Abstract:
Background: For future eradication strategies of malaria it is important to control the transmission of gametocytes
from humans to the anopheline vector which causes the spread of the disease. Sensitive, non-invasive methods to
detect gametocytes under field conditions can play a role in monitoring transmission potential.
Methods: Microscopically Plasmodium falciparum-positive patients from Jimma, Ethiopia donated finger-prick blood,
venous blood, saliva, oral mucosa and urine samples that were spotted on filter paper or swabs. All samples were
taken and stored under equal, standardized conditions. RNA was extracted from the filter paper and detected by
real-time QT-NASBA. Pfs16-mRNA and Pfs25-mRNA were measured with a time to positivity to detect gametocyte
specific mRNA in different gametocyte stages. They were compared to 18S-rRNA, which is expressed in all parasite
stages. Results were quantified via a known dilution series of artificial RNA copies.
Results: Ninety-six samples of 16 uncomplicated malaria patients were investigated. 10 (66.7%) of the slides
showed gametocyte densities between 0.3-2.9 gametocytes/μl. For all RNA-targets, molecular detection in blood
samples was most sensitive; finger-prick sampling required significantly smaller amounts of blood than venous
blood collection. Detection of asexual 18S-rRNA in saliva and urine showed sensitivities of 80 and 67%, respectively.
Non-invasive methods to count gametocytes proved insensitive. Pfs16-mRNA was detectable in 20% of urine
samples, sensitivities for other materials were lower. Pfs25-mRNA was not detectable in any sample.
Conclusions: The sensitivity of non-invasively collected material such as urine, saliva or mucosa seems unsuitable
for the detection of gametocyte-specific mRNA. Sensitivity in asymptomatic carriers might be generally even lower.
Finger-prick testing revealed the highest absolute count of RNA copies per μL, especially for Pfs25-mRNA copies.
The method proved to be the most effective and should preferably be applied in future transmission control and
eradication plans. A rapid test for gametocyte targets would simplify efforts.
