ABSTRACT
The family Paramyxoviridae is a group of viruses that significantly affect human and animal health. Paramyxoviruses are generally thought to enter host cells by direct fusion of the viral and host cell membranes. Membrane fusion, essential for syncytium formation, is not only a pathological hallmark of paramyxoviral infections, but also a kind of mechanism of cell-to-cell viral spread. Nevertheless, the process of membrane fusion is highly conserved, only consisting of two-component fusion apparatus: an attachment protein (HN/G/H) and a fusion (F) protein. However, there is a significant knowledge gap on the mechanism(s) by which HN/H/G couples receptor binding to F-triggering, since different attachment proteins possess special triggering process. In this review, we summarize the general property and distinction of the fusion process during paramyxoviral infection for further research on the pathogenic mechanism.
ABSTRACT
Diseases caused by avian paramyxovirus (APMV) occur in commercial, captive and wild birds worldwide, demonstrating the significant economic and ecological importance of these agents. Paramyxoviruses belong to the paramyxoviridae family, paramyxovirinae subfamily and avulavirus genus. During the period 2000 to 2011, stool and small intestine samples of 1647 birds species were sent to the Laboratory of Electron Microscopy, Biological Institute of São Paulo, Brazil, for diagnosis of viral agents. The samples were processed by negative staining (rapid preparation) and resin embedding techniques. Under the transmission electron microscope by negative staining technique, in 294 (17.8 percent) samples of 1647 were visualized paramyxovirus particles pleomorphic, roughly spherical or filamentous, measuring 100 to 500 nm of diameter containing an envelope covered with spikes and characteristic helical herring-bone-like nucleocapsid measuring 15 to 20 nm in diameter. Ultrathin sections of the small intestine fragments revealed the presence of amorphous granular intracytoplasmic inclusions surrounded by membrane and containing viral nucleocapsid measuring 10-14 nm in diameter. Immature particles budding from cell membranes, pleomorphic, spherical and tubular particles containing viral nucleocapsid strands, and the complete particles measured up to 170 nm in diameter were seen in the cytoplasm. Intranuclear inclusions containing viral nucleocapsid were also visualized. Nuclei showed a marginalized chromatin.
Las enfermedades causadas por paramixovirus (APMV) ocurren mundialmente, tanto en aves de corral, en aquellas en vida libre o en cautiverio, lo que demuestra la importancia económica y ecológica de estos virus. El paramixovirus aviario pertenece a la familia paramyxoviridae, subfamilia paramyxovirinae y género avulavirus. Durante el periodo de 2000 a 2011, muestras de heces y fragmentos del intestino delgado de 1647 especies de aves han sido enviados al Laboratorio de Microscopía Electrónica, Instituto Biológico de São Paulo, para el diagnóstico de agentes virales. Las heces y fragmentos del intestino delgado, se procesaron por las técnicas de contraste negativo (preparación rápida) y la inclusión en resina. Al microscopio electrónico de transmisión mediante la técnica de contraste negativo se visualizaron en muestras de 294 aves, partículas de paramixovirus, pleomórficas, más o menos esféricas o filamentosas, de 100 a 500 nm de diámetro que contenían un sobre cubierto por púas que presentaban característica helicoidal, con nucleocapside tipo espiga, midiendo de 15 a 20 nm de diámetro. Secciones ultrafinas de los fragmentos del intestino delgado, revelaron en el citoplasma la presencia de inclusiones granulares amorfas rodeadas por una membrana, contiendo nucleocapside viral midiendo de 10-14 nm de diámetro, partículas inmaduras brotando de las membranas celulares, partículas virales tubulares, esféricas o pleomórficas que contenían filamentos nucleocapside. Estas partículas completas alcanzaban a los 170 nm de diámetro. Fueron observadas también, inclusiones intranucleares contiendo nucleocapside viral. Los núcleos mostraron una cromatina marginal.