Laboratory #11: Nematoda II

Phylum Nematoda (continued)

In the previous lab (#10) you learned the general features of the Phylum Nematoda, and you examined representatives of 3 orders of the Class Chromadorea. Today you will examine additional members of Class Class Chromadorea, as well a couple species of the Class Enoplea.

I. Class Chromadorea / Order Rhabditea

Most species in this group are soil-dwelling forms. It seems likely that the parasitic species in this group evolved from free-living ancestors.

Infraorder Ascaridomorpha – see Lab #10

Infraorder Oxyuridomorpha – see Lab #10

Infraorder Rhabditomorpha – see Lab #10

Suborder Tylenchina

Members of this group seem to bridge a gap between free-living and parasitic modes of life because several species alternate between free-living and parasitic generations. Most members of this group live in decaying organic matter and are common in the soil, water, or rotting fruit and because of this end up in the bodies of larger animals, and in these cases they can become facultative parasites.

1. Strongyloides stercoralis free-living. Whole mount. Demonstration. See textbook Figure 24.2 page 393. Species of Strongylus are among the smallest nematode parasites of humans, and are especially interesting because of their ability to maintain parasitic life cycles, or to repeat free-living generations indefinitely. The slide contains adult free-living male and female worms; a rhabditiform esophagus can be seen. When these reproduce, their offspring will develop into rhabditiform–free-living and feeding– individuals, or into filariform individuals that will only develop further if they colonize a host via skin or orally and will subsequently develop in the intestinal submucosa. Development into the rhabditiform (free-living) form vs. filariform (parasitic) form seems to be determined by temperature.

List another species that can live either as a parasite, or free-living:______________

Suborder Spiruromorpha

The esophagus of spirurids is usually divided into an anterior muscular, and a posterior glandular portion, but spirurids never possess an esophageal bulb. All members of this group are heteroxenous. Their life cycles involve an arthropod intermediate host in which they undergo development to the J3 stage.

2. Spinitectis gracilis. Demonstration. This specimen was collected from the intestine of a Rock bass in Otsego Lake at Cooperstown, New York. A distinctive feature of this genus is the presence of rows of backwards-pointed spines on the cuticle. Be sure to recognize the spines. Species of Spinitectis utilize mayfly larvae as intermediate hosts.

How do you think the rock bass acquired this local nematode species?_______________

Can you see the spines (you may have to increase magnification)?________What is the function of the spines?

Filarial worms

The next 4 species belong are known as the filarial worms, a group within Suborder Spiruromorpha. As adults, filarial worms are tissue dwelling parasites in the definitive host. All species use arthropods as intermediate hosts, most of which deposit third stage juveniles on the skin of the definitive host with their bite. Most are parasites of wild animals (particularly birds) but several are important in humans and domestic animals. In general, filarial worms are long, and slender with reduced or no lips and a buccal capsule. The filarial worms possess vermiform embryos called microfilariae. These are pre-J1 stage that, depending on the species, may or may not retain the vitelline membrane as a sheath around the body. This stage is infective to the intermediate host. The key to microfilariae found in the peripheral blood of humans in your text (page 443) is useful for distinguishing among human infections.

3. Onchocerca volvulus– Adults in sections of fibrotic nodule from skin. Demonstration slide-skin tumor section. See text page 447 Fig. 29.5. This species is the etiological agent of “river blindness”. Adult worms are characteristically knotted together in groups in nodules in the subcutaneous tissues of the definitive host. Note the relationship between the worms and host encapsulation reaction. Females release unsheathed microfilariae that wander in the connective tissues of the host until they are picked up by an appropriate intermediate host.

What type of organism would serve the role of intermediate host?__________________

*4. Wuchereria bancrofti– microfilariae. Slide box slide #31. human blood smear. See text page 443 Figs. 29.3 & 29.4. This species is the etiological agent of “elephantiasis” in humans. Microfilariae of this species characteristically possess a sheath (vitelline membrane). The nuclei in the body of the microfilaria do not extend to the very posterior tip of the tail. Adults live in the lymphatic ducts of humans; the microfilariae are found in the circulatory system of the definitive host. A life cycle diagram is found page 462.

What stage of this species is infective to the intermediate host?____________________

What stage of this species is infective to the definitive host?______________________

*5. Dirofilaria immitis– microfilariae. Slide tray- dog blood smear. See attached Figure 2. Also see text page 454 Fig. 29.17 for pathology photo. Heartworm can be a severe and even fatal disease in domestic dogs throughout most of the world. Adult worms locate in the right side of the heart and pulmonary artery and can result in heart failure owing to vessel blockage. Adult worms mate and produce microfilariae, which then move to the peripheral circulation of the host. Microfilariae are transmitted to the mosquito host when a mosquito feeds.

The microfilariae of D. immitis are unsheathed and the nuclei of the body do not extend into the tip of the tail. Clinicians must be able to distinguish microfilariae of D. immitis, from microfilariae of the much less severe Dipetalonema sp., also found in dogs.

Does this species possess an egg stage during its life cycle?______________________

What is the name of the life cycle stage the follows microfilaria?__________________

6. Loa loa microfilariae. Demonstration. See text page 452 Fig. 29.14 & 29.15. This is the “eye worm” of Africa. Adult worms of this species have a tendency to wander through subcutaneous tissue and stimulate an immune inflammatory response. On occasion adults wander through the conjunctiva and cornea of the eye. Adult worms mate and produce microfilaria, the stage shown here. Microfilaria are found in the peripheral circulation of humans, and microfilaria are transmitted when a deerfly takes a blood meal.

What stages of Loa loa would occur within a deerfly? List them all.________________

II. Class Enoplea

Most members of this class are free living species, but some are parasites of plants or animals. Members of this group possess five or more esophageal glands.

Order Trichinellida

Members of this order are usually more slender anteriorly than posteriorly and possess a buccal capsule that is absent or very reduced. In addition, all species have an esophagus that is embedded within one or more rows of large, glandular cells called stichocytes along most of its posterior portion. As a consequence, this region of the esophagus is referred to as the stichosome. Trichurid eggs are distinctive in their possession of 2 polar plugs. Males in this group either possess only a single spicule, or lack spicules entirely.

*7. Trichuris trichiura– adult male. Slide tray. See text page 378 Fig. 23.1. Note the whip-like shape of the body, the single spicule, and the presence of a stichosome. This worm parasitizes the large intestine of humans, where they can cause extensive damage. Make a drawing of this specimen and label the following structures on your illustration: spicule, stichosome, anus, weak buccal cavity, intestine, and esophagus. Heavy infections of T. trichiura can cause rectal prolapse (see text page 379 Fig. 23.4).

Is the anterior or posterior end of this worm the thin end?________________________

What is the function of the spicule?____________________________

8. Trichuris trichiura– adult female. Slide tray. Note the very long stichosome. This and other worms in the same family are commonly known as “whipworms” because they are threadlike along most of the length of their body and then abruptly thicken at the posterior end, resembling the handle of a whip.

What feature definitively allows one to distinguish between the sexes of this species?____________________________________________________

Which sex of this species is larger? ____________________________

*9. Trichuris trichiura– eggs. Slide tray. See text page 378 Fig. 23.2. Note the distinct lemon shape and the two prominent polar plugs of these eggs. This egg morphology is characteristic of many of the members of the whipworm family. Make a drawing of an egg of this species. Label: polar plugs, egg shell, developing embryo.

List a feature that would help you distinguish this egg from that of other species:_______

*10. Trichinella spiralis– intracellular juveniles. Slide box slide #32. See text page 384 Figs. 23.10-23.12. This is the smallest nematode parasite of humans. It is the etiological agent of the disease known as “trichinosis” (or, “trichiniasis”, and “trichinelliasis”). Note how numerous juveniles are present in this small amount of muscle tissue. Be sure to label the juvenile (J1) worm, collagen capsule, and nurse cell in the drawing.

What aspect of the life cycle of T. spiralis accounts for the common occurrence of huge numbers of juveniles in a single host? ____________________________________

How would a person acquire this type of infection?_________________________

What stage of the parasite is found in this intracellular infection?______________

Order Dioctophymatida

Members of this group are parasites of terrestrial mammals or, in the case of the example below, aquatic birds. This is not a medically important group, though human infections do sometimes occur.

11. Eustrongylides tubifex. Juvenile. Demonstration. This is included because it occurs locally. The specimen in the dish was collected from the body cavity of a Yellow perch in Otsego Lake at Cooperstown, New York. This species is also commonly found in sunfish, such as the Pumpkinseed and the Red-breasted Sunfish, and Rock bass. The life cycle nicely exemplifies one branch in the food web; First-stage juveniles occur in aquatic oligochaete worms called Tubifex, which are then ingested by a fish in which further juvenile development takes place. The adult stage is reached in the intestine of a piscivorous (fish-eating) bird such as a Kingfisher or a heron.

Look at the size of this specimen. Provide an example of a pathological effect that this worm would have on its fish host._______________________________