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Comparative Morphological Studies of Plasmodium Falciparum Gametocytes in Variously Induced Infections¹

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

A study has been made of the morphological characteristics of P. falciparum gametocytes of four American strains: L from the temperate zone, and C, M, and P from the tropics. The object was to see whether there were morphological characteristics associated with strain that might permit identification. The present paper is concerned with the distribution of attributes of four morphological characters (1) in patients naturally inoculated and in those artificially infected with the parasite, (2) in two patients each artificially infected with more than one strain, and (3) in one patient naturally inoculated with L strain in 1936 and another in 1940.

Attributes of shape, chromatin and pigment arrangement, individual pigment, and individual chromatin were described for each gametocyte observed in a three-day sample beginning with the day of modal density. Sex, length, and width were noted. The significance of the differences observed was determined by statistical method.

The comparisons brought out a wide variety of types of gametocytes particularly among females. These were not due to age, since the three-day sample nullified this factor. They were not due to strain since replicate samples from persons infected with the same strain also presented a wide diversity of types. It was not possible to reinfect the same person with the same strain, but in the two persons infected with more than one strain the differences were still conspicuous. The factor or factors responsible for this multiplicity of forms, particularly among female gametocytes, remain unknown.

In spite of these apparently conflicting results the outstanding characteristics of falciparum gametocytes are clearly defined. They are:

1. Male and female gametocytes are usually sausage shaped, not as ordinarily described with the form of a crescent.

2. In males the chromatin and pigment occupy both central and outlying zones. Among females they are more likely to occupy the central zone only.

3. Individual pigment in males is diffuse and light, either fine or coarse. In females it is compact and dark and may be annular. In the case of P strain females it is likely to be diffuse, coarse, and dark.

4. Individual chromatin in males is always diffuse and vesicular and partly enveloped by the pigment. Among females it is compact and vesicular but may be either wholly or partly enveloped.

5. M strain gametocytes are likely to be longer and P strain specimens shorter than those of other strains. Females are longer and narrower than males. There is negative correlation between length and width of gametocytes.

In view of the many types observed it is gratifying to be able to summarize to this extent. It is not possible to set up criteria for identifying strains nor can the varied morphological picture presented by P. falciparum gametocytes be satisfactorily explained.

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.