Genomic sequence of infectious bursal disease virus from Zambia suggests evidence for genome re-assortment in nature

Infectious bursal disease virus (IBDV) is a bi-segmented RNA virus, which belongs to the genus Avibirnavirus of the family Birnaviridae. Two serotypes, 1 and 2, exist in IBDV. The serotype 1 IBDVs are the causative agents of infectious bursal disease (IBD) in chickens worldwide and lead to immunosuppression in young birds. Genome re-assortment has been speculated to occur and contribute to the emergence of new IBDV strains. However, evidence was lacking until recently when two re-assortant viruses were detected in China. In this study, we determined the complete nucleotide sequence of an IBDV, designated KZC-104, from a confirmed natural IBD outbreak in Lusaka, Zambia in 2004. The genome consisted of 3074 and 2651 nucleotides in the coding regions of segments A and B, respectively. Alignment of both nucleotide and deduced amino acid sequences, and phylogenetic analysis revealed that the genome segment A of KZC-104 was derived from a very virulent strain, whereas its segment B was derived from a classical attenuated strain. On BLAST search, the full-length segments A and B sequences showed 98% closest nucleotide homology to the very virulent strain D6948 and 99.8% closest nucleotide homology to the classical attenuated strain D78, respectively. This is a unique IBDV reassortant strain, which has emerged in nature involving segment B of a live attenuated vaccine. This observation provides direct evidence for the involvement of vaccine strains in the emergence of reassortant IBDV in the field. Taken together, these findings suggest an additional risk of using live IBDV vaccines, which may act as genetic donors for genome re-assortment. Further studies are required to investigate the epidemiology and biological characteristics of reassortant strains so that the appropriate and safe IBDV vaccines can be recommended

Molecular detection of tilapia lake virus (TiLV) genome in Nile tilapia (Oreochromis niloticus) from Lake Victoria

Tilapia lake virus (TiLV) is an emerging pathogen of Tilapiines associated with high mortalities of wild and farmed tilapia posing great threat to the fishery industry worldwide. The virus has been reported in Israel, Ecuador, Colombia, Thailand, Egypt, Taiwan, India and Malaysia. In this study, a reverse transcription polymerase chain reaction (RT-PCR) assay was developed and used to detect TiLV genome in Nile tilapia from Lake Victoria. Nile tilapia samples were collected from the Tanzanian (108 fish) and Ugandan (83 fish) parts of Lake Victoria in 2015 and 2016, respectively. Samples were screened for TiLV by using RT-PCR and the PCR products were sequenced. The findings show that out of the 191 fish examined, 28 had PCR products showing the presence of TiLV genome. The TiLV nucleic acids were detected in the spleen (10.99%, N=191), head kidney (7.69%, N=65), heart (3.45%, N=29) and liver (0.71%, N=140) samples while no PCR amplification was detected in the brain by the developed RT-PCR method. Generally, the findings show that the lymphoid organs, mainly comprising of the head kidney and spleen had the highest number of samples with positive nucleic acids for TiLV followed by heart samples. On the contrary, the liver and brain that have previously been shown to be target organs during acute infection either did not have or had the lowest level of TiLV nucleic acids detected in the present study. All the 28 sequences retrieved had an average length of 768 bp. A blast analysis on NCBI showed that all sequences obtained were homologous to TiLV segment-2 sequences obtained from previous outbreaks in Israel and Thailand. To our knowledge, this is the first detection of TiLV subclinical infections in Nile tilapia in Lake Victoria, a none-outbreak area.Keywords: Lake Victoria, Nile tilapia, PCR, phylogenetic, surveillance, tilapia lake viru