Trichuris trichiura Infection

Etiology

The most common cause of trichuriasis is the ingestion of infected eggs that are found in soil. This is often due to poor sanitary conditions, including open defecation and using human feces as fertilizer. Some recent studies show that people with certain chromosome traits may be predisposed or have increased susceptibility to acquiring trichuriasis.[2]

Epidemiology

The egg of the whipworm is the infective stage, and favorable conditions for its maturation are a warm and humid climate. This is why most of the disease burden is seen in tropical climates, specifically in Asia and less often, in Africa and South America. It is also found in rural parts of the southeast United States. It is estimated that worldwide there are between 450 million to 1 billion active cases with most diagnosed in children. It is thought there is partial protective immunity that develops with age.[3][4] 

Worldwide, almost half of the 5 billion people that live in developing countries are infected with at least one soil-transmitted helminth species, and 10% with two or more helminth species.[4] Young boys tend to be most affected as they are more likely to play outside and exhibit pica behavior.

Pathophysiology

The worm is acquired through fecal-oral transmission. A human host consumes infected eggs, typically while eating and drinking contaminated food or water. Once the embryonated eggs are ingested, the larvae hatch in the small intestine. From there they migrate to the large intestine, where the anterior ends lodge within the mucosa. This leads to cell destruction and activation of the host immune system, recruiting eosinophils, lymphocytes, and plasma cells. This causes the typical symptoms of rectal bleeding and abdominal pain. The parasite usually takes up residence in the terminal ileum and cecum. In some patients, the entire colon and rectum may be infested with the worm. The worm may live anywhere from 1-4 years without treatment. Eggs are expelled in the host feces unembryonated. The eggs will become embryonated in 2–4 weeks and are then infective.[5]

History and Physical

Patients with trichuriasis will typically reside in or have visited areas that are endemic to the whipworm. The patient will usually complain of abdominal pain, painful passage of stools, abdominal discomfort, and mucus discharge. Diarrhea and constipation are also common presenting complaints. Nocturnal passage of stools is a common occurrence. Many patients are asymptomatic as the clinical disease is dependent on parasite burden.[5] Rectal prolapse is known to occur in a heavy infestation. Children may develop anemia, growth deficiency, and even impaired cognitive development. The latter 2 are thought to be due to iron deficiency and poor nutrition secondary to worm burden and are not a direct cause of the infestation.[4][6]

In general, the physical examination of these patients is normal. The exam may reveal signs of anemia, including pallor. Patients with a prolonged infection may have clubbing.

Evaluation

Laboratory diagnosis of trichuriasis is based on the microscopic examination of stool samples to determine the presence and, if possible, the number of eggs.[5] During a heavy infestation, the eggs may be seen on a stool saline smear, but this has a low sensitivity. The WHO recommends using the Kato-Katz method for counting eggs per unit weight of feces. They also recommend using 2 slides per sample.[5] One weakness of stool sample examination is that from the time the eggs are ingested to the development of the mature worm, there is a time lag of about three months. During this period, there may be no signs of an infestation and the stools may not show evidence of any eggs or shedding.

Stool samples may also demonstrate red blood cells (RBCs), and white blood cells (WBCs), specifically eosinophils. A complete blood count may show anemia.

There have been case reports of patients reporting symptoms in areas that have adequate resources where the diagnosis has been made with sigmoidoscopy or colonoscopy. The classic finding is the “coconut cake rectum” from white bodies of adult worms dangling from inflamed mucosa.

There have recently been studies that show a "whipworm dance" on ultrasound which is when the lumen of the appendix wriggles continuously. This is a modality that can easily be used in resource-poor settings.[7]

Polymerase chain reaction (PCR) assays are currently being developed and used in research settings. This has improved the specificity and sensitivity of detecting the whipworm.[5][8]

Treatment / Management

The treatment of trichuriasis is with mebendazole or albendazole. The suggested dose of mebendazole is 100 mg twice a day for 3 days or albendazole is 200 to 400 mg twice a day for 3 days. Mebendazole has been shown to be more effective and is considered first-line treatment. Albendazole and mebendazole have an inhibitory effect on tubulin polymerization which results in the loss of cytoplasmic microtubules. Ivermectin 200 mcg/kg daily can be used; however, it is not as effective as mebendazole and albendazole. Ivermectin binds with high affinity to the glutamate-gated chloride channel which occurs in invertebrate nerve and muscle cells, causing an increase in permeability of cell membrane to chloride ions with hyperpolarization of the nerve and muscle cells. The hyperpolarization leads to paralysis and death of the parasite.

It is important to keep in mind that there are often co-infections with other helminths so treatments with multiple medications may be required. The household members of an infected patient are at low risk but if the home has no sanitation, then the clinician should consider the possibility of transmission to others.

Differential Diagnosis

Given that a whipworm infection can cause abdominal pain, there includes a large differential of abdominal processes. These include but are not limited to appendicitis, colitis, cholecystitis, and perforated intestine. Bloody diarrhea can be caused by inflammatory bowel disease (IBD), bacterial pathogens, or other soil-transmitted helminths. The constellation of cognitive disruption, constipation, and abdominal pain can also be seen with lead toxicity and is an important consideration for children. Other parasitic helminth infections should also be included in the differential including hookworms and ascariasis as these are frequently present as a co-infection.

Prognosis

The whipworm tends to be more resistant to treatment than other helminths, with some studies listing cure rates as low as 28% to 36%. Whipworms can still be present after treatment, however, it is thought that a low worm count leads to no significant disease burden. While trichuriasis is not fatal, it can cause anemia and nocturnal stooling. Many patients develop colitis and malabsorption. Deficiencies of fat-soluble vitamins are not uncommon. Children may have poor growth and rectal prolapse.

Complications

Trichuris dysentery syndrome can be found in children (with no adult cases noted) and is seen when there is a very high worm burden. This often leads to diarrhea, tenesmus, iron deficiency anemia, and poor growth. The poor growth is typically secondary to poor nutrition and consequently causes cognitive delay.