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Plasmodium Tenue (Stephens)

A Review of the Literature and a Case Report¹

1. The literature: Plasmodium lenue criteria: (i) Unusually ameboid form. (ii) Scanty cytoplasm. (iii) Abundant, irregular nuclear chromatin, as first grouped by Stephens (11) may be exhibited by any of the three well-known species of malaria parasites but more often by Plasmodium vivax and Plasmodium falciparum than by Plasmodium malariae. The cause of these deviations from what have been the commonly accepted characters of a well-behaved parasite of the accepted species is not known, but three classes of answers to this question are to be found in the literature.

(a) Deviations of this particular sort represent a new and distinct species called Plasmodium tenue by Stephens.

(b) An extracellular position of the parasite, as either the usual or occasional event, makes manipulations, or malnourishment, or the action of the chemical substances in the blood, factors in producing atypical morphology in the three commonly accepted species.

(c) Unusual variation in the blood complex due to the interplay of factors such as environment, medication, health or ill-health of host, and similar influences, is reflected in an unusual morphology of the parasites of the three commonly accepted species.

2. The case reported: A case is presented of a negro girl, aged three, always resident in Georgia, U. S. A., whose blood examined at weekly intervals over a period of a year, repeatedly revealed typical Plasmodium vivax and Plasmodium falciparum parasites. In addition to these typical forms, there were seen occasionally attenuated forms having the characters of Stephens' (11) and Sinton's (37) Plasmodium tenue.

The fact that these tenue forms appeared at intervals over a period of a year, and that their appearance and disappearance can not be correlated with any external factor might perhaps be an argument in favor of new species. But on the other hand the fact that the tenue forms were seen in the same smears as typical young and mature Plasmodium vivax and Plasmodium falciparum parasites, that no unusual mature forms were seen, that no unusual forms or activity were seen in fresh blood mears,—all of these observations would seem to indicate that these tenue forms belonged to either Plasmodium falciparum or Plasmodium vivax or both.

¹ (The observations upon which this paper is based were made with the support and under the auspices of the International Health Board of the Rockefeller Foundation at the suggestion of Dr. S. T. Darling in whose laboratories the work was carried on.)