OVERVIEW Some of the parasites transmitted via FOODBORNE PARASITES - PDF document

OVERVIEW � Some of the parasites transmitted via FOODBORNE PARASITES food & water, mostly from North America � Macroscopic, transmitted as PHR 250 microscopic forms � Reproduce sexually; some are Foodborne Infections hermaphrodites and Intoxications � Life cycles in >1 host species http://www.dpd.cdc.gov/dpdx www.dpd.cdc.gov/dpdx/ / http:// FOODBORNE PARASITE GROUPS � Roundworms � Tapeworms � Flukes Trichinella spiralis FOODBORNE ROUNDWORMS � Trichinosis (potentially fatal) � Trichinella spiralis � Larval cysts in muscles of swine, � Ascaris lumbricoides other carnivores (bears) � Anisakids � Mate in intestine, ovovivipary, larvae � Anisakis simplex (herringworm, via lymph & blood to muscles, whaleworm) encystation � Pseudoterranova decipiens � Prevention: thorough cooking (or (codworm, sealworm) freezing or irradiation) of meat

T. spiralis Larvae in Muscle Section Trichinella life cycle Ascaris lumbricoides Ascaris lumbricoides � Large roundworms — intestinal obstruction life cycle � Transmitted by eggs in human feces; under favorable conditions, eggs mature after 2 – 3 weeks, may remain viable in soil or sewage sludge for years Adult Ascaris lumbricoides Ascariasis in a child

Swine Ascariasis Ascaris eggs Anisakids (principal species Anisakis simplex , Pseudoterranova decipiens ) � Larvae from raw marine fish (sushi, ceviche, etc.), sometimes invasive � Prevention by cooking fish thoroughly, or freezing Baylisascaris larva emerging from egg following 4 months in formalin Anisakid life cycles Anisakid life cycles � Anisakis definitive hosts are cetacea (e.g., dolphins, porpoises → “whaleworms”) � Pseudoterranova definitive hosts are pinnipeds (seals, walruses → “sealworms”)

Anisakid in fish fillet Anisakid life cycles FOODBORNE TAPEWORMS Taenia life cycle � Taenia saginata (beef tapeworm) � Taenia solium (pork tapeworm) � Diphyllobothrium latum (fish tapeworm) Taenia saginata cysticerci Taenia saginata � Beef tapeworm (rare in US and Canada) � Cysticerci (macroscopically visible, “beef measles”) ingested with raw or undercooked beef

Taenia spp. tapeworm Taenia saginata in humans � Scolex attaches in intestine, generates a tape of proglottides; many years of essentially inapparent infection may follow, with shedding of eggs or proglottides in feces. Taenia Taenia saginata saginata gravid scolex proglottis Taenia (spp.?) eggs Taenia saginata transmission � If human feces are applied to land where cattle ingest them, the eggs produce oncospheres which give rise to cysticerci in the bovine tissues.

Taenia solium Taenia solium in humans � Pork tapeworm (in U.S. cases � Scolex attaches in intestine, principally imported from Latin generates a tape of proglottides; America) many years of essentially inapparent � Cysticerci (macroscopically visible, infection may follow, with shedding “pork measles”) ingested with raw of eggs or proglottides in feces. or undercooked pork Taenia Taenia solium solium gravid scolex proglottis Taenia solium eggs to humans Taenia solium transmission � Taenia solium eggs are infectious perorally for humans: tapeworm � If human feces are disposed where carriers may autoinfect themselves or swine can ingest them, the eggs contaminate food they touch, or their produce oncospheres, which give feces may transmit the eggs to other rise to cysticerci in the swine people via food or water; the result is tissues. cysticercosis, often of the CNS, in the recipient human.

Taenia solium neurocysticercosis Taeniasis Cysticercosis Taeniasis fecal undercooked oral pork fecal oral Cysticercosis T Taenia solium life cycle Diphyllobothrium latum Diphyllo- � Fish tapeworm (Asia, Europe, the bothrium Americas) � Plerocercoid ingested with fresh water fish D. latum proglottis D. latum definitive hosts � Scolex attaches in intestine, producing the largest tapeworm that infects humans. � Other species that eat raw fish are also definitive hosts, but produce a low proportion of viable eggs. � Eggs shed in feces that reach water infect copepods, which are later eaten by fish.

D. latum life cycle D. latum in humans � Symptoms in humans are usually trivial, but vitamin B 12 -deficiency anemia sometimes occurs. Clonorchis sinensis , FOODBORNE FLUKES Opisthorchis spp., � Clonorchis sinensis , Opisthorchis Metagonimus yokagawai , spp., Metagonimus yokagawai , Heterophyes heterophyes Heterophyes heterophyes (fish flukes) � Fish flukes (limited geographic � Paragonimus westermani (lung fluke) distributions) � Fasciola hepatica (liver fluke) � Definitive hosts are humans or � Fasciolopsis buski (intestinal fluke) other fish-eating vertebrates Paragonimus westermani Fish flukes � Lung fluke (limited distributions on � Hermaphroditic adults in liver several continents) produce eggs shed in feces. � Eggs from flukes in lung are passed � Intermediate host is a very specific with sputum or swallowed and snail species. passed in feces. � Fish are the food vehicle. � Snail intermediate hosts � Metacercariae the infectious form. � Food vehicles are crustacea (crabs and crayfish) eaten raw.

Chinese Mitten Crab (Oriental lung fluke) life cycle Paragonimus westermani Fasciola hepatica Fasciola hepatica � Liver fluke (widespread, but � Snail intermediate host sporadic in North America) � Vehicles for human infection are � Principal definitive hosts are sheep water plants (e.g., watercress) on and cattle (other species reported, which metacercariae have encysted, accidental in humans) eaten raw. � Eggs shed via bile in feces Fasciola hepatica (the sheep Fasciolopsis buski liver fluke), life cycle � Intestinal fluke (occurs in southeast Asia) – largest intestinal fluke of humans � Main definitive hosts are humans, pigs, and dogs. � Unembryonated eggs, shed in feces, develop and hatch in fresh water within 3 – 7 weeks at 27 – 32 E C.

Adult Fasciolopsis buski Fasciolopsis buski � Snail intermediate host � Food vehicles are water plants that have encysted metacercariae. Summary Summary � Roundworms, tapeworms, and � Careful disposal of human waste flukes are transmitted to humans via can have a significant effect in food and water in many parts of the reducing the threat of some of these. world. � Foods can be made safe by cooking, � Nonhuman hosts play a vital role in but not all foods are customarily the life cycles of many of these cooked. parasites. Parasites transmitted to humans Parasites transmitted to humans from foods contaminated in handling from drinking water Source or mode Parasite species Infectious Source or mode Parasite species Infectious of contamination form of contamination form Feces (human) Cyclospora cayetanensis Oocyst Handled by Cryptosporidium parvum Oocyst Entamoeba histolytica Cyst infected person Cryptosporidium hominis Oocyst Feces (human Cryptosporidium parvum Oocyst (feces ) Entamoeba histolytica Cyst and animal) Cryptosporidium hominis Oocyst Giardia lamblia Cyst Giardia lamblia Cyst Taenia solium Egg Toxoplasma gondii Oocyst (proglottis)

Parasites transmitted to humans from fruits Parasites transmitted to humans & vegetables contaminated in the field from raw or rare meats Source or mode Parasite species Infectious form of contamination Source or mode Parasite species Infectious Agent in feces— Ascaris lumbricoides Egg of contamination form contaminated Cryptosporidium parvum Oocyst soil & water Infected food Taenia saginata Cysticercus Cyclospora cayetanensis Oocyst animal Entamœba histolytica Cyst Taenia solium Cysticercus Fasciola hepatica Metacercaria Toxoplasma gondii Bradyzoite Fasciolopsis buski Metacercaria Giardia lamblia Cyst Trichinella spiralis Cyst (larval) Taenia solium Egg (proglottis) Toxoplasma gondii Oocyst Parasites transmitted to humans from raw or rare fish & seafood Source or mode Parasite species Infectious of contamination form Infected fish Anisakids Larva (ocean) Infected fish Clonorchis sinensis, etc. Metacercaria (fresh water) Diphyllobothrium latum Plerocercoid Crustacea Paragonimus westermanii Metacercaria