Scanning electron microscopy (SEM) was employed to observe the effects of ivermectin (IVM),
diethylcarbamazine (DEC), and albendazole (ALB) alone, and the drugs in combination (ALB+IVM and ALB+DEC)
against infective third stage larvae (L3) of nocturnally subperiodic (NSP) Brugia malayi (Narathiwat strain) in
vitro. IVM, at a concentration of 10-4 M, killed L3 within 1-2 h. The SEM data showed damage to the L3 surface
and loss of regular cuticular annulations. The cuticles were grooved in the middle region of the body. In comparison
with normal L3 before treatment with IVM, the cuticular surface showed transversed striations with periodic
annulations. The result demonstrated that IVM showed a larvicidal activity against L3 of NSP B. malayi cultivated
in vitro. Compared with those larvae in the control group, the treated larvae had no morphological changes in the
cuticular surface at the head, body, and tail regions after cultivation with all drugs alone, and in their combinations
at a concentration of 10-5 M for 7 d. In this system, and at that concentration, only the larvae cultured with ALB
alone remained highly motile. Although no morphological changes had been observed by SEM, those drugs used
alone (IVM and DEC) and in combinations (ALB+IVM and ALB+DEC), reduced larval motility throughout the
experiments at a concentration of 10-5 M. The minimum lethal concentration (MIC) of IVM against NSP B. malayi
was 10-4 M. Journal of Vector Ecology 29 (1): 101-108. 2004.