Small Group Parasites 1

Question 1

Outline the life cycle of the Plasmodium species that cause malaria.

Answer 1

bite by anophelus- will transmit sporozoites that travel to the liver and reproduce assexually before invading the RBC, reproduction causes RBC to rupture. some develop into gameocytes which require uptake by mosquito for sexual reproduction

Question 2

Describe how transmission of malaria parasites occurs.

Answer 2

bit by female anopheles mosquito

Question 3

Discuss the significance of identifying the geographic origin from which the infection
was acquired and the species of the infecting parasite.

Answer 3

strain and resistance can be prodicted from geographical origin of the infection

Question 4

Describe 2 proposed hypotheses to explain the pathogenesis of cerebral malaria.

Answer 4

Two hypotheses: 1) the mechanical hypothesis - parasitized and uninfected erythrocytes sequester in cerebral capillaries causing anoxia, ischemia, and acidosis; 2) the inflammatory hypothesis - parasites induce immunopathological responses involving cytokines.

Question 5

Discuss immunity to malaria in terms of duration, specificity, and the problems
encountered while attempting artificial immunization.

Answer 5

Immunity in context of malaria refers to lack of signs or symptoms despite presence of parasites, immunity to malaria is not durable or long-lasting

Question 6

Describe the measures that can minimize the risk of acquiring malaria.

Answer 6

Permethrin-impregnated bednets; long sleeves and pants; DEET or picardin repellents; avoid outdoor activity during peak time of mosquito feeding – nighttime for anopheline mosquitos; (midgut of infected mosquito covered with
oocysts); working and living areas screened

drug prophylaxis based on the most recent resistance patterns

Question 7

Outline the life cycle of Giardia lamblia.

Answer 7

guard cyst are resistant forms that are transmitted through contaminated water or foods, in the small intestine the excystation releases trophozoites which multiply and attach to the intestine, encystation occurs as the parasites transit toward the colon and are passed in feces

Question 8

Discuss the pathology of giardiasis.

Answer 8

protozoans cause decreased expression of brush boarder enzymes, morphological changes to the microvillus and programmed cell death of small intestinal epithelial cells (no invasion of guard trophozoites)

alteration of villi leads to inability to absorb nutrients and water, resulting in diarrhea, bloating, flatulance etc.

Question 9

List possible sources of infection and explain how infection may be prevented in each one.

Answer 9

hiking and drinking contaminated water
spread often in daycares

adequate chlorination of domestic water supplies does not reliably eliminate guard, cryptosporidium or entamoeba from drinking water (requires boiling or filtration through sand/membrane filter)

good hand hygienic procedures important for daycares

Question 10

Discuss how a diagnosis of giardiasis is made.

Answer 10

(1) giardia antigen test in stool samples using ELISA, (2) ova and parasite contraction from stool, (3) direct fluorescent antibody procedure also

tx with tinidazole or nitazoxanide, paromomycin in pregnant women

Question 11

Outline the life cycle of Toxoplasma gondii.

Answer 11

cats are the definitive host for Toxo and unsporulated oocysts that are shed in cat feces can sporulate and become infectious to humans

after ingestion, tachyzoites localize in neural and muscle tissue and develop cysts

Question 12

Discuss the pathology of toxoplasmosis.

Answer 12

bradyzoites or sporozoites penetrate the intestinal cells and spread locally to lymph and distant organs via lymph and blood, focal areas of necrosis may develop in a variety of organs– lead to fever, headache, muscle pain, anemia and sometimes lung complications

transmission during pregnancy can lead to 60% subclinical infection, 30% encephalitis/hydrocephalis/ retinochorodiditis or abortion 10%

Question 13

Discuss the significance of serology in the diagnosis of toxoplasmosis.

Answer 13

IgG positive means previously exposed
IgM means active infection, maybe
check IgG avidity if IgM is possitive

if negative retest in 3 weeks

Question 14

Discuss the impact of toxoplasmosis on human beings in utero and extending to old age.

Answer 14

transmission during pregnancy can lead to
60% subclinical infection,
30% encephalitis/hydrocephalis/ retinochorodiditis or
10%abortion

Question 15

Describe how toxopalsmosis can be prevented.

Answer 15

infection in humans can occur through

eating undercooked meat with tissue cysts
food or water contaminated by feces (gardening)
blood transfusion or transplantation
transplacentally mother to fetus

cook/freeze meats, wash vegetables and prevent infection in pregnant women by care with gardening and caring for cats (use gloves and change litter daily), TMP/sulfa prophylaxis in immunocompromised patients to prevent reactivation

screening in women is only done if there is abnormality in the prenatal ultrasound

Question 16

Describe the life cycle of Cryptosporidium and how it is transmitted.

Answer 16

transmission via ingestion of infected water containing oocysts, after encystation in intestine organism reproduces sexually and asexually, oocysts are excreted from host

Question 17

Describe how a diagnosis of cryptosporidiosis is made.

Answer 17

stool ELISA, DFA; acid fast stain for oocytes in stool or O&P testing

Question 18

Describe the characteristics of diarrhea caused by cryptosporidium.

Answer 18

profuse watery diarrhea that is not bloody

Question 19

What blood smear findings would you expect with P. falciparum infection?

Answer 19

more than one ring stage within RBC, very high parasitemia, presence of banana-shaped gametocyte

Question 20

Why is P. falciparum a more severe infection?

Answer 20

RBCs infected with P. falciparum adhere much more and are sequestered in small capillaries of the brain, lung, kidney and placenta which decreases the ability of the reticuloendothelial system to clear infected RBCs