Transmission
Humans can become infected with the parasite due to ingestion of infective eggs by mouth contact with hands or food contaminated with egg-carrying soil. However, there have also been rare reported cases of transmission of Trichuris trichiura by sexual contact.
Reservoirs
Humans are the only known reservoir for Trichuris trichiura.
Vector
Non-biting cyclorrhaphan flies (Musca domestica, Chrysomya rufifacies, Musca sorbens, Lucina cuprina, Calliphora vicina, Chrysomya bezziana and Wohlfarthia magnifica) have been found to carry Trichuris trichiura. A study in two localized areas in Ethiopia found cockroaches were carriers for several human intestinal parasites, including Trichuris trichiura.
Incubation Period
The exact incubation period of Trichuris trichiura is unknown, however immature eggs in soil under favorable conditions take about three weeks to mature: 15-30 days, 10 days minimum to mature before ideal ingestion by the human host. Favorable conditions for maturation of eggs is warm to temperate climates with adequate humidity or precipitation, as ova are resistant to cold, but not resistant to drying. Once ingested, the larva will remain dug into a villus in the small intestine for about 2-3 days until it is fully developed for migration to the ileo-cecum section of the gastrointestinal tract. The average total life span of Trichuris trichiura is one year, although there have been longer cases reported, lasting as long as five years (Note: inadequate treatment and re-infection are likely to play a role in this).
Morphology
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| Egg of whipworm |
Adult worms are usually 3-5 cm long, with females being larger than males as is typical of nematodes. The thin, clear majority of the body (the anterior, whip-like end) is the esophagus, and it is the end that the worm threads into the mucosa of the colon. The widened, pinkish gray region of the body is the posterior, and it is the end that contains the parasite’s intestines and reproductive organs.
Trichuris trichiura has characteristic barrel-shaped eggs, which are about 50-54 um long and contain polar plugs (also known as refractile prominences) at each end(bipolar plugs). ts color varies from yellow to brown and the "plugs" are colorless. It appears as 1 cell or unsegmented in its stage of development when being passed.
Life Cycle
Unembryonated eggs (unsegmented) are passed in the feces of a previous host to the soil. In the soil, these eggs develop into a 2-cell stage (segmented egg) and then into an advanced cleavage stage. Once at this stage, the eggs embryonate and then become infective, a process that occurs in about 15 to 30 days). Next, the infective eggs are ingested by way of soil-contaminated hands or food and hatch inside the small intestine, releasing larvae into the gastrointestinal tract. These larvae burrow into a villus and develop into adults (over 2-3 days). They then migrate into the cecum and ascending colon where they thread their anterior portion (whip-like end) into the tissue mucosa and reside permanently for their year-long life span. About 60 to 70 days after infection, female adults begin to release unembryonated eggs (oviposit) into the cecum at a rate of 3,00 to 20,000 eggs per day, linking the life cycle to the start.
Summary.....
For photo:
The unembryonated eggs are passed with the stool 1. In the soil, the eggs develop into a 2-cell stage 2, an advanced cleavage stage 3, and then they embryonate 4; eggs become infective in 15 to 30 days. After ingestion (soil-contaminated hands or food), the eggs hatch in the small intestine, and release larvae 5 that mature and establish themselves as adults in the colon 6. The adult worms (approximately 4 cm in length) live in the cecum and ascending colon. The adult worms are fixed in that location, with the anterior portions threaded into the mucosa. The females begin to oviposit 60 to 70 days after infection. Female worms in the cecum shed between 3,000 and 20,000 eggs per day. The life span of the adults is about 1 year.
Pathogenesis
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| Morphology of whipworm |
The whipworm derives its name from its characteristic whiplike shape; the adult (male, 30-45 mm; female, 35-50 mm) buries its thin, threadlike anterior half into the intestinal mucosa and feeds on tissue secretions, not blood. This relative tissue invasion causes occasional peripheral eosinophilia. The cecum and colon are the most commonly infected sites, although in heavily infected individuals, infection can be present in more distal segments of the GI tract, such as the descending colon and rectum.
Immunologically, cytokines such as interleukin 25 (IL-25) mediate type 2 immunity and are required for the regulation of inflammation in the gastrointestinal tract.
Recent linkage analyses of a genome-wide scan revealed that 2 quantitative trait loci on chromosomes 9 and 18 may be responsible for the susceptibility to infection with T trichiura in some genetically predisposed individuals.
Reference
