Altered dihydrofolate reductase associated with drug-resistance transfer between rodent plasmodia.

Resistance to pyrimethamine in strains of Plasmodium vinckei and of Plasmodium berghei is attributed to changes in amounts and properties of the dihydrofolate reductases. The resistant strain of Plasmodium berghei was isolated from an experimentally induced mixed infection of drug-resistant Plasmodium vinckei and drug-sensitive Plasmodium berghei, through biological filtration in hamsters. The drug resistance in Plasmodium berghei appears to have been acquired through transfer of part of the gene or genes coding for dihydrofolate reductase from the resistant Plasmodium vinckei to the sensitive Plasmodium berghei.