Usefulness of the pancreas as a prime target for histopathological diagnosis of Tilapia parvovirus (TiPV) infection in Nile tilapia, Oreochromis niloticus

Abstract

Tilapia parvovirus (TiPV) is an emerging virus reportedly associated with disease and mortality in farmed tilapia. Although previous descriptions of histopathological changes are available, the lesions reported in these are not pathognomonic. Here, we report Cowdry type A inclusion bodies (CAIB) in the pancreas as a diagnostic histopathological feature found in adult Nile tilapia naturally infected with TiPV. This type of inclusion body has been well-known as a histopathological landmark for the diagnosis of other parvoviral infections in shrimp and terrestrial species. Interestingly, this lesion could be exclusively observed in pancreatic acinar cells, both in the hepatopancreas and pancreatic tissue along the intestine. In situ hybridization (ISH) using a TiPV-specific probe revealed the intranuclear presence of TiPV DNA in multiple tissues, including the liver, pancreas, kidney, spleen, gills and the membrane of oocytes in the ovary. These findings suggest that although TiPV can replicate in several tissue types, CAIB manifest exclusively in pancreatic tissues. In addition to TiPV, most diseased fish were co-infected with Streptococcus agalactiae, and presented with multifocal granulomas secondary to this bacterial infection. Partial genome amplification of TiPV was successful and revealed high nucleotide identity (>99%) to previously reported isolates. In summary, this study highlights the usefulness of pancreatic tissue as a prime target for histopathological diagnosis of TiPV in diseased Nile tilapia. This pattern may be critical when determining the presence of TiPV infection in new geographic areas, where ancillary testing may not be available. TiPV pathogenesis in this landmark organ warrants further investigation.

Detection of Tilapia parvovirus in farm reared tilapia in India and its isolation using fish cell lines

“…The presence of TiPV in the egg of infected tilapia indicates the possibility of vertical transmission. Our observation corroborates the ndings of Dong et al [17] who reported the presence of TiPV in oocyte membranes and the capability of TiPV for vertical transmission. Histopathological examination revealed the lesions characterized by lymphocytic in ltration in all vital organs of infected sh as observed by Liu et al [6].…”

“…The viral infection has been con rmed by the appearance of the typical CPE of forming CAIB in the nucleus of infected cells and PCR. The CAIB observed in the infected cells of SHK and SPF was similar to the CAIB observed by Dong et al [17] in the pancreatic cells of TiPV infected tilapia. Dong et al [17] detected the CAIB in the pancreatic cells only but not in other infected tissues of tilapia and suggested the use of pancreas for histopathological diagnosis of TiPV infection.…”

“…It will also be useful to determine the suitable organ for diagnostic purpose. Different protocols such as In situ hybridization (ISH) and quantitative real time PCR have been employed by different workers to study the tissue distribution of TiPV in tilapia [6,16,17]. In the present study, PCR assay was performed to study the tropism of TiPV in different organs of naturally infected tilapia and the results revealed the occurrence of TiPV in gill, spleen, liver, heart, pancreas, intestine, kidney and egg as observed by previous workers [6,16].…”

“…Tilapia brain cells (TiB) were used to isolate the TiPV from infected sh and the same cells were used to propagate TiPV for experimental infection [6]. Various diagnostic tools such as histopathology, in situ hybridization, PCR and TaqMan probe-based qPCR are available to detect TiPV in infected sh samples [6,16,17]. The present study reports the detection of TiPV in Nile tilapia for the rst time in India based on the results of PCR using TiPV-speci c primers, sequence analysis, reproduction of infection, tissue distribution and TiPV isolation using sh cell lines.…”

Specific and rapid detection of tilapia parvovirus using loop‐mediated isothermal amplification (LAMP) method

“…Since TiPV is an emerging pathogen, until now, only molecular methods and virus isolation have been available for the detection of TiPV (Dong et al, 2022;Liu et al, 2020;Piewbang et al, 2022;Yamkasem et al, 2021), and techniques that offer rapid results with ready implementation for on-farm screening have not yet been developed. Although conventional and quantitative PCR assays have been developed and applied to identify TiPV in fish samples, these PCR methods require skilled technicians, expensive equipment, and sophisticated laboratories, which limits their application for disease screening at a farm level.…”