02-07-1977 Planning Packet - Laserfiche WebLink

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wcr than one percent is the large, recrca- are most often af- ’ itch have adversely orts, inconvenienced ’ators, spoiled some created temporary f. To these people, tch and its control nncsoia, Wisconsin, evinces of Canada, 1 from many parts imers ’ itch follows Iter-borne larvae — ic flaiworms. Small after a few hours rated, and arc ac- nsation which may about twenty dif- (blood flukes) arc an and produce a itize certain birds iriae mature inio mal, “accidental,” the human skin, her. loud flukes which I normally^therc I 1 i. t r , * A •1^ In • •. H <** • . *" . f -*• • I ■jt I W ex c ept ions-produce a sijnificant dermatitis after These latter cause /«,»„ dta^Stain'r » parasitic Africa, and Latin America but not. fortunately in the coiilincntal United States. * The life cycle of a-swimmers-itch ” parasite (Fie h ^really involves certain species of water birdsUme- timM mammals) and a few species of aquatic snails. SStoilif are required for eom- parasite ’s life cycle-the snail as an n^n^iT * ***“' P™«<«sation of the C? hi ’’!“*• '"''hrate as a definitive tot in which the worms reach sexual maturity. The fatot"l “/s”r * “k "’"»<*'"<« worms^ut 1/5 of an inch long, male and female, unlike fiatworms, which are hermaphroditic) in the ISITf f " other vertebrate. Each adult female fluke produces hundreds of eegs which »^h the intestine of the bird and are voided in the ^ 'hal reaches the water and hatches rfV«"P”i.*i “"T swimming larva (1/250 ^ms'^VlT Y “ The miracidium i-ZlSLi. h- “"I" “ “"“"'ars a snail :; *■ penetrates a snail of the proper It dewlops in the digestive gland or reproduc- after ^ml***^ '^v ’PO'oc.vsis, whichato sneral weeks produce thousands of fork-tailed enwno larvae, each about 1/32 of an inch long. This all bppens at the expense of the snail, but apparently a SimlirkT"^ 1;'“"* “• ">i"S •Xaur ^siw A good parasite-even from the parasite s pmnt of view-does not usually kill its host, at least ^ un 1 the parasite itself has developed to a stage where its host is no longer needed.) Under certain Umpemture and light conditions the cercariae leavj the snail and begin swimming about actively, u is the TZTJrTI “ "** *-•- •his " me• Haler bird (or other vertebrate, depending on the ^ speciesIf tlw life cycle is to be completed. If the cercaria ‘‘ penetrates the skin with the aid of special glandular secretions, then migrates through the circulatory system to the blood ve^ls of the liver and intestinal tract, where it crows and maitures into an adult male or female blood fluke. After mating, the female worm lays eggs and the cycle DCfins again. Most cercariae do not And an appropriate host and IC within a day or two after emerging from a snail. Some may accidentally find a human host, penetrate the skin, and cause the rash known as swimmers* «ch. the fate of the cercaria is again death, however. That IS the nature of parasitism; it is a chancy busi ness. The chances that at least some individuals will complete the life cycle are greatly increased statistically by. the hundreds of eggs produced in a season by a single adult female blood fluke; and the fact that each miracidium which succeeds in penetrating an f potential of producing thousands ol cercariae by asexual reproduction. This hli ! ^ parasitic species is helped to succeed; by placing a premium on reproduc tion. Many other subtle structural, behavioral, and physiological adaptations also enhance the chances ^ success as does the timing of various events in the ^rasite s life cycle to coincide with appropriate tot" hosif' ” •''' “““ '"‘mmers ’ itch was first dis- ologist and professor in the School of Hygiene and Public Health of Johns Hopkins University. Dr. Corfi nntal investigations were made during the 1920s at ^ University of .Michigan Biological Station at e^remhvextremit) of Michigan s Lower Peninsula in close Mch has been a serious problem over the years Biologists at the Station, after working at a small pond adjacent to Douglas Lake known as the Sedge Pool frequently had come down with a rash which came ’ be known locally as the “Sedge Pool Itch.” Dr Cort demonstrated that “Sedge Pool Itch ” was caused by the penetration into the skin of certain schis- rnl^Hi'a ” parasitiae birds and After this pioneering discovery, reports of schis. tosome dermatitis, under various names, began'^to wme in from many parts of the world. All thal hale b«n investigated have implicated various species of Khistosome cercariae. aquatic snail intermediri^hos J nd bird and mammal dclmiiive hosts. Much has been learned over the years about the life histories of several 0 the cicrniatiiis-causing schistosome species about the snail species which serve as in,erm7diaie 2„ts which may be eiiher naturally or experimentally r r- infecte The snails, implici are giv within very si cercarii mnizat adults I snail in of the I breathin Both fai America a limitet nre comi emc*MU flNCTBAI