Chapter 23 - Nematoda: Trichurida

Order Trichurida

Family Trichuridae

• Often referred to as whipworms because they are threadlike along most of their body and then become thick at the posterior end

Trichuris trichiura

• In both sexes, a capillary like esophagus extends 2/3 of the body length and is encircled along much of its length by a series of unicellular glands, the stichocytes • The posterior extremity of males is coiled and equipped with a single spicule enclosed in a spinose, retractile cuticular sheath

Life Cycle

• Adult worms occur primarily in the human colon but also inhabit the appendix and rectum• Unembryonated eggs are passed to the exterior with the feces and develop slowly in warm, damp soil• In about 3 weeks an unhatched eggs containing an infective, 3rd stage larva develops• New human hosts become infected when these embryonated eggs are ingested with contaminated food or water• Larvae hatch in the upper portions of the small intestine and quickly burrow into the cells of the intestinal villi near the crypts of Lieberkuhn, where they mature and molt in about 1 week• Later migrate to the caecal region, molting enroute, and develop into adults

Life Cycle of a

Whipworm

Epidemiology

• Most frequent in tropical countries• In the US, it occurs predominantly in the southeastern states; it’s the second most common nematode infecting humans (after Enterobius), • The worm is found in areas with lots of rain, warm climate, dense shade and sanitary conditions that are conducive to soil pollution• Children are more likely to be infected than adults because they are more likely to have have close physical contact with contaminated soil

Symptamology

• Most infections are light with no symptoms• Chronic infections can produce symptoms such as bloody stools, pain in the lower abdomen, nausea and anemia• Anemia may be the result of hemorrhaging when the worms penetrate the intestinal wall

Trichinella spiralis

• Males have curved posterior end with 2 lobed appendages called alae• Single testis in the posterior part of the body

• Female with a bluntly rounded posterior end and one ovary• Vulva in the anterior fifth of the body

Life Cycle

• Requires only 1 host in its life cycle (e.g., one host can serve both as the definitive host and the intermediate host), with larvae and adults occurring in different organs• Infections result from the consumption of meat containing encapsulated first stage larvae• Once ingested these larvae are released into the duodenum by the action of host enzymes • Larvae then penetrate the absorptive and goblet cells in the mucosa; here they reach sexual maturity• After copulation, the male passes out of the host, while the female borrows deeper into the mucosa and submucosa, entering the blood circulatory system• Female then begins to deposit 1st stage larvae

Life Cycle cont.

• The female then dies, while the 1st stage larvae are carried by the lymphatic and blood vessels to the right side of the heart in the venous blood• From the heart, the larvae enter the peripheral circulation and are carried to various tissues of the body• In striated muscle, especially those of the diaphragm, jaws, tongue, larynx, and eyes, the larvae develop into the infective stage• They penetrate muscle cells and establish themselves as intracellular parasites within myofibers

Life Cycle cont. • They absorb nutrients from the host muscle and become surrounded by a nucleated mass known as a nurse cell• The larvae are eventually encapsulated with collagen - enveloped by a double, ellipsoidal capsule of host origin

Life Cycle cont.

• Eventually the capsule become s calcified, anywhere from 6 months after the initial infection• During capsule formation, the enclosed larva enters developmental arrest, a state in which it can survive almost indefinitely• When muscle harboring the encapsulated larva is eaten by a carnivorous mammal, the larva excysts and reinitiates the life cycle

Epidemiology

• The term sylvatic trichinellosis denotes the cycling of the disease between wild carnivores and their prey or carrion• Urban trichinellosis on the other hand, is the term used to designate the cycling of the disease among humans, rats, and pigs• Rats and pigs feeding on garbage that includes infected pork waste, become infected in turn• Dead or dying infected rats are themselves eaten by pigs• Raw or poorly cooked pork (sausage) harboring infective larvae then becomes the vehicle for human infections• Trichinellosis is a cosmopolitan disease that occurs most commonly in Europe and the US• The disease is rare in the tropics for the opposite reason that it is found in the US: a low consumption of pork and meat in general• Also rare among Jews and Moslems

Symptomology and Diagnosis

• The primary symptoms of trichinellosis are the result of larval invasion of muscle and other tissue and the hyperimmune reaction of the host to the metabolic by-products and secretions of larvae• During penetration of adult females into the mucosa there is nausea, perfuse perspiration and diarrhea• During penetration and encapsulation of the larvae in muscle cells there is intense muscular pain, difficulty breathing, swelling of the facial muscles, etc• Most of the cases of trichinellosis are asymptomatic and go undetected