Cytopathological process by multiple nucleopolyhedrovirus in the testis of Bombyx mori L., 1758 (Lepidoptera: Bombycidae)

A cytopathological methodology was used to analyze infection by Bombyx mori multiple nucleopolyhedrovirus (BmMNPV), a geographic isolate of the family Baculoviridae, in the caterpillar testes of the B. mori. Japanese B. mori strain caterpillar, fifth instar, were inoculated with BmMNPV and their testes were collected and processed for light and transmission electronic microscopy. Epithelial coating cells and interfollicular septa in testes were susceptible to BmMNPV. The first evidence of infection was detected on the 6th day post-inoculation (p.i.) in the external epithelium, and on the 7th day p.i. in the internal epithelium and interfollicular septa. Cytopathological characteristics consisted of hypertrophied nuclei, the formation of virogenic stroma, and the occlusion of virions in polyhedron protein crystals in several stages of development. At the end of the infectious process, cell lysis and release of polyhedra into the extracellular medium occurred. Histopathology revealed early infection foci in the surrounding regions of tracheal insertions, thus underlining the role of the trachea as an infection-spreading organ in insects. This spreading occurs through penetration of the basal lamina, which facilitates entry of the budded virus into the testis. Additionally, an alignment of a partial sequence of the ORF 14 of the BmMNPV geographic isolate with other NPV certified the virus genera.