Peculiarities of the behavior of a low-virulence strain of toxoplasma in frequent passages
Savina, M.A.
Meditsinskaia Parazitologiia i Parazitarnye Bolezni 45(1): 69-74
1976
ISSN/ISBN: 0025-8326 PMID: 1264033 Document Number: 100483
Frequent passage is the most important factor in increasing virulence of Toxoplasma of low virulence. Twenty serial passages were carried out in mice mostly by the i.p. route at 7-day intervals. When sufficient numbers of parasites were used for inoculation (i.p. passage with peritoneal cavity washings) the strain increased its virulence regularly, and this increased virulence persisted. Toxoplasma virulence increased more rapidly in animals highly susceptible to them (random-bred mice) and, in some cases, in animals with reduced immune response and immature as compared to more resistant (CC57W and BALB/c mice) adult animals with normal immune response. It is unclear whether the number of the parasites passaged (greater in passages in more susceptible and weakened animals) was important, increasing the possibility of variability of virulent specimens, or whether reproduction in animals itself influenced the manifestation of virulent properties of the parasites. Further studies of variability in Toxoplasma clones are necessary to elucidate these questions.