The need to use ex-vivo rather than culture methods to source Plasmodium vivax (P.vivax) parasites for biologic investigation hampers many aspects of research on this parasite, including evaluation of candidate hypnozoiticidal drugs. Currently parasites can only be sourced using expensive, logistically complex and unreliable processes requiring transportation of P.vivax-infected mosquitoes from endemic areas, where parasites are not genetically homogenous. Apheresis is the removal of a specific component of blood with the remainder being returned to the individual. We aim to assess a) the safety of apheresis following inoculation of healthy subjects with P.vivax, and b) the feasibility of apheresis to extract and concentrate all stages of P.vivax parasites.
We inoculated one non-immune healthy human subject with blood stage P.vivax parasites, and subjected him to apheresis 10 days later when he developed symptomatic infection. Blood samples from haematocrit (HCT) levels; 1%, 2%, 3%, 5% and 7% were tested by qPCR for the presence and concentration of asexual and sexual stages of P.vivax. Safety was ascertained by clinical evaluation and safety testing.
There were no serious adverse events. The subject experienced typical symptoms of mild uncomplicated P.vivax malaria, including short lived fevers peaking 40.2oC, which were controlled by antipyretics. Apheresis related adverse events included transient worsening of pre-apheresis lymphopenia and subsequent Herpes Simplex Virus-1 cold sore. Typical adverse events, such as citrate reactions, syncope and venous access issues, did not occur. Asexual and sexual parasites were successfully harvested using apheresis, with highest concentrations in the 7% HCT and 5% HCT layers respectively.
Apheresis was safe with only short lived non-serious adverse events, all of which resolved spontaneously or with simple analgesia. Apheresis can achieve extraction and concentration of asexual and sexual P.vivax parasites. Current studies are underway to optimise laboratory processing to achieve greater levels of parasite concentration.