New Insights into Morphological and Biological Features of Capillaria aerophila (Trichocephalida, Trichuridae) D. Traversa1, A. Di Cesare1, R. P. Lia2, G. Castagna1, S. Meloni1, J. Heine3, K. Strube3, P. Milillo1, D. Otranto2, R. Schaper3 1 Department of Comparative Biomedical Sciences, University of Teramo, Italy; 2 Department of Veterinary Public Health, University of Bari, Italy; 3 Bayer Animal Health, Leverkusen, Germany Background: Capillaria aerophila is a trichuroid nematode affecting carnivores (e.g., cats and dogs) and humans. Animals become infected by ingesting larvated eggs or earthworms, which act as facultative intermediate hosts. Adult stages live underneath respiratory epithelia and cause different degrees of respiratory distress and symptoms. Indeed, this nematode is underestimated and several aspects remain to be elucidated and better clarified, including routes of transmission and diagnostic aspects. The aim of this study is to present new insights into morphological and biological features of this neglected lungworm. Methods: Eggs of C. aerophila were collected from four naturally infected dogs and one cat with monospecific infection. Eggs were used to examination and measurements by light microscopy (LM; Leica DM LB2 microscope) and to scanning electron microscopy (SEM; FEI Quanta 200 SEM), respectively, and compared with eggs of the intestinal trichuroid Trichuris vulpis. Eggs were also split in different coprocultures for their in vitro developing over a period of two months at a temperature of 20 ± 2 °C and relative humidity from 80 % to 85 %. Results: LM showed typical features of C. aerophila eggs: size, asymmetry of bipolar plugs and a wall with a network of anastomosing ridges. These features were all confirmed upon SEM, in that all examined eggs showed an outer densely striated and net-like shell. Eggs of T. vulpis were bigger than those of C. aerophila and showed a thick and smooth wall at both LM and SEM. Eggs of C. aerophila started to develop after 35 days, and at day +60 all eggs contained a mobile larva. Conclusions: This study reports a thorough LM and SEM morphological and morphometric analysis of eggs of the neglected lungworm C. aerophila and provides key information for their identification, which in turn represent a diagnostic dilemma, especially in comparison with whipworm eggs. Furthermore, this is the first information on the in vitro developing of C. aerophila eggs, providing important information on the biological cycle of this nematode, to be still fully elucidated. .