HEALTH AND DISEASE 31I 



and trichina, are the most important parasites of man in the United States 

 that are transmitted through the consumption of animal food. The pork 

 tapeworm, though only of slight importance in this country, must be added 

 to the list. We shall briefly consider each of these parasites and its bearing 

 on human health. 



THEFISHTAPEWORM 



The so-called fish tapeworm, Diphyllobothrhim latum, is really a human 

 tapeworm that spends part of its early hfe (plerocercoid stage) in certain 

 species of fresh-water fish. According to Wardle the following species 

 of fish in North America are known to be intermediate hosts of the tape- 

 worm under discussion: Pike, Esox estor; pickerel, Stizostedion vitreum; 

 sauger or sand pike, Cynoperca cajiadejjse; and perch, Perca flavescens. 

 Prior to getting into fishes this parasite occurs as a larva in fresh-water cope- 

 pods or so-called water fleas, that constitute a part of the microscopic and 

 near-microscopic aquatic life — plankton — which is an important item in 

 the food of fishes. The life cycle of the tapeworm is rather complicated and 

 is briefly as follows: 



The tapeworm, which may attain a length of about twenty-five feet and, 

 in exceptional cases, a length of sixty feet, in the human intestine, produces 

 eggs which are microscopic in size and which are eliminated from the ripe 

 or gravid tapeworm segments into the lumen of the host's intestine. Oc- 

 casionally long chains containing as many as one hundred or more segments 

 may be passed with the excreta of infested animals, including dogs, cats 

 and wild carnivores, such as bears and foxes, that also serve as hosts of this 

 tapeworm. The tapeworm eggs passed with excreta and those which be- 

 come liberated from the passed segments, as a result of the disintegration 

 of the latter, hatch in water following their normal development. The 

 newly hatched larvae, provided with cilia, may be swallowed by copepods 

 which are usually found teeming in fresh-water lakes. When swallowed 

 by suitable intermediate hosts the larvae undergo further development but 

 do not become infective to man and other definitive hosts unless they reach 

 the body of a second intermediate host, namely, a suitable species of fish, as 

 already noted, and develop there to the plerocercoid stage that is infective 

 to mammals. Fishes become infested by swallowing the infested copepods, 

 and human beings acquire the fish tapeworm as a result of eating raw, or 

 nearly raw, or cold-smoked or salted fish that harbors the stages of the 

 parasites infective to man. 



According to Magath the Finlanders, as well as other northern Europeans 

 in iMinnesota, have retained their native fondness for raw fish, and the 

 more nearly raw the fish is the better the Finlanders like it. Magath makes 

 the following statements: "One Finlander remarked that he was in the 

 habit of not carrying a luncheon on a fishing trip, being satisfied with the 

 raw fish he caught. A common dish is fish which has been salted in brine 



