Mawworm

Ascaris lumbricoides

ORDER Ascaridida

FAMILY

Ascarididae

TAXONOMY

Ascaris's lumbricoides Linnaeus, 1758, Homo sapiens, Europe.

OTHER COMMON NAMES English: Large roundworm.

PHYSICAL CHARACTERISTICS

One of the largest and most common parasites, it measures 8-18 in (20-46 cm) in length by 0.12-0.24 in (3-6 mm) in width for females; males generally more slender and shorter at 6-12 in (15-30 cm) in length by 0.08-0.16 in (2-4 mm) in width. Bodies are cylindrically shaped, with a head that is slightly narrower. Males have a curved tail with two spicules, but no copulatory bursa; females have a vulva approximately one-third of the length of the body down from the head, and a blunt tail. Characterized with smooth, finely striated cuticle; lip region is well developed and separated from the cervical region. The mouth has three lips, each equipped with small papillae. Internally, they have a cylindrical esophagus opening into a flattened ribbon-like intestine. Female ovaries can be 3.3 ft (1 m) in length). The eggs have thick shells consisting of a transparent inner shell covered in a warty, albuminous coat, and are sticky to the touch. The size of the eggs are 0.00197-0.00295 in (50-75 pm) in length by 0.00158-0.00197 in (40-50 pm) in width. The excretory system empties every three minutes or so.

DISTRIBUTION

Cosmopolitan. In 1986 they caused over 64 million infections worldwide. (Specific distribution map not available.)

HABITAT

Most common in warm, moist climates or in regions with temperate or tropical climates. They live in the small intestines of humans and pigs.

BEHAVIOR

Have a direct and simple lifestyle, with no intermediate hosts, unlike many parasites. Adults live in the lumen of the small intestines and eggs are passed in the feces. The eggs hatch in the small intestine. Once they grow into an adult worm and mate, they become as large as 12 in (31 cm) in length by 2 in (4 cm) in width.

FEEDING ECOLOGY AND DIET

Feeds on the semi-digested contents of the gut, although there is some evidence that it can bite the intestinal mucous membrane and feed on blood and tissue fluids.

REPRODUCTIVE BIOLOGY

Females can produce 200,000 to 2 million eggs per day, and 70 million in a year with very developed ovaries. The ovaries can contain 27 million eggs at one time. The fertilized eggs are broadly oval, and the shell is thickened, tuberculate and measure about 0.0098 in (250 pm) in length by 0.00059 in (15 pm) in width. About 2-3 weeks after passage in the feces and with ideal environmental conditions, the eggs contain an infective juvenile, and humans are infected when they ingest such infective eggs. Adults can live in the small intestine for six months or longer. In the intestine, eggs are only embryonated mass of cells, with further differentiation occurring outside the host. Eggs can stay alive in the soil for many years if conditions are adequate. The cycle from egg ingestion to new egg production takes approximately two months.

CONSERVATION STATUS Not listed by the IUCN.

SIGNIFICANCE TO HUMANS

About a sixth of the world's population suffers from ascariasis, a maw-worm infection often called "large roundworm infection." An estimated 25% of the people in developing countries are believed to be infected. In the United States, occurrence is uncommon with only four million people infected, mostly in the rural southeast. Infection occurs from ingestion of raw food such as fruit or vegetables. Infection with the species is rarely fatal, but death may occur because of mechanical intestinal obstruction. ♦

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