasitic diseases
diseases of humans caused by infections with:
protozoa
helminths
arthropods
human parasitic diseases
many more worm infections in tropics than people
infrequent in temperate, sanitated, industrialized world
found in US primarily among poor, immunocompromised, sexually active
27% of US population harbor worms
becoming more important in the US as a result of immigration, travel to endemic areas, AIDS (unusual parasites)
host
organism in which parasite lives
definitive host
harbors adult (sexual) stage of the parasite
paratenic host
harbors a form of the parasite that does not undergo further development
reservoir
animal (definitive) host that enables a parasite to persist in the environment
vector
insect that transmits infectious microorganisms from one host to another
cestode
tapeworm
nematode
roundworm
termatode
flatworm or fluke
zoonosis
disease or infection that is naturally transferable between animals and humans
autochthonous
local, type of disease transmission in which infection acquired in the area which it is diagnosed
general principles of parasite evolution
population genetics/natural selection
host range, life cycle transitions occur in specific hosts
parasite and host genetic heterogeneity
protozoa multiply in the human host
helmminths do not multiply in the human host, worm burden determines outcome
eosinophilia
important considerations for infectious agents
route of infection
disease pathophysiology
method of diagnosis
strategies for public health intervention - lif cycle (hosts)
problems with control of parasitic disease
development of resistance to chemotherapeutic agents
political and socioeconomic problems
genomic plasticity
intestinal protozoa
amoebae or rhizopods (entamoeba histolytica)
ciliates (balantidium coli)
flagellates (giardia lamblia)
sporozoans (cryptosporidium spp.)
amebiasis
amoeba (rhizopod) - most primitive of protozoa, multiplies by binary fission and moves by means of cytoplasmic organelles called psudopodia
life cycle: cyst (passed in stool) -> ingested, excysts in the small intestine -> trophozoite (colon) -> encysts (colon)
epidemeology:
- human is only reservoir
- cysts are infective, allows person-to-person (fecal-oral) transmission
- transferred among family members, in day care centers
- affects 10 percent of world population
- risk factors include travel to endemic area and instiutionalization
disease properties:
- 90% are asymptomatic cyst passters
- intestional amebiases, symptomatic cyst passer, acute rectocolitis (dysentry), rare findings include toxic megacolon, ameboma, acute amebic appendicitis
- extraintestinal amebiasis
- diagnosis made by examination of stool for cysts or trophozoites
giardiasis
life cycle of Giardia lamblia:
cyst (passed in stool -> ingested, excysts in small intestine -> trophozoite (small intestine) -> encysts (colon) -> cyst
epidemiology:
- cysts survive in water
- spread by fecal-oral transmission
- reservoirs are humans and beavers
- isolated causes in hikers and campers who drink untreated water
- outbreaks due to contaminated water supply, person-to-person transfer in day care center
disease properties:
- bloating, gas, chronic diarrhea
- epigastric pain, malabsorption
- villous atrophy
- diagnosis made by examination of stool for cysts or trophozoites
cryptosporidiosis
sporozoan - protozoan with two replicatory modes (sporogony and schizogony)
Cryptosporidium spp. - obligate intracellular organism (small bowel epithelial cells)
sporogenic (sexual) cycle leads to formation of occysts, which are shed into bowel luman and passed
fecal-oral transmission (oocyst immediately infective), sporozoites released from ingested oocyst infect small bowel epithelial cells
disease properties:
- normal host, watery diarrhea lasting about two weeks, self-limiting
- immunocompromised host, profound, watery diarrhea, weight loss, malabsorption, eventual death
- diagnosis made by examination of stool for oocysts, modified acid-fast stain
blood and tissue protozoa
amoebae
flagellates
sporozoans
pneumocystis carinii
Name the four flagellates covered.
Trypanosoma brucei
Trypanosoma cruzi
- Leishmania spp.*
- Trichomonas vaginalis*
Name the two sporozoans covered.
- Plasmodium spp.* (malaria)
- Toxoplasma gondii*
primary amoebic meningoencephalitis
most often caused by amoeba Naegleria fowleri, found in fresh water, soil
occurs most often during summer months in individuals who have been in contaminated water, parasite throught to enter human through nasal mucosa
fulminating meningoencephalitis leading to death within one week
factors involved in pathogenesis poorly understood
diagnosis made by examination of cerebrospinal fluid for motile amoebae
African Sleeping Sickness
caused by flagellate Trypanosoma brucei, insect vector is the tsetse fly
life cycle - introduced to mammal during bloodmeal, bloodform trypomastigote (mammalian bloodstream) -> antigenic variation (mammalian bloodstream) -> taken up by tsetse during bloodmeal, epimastigote (tsetse gut) -> metacyclic trypomastigote (tsetse salivary gland) -> introduced to mammal
clinical manifestation
- results from high parasitemias, diffuse meningoencephalitis
- East African sleeping sickness caused by T. b. rhodesiense (acute disease) - abrupt onset of fever, headache, occipital lymphadenopathy)
- West African sleeping sickness caused by T. b. gambiense (subacute, chronic meningoencephalitis) - subtly personality changes -> somnolence -> coma -> death
- nagana caused by T. b. brucei - diseaes of cattle that renders much of subsaharan Africa unsuitable for raising livestock
- diagnosis made by identification of trypomastigoes in blood smear
VSG genes and antigenic variation
>1000 distinct genes
proteins are antigenically distinct
must be expressed at the end of chromosomes with the transferrin receptor genes
allows for VSG switching and gene conversion to stay ahead of the immune response
Chagas’ Disease
caused by flagellate Trypanosoma cruzi, insect vector is the reduviid bug
found throughout the Americas, about 300,000 infected in the US
Life Cycle - insect takes bloodmeal, defecates; metacyclics in feces contaminate bite wound or mucous membrane -> penetrates host cell, amastigote (insdie mammalian cell) -> bloodform trypomastigote, cell ruptures (mammalian bloodstream) -> taken up by reduvid during bloodmeal,epimastigote (reduviid midgut), metacyclic trypomastigote (reduviid hindgut) -> insect takes blood meal
Clinical Manifestations:
- acute phase (high parasitemia) - periorbital edema (Romana’s sign), fever, anorexia, hepatomegaly, lymphadenopathy, occasional death (mostly infants)
- chronic phase (undetectable parasitemia) - cardiomyopathy, megaesophagus, megacolon (autoimmune disease
diagnosis made xenomologically or serologically
additional modes of transmission, oral route (contaminated juices), glood transfusion, transplantation, vertical transmission
US blood supply screened for T. cruzi
Leishmaniasis
caused by several species of the genus Leishmania, vector is the sandfly
visceral leishmaniasis - L. donovani, L. donovani chagasi
Old World cutaneous leishmaniasis - L. major, L. tropica, L. ethiopia
New World cutaneous leishmaniasis - L. mexicana and L. braziliensis
New WOrld mucocutaneous leishmaniasis - L. braziliensis
Life Cycle - intracellular amastigote (host macrophage) -> extracellular promastigote (sandfly vector) -> intracellular amastigote
Epidemiology
- visceral disease in Africa, India, Brazil
- cutaneous disease throughout Latin America, Middle East
- mucocutaneous disease in Latin America, Middle East
- mucocutaneous disease in Latin America
Disease Syndromes
- visceral (kala azar) - parasites in macrophages of reticuloendothelial sysstem
- cutaneous (oriental sore) - chronic, non-healing ulcer with heaped-up margins
- mucocutaneous (espundia) - occurs months to years after cutaneous infection with L. braziliensis, mutilating disease of cartilage
Diagnosis made by detection of trophozoites in vaginal discharge or urethral exudate (men)
trichomoniasis
caused by flagellate Trichomonas vaginalis
trophozoite stage only
venereal transmission
disease properties include vaginitis, prostatitis, urethritis
diagnosis made by detection of trophozoites in vaginal discharge or urethral exudate (men)
Malaria
caused by several species of the genus Plasmodium, vector is the mosquito
Life Cycle - circulating gametocytes taken up by mosquito during bloodmeal, sporogony (sexual reproduction) occurs, sporozoites -> mosquito takes bloodmeal, sporozoites introduced, infect hepatocytes, merozoites form -> merozoites may remain dorman ain hepatocyte or may divide -> cell ruptures, merozoites released -> merozoite infects red blood cell -> male and female gametocytes develop -> circulating gametocytes taken up by mosquito
erythrocytic cycle - trophozoit, multinucleated schizont, merozoites -> cell ruptures, merozoites released -> merozoite infects red blood cell -> trophozoite
Epidemiology
- number one cause of infectious disease in the world
- human is the only reservoir
Clinical Differentiation
- all species give rise to anemia, hypoglycemia, splenomegaly, splenic rupture
- diagnosis made by exmination of blood smear
toxoplasmosis
caused by obligate intracellular sporozoan Toxoplasma gondii
Life Cycle and Epidemiology
- both sexual and asezual cycles in cate, the definitive host
- oocysts found in cat feces
- livestock may ingest oocysts which break down and releases trophozoites -> invade a variety of tissues -> replicate to form tissue cysts
- transmission to humans after ingestion of oocysts or tissue cysts -> trophozoites -> tissue cysts
- 1 of 500 pregnant women acquires acute toxoplasmosis -> parasite transmitted to fetus in half of these women
Disease Properties
- acute acquired disease in normal host - no symptoms or mononucleosis - like sympotoms
- acute acquired or reactivation disease in immunocompromise host - encephalitis, pneumonitis, myocarditis, chorioretinitis
- congenital disease - spontaneous abortion, stillbirth, severe CNS manifestations, chorioretinitis
diagnosis made serologically or by demonstration of trophozoites in tissue biopsies
pneumocystosis
caused by fungus Pneumocystis carinii
cystic and extracystic forms
cyst spherical to oval, contains up to 8 intracystic cells
extracystic form is trophozoite
found in lungs of many mannals, global distribution
transmission probably airborne
Disease Properties
- occurs in immunocompromised patients
- pneumonia
diagnosis made by detection of trophozoites in psutum or bronchial lavage/brush biopsies
