Schistosoma

Schistosoma

These blood flukes infect hundreds of millions of people worldwide and are cause the second most socioeconomically devastating parasitic disease (after malaria).   Despite effective treatments and drugs that can preventing infection, this parasite is endemic (always present) in many tropical countries in Africa, the Caribbean, South America, Southeast Asia and the Middle East.  More than 250 million people each year are infected with this parasite and live with its damaging effects.  Children who are repeatedly infected can develop anemia, malnutrition, and learning difficulties. After years of repeated infections, the parasite can also damage the liver, intestine, lungs, and bladder. Rarely, eggs are found in the brain or spinal cord and can cause seizures, paralysis, spinal cord inflammation or even death.

One example of where this disease spreads quickly is in tropical areas where farming is done in shallow water (like rice paddies).  Farmers  work in rice paddies for many hours a day.  When there is no separation of the water they are working, swimming and playing in from the contaminated urine and feces, the situation is ripe for infection.  

Schistosoma mansoni is one of the six species of pathogenic blood flukes.  They have a complicated life cycle where eggs hatch into a snail host and go through several stages of development. After maturation in the snail, mature larvae are released into fresh water.   If a person swims or wades in the contaminated water, the mature larvae can burrow through the skin and migrate to the capillaries in the intestine.  As the larvae mature into an adult in the capillaries, a male and female fluke pair up, mate, and the female lays eggs that are passed in feces of the infected person. Snails eat the eggs from water contaminated with feces and the cycle begins again. 

Answer the following questions about Schistosoma: 

1. Is Schistosoma dioecious or hermaphroditic?         [ Select ]      ["dioecious", "hermaphroditic"] 
2. There are four possible modes of transmission  (Fecal/oral, predator/prey, transdermal and vector) .  Which one best describes how a human gets infected with Schistosoma?         [ Select ]      ["Transdermal", "Predator/Prey", "Vector", "Fecal/oral"] 
3. What form of Schistosoma is infectious for humans?         [ Select ]      ["larvae", "egg"] 
4. What is the intermediate host Schistosoma?         [ Select ]      ["human", "snail"] 
5. What is the definitive host Schistosoma?         [ Select ]      ["snail", "human"] 

 Based on everything you read about Schistosoma, could a human get infected with Schistosoma via direct contact with an infected person or their feces? Why or why not?

Schistosoma could not direct contact with infected person or their feces because the pathogen need the intermediate host (snail ) to complete its life cycle. 

1. 1. egg pass from human the feces contaminated the water source or water reservoir  
2.   larvae must infect the snail 
3. infected snails leave the infectious larvae in the water 
4. humans get infected when contaminated with infected water