However, whether this increased ability to detect low level parasitaemia makes it a better diagnostic test is uncertain, as sub-microscopic parasitaemia are of unknown clinical significance and the prevalence of asymptomatic sub-microscopic infection is high in some areas (May 1999).
These 'sub-microscopic infections' completely change the game for elimination.
The presence of gametocytes within these sub-microscopic infections has been demonstrated using sensitive gametocyte-specific RT-PCR [4] [6].
This might simply reflect the fact that most of the DNA templates were extracted from archival blood dried on filter paper, and might have corresponded to a small volume of blood (<1 µl), which would reduce the sensitivity for the detection of sub-microscopic infections.
Sub-microscopic infections have been primarily studied in areas of low and seasonal malaria transmission [ 3- 6].
Sub-microscopic infections may therefore play a role in maintaining malaria transmission in areas of low malaria endemicity.
40, 41 Recent studies have highlighted the extent of sub-microscopic infections, indicating that microscopy misses more than half of the infections detected by PCR.
42, 43 This finding could lead to an under-estimation of RDT performance because of sub-microscopic infections commonly harbored by school age children.
Despite indications from an experimental study showing that exposure to ultra low-dose infections may elicit protective immunity [ 12], there have been no field studies confirming the capacity of sub-microscopic infections to elicit or maintain immune responses.
The presence of sub-microscopic infections when microscopy is used as the comparator may result in false-positive results as a result of infections below the threshold of detection by microscopy.
Here, it has been shown that sub-microscopic infections can persist for several months [ 3, 5], produce gametocytes [ 5] and, despite low gametocyte concentrations in the infected individual, contribute to the transmission of malaria to mosquitoes [ 7- 9].
