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Thick film appearance of malaria parasites
201
CORRESPONDENCE.
THICK FILM APPEARANCE OF MALARIA PARASITES.
To the Editor, TRANSACTIONS of the Royal Society of Tropical Medicine and Hygiene. SIR,
Dr. J. W. FIELD has filled a long felt need in his series of papers on the thick film appearance of malaria parasites, and both those who have a special interest in malaria, and general practitioners in the tropics, are greatly in his debt. But, for the sake of those who may read his latest paper as they commence practice, I feel that some qualification is required of one or two of the points which he makes. In East Africa, and I make no suggestion that the following remarks apply elsewhere, the figures given in his Table I would not be found in the course of routine diagnosis.* In other words, parasites are likely to be just as scanty in an early subtertian infection as in any other, and diagnosis of cases in Europeans has frequently to be made on the presence of two or three parasites in a thick film. When parasites are present in such small numbers, species diagnosis in thick films does, as Dr. FIELD himself states, become almost impossible except to the very expert, and recourse must necessarily be made to the thin film. In the early stages of an infection with P. falciparum, the parasites are so minute that they may only be seen with difficulty in a thin film, and when this is the case I have on a number of occasions been unable to find them in a thick film. It is in fact just such cases which, in my opinion, provide an explanation of a number of those " negative " blood films which are found in the obvious presence of clinical malaria. I do not, however, wish to suggest in any way that the thick film technique is not the method of choice in the diagnosis of malaria, and the mainstay of malaria survey work. Yours faithfully, Nairobi. D. BAGSTER WILSON,
Major, E.A.A.M.C. ~' FIELD, J. W. (1941). T h e morphology of malarial parasites in thick blood films. Part IV. Identification of species and phase. Trans. R. Soc. trop. Ned. Hyg., 34, 405.
Printed by H. R. GRUBB.LTD., Poplar Walk, Croydon.
CORRESPONDENCE.
THICK FILM APPEARANCE OF MALARIA PARASITES.
To the Editor, TRANSACTIONS of the Royal Society of Tropical Medicine and Hygiene. SIR,
Dr. J. W. FIELD has filled a long felt need in his series of papers on the thick film appearance of malaria parasites, and both those who have a special interest in malaria, and general practitioners in the tropics, are greatly in his debt. But, for the sake of those who may read his latest paper as they commence practice, I feel that some qualification is required of one or two of the points which he makes. In East Africa, and I make no suggestion that the following remarks apply elsewhere, the figures given in his Table I would not be found in the course of routine diagnosis.* In other words, parasites are likely to be just as scanty in an early subtertian infection as in any other, and diagnosis of cases in Europeans has frequently to be made on the presence of two or three parasites in a thick film. When parasites are present in such small numbers, species diagnosis in thick films does, as Dr. FIELD himself states, become almost impossible except to the very expert, and recourse must necessarily be made to the thin film. In the early stages of an infection with P. falciparum, the parasites are so minute that they may only be seen with difficulty in a thin film, and when this is the case I have on a number of occasions been unable to find them in a thick film. It is in fact just such cases which, in my opinion, provide an explanation of a number of those " negative " blood films which are found in the obvious presence of clinical malaria. I do not, however, wish to suggest in any way that the thick film technique is not the method of choice in the diagnosis of malaria, and the mainstay of malaria survey work. Yours faithfully, Nairobi. D. BAGSTER WILSON,
Major, E.A.A.M.C. ~' FIELD, J. W. (1941). T h e morphology of malarial parasites in thick blood films. Part IV. Identification of species and phase. Trans. R. Soc. trop. Ned. Hyg., 34, 405.
Printed by H. R. GRUBB.LTD., Poplar Walk, Croydon.