title: Detailed investigation of the sequential pathological changes in silkworm larvae infected with Bombyx densovirus type 1.
abstract: Bombyx mori densovirus type 1 (BmDNV-1) is a pathogen causing flacherie disease in silkworms. BmDNV-1 multiplies only in the nuclei of the columnar cells of larval midgut epithelium. Although several immunohistochemical studies using anti-BmDNV-1 antibody have been reported to date, sequential pathological changes in BmDNV-1-infected larvae have not been completely elucidated. In this paper, sequential investigations were performed on the pathological features of BmDNV-1-infected larvae and BmDNV-1 propagation. Oral infection experiments using newly ecdysed 4th instar larvae revealed that the larvae began to die 9 days post infection (dpi), and the remaining died 10 dpi. Histological observations revealed phenotypic alterations in the midgut cells from 4 dpi, and complete disruption of the midgut structure at 9 dpi. Quantitative RT-PCR of two BmDNV-1 genes indicated that BmDNV-1 began to propagate from 4 dpi, and gradually increased until the larvae died. These expression patterns revealed marked correlation with the histological changes observed in the virus-infected midgut cells. Moreover, bioassays using larvae at various developmental stages clearly indicated that the pathogenicity of this virus is not dependent on the larval stage or the molting process.
authors.affiliation: Insect Genome Research Unit, National Institute of Agrobiological Sciences, 1-2 Owashi, Tsukuba, Ibaraki 305-8634, Japan. katsuito@affrc.go.jp
authors.forename: Katsuhiko
authors.initials: K
authors.lastname: Ito
authors.forename: Kurako
authors.initials: K
authors.lastname: Kidokoro
authors.forename: Sachiko
authors.initials: S
authors.lastname: Shimura
authors.forename: Susumu
authors.initials: S
authors.lastname: Katsuma
authors.forename: Keiko
authors.initials: K
authors.lastname: Kadono-Okuda
mesh_terms: D000818:Animals; D012831:Bombyx / Q000033:anatomy & histology / Q000254:growth & development / Q000821:virology*; D017990:Densovirus / Q000472:pathogenicity*; D054884:Host-Pathogen Interactions; D007814:Larva / Q000033:anatomy & histology / Q000254:growth & development / Q000821:virology; D013997:Time Factors