Effect of 25 Milligrams of Pyrimethamine on the Infectivity of Plasmodium Vivax, St. Elizabeth Strain, to Anopheles Quadrimaculatus

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  • National Institutes of Health, National Institute of Allergy and Infectious Diseases, Laboratory of Tropical Diseases, P. O. Box 717, Columbia, South Carolina

A preliminary announcement that pyrimethamine (Daraprim®) sterilizes Plasmodium vivax (St. Elizabeth strain) gametocytes was made in 1953 by Coatney et al. The present report gives the details of these observations. The malaria had been induced in neurosyphilitic patients. Medication consisted of a single 25-milligram tablet of pyrimethamine given orally.

Anopheles quadrimaculatus, Q-1 strain, was used to test infectivity of the treated patients to mosquitoes. Control mosquito feedings were made on all patients from one to four hours before drugging. Infections in these mosquitoes demonstrated the presence of viable gametocytes.

Mosquitoes were fed at four-hour intervals for the first 24 hours after treatment on Patient number 1; otherwise all feedings were approximately at 24-hour intervals from time of dosage until at least no more gametocytes could be demonstrated in the smears.

Parasites and gametocytes were counted on Earl-Perez smears made at the time of feeding. Such smears were continued for 7 to 28 days after the disappearance of parasites.