PLASMODIUM OVALE STEPHENS, 1922

A recent paper by James, Nicol and bhute (1932) raises once again the question of the validity of this

new species of malaria parasite, and it may be of

interest to summarise briefly the evidence to date with regard to it. Plasmodium ovale was first described by Stephens

(1922) in blood films from a British soldier invalided from East Africa during the war in January 1918. On admission to the Liverpool School of Tropical Medicine from 8th April, 1918, to 27th July, 1918, blood films from this patient showed what was diagnosed as a pure infection. with Plasmodium vivax. For the next four days the films were negative. On the 28th July, 1918, parasites were again present and the diagnosis was

? simple tertian. On the 29th July, 1918, the diagnosis was ? simple tertian, ? quartan. Owing to the. peculiar character of the forms seen

blood films were taken four hourly during the day time from 30th July, 1918, to 3rd August, 1918, and stained for one hour with Leishman's stain. The temperature chart during this period showed a tertian periodicity, with which the parasite phases seen in the blood films appeared to correspond. Before and after this period, however, the temperature chart was irregular'. On examination of these films Professor Stephens concluded that he was dealing with a new species to which he gave the name Plasmodium ovale to emphasise the fact that the infected red corpuscles were frequently oval in shape, and often with fimbriated or crenated edges.

(It would appear that this conclusion was reached on a re-examination in 1922 of the original films taken in 1918). The appearances seen are illustrated in a very clear

colour plate. The ring forms are round or oval and non-amoeboid. The infected red corpuscles are not

uncommonly oval?sometimes oval with a drawn-out

pointed tail?and with irregular margins. The growing trophozoite forms are very characteristic. They rather closely resemble those of Plasmodium malarice and

present the solidity or compactness of that species. The amount of chromatin and the distribution of the

pigment in a lateral band also recalled the appearances seen in Plasmodium malarice, but equatorial and band- like trophozoites were not seen.

' The characteristics of this parasite so far as concerns the medium forms are a non-amoeboid, pigmented, round or oval parasite, resembling quartan, in a red cell showing Schiiffner's

dots, which is either normal in size or only slightly enlarged. The pigment, so far as can be judged in stained specimens, appears to be brownish black, and granular rather than spicular'. (It may be remarked that the stippling of the erythrocytes shown in the plate is rather coarser than are Schiiffner's dots, and perhaps scantier in the number of dots). The maximum num- ber of merozoites seen in mature schizonts was 12. Mature schizonts occupy red cells which are either normal in size or slightly enlarged. A slight margin showing Schiiffner's dots is often seen, and the cell is

clearly decolorised. No gametocytes were seen. The next contribution to the subject is the paper by

Stephens and Owen (1927). The patient here concerned came from Nigeria. The first diagnosis made was

Plasmodium malarice, but further examination showed that forms corresponding to Plasmodium ovale were

present. A series of slides, thirty-six in all, was taken from 17th February, 1925, to 2nd March, 1925, and

carefully studied. The parasite forms encountered are stated to have conformed in all respects with Plasmodium ovale, and a very interesting set of photomicrographs accompanies the paper. The oval shape of the infected red corpuscles was a conspicuous feature throughout the films, both in thin and thick parts. There is often distinct decolorisation of the red cells. The dots are

distinct and numerous, but the stippling more faintly stained than are Schiiffner's dots. The trophozoites are round or oval and non-amceboid. Pigment is coarse, dark and abundant, resembling that of Plasmodmm malarice. The largest number of merozoites in the mature schizont was fourteen, whilst daisy-like forms with eight to ten merozoites arranged around a central mass of pigment were seen. Equatorial and band forms also occurred, whilst the gametocytes were indistinguish- able from those of Plasmodium malarice except for the stippled decolorised margin of the red cell. The

periodicity could not be determined from examination of the slides. The third paper is by Warrington Yorke and Owen

(1930). This patient also came from Nigeria. Examination of blood films showed parasites identical with Plasmodium ovale. The strain was passaged by direct blood inoculation through a series of five general paralytics or tabetics, and throughout maintained its characteristic morphology. As the temperature charts in the paper very clearly show, the fever shows a very definite tertian periodicity in all six cases. ' The para- site itself appears to be indistinguishable morphologically from Plasmodium malaria;', write the authors. ' It

differs, however, in that its cycle of schizogony is com- pleted in forty-eight hours, and temperature charts of infected cases are of the tertian type The characteristic appearance of the infected red cells, to

which Stephens' attention was originally drawn, was clearly seen in the naturally infected case and in all five subinoculated cases. The infected red cells are

moderately enlarged?occasionally enormously so; they are pale, fragile, frequently oval, usually with irregular ragged outline, and heavily stippled'.

Finally comes the important paper by James, Nicol and Shute (1932). The strain of Plasmodium ovale

Nov., 1932| IMPLANTATION OF THE URETERS: GREEN-ARMYTAGE 631

with which these workers curried out their experiments was obtained in citrated blood from a patient in the

Belgian Congo. II was first inoculated intramuscularly into a general paralytic, and lie developed malaria six

days later. By direct blood inoculation the strain was

sub-passaged into fourteen other patients with general paralysis, and in all of them the course of the fever and the morphological characters of the asexual forms of the parasite were the same. The infections were mild and tended to clear up spontaneously without treatment, with only a scanty production of gametocytes. Instead of increasing gametocyte production, a single dose of quinine cured the infection. Finally, however, a patient was available who showed 12 male and 72 female gametocytes per c.nim. of blood. A batch of 10 Anopheles macidipennis was now fed on this patient and kept at 25?G. Later, a second patient with a fair production of gametocytes became available for mos-

quito feeds; a batch of 100 Anopheles maculipennis was fed on this patient during five days, and kept at 25"C. The donor's temperature chart showed typical tertian

periodicity. Of 37 mosquitoes fed and subsequently dissected,

20 (or 54 per cent.) were found infected, but the infections were always slight. Sporozoites were found in the salivary glands from the sixteenth day onwards.

Infected mosquitoes were now fed on four further

patients, all of whom developed malaria. The incuba- tion periods were 14 to 15 days, and the fever which developed showed typical tertian periodicity. Examina- tion of blood films showed that the parasites conformed in all respects to the previously described morphology of Plasmodium ovale, and that the schizogony cycle took 48 hours. Further,

' the arrangement of the pig- ment in the stage of young oocysts is so different from that of any of the species hitherto known as to enable the parasite to be identified without difficulty at this stage of its life cycle'.

At this point, the authors most unfortunately come to a stop. 'We shall take an early opportunity of

describing and illustrating these and later stages of the mosquito cycle, as well as the sexual stages of the

parasite in the human host which were not studied by previous observers. In the meantime we can say defi- nitelv that there remains no doubt that Plasmodium ovale is ;i separate species, and that its morphological characters in the human and insect hosts are character- istic and constant '.

* * * * *

Whilst we must admit that the evidence analysed above is strongly in favour of the validity of the new species, yet we think that malariologists and laboratory workers in general throughout the tropics will not rest content with the cx-eathedra pronouncement with which Colonel James and his colleagues conclude their paper. It is precisely that full, detailed and illustrated account of the morphology and life cycles of Plasmodium ovale that has been promised that they will look forward to for final proof.

It will be noted that, so far, Plasmodium ovale has been reported only from Africa. Yet there is now

sufficient evidence to enable laboratory workers to

diagnose the new species, should they come across it. Plasmodium ovale infection can presumably be diag-

nosed by the following observations:? (1) The temperature chart shows very regular tertian

periodicity. (2) The infection is as a rule a light one. with a low

degree of infection and only scanty production of

gametocytes. (3) It is extremely amenable to quinine treatment. (4) The general morphology of the parasite, on the

other hand, conforms very closely to that of Plasmodium malaricc, the parasite of quartan malaria.

(5) The infected red corpuscles are of normal size, or only slightly enlarged. They are often paler than normal. It is very characteristic of the infection that the infected erythrocytes are distorted into an

oval shape, whence the name of the species. They (Continued at Joot oj next column)

(Continued from previous column) frequently show fimbriated or crenated margins. They show a very well-marked stippling, recalling in general Schiiffner's dots, but which is perhaps rather coarser

and more scanty in distribution. These points may perhaps enable the laboratory

worker in India to identify Plasmodium ovale, if he should encounter this new and interesting species of malaria parasite.

R. K.

References

James, S. P., Xicol, W. D., and Shute, 1'. G. (1932). Plasmodium ovale Stephens: Passage of the Parasite through Mosquitoes and successful transmission by their bites. Annals of Trop. Med. anil Parasit., Vol. XXVI. No. 2. p. 139.

Stephens. J. W. W. (1922). A New Malaria Para- site of. Man. Annals of T rop. Med. ami Par a si I., Vol. XVI, p. 383.

Stephens. .T. W. W., and Owen, D. U. (1927). Plasmodium ovale. Annalst of Trop. Med. and Parasit., Vol. XXI, p. 293.

^ orke. W., and Owen, D. U. (1930). Plasmodium ovale. Annals of Trop. Med. and Parasit., Vol. XXIV, p. 593.