Objective: Microfilaria of Wuchereria bancrofti has been described in many cytological specimens, where typical blood film morphology has been used for evaluation. However, these studies have not documented the morphological variations in microfilaria in cytological smears. In the present study, cytological findings in 32 clinically unsuspected cases of filariasis were reviewed with emphasis on morphological details and image morphometric measurements. Study Design: A retrospective analysis of 32 cases of clinically unsuspected filariasis diagnosed by cytology from April 2001 to March 2011 was carried out. Results: All microfilariae were characterized as W. bancrofti and showed a wide variation in their length (202 to 300 µm) and width (6.2 to 8.4 µm). Terminal and subterminal swellings were seen in one of the cases causing diagnostic confusion with Brugia malayi. Microfilariae were shorter and wider in May-Grünwald-Giemsa stain than in Papanicolaou-stained smears. Conclusions: Natural variations in the size of microfilariae of W. bancrofti are the probable reason for the range of these findings. The overlapping features with microfilaria of B. malayi might be related to subspecies variations in W. bancrofti. Fixation, degeneration and staining procedure also seem to influence the morphological features. This morphometric study highlights the morphological disparities of microfilaria and the differential diagnostic considerations.

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