Parasitic Infections I - Protozoa Flashcards Preview

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Flashcards in Parasitic Infections I - Protozoa Deck (37):
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

31

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

32

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

33

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)

34

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)

35

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

36

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

37

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