Human blood fluke

Schistosoma mansoni

ORDER

Strigeatida

FAMILY

Schistosomatidae

TAXONOMY

Schistosoma mansoni Sambon, 1907, Africa. OTHER COMMON NAMES

French: Schistosome intestinal; German: Parchenegel PHYSICAL CHARACTERISTICS

A sexually dimorphic species, the female is thin and cylindrical, reaching between 0.5-1 in (1.2-2.5 cm) in length. The male is elongated but thicker, and reaches 0.39-0.78 in (1-2 cm) in length. He also has small spiny oral and ventral suckers, and a wrinkled dorsal surface dotted with tubercles (small nodules). A female typically exists in the male's gynecophoric canal, absorbing nutrients by diffusion from the male.

DISTRIBUTION

The human blood fluke is found in warm regions around the world, particularly in developing countries in South America, Africa, the Caribbean, and the Middle East.

HABITAT

Larvae of this digenetic parasitic flatworm infect the hepatic pancreas of freshwater snails of the genus Biomphilaria. Adult worms infect mesenteric veins of mammals ranging from rodents, dogs, cattle, and baboons to humans.

BEHAVIOR

Eggs, which have spines, lodge in the intestinal mucosa and cause ulceration as well as the formation of granulomata (lesions that result from a chronic inflammation). The eggs hatch in freshwater areas and develop into miracidia, which follow chemical, light and gravitational cues to find and then penetrate the soft tissues of the snails. A sporocyst then forms. Cer-cariae develop within the sporocyst. The cercariae leave the snail by swimming and actively seek out their next host, apparently targeting certain fatty acids of the skin. They then penetrate the skin of a secondary host, which may be a human being or other mammal. Once in the host, they become immature flukes called schistosomules, migrate to the circulatory system, and travel to a site (specifically the superior and inferior mesenteric veins and related smaller veins) near the large intestine. Once in the mesenteric veins, they mature, mate, and lay eggs, many of which leave the host's body with the feces. The cycle begins again when the eggs make their way into the freshwater habitat of the snail.

FEEDING ECOLOGY AND DIET

The hosts of the human blood fluke include Biomphilaria snails and mammals, including humans. They enter both snails and mammals by burrowing into the skin and other soft tissue. They feed on blood from the hepatic and mesenteric veins.

REPRODUCTIVE BIOLOGY

Adult males are typically found conjoined with the females, with the female remaining in the male's spine-covered gy-necophoric canal, a groove that runs along the lower surface of the body. Larger spines cover the lateral margins of the canal, which suggests that they may play a role in mating. The eggs, which bear a lateral spine, range from 0.0045-0.0068 in (115-175 pm) long and 0.0017-0.0027 in (45-70 pm) wide. The free-swimming miracidia are tadpole-like in appearance with a tail slightly smaller than the body. The cercariae are about 0.019-0.039 in (0.5-1 mm) long, with constricted waists and forked tails.

CONSERVATION STATUS Not listed by IUCN.

SIGNIFICANCE TO HUMANS

Infection with this species results in schistosomiasis, also known as bilharziasis, in humans. The condition causes abdominal pain, dysentery, lethargy, and anemia, leaving the victim weak and susceptible to other diseases. ♦

Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

Get My Free Ebook


Post a comment