Stichosome esophagus
Trichuris trichiura
The human whipworm is transmitted directly by ingestion of eggs. Examine the
egg,
noting the characteristic barrel shape and translucent polar plugs
(Figure 4.1A).
Trichinella spiralis
Hosts of this worm act as both definitive and intermediate hosts. Fertilized
females penetrate the mucosa of the intestine, and produce juveniles
(the eggs hatch in utero) that enter the venous system, migrate to muscle tissue,
and encyst within nurse cells. Infection occurs through the ingestion of
infected meat (usually pork). Examine the adults
(comparing to the generalized
nematodes diagrammed in Fig. 5.1 on page 162 of your textbook) noting the
anterior muscular portion of the esophagus, and the posterior stichosome esophagus.
The posterior end of the male is blunt, bearing a conical copulatory papilla on
either side of the terminal anus. The testes lie posteriorly, with the vas deferens
extending anteriorly, then doubling back to connect to the cloaca.
There is no spicule on the male. The female also has a blunt posterior and terminal
anus. The single ovary lies in the posterior portion of the body, and the uterus
extends anteriorly, with the vulva lacated in the posterior third of the
stichosome esophagus.
Examine the juveniles encysted within the nurse cells (Fig.5.13 on page 177 of your textbook). The nurse cells are muscle cells that are modified by the nematode.
Strongyliform esophagus; males with copulatory bursa.
Examine the strongylid (hookworm) eggs, noting the thin hyaline shell (Figure 4.1B). It is not possible to distinguish among species of hookworms by examining the eggs or the juveniles. Examine the infective (J3) juveniles, noting the filariform esophagus. Prior to this stage, the esophagus is rhabditiform. The J3 stages �quest� and will burrow into vertebrate hosts they come into contact with.
Ancylostoma caninum
Examine the adult female, comparing to the generalized
female nematode
diagrammed in Fig. 5.1 on page 162 of your textbook, and the electron micrograph
of A. caninum on Fig. 5.3A on page 163 of your textbook.
Note the sclerotized buccal capsule with teeth.
Compare the copulatory
bursa of the male to Fig. 5.15 on page 178 of your textbook.
Muscular esophagus; robust worms with 3 lips.
Ascaris lumbricoides
Examine the eggs of Ascaris lumbricoides
(Fig. 4.1C). Fertilized eggs will be round with a mammalated,
thickened, outer shell. Infertile eggs will have a thinner coat, or no coat at
all (decorticated), and might be elongated, which can lead to them being confused
with hookworm eggs. Examine a cross section of the adult worm,
noting the densely
stained gonadal tissue and ducts, the intestine, the dorsal, ventral, and
lateral nerve chords, and the thick cuticle.
Oxyuriform esophagus; single spicule on males.
Enterobius vermicularis
The human pinworm infects 50% of children (and usually their parents) in the United
States. Examine the egg (Figure 4.1D),
noting the characteristic flattened side. The eggs generally, are not recovered in the
feces, so diagnosis is based upon the recovery of eggs deposited around the anus by
migrating females. The sample is obtainedby taking a piece of cellulose tape and holding
it, adhesive side out, on the end of a tongue depressor with the thumb and index finger.
The depressor is pressed against the left and right perianal folds, and the tape is spread
flat on a microscope slide for examination. The buttocks should be spread enough to
allow pressing of the tape firmly against the line of junction between the moist outer
part of the anal canal, and the somewhat dry, waxy, perianal folds.
Examine the adult worm, noting the oxyuriform esophagus (Fig. 5.17 on page 183 of your textbook; the figure is upside down), and the three lips of the mouth. Note also the cervical alae (similar to those depicted in Fig. 5.3C on page 163 of your textbook). The male bears a single spicule, and posesses a single, thread-like testis. Females are amphidelphic, with the vulva located just anterior to the equator of the body on the ventral surface.
Dirofilaria immitis
Adults of the dog heartworm reside in the right atrium of canids and felids. Females are
viviparous, releasing microfilariae into the blood where they can be ingested and
transmitted by mosquitos. Examine unsheathed microfilariae
in a blood smear (Figure 5.27 on page 189 of your textbook).
Ligament sac of female not persistent; cement glands separate; tegumental nuclei fragmented.
Acanthocephalus sp.
Examine both the male and female
of Acanthocephalus, comparing to Fig. 6.5 on
page 202 of your textbook. Note in the male the testes, separate cement glands, and
copulatory bursa. In the females note the ovarian balls, ligament sac, and uterine bell.
Fessisentis fessus
Examine both the male and female of
Fessisentis fessus, comparing to Fig. 6.5 on page 202 of
your textbook. Note the characteristics of the class.
small number of large hypodermal nuclei; 2 persistent ligament sacs in female; cement gland syncitial with cement reservoir attached.
Neoechinorhynchus cylindratus
Examine the male and female, noting the persistent ligament sacs in the female, and
the single, syncitial cement gland of the male (Figure 4.2).
