Genotype Diversity and Spread of White Spot Syndrome Virus (WSSV) in Madagascar (2012–2016)

Abstract

White Spot Disease (WSD) caused by the White Spot Syndrome Virus (WSSV) is the most devastating viral disease threatening the shrimp culture industry worldwide, including Madagascar. WDS was first reported on the island in 2012; however, little is known about the circulation of the virus and its genetic diversity. Our study aimed at describing the molecular diversity and the spread of WSSV in the populations of Madagascan crustaceans. Farmed and wild shrimps were collected from various locations in Madagascar from 2012 to 2016 and were tested for WSSV. Amplicons from positive specimens targeting five molecular markers (ORF75, ORF94, ORF125, VR14/15 and VR23/24) were sequenced for genotyping characterizations. Four genotypes were found in Madagascar. The type-I genotype was observed in the south-west of Madagascar in April 2012, causing a disastrous epidemic, then spread to the North-West coast. Type-II strains were detected in October 2012 causing an outbreak in another Penaeus monodon farm. In 2014 and 2015, types II and III were observed in shrimp farms. Finally, in 2016, types II and IV were found in wild species including Fenneropenaeus indicus, Metapenaeus monoceros, Marsupenaeus japonicus and Macrobrachium rosenbergii. Considering the economic importance of the shrimp industry for Madagascar, our study highlights the need to maintain WSSV surveillance to quickly take appropriate countermeasures in case of outbreak and to sustain this industry.

Identification of Various InDel-II Variants of the White Spot Syndrome Virus Isolated from Frozen Shrimp and Bivalves Obtained in the Korean Commercial Market

“…The quantification of viral copy values within shrimp tissues revealed differences between the two variants at both 12 and 24 hpi, which were found to be statistically significant (p-value = 0.0385 at 12 hpi and p-value = 0.0359 at 24 hpi). These findings are consistent with those of a study by Krell [38], which suggested that a virus with a smaller genome size provides an advantage for replication. Additionally, in the InDel-II regions of the ancestral strains, two ORFs (WSSV006 and WSSV025) are adjacent to WSSV004, an essential early viral gene [39].…”

“…However, the samples of first-and second-step PCR positives were not amplified in the InDel-II region. This phenomenon may attributed to the very low copy number of WSSV, which corresponds to patterns identified in previous studies [38].…”

Nanopore MinION Sequencing Generates a White Spot Syndrome Virus Genome from a Pooled Cloacal Swab Sample of Domestic Chickens in South Africa

“…The white spot disease (WSD) caused by WSSV causes serious economic losses to the shrimp-farming industry globally [2,52]; WSD outbreaks occur in crustaceans worldwide, including countries in Asia [1,[12][13][14], Africa, the Middle-East [53,54], Europe [16], Australia [17], North America [55,56], Central America [20], and South America [18,19]. The available literature suggests that while crustacean hosts may serve as the primary reservoir of WSSV, several non-crustacean species, such as piscivorous birds [27], molluscs [57], and aquatic insects [30][31][32] may serve as the carrier of WSSV and therefore may facilitate further ecological dissemination.…”

“…Species of shrimp (Penaeus japonicus and Penaeus indicus) and oysters (Crassostrea gigas) were reported to be farmed in KwaZulu-Natal [62]. In addition, in Southern Africa, Mozambique [54] and Madagascar [53,54] are two prominent shrimp-producing countries, with geographical proximity to South Africa. Of particular note was a commercial shrimp farm situated in Coega, approximately 110 km from the study site.…”

“…Previous studies reported genotypic diversity of WSSV in Madagascar and Mozambique [53,54]; however, these studies only reported partial WSSV gene sequences and therefore were not included in the present study, since we utilized full-length WSSV genome sequences in this study. It is noteworthy that intercontinental migration of wild and aquatic birds has been linked to virus dispersal and spillover to domestic avian species, including domestic chickens [63][64][65][66][67][68].…”