Answer: Brugia species.
This is actually a case of B. malayi. However, the sheath is not stained as deep pink as would be expected with a routine Giemsa stain, so B. timori is also in the differential diagnosis. The size (which I didn't provide) would give you some help in differentiating these 2 species, since B. malayi is 177-230 microns in length, while B. timori is 265-323 microns in length in blood smears.
The important differential diagnosis is Wuchereria bancrofti, which can be excluded by the presence of the long head space and tail nuclei (terminal and subterminal nuclei).