Plasmodium species identification by ELISA for sporozoites removed from dried dissection slides

This study tested the feasibility of identifying salavary gland sporozoites to species by Plasmodium falciparum ELISA by drying them on slides or in vials. The glands were dissected from Anopheles gambiae Giles s.l. and An. funestus Giles collected in western Kenya. In 119 gland infections containing a geometric mean of 1,222 sporozoites, a mean of 72.5% of sporozoites were removed in 60 microliters saline from slides at the time of dissection. Each of the 119 samples was divided into three 18 microliters aliquots. Subsamples were stored at -70 degrees C, dried in vials, or dried on a microslide. When tested by Plasmodium falciparum ELISA, positive reactions were observed in 86.6% of frozen samples, 70.6% of samples held dry in vials, and 50.4% of samples held dry on microslides for 1 mo. Of 90 gland infections where coverslips were removed and slides were left to dry for 1 mo before adding blocking buffer, 81.1% were positive for P. falciparum. This was not significantly different from either frozen gland samples (where 85.5% of 392 infections were identified or frozen gland plus corresponding thorax samples where 86.2% of 160 samples were identified). In malaria field studies, where it is not always practical to freeze samples, sporozoites from dissected mosquitoes can be preserved adequately for ELISA identification by simply removing coverslips and drying dissection slides.