Hello, Plasmodium is haploid, so only one allele to KO. I guess if several strategies are employed and you can't ever get a KO it might suggest that the gene is essential. The problem is that it is never the most convincing way of saying "it is essential", you are never 100% sure if the parasite can't live without the gene or the transfection rate is too low, or something went wrong with it. And the problem in Plasmodium is that you transfect the parasites in the blood stage, and an essential gene in that stage might not be so in the other stages. I would look at papers that have been successful or attempted KO genes for more info. Also, I think that there are some groups working on conditional KO systems, I would take a look at them as well. Good luck.

Hey, I never came across with msp2 deleted Plasmodium study. Most probably, as Catarina said gene must be extremely essential. Therefore, effort will be always unsuccessful. Good luck with your studies!