Trichuris trichiura

Author: MBLOGSTU

Introduction

Trichuris trichiura, the whipworm, is most common in warm, moist, tropical and subtropical countries, where prevalences in children can be over 90%, although it is also found in temperate climates.

The Trichuris dysentery syndrome (TDS) associated with heavy T. trichiura, which includes chronic dysentery, rectal prolapse, anaemia, poor growth, and clubbing of the fingers, constitutes an important public health problem.

The profound growth stunting in TDS can be reversed by repeated treatment for the infection and, initially, oral iron.

Epidemiology

An estimated 1049 million persons harbour Trichuris, including 114 million pre-school age children and 233 million school-age children (5-14 years).

At least 27 million school-age children in Sub-Saharan Africa are considered to be infected, as are 36 million in India, 42 million in China, 70 million in the rest of Asia and nearby islands, 39 million in Latin America and the Caribbean, and 18 million in the Middle Eastern Crescent. Approximately half as many preschool-age children in each region are believed to be infected.

Humans become infected directly by ingesting the embryonated eggs from contaminated hands, food, soil, or water.
Transmission: via geophagia.

Morphology

Adult Worms

The adult worm resembles a whip:

• The anterior three-fifth is very thin and hair-like.
• The posterior two-fifth is thick and stout, resembling the handle of a whip.
• Adult worms inhabit the large intestine.
• The male measures about 3–4 cm in length and its caudal extremity is coiled ventrally.
• The oviparous female measures about 4–5 cm in length.

Eggs

• Measure approximately 50 μm in length and 25 μm in breadth.
• Barrel shaped (with a mucous plug) and bile stained.
• Contain an unsegmented ovum when the egg leaves the human host.
• Float in a saturated solution of common salt.

Pathogenesis

Two mechanisms underlie the clinical disease:

• Mechanical Damage: In heavy infections, the rate of damage to the intestinal mucosa is high. The anterior end of the worm becomes embedded in the mucus membrane of the intestinal tract, and a matted mass of worms may block the appendical lumen. Hartz suggested that this irritation of the nervous plexus of the mucosa causes diarrhoea and cramps.
• Allergic Reactions: Some investigators propose that the parasite exhibits a lytic action responsible for the loss of microvilli height associated with the loss of filament bundles that normally support these structures. Colonic inflammation—with characteristic eosinophils and Charcot-Leyden crystals present in the colonic exudate—further suggests allergic manifestations.

Pathophysiology of Trichuris Dysentery Syndrome (TDS)

Major progress has been made in the last decade in understanding the pathophysiology of T. trichiura infection, particularly in Trichuris dysentery syndrome.

The inflammatory response leads to anaemia, growth retardation, and intestinal leakiness—consequences that correlate with the intensity of infection. A specific IgE-mediated local anaphylaxis partially mediates the deleterious effects. Additionally, increased numbers of mucosal macrophages contribute to the chronic systemic effects of trichuriasis through their cytokine output.

Laboratory Diagnosis

Most whipworm infections can be easily diagnosed by identifying characteristic eggs in the stool. Since light infections usually cause no problems and may not require treatment, the eggs should be quantitated.

Note that T. trichiura eggs submitted in stools preserved in PVA do not concentrate as well as those preserved in formalin. However, the very small numbers of eggs that could be missed in a concentrate obtained from PVA-preserved stool material are not clinically significant.

Although dysentery due to T. trichiura and that due to E. histolytica share similarities, whipworm dysentery is generally more chronic, associated with malnutrition, and more likely to cause rectal prolapse. The recovery and identification of the eggs or the protozoan trophozoites would differentiate the two infections. In severe infections, adult worms are sometimes visible in the rectal mucosa.

Key Points of Diagnosis:

• Eggs are usually recovered using the routine ova and parasite examination from a direct smear or via a concentration procedure.
• The eggs should be quantitated in the laboratory report since light infections may not require treatment.
• Adult worms are very rarely seen.
• In heavy infections, dysentery must be differentiated from that caused by E. histolytica.
• Eggs can usually be identified from a permanent stained smear, though morphology is often more visible in wet smear preparations.
• In heavy infections, Charcot-Leyden crystals are observed in the stool and peripheral blood shows eosinophilia.

Treatment

Commonly used treatments include:

• Mebendazole
• Albendazole