Efficiency of mitochondrial genes and nuclear Alu elements in detecting human DNA in blood meals of Anopheles stephensi mosquitoes: a time-course study.

BACKGROUND

The time required for PCR detection of DNA in human blood meals in vector mosquitoes may vary, depending on the molecular markers used, based on the size and copy number of the amplicons. Detailed knowledge of the blood-feeding behavior of mosquito populations in nature is an essential component for evaluating their vectorial capacity and for assessing the roles of individual vertebrates as potential hosts involved in the transmission of vector-borne diseases.

METHODS

Laboratory experiments were conducted to compare the time course of PCR detection of DNA in human blood meals from individual blood-fed Anopheles stephensi mosquitoes, using loci with different characteristics, including two mitochondrial DNA (mtDNA) genes, cytB (228 bp) and 16S ribosomal RNA (rRNA) (157 bp) and nuclear Alu-repeat elements (226 bp) at different time points after the blood meal.

RESULTS

Human DNA was detectable up to 84-120 h post-blood-feeding, depending on the length and copy number of the loci. Our results suggest that 16S rRNA and Alu-repeat markers can be successfully recovered from human DNA up to 5 days post-blood-meal. The 16S rDNA and Alu-repeat loci have a significantly (P = 0.008) slower decline rate than the cytB locus. Median detection periods (T50) for the amplicons were 117, 113 and 86.4 h for Alu-repeat, 16S rDNA and cytB, respectively, suggesting an inverse linear relationship between amplicon size/copy number and digestion time.

CONCLUSION

This comparative study shows that the Alu-repeat locus is the most efficient marker for time-course identification of human DNA from blood meals in female mosquitoes. It is also a promising tool for determining the anthropophilic index (AI) or human blood index (HBI), i.e. the proportion of blood meals from humans, which is often reported as a relative measure of anthropophagy of different mosquito vectors, and hence a measure of the vector competence of mosquito species collected in the field.