F. Coquelin et al., MODIFICATIONS IN THE RHYTHM OF SCHIZOGONY IN PLASMODIUM-CHABAUDI CHABAUDI ASSOCIATED WITH THE SELECTION OF CHLOROQUINE RESISTANCE, Parasitology research, 83(5), 1997, pp. 504-509
A high level of drug resistance was obtained with a line of Plasmodium
chabaudi maintained under intense chloroquine selection pressure acco
rding to the protocols established for P. berghei. The main objective
of this work was to verify if the characteristic asynchronous schizogo
nic rhythm of naturally resistant rodent malaria parasites was also fo
und when the drug resistance was induced experimentally. The degree of
resistance was evaluated through the use of the ''2% delay test'' (DT
) and the schizogonic rhythm, by reference to the synchronicity index
(SI). The strain had originally a DT of 4.26 and an SI of 0.52. Follow
ing the application of 80 mg/kg chloroquine at each passage, as early
as at the 8th passage the parasites rapidly became resistant and async
hronous. At the 17th passage the DT was 3.32 and the SI, 0.20. In the
drug-resistant line the original indices, both the DT and the SI, were
restored after deep-freezing, sporogony, or passage through a Percoll
gradient, or simply by repeated intravenous subinoculations of blood.
The clear correlation between asynchronicity and drug resistance is e
asily explained by the action of chloroquine, which favours the schizo
gonic cycles initiated by latent merozoites.