A study of gametocytes in a west african strain of plasmodium falciparum

A West African strain of P. falciparum was maintained in our laboratory over a period of 17 months and during this time 85 patients were infected. The percentage of our patients who developed gametocytes was very much higher than the percentage in any age group of the cases examined by malariologists where the strain originated. The density of gametocytes per c.mm. in our patients has greatly exceeded the number found by workers who have examined cases where the strain originated. Anopheles stephensi (type) imported from Delhi, has proved to be an efficient carrier of this strain of parasite. On the other hand, the strain of English Anopheles atroparvus maintained in our insectarium is a very poor carrier. Gametocyte output was always greater in cases in which the primary attack was aborted by the administration of antimalarial drugs. It is believed that inadequate treatment of the primary attack, irrespective of the drug used, conduces to gametocyte production. If this is so, it indicates at least two important factors—(1) that patients leaving hospital should be given a course of a gametocytocidal drug, e.g., proguanil, between the 14th and 21st day after the last day of fever; (2) that a clinical and radical cure of a primary attack, in addition to being in the best interests of the patient, is also of major importance epidemiologically in preventing mosquitoes from becoming infected. This applies especially to unseasoned personnel in the services. In this series of cases, macrogametocytes always appeared before microgametocytes and persisted for days or weeks after microgametocytes disappeared. Gametocytes were never found in cases where antimalarial drugs cured the disease in the primary attack. The study of gametocytes in this series of cases indicates that the maximum longevity of individual gametocytes is about 60 days. Many of our patients showed gametocytes for the first time about 3 weeks after the beginning of the primary attack and 2 to 4 days after the first day of the recrudescence. We suggest that gametocytes evolve from asexual parasites circulating in the blood during the remissions between attacks. The percentage of gametocyte carriers, calculated from the findings in thick films, may not be an accurate index to the percentage of a population infective to Anopheles. Differentiation of the sexes is more difficult in thick films than in thin films. Thick films take several minutes to dry. The gametocytes, providing they are ripe, may become round organisms and be mistaken for other parasites, especially P. malariae.