Photographic reference material for Chapter 3 HELMINTH PARASITES Phylum Platyhelminthes Fig. 3.1: Live free-living planarian worm. Two prominent eye-spots can be seen towards the front of the worm. The number and distribution of these eye-spots vary between species. This specimen was 10 mm in length and had a protrusible pharynx situated towards the middle of the body. Fig. 3.2: Stained whole mount of a free-living planarian worm. Note how there are numerous small eye-spots distributed at the anterior of the worm and the pharynx can be seen in the centre of the body. Scale in mm.
CLASS TREMATODA Family Fasciolidae Fasciola hepatica Fig. 3.3: Live adult Fasciola hepatica. The adult worms live in the bile ducts of sheep, cattle, and some other mammals and grow to about 3 cm in length. Fig. 3.4: Stained whole mount of an adult Fasciola hepatica.
Fig. 3.5: Stained whole mount of an adult Fasciola hepatica.
Fig. 3.6: Scanning electron micrograph of the anterior sucker and mouth of an adult Fasciola hepatica. Fig. 3.7: Polarised light microscope photograph of the anterior sucker and mouth of an adult Fasciola hepatica. The flukes lack teeth or cutting plates but have a powerful pharynx that is used to suck in host tissue.
Fig. 3.8: False colour scanning electron micrograph of the tegument of an adult Fasciola hepatica. Fig. 3.9: Fasciola hepatica egg. Note the operculum (lid). The eggs are 130 150 m in length and 63 90 m in width.
A B Figs 3.10 A & B: The redia stage of development of Fasciola hepatica. This stage occurs in the mollusc intermediate host (e.g. Lymnaea truncatula). The redia stage is motile and has a mouth and gut.
Fig. 3.11: Cercaria of Fasciola hepatica. The globular body of the cercaria can be up to 0.35 mm in length. After swimming away from the snail intermediate host, the cercaria loses its tail and transforms into a metacercaria. Unlike the cercariae of schistosomes, the cercariae of Fasciola hepatica do not actively invade the definitive host.
Family Dicrocoeliidae Dicrocoelium dendriticum Fig. 3.12: False colour whole mount preparation of an adult Dicrocoelium dendriticum. The adult flukes lack the broad shoulders of adult Fasciola hepatica and are much more slender. They grow up to about 10 mm in length and 2.5 mm in width.
Family Opisthorchiformes Opisthorchis viverrini Fig. 3.13: Stained whole mount of an adult Opisthorchis viverrini. The adult worms are 0.5 1 cm in length. Fig. 3.14: Anterior region of an adult Opisthorchis viverrini. Note the muscular pharynx. Fig. 3.15: Egg of Opisthorchis viverrini. Note the operculum (lid). The developing miracidium can be seen inside the egg.
Family Paragonomidae Paragonimus heterotremus Fig. 3.16: Whole mount, false colour photomicrograph of an adult Paragonimus heterotremus. This lung fluke is a common human parasite in some Asian countries, especially Thailand. The adult worms grow to about 10 12 mm in length. Fig. 3.17: Anterior region of an adult Paragonimus heterotremus.
Fig. 3.18: Egg of Paragonimus spp. Note the operculum (lid).
Family Schistosomatidae Fig. 3.19: Diagrammatic representation of a male and female schistosome.
Fig. 3.20: Stained whole mount slide preparation of a male and female schistosome. In Schistosoma mansoni the female is up to 1.6 cm in length while the male is slightly shorter and grows to up 1.1 cm.
Schistosoma mansoni Fig. 3.21: Egg (in rather poor condition) of Schistosoma mansoni. Note the prominent sharply pointed spine. The presence of a spine and its position is a useful taxonomic indicator. Schistosomes have relatively large eggs for the size of the worm. Those of Schistosoma mansoni are typically 142 m in length and 60 m in width. Fig. 3.22: Cercaria of Schistosoma mansoni. The cercariae of trematodes vary in their shape. Those of schistosomes are said to be furcocercous because the tail terminates in two short branches (furci). The cercariae of Schistosoma mansoni can be up 275 m in length (body + tail) and they exhibit a circadian pattern of emergence from the snail intermediate host.
Schistosoma japonicum Fig. 3.23: Egg of Schistosoma japonicum. Note the absence of a spine. The eggs are 70 100 m in length and 50 80 m in width and are passed in the faeces.
CLASS CESTODA Fig. 3.24: Stained whole body mount of the tapeworm Taenia pisiformis. The scale is in mm. It exhibits the typical adult cestode body pattern of a small scolex which grips the lining of the intestine using four suckers. New proglottids (segments) are generated in the neck region and these become progressively more mature as they progress further from the scolex.
Order Pseudophyllidea/ Diphyllobothriidea Genus Diphyllobothrium Fig. 3.25: Stained whole mount preparation of Diphyllobothrium spp. illustrating the scolex, mature, and gravid segments. Scale in mm. A B Fig. 3.26: Scolex (A) and gravid proglottids (B) of Diphyllobothrium spp.
Order Cyclophyllidea Family Taeniidae Taenia pisiformis Fig. 3.27: Stained whole mount of the anterior region of Taenia pisiformis. The scolex is armed with four suckers and there are two rows of hooks (34 48 in total) borne on the rostellum. This species parasitises the small intestine of dogs and other caniids. The intermediate hosts are usually rabbits or other lagomorphs. The adult worm grows up to about 2 metres in length.
Fig. 3.28: Stained whole mounts of mature and gravid proglottids of Taenia pisiformis. The arrows indicate the genital aperture. Fig. 3.29: Eggs of Taenia pisiformis. It is virtually impossible to distinguish the eggs of the various species belonging to the genus Taenia on the basis of their morphology.
Taenia saginata Fig. 3.30: Stained histological section through the skeletal muscles of a cow illustrating the presence of the larval stage (cysticercus) of Taenia saginata. Fig. 3.31: Stained whole mount of the scolex of Taenia saginata. Scale in mm.
Fig. 3.32: Stained whole mount preparation of the scolex of Taenia saginata. Note the absence of a rostellum and hooks. The brightly coloured object on the upper right sucker is an artefact. Fig. 3.33: Stained whole mount of mature segments of Taenia saginata. Scale in mm.
A B Figs 3.34 A & B: False colour photomicrographs of mature segments of Taenia saginata. Fig. 3.35: Gravid segment of Taenia saginata. These are usually shed one at a time rather than in strings.
Taenia solium Fig. 3.36: Stained histological section through the cysticercus of Taenia solium. A B Fig. 3.37: False colour (A) and unadjusted (B) histological section through cysticerci of Taenia solium. Note how thin the cyst membrane is and how little inflammatory reaction has taken place around the cysts.
Fig. 3.38: Stained whole mount preparation of the cysticercus of Taenia solium.
Taenia multiceps Fig. 3.39: Live coenurus of Taenia multiceps. Note the large number of protoscolices budding from the germinal membrane.
Fig. 3.40: Stained histological section through the coenurus of Taenia multiceps.
Taenia hydatigena Fig. 3.41: Cysts (cysticerci) of Taenia hydatigena attached to the liver of a sheep. Adult Taenia hydatigena are found in the small intestine of dogs and a variety of other mammalian carnivores and can grow to 5 metres in length. The cysticerci are often found in the peritoneal cavity of sheep and cattle although a number of other mammals, including humans, can be infected. In sheep, they are often seen attached to the liver or within the omental fat.
Fig. 3.42: Cysticercus of Taenia hydatigena. Fig. 3.43: Live cysticercus of Taenia hydatigena. If the cysts are removed from the hostderived membrane that surrounds them and placed in physiological saline, waves of muscular contractions can be seen spreading across the cyst wall. Sometimes the whole cyst will bounce around within a beaker. The muscular contractions probably serve to keep the cyst fluid in constant motion and thereby keep up a flow of oxygen, nutrients, and waste material.
Echinococcus granulosus A B Fig. 3.44: Diagrammatic representation of an adult Echinococcus granulosus (A) and a hydatid cyst (B). The two diagrams are not to the same scale.
Fig. 3.45: Scolex of Echinococcus granulosus. This is one of the smallest tapeworms and is often only 2 5 mm in length. Fig. 3.46: Close up of the armed rostellum of Echinococcus granulosus. There can be as many as 60 hooks arranged in two rows.
Fig. 3.47: Hydatid cysts developing within the liver of a donkey. Scale in cm. Fig. 3.48: Hydatid cysts developing within the liver of a donkey. The cysts are surrounded by a thick layer of host-derived connective tissue. Scale in cm.
Fig. 3.49: False colour scanning electron micrograph illustrating the layers of a hydatid cyst. Fig. 3.50: Scanning electron micrograph of developing protoscolices found within a hydatid cyst.
Fig. 3.51: Unstained protoscolices retrieved from within a hydatid cyst. Fig. 3.52: Single unstained protoscolex from within a hydatid cyst.
Echinococcus multilocularis Fig. 3.53: Stained histological section through the liver of a rodent infected with the multilocular (alveolar) cyst of Echinococcus multilocularis.
Family Hymenolepididae Fig. 3.54: Stained whole mount of a series of mature segments of Hymenolepis diminuta. The adult worms are normally found in rats and other rodents but they may occasionally infect humans. The adult worm can grow up to 90 cm in length. The larvae develop as cysticercoids within grain beetles and other insects. A B
Figs 3.55 A & B: Stained whole mounts of a series of gravid segments of Hymenolepis diminuta. The eggs can be seen clearly within the segments. Fig. 3.56: Stained whole mounts of Hymenolepis cysticercoids.
Family Dilepididae Dipylidium caninum A B Fig. 3.57: Stained whole mount preparation of the scolex of Dipylidium caninum viewed using polarised light (A). The adult worms are usually found in the small intestine of dogs although human children are occasionally infected. The adult worms are rather delicate and grow to about 30 cm. Fleas are the normal intermediate hosts. The rostellum is retractable and is armed with hooks: these are not visible in the specimen on the left (A) but can be seen on the poorer slide on the right (B).
Fig. 3.58: Stained whole mount of Dipylidium caninum. Scale in mm.
A B Figs 3.59 A & B: False colour photomicrographs of mature proglottids of Dipylidium caninum. The proglottids have a characteristic elongate shape with paired gonads on either side of each segment.
Family Anoplocephalidae Moniezia expansa Fig. 3.60: Stained whole mount preparations of Moniezia expansa. Scale in mm.
Fig. 3.61: Genital aperture on a mature proglottid of Moniezia expansa. Note the protruding male copulatory organ that is referred to as a cirrus. Closely aligned segments are able to mate with one another although if adult worms are kept alive in vitro for a few hours, large numbers of spermatozoa can be found in the supporting medium. It is possible that some spermatozoa are shed into the surrounding medium and swim to the genital aperture of another proglottid. Fig. 3.62: Transmission electron micrograph of the tegument of a mature proglottid of Moniezia expansa. As in other cestodes, the surface of the tegument is covered with pointed projections referred to as microtrichs. Each microtrich terminates in an angled electron opaque cap.
Fig. 3.63: Transmission electron micrograph of an interproglottidal gland of Moniezia expansa. The specimen was prepared to demonstrate acetylcholinesterase staining. Note how numerous membrane-bound vesicles are also being secreted from the glands. The purpose of these secretions is not known but must involve a considerable metabolic cost. Interproglottidal glands are only found in the genus Moniezia.
Fig. 3.64: Sheep faeces containing strings of gravid proglottids of Moniezia expansa.
PHYLUM NEMATODA Dictyocaulus viviparus Fig. 3.65: Whole mount of adult male Dictyocaulus viviparus. Scale in mm. A B Fig. 3.66: Adult male Dictyocaulus viviparus. Anterior region (A) and bursa (B).
Haemonchus contortus Fig. 3.67: Whole mount of adult male Haemonchus contortus. Scale in mm. A B Fig. 3.68: Anterior (A) and posterior (B) of adult male Haemonchus contortus.
Trichuris suis Fig. 3.69: Whole mount preparation of a male Trichuris suis. Note how the worm has a long slender anterior region and a thicker posterior region. Scale in mm. A B Fig. 3.70: False colour (A) and unstained (B) Trichuris eggs. Note the characteristic polar plugs at either end of the egg.
Trichinella spiralis Fig. 3.71: Stained histological section through muscle tissue containing an encysted larva of Trichinella spiralis.
Genus Ancylostoma Ancylostoma caninum Fig. 3.72: Stained whole mount preparation of the hookworm Ancylostoma caninum. The specimen is an adult male; the mouth is at the top of the picture and the swelling at the posterior end is the copulatory bursa. Scale in mm.
A B Fig. 3.73: Stained whole mount preparation of the hookworm Ancylostoma caninum illustrating the anterior (A) and bursa (B) of an adult male worm. Fig. 3.74: Polarised light photomicrograph of the anterior region of a female Ancylostoma caninum. Note the well-developed teeth and the wide mouth.
Fig. 3.75: Bursa of a male Ancylostoma caninum.
Genus Necator Fig. 3.76: Stained whole mounts of male (left) and female Necator americanus. Scale in mm.
A B Figs 3.77 A & B: Stained whole mounts of the anterior region of adult Necator americanus. Note the cutting plates and large muscular pharynx.
A B Figs 3.78 A & B: Stained whole mounts of the posterior region of an adult male Necator americanus. Note the well developed rays and long thin spicules. Fig. 3.79: Infective larvae of the hookworm Necator americanus.
Genus Ascaris Fig. 3.80: Recently shed egg of Ascaris suum. Note the thick mammilated outer layer and how the egg does not yet become embryonated.
Genus Toxocara Fig. 3.81: False colour photomicrographs of adult Toxocara canis. Note the three welldeveloped lips around the mouth. The male worms are 4 6 cm in length while the females can reach up to 15 cm.
Fig. 3.82: Unstained eggs of Toxocara canis viewed with polarised light.
Genus Enterobius Fig. 3.83: Stained whole mount preparation of a male Enterobius vermicularis. The males are much smaller than the females and average only 2 5 mm in length. Fig. 3.84: Stained whole mount preparation of an adult female Enterobius vermicularis. The female worms are typically 8 13 mm in length. Note how the posterior region tapers to a sharp point.
Fig. 3.85: Anterior region of a female Enterobius vermicularis.
Family Heterakidae Heterakis gallinarum A B Figs 3.86 A & B: Whole mount preparation of an adult Heterakis gallinarum. This is a common parasite found in the caeca of chickens, ducks, geese and many other birds. The female worms grow up to 15 mm in length and the males are slightly smaller, growing up to 13 mm in length. The worms do not cause serious problems unless there are very high numbers present. Their main importance is as carriers of the protozoan parasite Histomonas meleagradis.
Family Onchocercidae Fig. 3.87: Stained histological section through a nodule that has developed around adult Onchocerca volvulus. Scale in mm.
Fig. 3.88: Closer magnification of a stained histological section through a nodule that has developed around adult Onchocerca volvulus. Scale in mm. A B Figs 3.89 A & B: Stained tumour smear of a nodule caused by Onchocerca spp. illustrating the presence of microfilariae.
Genus Wuchereria Fig. 3.90: Stained blood smear showing the microfilarial stage of Wuchereria bancrofti.