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Morphological Studies of Plasmodium Falciparum Gametocytes of Different Strains in Naturally Induced Infections¹

Persis Putnam
The Rockefeller Foundation, New York, N. Y.

The morpholoical characteristics of P. falciparum gametocytes have been described in minute detail. Observations for this purpose were made on daily smears taken over a two-week period from the peripheral blood of four patients each naturally infected with one of four heterologous strains of this parasite obtained from fairly widely separated localities in the temperate and tropical zones.

The gametocytes of each strain displayed pronounced diversity as to shape and attributes of chromatin and pigment. This was particularly true of the female forms. Daily mean lengths and widths varied considerably. Male gametocytes always showed a greater mean width. Female gametocytes on the 14-day basis had a greater mean length, although the daily means for males were occasionally longer.

Classification of gametocytes with certain morphological attributes as to age was effected by determination of their mean days of occurrence. That this method had some validity is shown by the significant association between younger and older attributes of two morphological characters when all four strains were combined. Strain L from the temperate zone, however, contained a conspicuous number of presumably younger forms, and when its data were removed, the association although still apparent was no longer statistically significant.

The data for the two-week period were compared with those for a three-day sample of the same which commenced with the day of modal density. Observations for the shorter interval were found more suitable for purposes of strain comparison since they comprised a more even inter-strain distribution of younger and older forms.

There was a tendency for the length of gametocytes to vary inversely with width. Correlation was better for the males than for the females and was signifciant for both in one strain (M) only.

The wide intra-strain diversity of attributes of gametocytes in these four patients indicates the precariousness of any attempt to identify strains on the basis of morphological differences.

Received November 5, 1942.
¹ The studies and observations on which this paper is based were conducted with the support and under the auspices of the International Health Division of The Rockefeller Foundation, in cooperation with the Florida State Board of Health and the Florida State Hospital.