Diversity of Surface Fibril Patterns in Mimivirus Isolates.

Among the most intriguing structural features in the known virosphere are mimivirus surface fibrils, proteinaceous filaments approximately 150 nm long, covering the mimivirus capsid surface. Fibrils are important to promote particle adhesion to host cells, triggering phagocytosis and cell infection. However, although mimiviruses are one of the most abundant viral entities in a plethora of biomes worldwide, there has been no comparative analysis on fibril organization and abundance among distinct mimivirus isolates. Here, we describe the isolation and characterization of Megavirus caiporensis, a novel lineage C mimivirus with surface fibrils organized as "clumps." This intriguing feature led us to expand our analyses to other mimivirus isolates. By employing a combined approach including electron microscopy, image processing, genomic sequencing, and viral prospection, we obtained evidence of at least three main patterns of surface fibrils that can be found in mimiviruses: (i) isolates containing particles with abundant fibrils, distributed homogeneously on the capsid surface; (ii) isolates with particles almost fibrilless; and (iii) isolates with particles containing fibrils in abundance, but organized as clumps, as observed in Megavirus caiporensis. A total of 15 mimivirus isolates were analyzed by microscopy, and their DNA polymerase subunit B genes were sequenced for phylogenetic analysis. We observed a unique match between evolutionarily-related viruses and their fibril profiles. Biological assays suggested that patterns of fibrils can influence viral entry in host cells. Our data contribute to the knowledge of mimivirus fibril organization and abundance, as well as raising questions on the evolution of those intriguing structures. IMPORTANCE Mimivirus fibrils are intriguing structures that have drawn attention since their discovery. Although still under investigation, the function of fibrils may be related to host cell adhesion. In this work, we isolated and characterized a new mimivirus, called Megavirus caiporensis, and we showed that mimivirus isolates can exhibit at least three different patterns related to fibril organization and abundance. In our study, evolutionarily-related viruses presented similar fibril profiles, and such fibrils may affect how those viruses trigger phagocytosis in amoebas. These data shed light on aspects of mimivirus particle morphology, virus-host interactions, and their evolution.

Evaluation of parasitological and immunological aspects of acute infection by Ancylostoma caninum and Ancylostoma braziliense in mixed-breed dogs.

This study compared the course of infection by Ancylostoma caninum and Ancylostoma braziliense in mixed-breed dogs infected with L3 larvae. Dogs infected with A. caninum eliminated more eggs than did those infected with A. braziliense. A total of 38 % of A. caninum and 44 % of A. braziliense larvae were recovered as adult worms. There were no marked clinical abnormalities in dogs with either infection. A. caninum was associated with anemia and an increased number of circulating neutrophils, whereas infection with A. braziliense led to a decrease in the number of leukocytes. The humoral response against excreted and secreted antigens from adult worms was more sensitive and specific than the response induced with the crude antigen. No immune response was observed for either crude or excreted-secreted (ES) antigens from larvae of either species. A nonspecific response against the crude antigen of A. braziliense was found at 0 and 7 days postinfection and maintained throughout the infection period. However, antibody titers against ES antigens were elevated in A. caninum infection at patency and death, showing that this antigen has a higher specificity. The immune response elicited by infection with A. braziliense in dogs has not been described previously. No significant differences were observed in the infection processes of the two Ancylostoma species, except for the higher number of eggs eliminated from dogs infected with A. caninum, which may indicate a better evolutionary adaptation of the parasite to its host in comparison with A. braziliense.