Effect on Virulence of Trichinella Spiralis.pdf

The <strong>Effect</strong> on-Virulence of TrichinellaSpiralis from Passage Through Rabbits,Guinea Pigs and Rats"An AbstractBy JO S r~OLIVEH GONZALEZFrom the Department of .If edical Z oolo{/!/ I\f the School of Trop ical .Ifediciue ,San J uun, Puerto RicoVIHU L E ",.' n ; is an innate physiological potentiality which variesrapidly and significantly in any give n strain of micro -organ ­isms. These variations which occ ur under certain circ umstancesare a co mmon obse rvat ion in almost all st rains of parasiti cforms .Variations in the viru lence of man y organ isms are often broughtabout by changes in t he en viron me rrt. In bacteri a a cha nge from ahigh to a low gra de of virulence is commo nly seen as the result of theuse of an unsui tabl e cult ure med ia, or as th e result of t he prolongedartificial gro wth of t he organism . The change from a low to a highgra de virulence has bee n accomplished by al tering the environmen tin wh ich th e organ ism gl'ows. P assa ges of culture through bloodser um has been found effective as a method of raising virulence.On e of the earliest known obser va tions on th e cha nges in viru lenceof an organis m which occ urs as a resul t of animal passa ge is P asteur'swor k on rab ies. Pasteur showed that t he virus of hydrophobi awhen successively passed thro ugh rabbits gained in virulence, whilewith only three pa ssages t hro ugh monkeys the virul ence was reducedalmos t t o ext inction. The sa me rcluti onship bet ween hostand parasite also exis ts with ot her micro-organism s. The virulen ce ofattenuated pneu mococci is increa sed by successive passage throughnu ce.Wi th parasitic helminth s no work has been done with the intentionof studying t he change in viru lence of parasites in relation toanimal pa ssage, but with indirect ev ide nce the same cond itions aswith bacteri a are kn own t o occ ur . Boyd, working with Plasmodiumpraecox in cana ries, obser ved th at the virul ence of t he parasite in ­cre ased by rapid passage from one bird to a no ther ."Abstra cted from a D issert a tion sub mitt ed to th e Faculty of the D ivision of the BiologicalSciences, University of Chicago, in can didacy for the Degree of ~las le r of Science, August,l!) ~l(l . . .(j1

..( ' e) l~ 'I'hc j~:trec{ Oil Virulence cd Trichi uella S piralisIn this studv of th e effec t on th e virulen ce of Trichin ella spirali«from passa ges' through rats, rabbits and guinea pigs, it. ha s beendemonstrated that th e parasite suffers a gradual diminution illvirulence as the infection is passed from rabbit to rabbit and fromzuincu !Ji,,' to sruiucu pig. The loss in virulence of th e str a ins wasb b b