Science Daily | The wide range of genetic diversity in parasites means humans may often be infected with multiple strains at once, which could make infections worse and increase the prevalence of the parasite over time, according to a new study.
Schistosoma mansoni is a water-borne parasite with two hosts: snails and humans.
When eggs in excrement from infected humans make their way into bodies of water, they hatch and infect snails, where they multiply.
The parasite leaves the snail and enters the water, where it can infect humans by penetrating the skin.
To figure out what factors influence the amount of damage, or virulence, done to either host, Purdue University researchers studied the effects of two strains separately and then together.
“The amount of virulence that occurs when these two strains are together differs depending on which host they’re in,” explained Dennis Minchella, a professor of biological sciences at Purdue.
“In the snail, the nastier strain was suppressed by the dominant competitor, and the overall virulence was lower. But in the mouse, the harsher strain dominates.”
Mice with two strains of the parasite, or unrelated infections, fared similarly to those with only the nastier strain, but much worse than those with the weaker strain.
The findings were published in the International Journal for Parasitology.
Schistosoma mansoni starts to cause problems for humans several weeks after infection, when worms begin to reproduce.
Most eggs exit the body, but some get stuck in the liver and intestines, where they cause inflammation. This leads to swelling and an inflated, enlarged abdomen. Read the full story at Science Daily.
From Wikipedia, the free encyclopedia
- Kingdom: Animalia
- Phylum: Platyhelminthes
- Class: Trematoda
- Order: Diplostomida
- Family: Schistosomatidae
- Genus: Schistosoma
- Species: S. mansoni
Schistosoma mansoni is a water-borne parasite of humans, and belongs to the group of blood flukes (Schistosoma).
The adult lives in the blood vessels (mesenteric veins) near the human intestine.
It causes intestinal schistosomiasis (similar to S. japonicum, S. mekongi, S. guineensis, and S. intercalatum).
Clinical symptoms are caused by the eggs. As the leading cause of schistosomiasis in the world, it is the most prevalent parasite in humans.
It is classified as a neglected tropical disease.
As of 2016, 206.5 million people have schistosomiasis and S. mansoni is the major parasite. It is found in Africa, the Middle East, the Caribbean, Brazil, Venezuela and Suriname.
Unlike other flukes (trematodes) in which sexes are not separate (monoecious), schistosomes are unique in that adults are divided into males and females, thus, (dioecious).
However, the two adults live in permanent partnership, a condition called in copula; for this, they are considered as hermaphrodites.
The life cycle of schistosomes includes two hosts: humans as definitive hosts, where the parasite undergoes sexual reproduction, and snails as intermediate hosts, where a series of asexual reproductive takes place.
S. mansoni is transmitted through water, where freshwater snails of the genus Biomphalaria act as intermediate hosts. The larvae are able to live in water and infect the hosts by directly penetrating the skin. Prevention of infection is done by improved sanitation and killing the snails. Infection is treated with praziquantel.
S. mansoni was first noted by Theodor Maximillian Bilharz in Egypt in 1851, while discovering S. haematobium.
Sir Patrick Manson identified it as unique species in 1902. Louis Westenra Sambon gave the name Schistosomum mansoni in 1907 in honour of Manson.