Flat worms and Round worms HELMINTHES Flat worms and Round worms

HELMINTHOLOGY Phylum Platyhelminthes = Flat worms Class Trematoda = Flukes Class Cestoda = Tape worms Phylum Ashelminthes = Round worms Class Nematoda Genus Ascaris Genus Trichinella Genus Necator, Ancylostoma Genus Enterobius Genus Dranunculus Genus Wucereria

HELMINTHOLOGY Phylum Platyhelminthes = Flat worms Class Trematoda = Flukes Some flukes are single sex, some are hermaphroditic possessing both ovaries and testes.

Hermaphroditic Flukes

O FIGURE 13-39  Clonorchis sinensis egg in a fecal specimen (X1000, D’Antoni’s iodine stain). The eggs are thick shelled and between 27 and 35 µm long. There is a distinctive operculum (O) (positioned to give the appearance of shoulders) and often a knob at the aboperular end (not visible in this specimen).

FIGURE 13-45  Schistosoma mansoni egg in a fecal specimen (X1000, D’Antoni’s iodine stain). Schistosoma mansoni eggs are large (114 to 175 µm long by 45 to 70 µm wide) and contain a larva called a miracidium. They are thin-shelled, lack an operculum, and have a distinctive lateral spine (arrow).

FIGURE 13-46 Schistosoma mansoni egg in a fecal specimen (X1000) FIGURE 13-46  Schistosoma mansoni egg in a fecal specimen (X1000). The lateral spine may be oriented in such a way as to be difficult to see. In this specimen, the spine (arrow) is above the egg and the egg may be misidentified as S. haematobium.

FLAT WORMS Phylum Platyhelminthes = Flat worms Class Cestoda = Tape worms Scolex contained in egg holdfast structure with hooks and suckers Proglottids major body of tapeworm contains both ovaries and testes = hermaphroditic Eggs can penetrate intestine of host and form hydatid cysts in tissues

FIGURE 13-57 Taenia solium scolex (X64) FIGURE 13-57  Taenia solium scolex (X64). The Taenia solium scolex has two rings of hooks and four suckers.

FIGURE 13-55 Taenia spp. egg in feces (X1000) FIGURE 13-55  Taenia spp. egg in feces (X1000). Taeniid eggs are distinctive looking enough to identify to genus, but not distinctive enough to speciate. Eggs are spherical and approximately 40 µm in diameter with a striated shell. The oncosphere contains six hooks.

ROUND WORMS Phylum Ashelminthes = Round worms Class Nematoda Genus Ascaris – most common Genus Trichinella Biblical worm Genus Necator, Ancylostoma - hookworms Genus Enterobius – pinworm 2nd most common Genus Dranunculus - Guinae Genus Wuchereria - Elephantiasis Mosquito borne

Hookworms Ancylostoma duodenali and Necator americanus Old world and new world hookworms differ only in their geographic location. Human phase of this worm begins with a filaform larvae penetrating the skin, enters circulation, carried to the lungs, coughed up and swallowed, develops to adulthood in small intestine. Adult worms lay between 10,000 and 20,000 eggs per day. Daily blood loss 0.2ml/adult/day. Microcytic hypochromic anemia develops.

b a FIGURE 13-64  Heads of adult hookworms. (a) Ancylostoma duodenale head (X64) showing the pairs of chitinous teeth (arrow). (b) Necator americanus head (X160) showing the cutting plates (arrow).

FIGURE 13-63 Hookworm egg in feces (X1000, D’Antoni’s iodine stain) FIGURE 13-63  Hookworm egg in feces (X1000, D’Antoni’s iodine stain). Hookworm eggs are 55 to 75 µm long and 36 to 40 µm wide. They have a thin shell and contain a developing embryo (seen here at about the 16 cell stage) that is separated from the shell when seen in fecal samples.

Biblical worm Trichinella spiralis etiological agent of trichinosis. Infectious larva is present in the striated muscle of carnivorous and omnivorous mammals. Swine most common organism to transmit to humans. Encysted larvae live for many years. Polar bears and walruses are accounting for new human infestations in our Alaskan artic regions.

FIGURE 13-68 Trichinella spiralis larva in skeletal muscle (W. M FIGURE 13-68  Trichinella spiralis larva in skeletal muscle (W.M., X260). The spiral juvenile and its nurse cell are visible in this preparation.

FIGURE 13-69 Trichinella spiralis larvae in skeletal muscle (sec FIGURE 13-69  Trichinella spiralis larvae in skeletal muscle (sec., X260). Each larva has entered a different skeletal muscle cell and converted it into a nurse cell that sustains it with nourishment.

Pin worms or Seat worms Enterobius vermicularis most common helminthic infestation in America, 500 million cases annually globally second globally to Ascaris infestations. Eggs are ingested mainly fecal-oral.Egg laden dust can be inhaled. Autoinfection occurs frequently. “Scotch Tape Test” from perianal folds of diagnostic value.

FIGURE 13-62  Enterobius vermicularis egg (X1000, D’Antoni’s iodine stain). The eggs of Enterobius vermicularis are 50 to 60 µm long and 20 to 40 µm wide with one side flattened (arrow). They are usually embryonated in typical preparations.

Ascaris Lumbricoides Large worms 25cm – 45cm in length. Most common helminth with over a billion infested a year. Prevalent in areas where sanitation is poor and human waste is used as fertilizer. Ingested egg releases a larva that penetrates the duodenal wall and carried to the liver and the heart, enters the pulmonary system, enters the alveoli where they molt and mature. They are coughed up, swallowed and returned to the small intestine. Adults can be passed out into the feces.

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Pathogenesis of Ascaris suum (Larvae) Damage associated with larval migration Liver within 24 hr PI hemorrhage, inflammation, necrosis “milk spots” - fibrosis resolves after treatment 30

Pathogenesis of Ascaris suum (Adults) Interfere with digestion and absorption poor feed conversion, stunting Obstruction or rupture of intestine Migrate up bile duct obstructive jaundice 32

FIGURE 13-59  Fertile Ascaris lumbricoides egg in feces (X1000, D’Antoni’s iodine stain). Fertile Ascaris lumbricoides eggs are 55 to 75 µm long and 35 to 50 µm wide and are embryontated. Their surface is covered by small bumps called mammillations.

S N FIGURE 13-71  Wuchereria bancrofti microfilaria in a blood sample (X960). The microfilariae of Wuchereria bancrofti can be distinguished from others in the blood by the sheath (S) and the single column of nuclei (N) not extending to the tip of the tail.