with Brazilian samples by Post et al. (2003) what may be related to factors such as source of the material, larval developmental stage, and procedures like drying, fixation, and staining of the smear. The unusual microfilaria presented here has some characteristics of those of O. volvulus in the cephalic space and similarities in caudal space with M. ozzardi and its measures were closer to this last one. Comparison of this microfilaria with those of O. volvulus showed that there are some resemblance at the cephalic space, which is followed by two paired nuclei following this region but that similarity was absent at the posterior extremity, where a nuclear column with 7-8 nuclei are present in a regular and aligned arrangement and a detachment from cuticle are very perceptible (Fig. 3). Fig. 3 Whole O. volvulus microfilaria, Scale = 10 m (photomicrography from A. J. Shelley) Some questions raised from these results: do these microfilarias belong to an unknown human filarial species or even to a species parasite of an animal? Are they morphological variations of M. ozzardi? Further morphological, ultrastructural, and molecular studies are being carried out in our laboratory in order to provide additional evidences capable to answer these questions. Acknowledgements We wish to thank Dr. Sixto Coscaron for his suggestions on the manuscript, Prof. Eduardo Jose Lopes Torres for helping me with the photographic material and Ana Carolina Valente for technical assistance. Brazilian financial support: Instituto Oswaldo Cruz, Coordenacao de Pos Graduacao em Biologia Parasitaria, FarManguinhos, Conselho Nacional de Desenvolvimento Cientifico e Tecnologico, Coordenacao de Aperfeicoamento de Pessoal de Ensino Superior, Programa CAPES - PROCAD, Fundacao Carlos Chagas Filho de Amparo a Pesquisa do Estado do Rio de Janeiro, Secretaria Estadual de Saude do Acre, and Fundacao de Tecnologia do Acre. References Batista D, Cerqueira NL, Moraes MAP (1960) Epidemiologia da Mansonelose em Localidade do Interior do Amazonas*. Rev Assoc Med Bras 6(2):176-184 Bradley JE, Unnasch TR (1996) Molecular approaches to the diagnosis of onchocerciasis. Adv Parasitol 37:57-106 Deane MP (1949) Sobre a incidencia de filarias humanas em Manaus, Estado do Amazonas. Revista do SESP 2(3):849-858 Deane LM, Rachou RG, Lacerda NB, Martins J (1953) Alguns Dados Relativos a Prevalencia da Mansonella ozzardi no Brasil. Rev Bras Malariol Doencas Trop 6:219-224 Jorg ME (1983) Filariasis por Mansonella ozzardi (Manson, 1897) Faust 1929 en la Argentina. Prensa Med Argent 70(5):181-191 Knott J (1939) A method for making microfilarial surveys on day blood. Trans R Soc Trop Med Hyg 33:191-196 Kozek WJ, Raccurt C (1983) Ultrastructure of Mansonella ozzardi microfilaria, with a comparison of the South American (Simuliid-transmitted) and the Caribbean (Culicoid-transmitted) forms. Tropenmed Parasitol 34:38-53 Kozek WJ, Eberhard ML, Raccurt C (1983) Comparative morphology of Mansonella ozzardi microfilariae from Colombia and Haiti. A light microscope study. Tropenmed Parasitol 34:33-37 Moraes MAP, Shelley AJ, Luna Dias APA, Mangabeira Silva CJ (1983) The concentration of Mansonella ozzardi microfilariae in skin capillaries. Trans R Soc Trop Med Hyg 77(4):463-466 Moraes MAP, Shelley AJ, Luna Dias APA (1985) Mansonella ozzardi no Territorio Federal de Roraima, Brasil. Distribuicao e achado de um novo vetor na area