 A substantial amount of the HRP II is secreted by the parasite into the host bloodstream and the antigen can be detected in erythrocytes, serum, plasma, cerebrospinal fluid and even urine as a secreted water-soluble protein.These antigens persist in the circulating blood after the parasitaemia has cleared or has been greatly reduced.It generally takes around two weeks after successful treatment for HRP2-based tests to turn negative, but may take as long as one month, which compromises their value in the detection of active infection.