Protozoan and Helminth Parasites
See Alcamo, 4th , p 451-465, Campbell’s 5th, pp 524-528, Tortora, Funke& Case, 7th, pp 349-366, 8th: 352-375.
Illustrate the protozoans (first three specimens) at 1000x, and the last, the nematode Trichinella, at 400x (or 100x). As always, scan at lower power to find a field rich in organisms. Take care to maintain correct scale. Label features which can be observed, note diseases they cause.
MASTIGOPHORA: Class of whip-bearing protozoans, in kingdom protista, phylum protozoa
Slide 22 Trypanosoma gambiense (PS 310)
(or view Trypanosoma lewesi PS 300, harder to see)
In an infected blood smear, among the erythrocytes (RBCs), wavy organisms with nucleus, flagella and (hard to see) undulating membrane. A member of the kinetoplastids.
Causes sleeping sickness. Spread by the tsetse fly vector in Central Africa. Forms a chancre at bite, fever, facial edema, lymphadenopathy, CNS symptoms, finally, after several years, fatal coma.
Slide 19 Giardia lamblia (PS 210)
In an infected fecal smear. Bilateral trophozoites: two cells adhered looks like a tear drop with two nuclei appearing like eyes. Note “old man” appearance due to diploid structure. The eyes are the nuclei of two cells.
giardiasis: Most common protozoal disease, 4% of USA population are infected, commonly asymptomatic. Causes small intestine enteritis (nausea, flatulence, eructation, copious, frothy, foul smelling diarrhea). Coats wall of sm intestine, can prevent absorption of nutrients, esp. lipids. Transmitted in feces as cysts, human and wild animals. One cause of traveler’s diarrhea, not killed by Cl2 .
Slide 20 Trichomonas vaginalis (PS 250)
In an infected vaginal smear: Roughly circular, nucleus is barely visible within cell. The flagellum is only occasionally visible. Note squamous cells and polymorphonucleocyts.
8 additional views of T. vaginalis:
Here is a cluster with a polymorphonucleocyte in the field.
Causes vaginitis, when pH is 5.5 or above. Found in GU of males & females. Causes pruritus, copious green/yellow frothy discharge (ingests lactobacilli which raises vaginal pH from 3 to 4.5). 30% of the population is colonized. STD, spread also on towels, toilet facilities, very sensitive to drying.
Plasmodium vivax causes malaria, infecting 250 mil in world, 1 mil die/yr in Africa):
REPRODUCTION: Plasmodium vivax infects salivary glands of Anopheles mosquito: several 100 sporozoites injected with a bite. These migrate to liver where (in 2-4 wks) they are transformed to many thousand asexual spores, merozoites. These infect RBC, form ring stage, asexually generating more merozoites by schizogony (multiple fission), released by lysis (fever). Anopheles mosquito draws blood containing gametocytes (develop from merozoites), sexual reproduction occurs in female mosquito (zygote formed) in salivary glands. meiotic products form sporozoites.
Signs: fever with each coordinated RBC rupture cycle. Last 8 hrs, then 48 hr remission, repeat fever, RBC destroyed, anemia, splenomegaly, “blackwater fever”, RBC fragments block arteries to organs.
PHYLUM NEMATODA (Kingdom Animalia)
Slide 24 Trichinella spiralis (PS 2430)
At 100x or 400x: Illustrate several cysts in striated muscle (tongue) . Note numerous sections through the coiled nematode. The roundworm is suspended in a jelly-like material within the capsule.
Trichinosis is caused by this eukaryote. Encysted larvae occur in pork, bear meat, and flesh of other carnivores. They mate in intestine, lay living larvae. Cross GI track, migrate through blood to muscles (frequently to the eyelids, causing puffiness over the eyes). Can cause heart, kidney failure. Only 150 cases/yr these years in the USA, but >90% of Americans carry Ab, i.e., carry at least a few worms. They are killed by >77 C temperatures, but often survive microwave cooking because of cooler spots within the meat.