Whipworm

Background:

Trichuris trichiura (whipworm) is a roundworm of the phylum Nematoda. It is one of the most common human parasites. The common name is derived from the worm's distinctive whiplike shape. The adult worm usually reaches 3-5 cm in length and has a lifespan of 1-3 years.

Pathophysiology:

Humans are the only known host of T trichiura. The organism is spread via the fecal-oral route. Potential hosts ingest the embryonated (mature) eggs. The eggs hatch in the small intestine, and the larvae attach to and penetrate the small intestinal mucosa, where they begin to mature. After approximately 1 week, the immature worms move passively to the large intestine and proximal colon. The worms' anterior portions penetrate the mucosal epithelium, and the worms can imbed over one half of their length into the mucosal surface.

Once the worms are sexually mature, mating begins. Egg production occurs 2-3 months after initial ingestion. The female worm is capable of producing 3,000-20,000 eggs a day. Once the eggs are passed in the feces, they develop in a warm humid environment. Egg maturation occurs in approximately 2-6 weeks. The embryonated egg can maintain viability for several months under suitable conditions. Destruction occurs with exposure to direct sunlight for more than 12 hours and to temperatures of less than -8°C or higher than 40°C for 1 hour.

Frequency:

· In the US: Prevalence of whipworm infestation is less than 0.1%. The most common areas of infection are the southern Appalachian range and Gulf coast states.

· Internationally: Whipworm infections are among the most common of all human parasites, with an estimated 750-800 million infections worldwide. The most affected regions are rural areas with poor sanitation and tropical climates, including Southeast Asia, Africa, the Caribbean, and Central and South America. Prevalence rates as high as 80% exist in these regions. In contrast, prevalence in areas of Western Europe and Japan is similar to that in the United States.

Mortality/Morbidity:

Most infections are asymptomatic. Symptoms are related to the worm load or number of worms involved in an infection. Heavy infections (hundreds to thousands of worms) can lead to death secondary to GI and hematologic complications.

Age

: Although infections are observed in all age groups, most heavy infections are observed in the pediatric population. This probably reflects the increased likelihood of children to have poor hygiene and to play in soil that carries the worms' mature eggs.
History:

· When evaluating a patient suspected of having a whipworm infection, the most important part of the history is travel to or living in an area of known infestation.

· GI complaints associated with these infections are diverse. Long-term GI complaints with associated exposure suggest whipworm infection.

· Most infections are asymptomatic.

· Light infections: Patients with fewer than 100 worms are frequently asymptomatic; however, they may present with lower abdominal discomfort, flatulence, and diarrhea or constipation.

· Heavy infections

o Patients with heavy infection have hundreds to thousands of worms and may present with lower or epigastric pain, vomiting, abdominal distension, anorexia, weight loss, anemia, diarrhea, tenesmus (painful straining), and rectal prolapse.

o Trichuris dysentery syndrome is observed in heavy infections and characterized by bloody mucoid diarrhea, small frequent stools, tenesmus, anemia, and growth retardation.

· Polyparasitic infections can occur with whipworms, ascaris, and hookworms because all these parasites live in similar environments.

Physical:

· Generally, physical examination findings are normal.

· Each worm causes an estimated 5 mL of blood loss every day.

· Heavy infections are required to cause anemia.

· Prolonged infections are reported to lead to growth failure, intellectual delays, and digital clubbing; however, growth and intellectual delays are likely to be multifactorial.

Causes:

· The organism is spread via the fecal-oral route. Potential hosts ingest the embryonated (mature) eggs.

· Most heavy infections are observed in the pediatric population because children are more likely to have poor hygiene and to play in soil that carries the worms' mature eggs.

Lab Studies:

· Diagnosis is usually established by means of microscopic examination of stool.

o Whipworm eggs have a characteristic barrel (American football) shape with translucent polar plugs.

o The stool commonly contains red and white blood cells, including eosinophils/Charcot-Leyden crystals.

· Perform a CBC count. Eosinophilia is uncommon; however, when present, it ranges from 5-20%.

Procedures:

· Anoscopy may be useful. In heavy infections, worms can be directly visualized.

Medical Care: Infections are treated with broad-spectrum anthelminthic agents. Most infections can be treated successfully with mebendazole. Retreatment is occasionally necessary if symptoms persist longer than 2 weeks after initial treatment.

Drug Category: Anthelmintics -- Parasite biochemical pathways are different from the human host; thus, toxicity is directed to the parasite, egg, or larvae. Mebendazole is the treatment of choice for trichuriasis. Albendazole is an alternative medication that can be used. Both are broad-spectrum anthelminthic agents. These drugs interfere with the organism's microtubule formation. Recently, nitazoxanide has been studied as a possible treatment option.

Drug Name


Mebendazole (Vermox) -- The treatment of choice for whipworm infections. Causes worm death by selectively and irreversibly blocking uptake of glucose and other nutrients in adult intestine where helminths dwell.

Adult Dose


100 mg PO bid for 3 d or 500 mg PO once

Pediatric Dose


<2 years: Not established
>2 years: Administer as in adults

Contraindications


Documented hypersensitivity

Interactions


Carbamazepine and phenytoin may decrease effects of mebendazole; cimetidine may increase mebendazole levels

Pregnancy


C - Safety for use during pregnancy has not been established.

Precautions


Adjust dose in hepatic impairment; use caution when breastfeeding because extent of drug excretion is not known; use caution in patients <2 y because limited data exist



Drug Name


Albendazole (Albenza) -- Decreases ATP production in worms, causing energy depletion, immobilization, and, finally, death. Considered investigational for use in treating this condition.

Adult Dose


400 mg PO as a single dose for 1 d, 3-d treatment often required for heavy infestations; may repeat in 3 wk prn

Pediatric Dose


<2 years: 200 mg PO qd for 3 d; repeat in 3 wk prn
>2 years: Administer as in adults

Contraindications


Documented hypersensitivity

Interactions


Coadministration with carbamazepine may decrease efficacy; dexamethasone, cimetidine, and praziquantel may increase toxicity; abdominal pain, nausea, vomiting, diarrhea, dizziness, vertigo, fever, increased intracranial pressure, and alopecia may occur

Pregnancy


C - Safety for use during pregnancy has not been established.

Precautions


Discontinue use if serum transaminases increase significantly (resume when levels decrease to pretreatment values)



Drug Name


Nitazoxanide (Alinia) -- Inhibits growth of Cryptosporidium parvum sporozoites and oocysts and Giardia lamblia trophozoites. Elicits antiprotozoal activity by interfering with pyruvate-ferredoxin oxidoreductase (PFOR) enzyme-dependent electron transfer reaction, which is essential to anaerobic energy metabolism. Available as a 20-mg/mL oral susp. May have activity in trichuriasis.

Adult Dose


500 mg PO bid for 3 d

Pediatric Dose


<1 year: Not established
1-3 years: 100 mg (5 mL) PO q12h for 3 d with food
4-11 years: 200 mg (10 mL) PO q12h for 3 d with food
>11 years: Administer as in adults

Contraindications


Documented hypersensitivity

Interactions


Tizoxanide (nitazoxanide metabolite) is >99.9% bound to plasma protein and may potentially increase toxicity of other highly plasma protein-bound drugs

Pregnancy


C - Safety for use during pregnancy has not been established.

Precautions


May cause abdominal pain, diarrhea, vomiting, or headache; administer with food; caution when coadministered with other highly plasma protein-bound drugs with narrow therapeutic indices



Consultations: Infectious diseases, gastroenterology, and hematology consultations may be appropriate.
Further Outpatient Care:

· Retreatment may be necessary if symptoms persist 2-3 weeks after initial therapy.

Deterrence/Prevention:

· Limiting the morbidity associated with this disease centers around improved sanitation for areas with heavy infestation.

· Some clinicians have suggested periodic deworming programs for children in endemic areas.

Complications:

· Rectal prolapse, dysentery, anemia, malnutrition, and growth retardation all can complicate heavy infections.

Prognosis:

· With treatment, prognosis is typically excellent.

Patient Education:

· Emphasize good hygiene and avoidance of pica.

Medical/Legal Pitfalls:

· Failure to recognize the most severe infections as parasitic is a pitfall. Resultant delay in antiparasitic treatment can lead to morbidity associated with blood loss, malnutrition, and electrolyte imbalances.