Trichuris suis
Encyclopedia
Trichuris suis is a whipworm
Whipworm
The human tapworm is a roundworm, which causes trichuriasis when it infects a human large intestine. The name whipworm refers to the shape of the worm; they look like whips with wider "handles" at the posterior end.-Life cycle:The female T. trichiura produces 2,000–10,000 single celled eggs per day...

; the variations in thickness of the anterior and posterior segments give the parasite the characteristic “whip-like” appearance. Adult females measure 6 to 8 cm and adult males 3 to 4 cm. T. suis eggs are oval (60 × 25 μm) and yellow-brown with bipolar plugs.
T. suis is also used in helminthic therapy
Helminthic therapy
Helminthic therapy, a type of immunotherapy, is the treatment of autoimmune diseases and immune disorders by means of deliberate infestation with a helminth or with the ova of a helminth. Helminths are parasitic worms such as hookworms and whipworms....

 studies.

Life cycle

The life cycle of T. suis is direct and does not require any intermediate host
Intermediate host
A secondary host or intermediate host is a host that harbors the parasite only for a short transition period, during which some developmental stage is completed. For trypanosomes, the cause of sleeping sickness, humans are the primary host, while the tsetse fly is the secondary host...

. Eggs are passed in feces from infected animals, but are single-celled and are not initially infectious. Infective J1 stage larvae develop within the shell in 3 weeks to 2 months, depending on environmental temperature. The infective J1 stage within the egg is highly resistant and can remain in this form for several years in favorable conditions. Once the infective J1 egg is ingested, the bipolar plugs are digested and the J1 larvae hatch in the small intestine
Small intestine
The small intestine is the part of the gastrointestinal tract following the stomach and followed by the large intestine, and is where much of the digestion and absorption of food takes place. In invertebrates such as worms, the terms "gastrointestinal tract" and "large intestine" are often used to...

 and cecum
Cecum
The cecum or caecum is a pouch, connecting the ileum with the ascending colon of the large intestine. It is separated from the ileum by the ileocecal valve or Bauhin's valve, and is considered to be the beginning of the large intestine. It is also separated from the colon by the cecocolic...

. The J1 larvae penetrate the mucosa via the crypts of Lieberkühn
Crypts of Lieberkühn
In histology, an intestinal crypt is a gland found in the epithelial lining of the small intestine and colon...

 in the distal ileum, cecum
Cecum
The cecum or caecum is a pouch, connecting the ileum with the ascending colon of the large intestine. It is separated from the ileum by the ileocecal valve or Bauhin's valve, and is considered to be the beginning of the large intestine. It is also separated from the colon by the cecocolic...

, and colon
Colon (anatomy)
The colon is the last part of the digestive system in most vertebrates; it extracts water and salt from solid wastes before they are eliminated from the body, and is the site in which flora-aided fermentation of unabsorbed material occurs. Unlike the small intestine, the colon does not play a...

. During the next 5 weeks, the larvae undergo four molts (J2, J3, J4) to the adult stage (J5) within the mucosal layers. The adult’s thicker posterior one-third then emerges through the mucosal surface into the lumen while the thin anterior two-thirds remains embedded in the mucosal layers. Adults can be recovered anywhere from the distal ileum to the rectum, but most are located in the cecum
Cecum
The cecum or caecum is a pouch, connecting the ileum with the ascending colon of the large intestine. It is separated from the ileum by the ileocecal valve or Bauhin's valve, and is considered to be the beginning of the large intestine. It is also separated from the colon by the cecocolic...

 and proximal colon. The prepatent period is 6 to 8 weeks and life span is 4 to 5 months.

Epidemiology

Pigs are the natural host for T. suis, but it can also affect other species - including people. Humans probably become infected with T. suis by ingesting contaminated soil or water. T. suis is found worldwide, but is most prevalent in warm, humid climates. It is rare or nonexistent in arid, very hot, or very cold regions.

Pathology and symptoms

In adult pigs infections with T. suis can cause diarrhea
Diarrhea
Diarrhea , also spelled diarrhoea, is the condition of having three or more loose or liquid bowel movements per day. It is a common cause of death in developing countries and the second most common cause of infant deaths worldwide. The loss of fluids through diarrhea can cause dehydration and...

, anorexia
Anorexia (symptom)
Anorexia is the decreased sensation of appetite...

, anemia
Anemia
Anemia is a decrease in number of red blood cells or less than the normal quantity of hemoglobin in the blood. However, it can include decreased oxygen-binding ability of each hemoglobin molecule due to deformity or lack in numerical development as in some other types of hemoglobin...

, poor growth, dehydration
Dehydration
In physiology and medicine, dehydration is defined as the excessive loss of body fluid. It is literally the removal of water from an object; however, in physiological terms, it entails a deficiency of fluid within an organism...

, and emaciation
Emaciation
Emaciation occurs when an organism loses substantial amounts of much needed fat and often muscle tissue, making that organism look extremely thin. The cause of emaciation is a lack of nutrients, starvation, or disease....

, but acuteness is usually connected to the infective dose or concurrent bacterial enteritis. Dysentery
Dysentery
Dysentery is an inflammatory disorder of the intestine, especially of the colon, that results in severe diarrhea containing mucus and/or blood in the faeces with fever and abdominal pain. If left untreated, dysentery can be fatal.There are differences between dysentery and normal bloody diarrhoea...

, anemia
Anemia
Anemia is a decrease in number of red blood cells or less than the normal quantity of hemoglobin in the blood. However, it can include decreased oxygen-binding ability of each hemoglobin molecule due to deformity or lack in numerical development as in some other types of hemoglobin...

, and death have also been described in infections in younger pigs. Critical infestations of T. suis may cause acute morbidity and mortality in young female pigs.
T. suis has been shown in trials to colonize humans briefly without triggering infections.

Diagnosis

In pigs T. suis egg production is sporadic, complicating diagnosis by fecal floatation. Necropsy of clinical cases of trichuriasis may be necessary to validate a diagnosis, since clinical signs may develop prior to patency, thus inhibiting diagnosis by fecal examination alone. On gross necropsy, the intestine may be filled with semisolid to watery to bloody mucoid feces, depending on acuteness of the infection and simultaneous bacterial infections. The anterior portion of adult worms may be observable breaching the cecal and colonic mucosa. Inflammatory nodules may be seen adjacent to the adults where they penetrate the mucosa. In earlier infections, the nodules may suggest pre-erupted larvae beneath the mucosa. Depending on the acuteness of infection, there is generalized moderate to severe typhlitis and colitis
Colitis
In medicine, colitis refers to an inflammation of the colon and is often used to describe an inflammation of the large intestine .Colitides may be acute and self-limited or chronic, i.e...

. In severe infections, the walls of the intestine may be thickened and a necrotic membrane may be located on the surface of the mucosa.

Treatment

The pathogencity and symptoms are generally mild in human and it can be treated with medicines such as Doramectin
Doramectin
Doramectin is a veterinary drug approved by the Food and Drug Administration for the treatment of parasites such as gastrointestinal roundworms, lungworms, eyeworms, grubs, sucking lice and mange mites in cattle....

, Ivermectin, Febantel.

Although no treatment is initiated for pigs that are infected with T. suis due to the lack of clinical impact, Piperazine
Piperazine
Piperazine is an organic compound that consists of a six-membered ring containing two opposing nitrogen atoms. Piperazine exists as small alkaline deliquescent crystals with a saline taste....

 can be applied to minimize the negative impact that the parasite reflect on the host.

Helminthic therapy

T. suis ova therapy may produce significant and long lasting improvements in active Crohn’s disease. In a study conducted at the University of Iowa
University of Iowa
The University of Iowa is a public state-supported research university located in Iowa City, Iowa, United States. It is the oldest public university in the state. The university is organized into eleven colleges granting undergraduate, graduate, and professional degrees...

, patients who had been administered with T. suis ova for 24 weeks had a response rate of nearly 80% and a remission rate of nearly 73%. Crohn’s disease involves over reactive Th1 pathways and colonization with parasitic worms expands several immunoregulatory pathways that limit Th1-type inflammation. Parasitic worms generate production of interleukin 4
Interleukin 4
Interleukin-4, abbreviated IL-4, is a cytokine that induces differentiation of naive helper T cells to Th2 cells. Upon activation by IL-4, Th2 cells subsequently produce additional IL-4. The cell that initially produces IL-4, thus inducing Th0 differentiation, has not been identified, but recent...

 and interleukin 13
Interleukin 13
Interleukin 13 is a protein that in humans is encoded by the IL13 gene. IL-13 is cytokine secreted by many cell types, but especially T helper type 2 cells, that is a mediator of allergic inflammation and disease.-Functions:...

, which are Th2 cytokines. This Th2 response restrains production of Th1 cytokines thereby reducing colitis severity. Parasitic worms also generate regulatory T cells and immune regulatory substances such as transforming growth factor β, interleukin 10
Interleukin 10
Interleukin-10 , also known as human cytokine synthesis inhibitory factor , is an anti-inflammatory cytokine. In humans IL-10 is encoded by the IL10 gene....

, and prostaglandin E2 that assist in sustaining host mucosal homeostasis
Homeostasis
Homeostasis is the property of a system that regulates its internal environment and tends to maintain a stable, constant condition of properties like temperature or pH...

.

The FDA has granted pig whipworm (Trichuris suis) the status of Investigational New Drug
Investigational New Drug
The United States Food and Drug Administration's Investigational New Drug program is the means by which a pharmaceutical company obtains permission to ship an experimental drug across state lines before a marketing application for the drug has been approved...

, allowing clinical trials in humans.

Prevention and control

Prevention of T. suis depends on the treatment and prevention of infections in animals, the removal of feces before the eggs can become embryonated, good hygiene and public education.
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