The statement "There is currently no specific diagnostic test for Plasmodium knowlesi" (see Fatal malaria strain 'mistaken for more benign form') is not strictly correct.

There is a P. knowlesi-specific nested PCR assay, which was developed at the Malaria Research Centre, University Malaysia Sarawak. This assay was used in our initial study that lead to the discovery of the large concentration of human P. knowlesi malaria patients in Kapit [1] and also in our latest study. [2] It is the only diagnostic test that can correctly identify P. knowlesi and accurately distinguish it from P. malariae.

Nested PCR assays are clearly not a viable and economical option for hospitals or rural areas where P. knowlesi malaria is prevalent, so it would be more accurate to state that, "while there are PCR assays for diagnosis of P. knowlesi malaria, there is no specific routine diagnostic test that is suitable for use in remote areas".

References

[1] Singh B., Sung L. K., Matusop A., et al. A large focus of naturally acquired Plasmodium knowlesi infections in human beings. The Lancet 363, 1017–1024 (2004)

[2] Cox-Singh J., Davis T. M. E., Lee K. S., et al.  Plasmodium knowlesi Malaria in Humans Is Widely Distributed and Potentially Life Threatening. Clinical Infectious Diseases 46, 165–171 (2008)