Para Lab 1

PARASITOLOGY LABORATORY 1 – NEMATODES USTMED ’07 Sec C – AsM; pictures provided by JV.N. TRICHURIS TRICHIURA

ENTEROBIUS VERMICULARIS Enterobius vermicularis (adult male)

Note the gross features of the typical, unembryonated, fertile egg, ie, the bile-stained, thick, smooth shell with polar prominences, often called polar “plugs.”

Adult male worms are much smaller than females and are detected less frequently in feces or on cellulose tape. The oral end lacks a true buccal capsule but is provided with three lips and dorsoventral bladder-like expansion of the cuticula. Note the posterior end strongly curved ventrad. It has a single conspicuous copulatory spicule.

conspicuous copulatory spicule.

(below) Higher magnification of the posterior end of the adult male showing strongly curved ventral end and the

Trichuris trichiura X-section Appendix

Enterobius vermicularis

Trichuris trichiura fertilized ova. Female worms in the human cecum shed 3,000 to 20,000 eggs per day. Embryonation occurs after the egg passes into the environment (requires tropical temperature). On average, an infective egg (embryonated) survives for less than 1 year. Female and male adult worms. The female worms of E. vermicularis (pinworm) is white and measures from 8 to 15 mm in length by approximately 0.4 mm in width. In contrast, the male adult worm is much smaller, measuring 2 to 3 mm in length by 0.1 to 0.2 mm in width. The dilated cephalic region is similar in both sexes, while the tail is pointed in the females (left) and blunted in the males (right). Females are more frequently found in cellophane tape preparations than the males. The cephalic inflation of the cuticle and the muscular and bulbous protions of the esophagus separated by a narrow region can be observed in the right figure.

T. trichiura in sect. appendix.

Trichuris trichiura This illustration demonstrates the gross features of male and female adult worms. Note that both are whip-like, that the male, in contrast to the female, has a characteristically coiled tail. These worms, though small, are readily seen but rarely found in feces, except following treatment.

Trichuris trichiura (adult male)

Enterobius vermicularis ova

Trichuris trichiura (female)

Clear adhesive tape applied to the perianal area of a child reveals numerous football – shaped Enterobius vermicularis embryonated ova. Scratching the perianal area leads to hand contamination with infected ova and retroinfections of the host.

Clear adhesive tape applied to the perianal area of a child reveals numerous football-shaped Enterobius ova. Scratcing the perianal area leads to hand contamination with infective ova and

reinforcement of the houst. Enterobius vermicularis female

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and other active muscle tissues. Diagnostic problems – in light infections, symptoms may be vague and trichinosis not considered in a differential diagnosis. In animal infections, a few press preparations of muscle tissue may not be adequate to demonstrate larvae. Thus, artificial digestion of large amounts of muscle tissue may be required.

COMMENTS

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Most infections in the United States now are attributable to eating of poorly cooked or smoked pork products derived from hogs raised on private farms, rather than from processed by commercial meat packing firms. Bear meat has been shown to be infected, and numerous cases of human infection have been traced to this source.

Trichinella spiralis encysted larvae

Enterobius vermicularis male

The larvae produced by adult females migrate via the blood-stream to the musculature where they undergo considerable growth and development, and become encapsulated by host tissue. Larvae may be found in press preparations of skeletal muscle (left) or in hematoxylin-eosin-stained histologic sections of the same tissues. In this stained section (right) of diaphragm, not the presence of four larvae surrounded by the host tissue reaction.

TRICHINELLA SPIRALIS CLASSIFICATION

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Nematode

DISEASE

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trichinosis

GEOGRAPHIC DISTRIBUTION

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Cosmopolitan, but more prevalent in Europe and North America than in tropical countries.

LOCATION IN HOST

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Adult worms live in intestinal tract for several weeks to several months. The larval stage, encapsulated in muscle tissue, may live for several years

MORPHOLOGY

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Adult worms. The adult male is minute, measuring 1.41.6 mm in length by 40-60 u, and has two large, fleshy papillas(?) at the posterior end. Adult females are 2.54.0 mm long by 100-150 u wide. The reproductive tract is filled with developing eggs and larvae. In both sexes, the esophagus (stichosome) consists of a thin, narrow tube surrounded by a column of glandular cells called stichocytes.

CAPILLARIA PHILIPPINENSIS Capillaria philippinensis

LARVAE

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Minute larvae, produced by the adult female, measure 100 u long by 6 u in diameter. Infective larvae in muscle tissue measure 0.8-1.0 mm long.

Stichosome

LIFE CYCLE

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When infective larvae in muscle tissue are ingested, they reach maturity in the intestine in approximately one week. Adult females deposit their minute larvae in the mucosal epithelium. These larvae enter the bloodstream and are carried to the muscle tissue throughout the body. The larvae grow in muscle tissue, become infective in approximately one month,, and are encapsulated by host tissue. All mammals may be infected by this parasite, but pigs and rats are the most important reservoir hosts in nature.

Egg

Spicule

DIAGNOSIS

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usually based on clinical symptoms and history of ingestion of poorly cooked meat, especially pork products. Serologic tests are useful. Although muscle biopsies usually are not performed to detect larvae, the procedure may be used. Diagnosis of animal infections is best established by examination of tissue. Larvae are most abundant in tongue, masseter muscle, diaphragm,

Spicule sheath

Adult female

Adult male

Capillaria Ova

Capillaria philippinensis adult

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Capillaria philippinensis ova