Parasitic Infections I - Protozoa Flashcards Preview

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1

symbiosis

when two species live together

2

mutualism

symbiosis that brings benefit to both species

3

commensalism

symbiosis where one species receives all the benefit, while the othe ris neithe rbenefited nor harmed

4

parasitism

when one species lives at the expense of the other and often inflicts injury or damage on the other

5

Name the five types of infectious agents from most to least numerous on Earth.

bacteria

viruses

fungi

parasites

prions

6

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

7

parasitic diseases

diseases of humans caused by infections with:

protozoa

helminths

arthropods

8

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)

9

host

organism in which parasite lives

10

definitive host

harbors adult (sexual) stage of the parasite

11

paratenic host

harbors a form of the parasite that does not undergo further development

12

reservoir

animal (definitive) host that enables a parasite to persist in the environment

13

vector

insect that transmits infectious microorganisms from one host to another

14

cestode

tapeworm

15

nematode

roundworm

16

termatode

flatworm or fluke

17

zoonosis

disease or infection that is naturally transferable between animals and humans

18

autochthonous

local, type of disease transmission in which infection acquired in the area which it is diagnosed

19

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

20

important considerations for infectious agents

route of infection

disease pathophysiology

method of diagnosis

strategies for public health intervention - lif cycle (hosts)

 

21

problems with control of parasitic disease

development of resistance to chemotherapeutic agents

political and socioeconomic problems

genomic plasticity

22

intestinal protozoa

amoebae or rhizopods (entamoeba histolytica)

ciliates (balantidium coli)

flagellates (giardia lamblia)

sporozoans (cryptosporidium spp.)

23

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

24

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

25

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

26

blood and tissue protozoa

amoebae

flagellates

sporozoans

pneumocystis carinii

27

Name the four flagellates covered.

Trypanosoma brucei

Trypanosoma cruzi

Leishmania spp.

Trichomonas vaginalis

28

Name the two sporozoans covered.

Plasmodium spp. (malaria)

Toxoplasma gondii

29

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

30

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