Trichuriasis, also known as whipworm infection or trichocephaliasis, is an infection by the parasitic worm Trichuris trichiura (whipworm). If the infection is only with a few worms, there are often no symptoms. In those who are infected with many worms, there may be abdominal pain, fatigue and diarrhea. The diarrhea sometimes contains blood. Infections in children may cause poor intellectual and physical development. Low red blood cell levels may occur due to loss of blood.

The disease usually spreads when people eat food or drink water containing these worm eggs. This may occur when contaminated vegetables are not fully cleaned or cooked. Often these eggs are in the soil in areas where people defecate outside and where untreated human feces is used as fertilizer. These eggs originate from the feces of infected people. Young children playing in such soil and putting their hands in their mouths also become infected easily. The worms live in the large bowel and are about four centimetres in length. Whipworm is diagnosed by seeing the eggs when examining the stool with a microscope. Eggs are barrel-shaped. Trichuriasis belongs to the group of soil-transmitted helminthiases.

Prevention is by properly cooking food and hand washing before cooking. Other measures include improving access to sanitation such as ensuring use of functional and clean toilets and access to clean water. In areas of the world where the infections are common, often entire groups of people will be treated all at once and on a regular basis. Treatment is with three days of the medication: albendazole, mebendazole or ivermectin. People often become infected again after treatment.

Whipworm infection affected about 464 million and 1 billion people in 2015. It is most common in tropical countries and subtropical countries, particularly in parts of Sub-Saharan Africa, Asia and South America where the environmental conditions favor transmission. Those infected with whipworm often also have hookworm and ascariasis infections. These diseases have a large effect on the public health and economy of many countries, especially low and middle income countries. Transmission is strongly associated with poor sanitation and hygiene as infection occurs through ingestion of parasite from soil contaminated with human feces. For this reason, children are disproportionately affected and carry the heaviest burden of the disease from playing outdoors. Work is ongoing to develop a vaccine against the disease. Trichuriasis is classified as a neglected tropical disease.

Light infestations (<100 worms) frequently have no symptoms. Heavier infestations, especially in small children, can present gastrointestinal problems including abdominal pain and distension, bloody or mucus-filled diarrhea, and tenesmus (feeling of incomplete defecation, generally accompanied by involuntary straining). Mechanical damage to the intestinal mucosa, and toxic, or inflammatory damage to the host's intestines may occur. While appendicitis may be brought on by damage and edema of the adjacent tissue, if there are large numbers of worms or larvae present, it has been suggested that the embedding of the worms into the ileocecal region may also make the host susceptible to bacterial infection. A severe infection with high numbers of embedded worms in the rectum leads to edema, which can cause rectal prolapse, although this is typically only seen in small children. The prolapsed, inflamed, and edematous rectal tissue may even show visible worms.

Physical growth delay, weight loss, nutritional deficiencies, and anemia (due to long-standing blood loss) are also characteristic of infection, and these symptoms are more prevalent and severe in children. It can cause eosinophilia but it is not common.

Coinfection of T. trichiura with other parasites is common and with larger worm burdens can cause both exacerbations of dangerous trichuriasis symptoms such as massive gastrointestinal bleeding (shown to be especially dramatic with coinfection with Salmonella typhi) and exacerbation of symptoms and pathogenesis of the other parasitic infection (as is typical with coinfection with Schistosoma mansoni, in which higher worm burden and liver egg burden is common). Parasitic coinfection with HIV/AIDS, tuberculosis, and malaria is also common, especially in Sub-Saharan Africa, and helminth coinfection adversely affects the natural history and progression of HIV/AIDS, tuberculosis, and malaria and can increase clinical malaria severity. In a study performed in Senegal, infections of soil-transmitted helminths like T. trichiura (as well as schistosome infections independently) showed enhanced risk and increased the incidence of malaria.

Heavy infestations may have bloody diarrhea. Long-standing blood loss may lead to iron-deficiency anemia. Vitamin A deficiency may also result due to infection.