Identification of microfilariae encountered in West Africa.

THE standard morphological descriptions of microfilarire tend to gloss over several very real difficulties in identification. Satisfactory staining of the dead organism sometimes seems impossible, measurement of distances along the organism (see, e.g., Belding, 1952) is often impractic'able because of its irregular disposition, and the tip of the tail, recognised as the site of certain distinctive features, is frequently hidden under another part of the organism.' In addition, sheaths are not always stained sufficiently to be recognisable, and the characteristic rhythmicity of certain species is not absolute, so that microfilarire may be found "out of hours," particularly in heavy infections. Supra-vital staining with methylene blue, which brings out certain other characteristics, has not been found adequate for final identification in many cases. These notes are based on work done in evolving satisfactory methods of species identification, and it is hoped that they may be useful especially to those unaccustomed to these organisms. The microfilarire concerned are those of Wuchereria bancrofti, Loa loa and Acanthocheilonema perstans in the blood, and Onchocerca volvulus and A. streptocerca in the skin.