Question

Medical Microbiology Tutorial: Trematode Infections

Answer 1

fair warning, this gets pretty gross even by medical micro standards

Answer 2

\({\bf{Trematode~Characteristics:}}\)



- informally known as flatworms even though some are not flat in appearance
- typically hermaphroditic w/ a notable exception being Schistosoma (which will be the main focus of this tutorial)
- lack segmented bodies
- lack a body cavity
- their digestive tube ends in a cecum
- 2 suckers (one at the "mouth" and one on the "belly" or ventral side)
- life cycle contains 2 hosts
- have a secretory pore at posterior end

Answer 3

\({\bf{Schistosomiasis:}}\) (other names: bilharzia, snail fever)
- 2nd most prevalent parasitic infection w/ the 1st being malaria
- typically affects tropical climates and less-developed areas
- three main species (S. haematobium, S. mansoni, S. japonicum) although we'll just be covering the first two here

Life Cycle
1. Eggs are shed from human host into a water source
2. Eggs hatch into water. Miracidia are released.
3. Miracidia swim and infect snails
4. In the snail, miracidia form cercariae (characterized by long tail)
5. Cercariae are released into the water and enter human host again
6. Cercariae form schistosomulae, and follow human circulation to the liver.
7. Maturation in liver to the mature male and female forms. Reproduction in mesenteric venules (mansoni) or bladder (haematobium).
8. Eggs are deposited in portal/perivesical system.
9. Eggs move to the intestine (mansoni) or urinary tracts (haemotobium)
10. Eggs are expelled through solid/liquid waste. Will typically end up in a water source one way or another, and repeat the cycle.

Answer 4

\({\bf{Symptoms:}}\) are different between mansoni and haematobium but the shared ones are:
- swimmers itch
- allergic reactions such as rashes, fever, muscle pain, pneumonitis

now, considering them separately
mansoni
- bloody stool/diarrhea
- ulcers and fibrosis (fibrous CT buildup)
- strictures (restriction of blood vessels)
- varices (vein enlargement)
- hypertension in abdominal blood vessels

haematobium:
- bloody urine
- UTIs
- fibrosis
- kidney/renal failure
- bladder cancer

Answer 5

\({\bf{Diagnosis:}}\) analysis of urine or stool samples as appropriate to identify the presence of worms or eggs. immunobody assays can identify parasite antigens.

\({\bf{Treatment:}}\)
predominant treatment is praziquantel

\({\bf{Prevention:}}\)
environmental considerations, improvements to water quality and infrastructure.

Answer 6

Sources:
- https://www.cdc.gov/dpdx/schistosomiasis/index.html#targetText=Life%20Cycle&targetText=Schistosoma%20eggs%20are%20eliminated%20with,and%20the%20production%20of%20cercariae%20.
- https://www.cdc.gov/parasites/schistosomiasis/diagnosis.html
- https://www.who.int/news-room/fact-sheets/detail/schistosomiasis