Some factors affecting the cultivationin vitroof the erythrocytic stages ofPlasmodium knowlesi

Abstract

A study was made of some of the factors which affect the growth of Plasmodium knowlesi in blood diluted in the Harvard medium. Some slight enhancement of growth and re-invasion of new host cells was obtained when P. knowlesi was incubated in low oxygen tensions. Some growth but no re-invasion was obtained under anaerobic conditions. High oxygen tensions were also inhibitory.The lipids present in the plasma are important for the growth of P. knowlesi in vitro. Stearic acid and cholesterol are required by the parasite but do not account for all the growth promoting properties of plasma. A requirement for vitamin B12 was also demonstrated.I should like to thank Dr F. Hawking and Dr J. Williamson for their advice and for reading through the manuscript, Mr T. J. Scott-Finnigan for technical assistance, Dr K. Mervyn (Glaxo Research Ltd.) for samples of vitamin B12 analogues and the Hachmeister Company (Pittsburgh) for a sample of TEM 4T. This work received financial assistance from the World Health Organization.