Biology subjects

FLEGEL, T. W.

Publications and source records attributed to FLEGEL, T. W..

3 recordsLinked to original sources

bioRxiv2026

Shrimp endogenous viral elements (EVE) correlate with survival in white spot syndrome virus (WSSV) challenges

Shrimp and other arthropods are capable of specific, adaptive immune responses to viruses based on viral copy DNA (vcDNA) fragments in the host genome called endogenous viral elements (EVE). These may produce negative sense RNA transcripts leading to an RNA interference (RNAi) defense response against cognate viruses. We first reported high-frequency-read sequences (HFRS) of white spot syndrome virus EVE (named WSSV-EVE 4,6,8) in a WSSV-free breeding stock of whiteleg shrimp (Penaeus vannamei). Here we describe screening for the same HFRS-EVE in a captured giant tiger shrimp (Penaeus monodon) breeding stock, also free of WSSV. WSSV-EVE 4,6,8 was detected in some of the P. monodon stock individuals with positive or negative RNA expression. Eight broodstock individuals were selected for mating in 4 crosses. The offspring from these crosses were grown sufficiently to allow tagging and pleopod sampling for DNA and RNA analysis prior to challenge with WSSV. This allowed for Mendelian analysis of EVE inheritance and for its expression or not in the offspring, together with analysis of their relationships to survival and WSSV infection level after challenge. The results revealed that EVE inheritance was Mendelian, but that their RNA expression or not was independently controlled. In Crosses 1 and 2, all the offspring died and none of them carried 2 or more of the expressed EVE in their parental shrimp. In contrast, 100% of 10 arbitrarily selected surviving shrimp from Cross 3 and 90% from Cross 4 carried and expressed 2 or more of the 3 expressed EVE transmitted from the parental shrimp. These results reveal a potential protocol for development of viral tolerant shrimp stocks.

zoology↗

bioRxiv2025

Novel midgut smooth muscle necrosis (MSMN) in translucent or glass post-larvae of whiteleg shrimp

From the Asia-Pacific region, the suspected TPD/GPD specimens of postlarvae (PL) preserved in Davidsons fixative and 95% ethanol were sent to our laboratory to prepare for PCR and histological analysis. Interestingly, PCR tests with the specimens were negative with the VPHLVD(vtcc2 and vtcc3 gene) primers, but positive with the VPTPD(vhvp-2 gene) primers. There were no characteristic lesions of acute hepatopancreatic necrosis disease detected in these specimens. However, in the sections of several specimens from two affected tanks, the midgut was cut tangentially in the abdominal region, revealing a novel histopathology characterized by severe necrosis specifically in the thin, smooth muscle tissues underlying the midgut lumen epithelium. This comprised nuclear pyknosis and karyorrhexis limited to the smooth muscle and occasionally affecting the midgut epithelium but not involving the surrounding skeletal muscles. The pathology is called midgut smooth muscle necrosis (MSMN). Such pathology would undoubtedly lead to loss of midgut peristalsis and cessation of feeding, but it can be easily overlooked without careful histological examination using a high magnification microscope objective. No bacterial cells were evident, suggesting that the lesions arose from a virus or from a specific toxin response. This report is an urgent plea for colleagues studying TPD/GPD to review their samples histologically to help in determining whether MSMN is pathognomonic for TPD/GPD.

zoology↗

bioRxiv2023

Production results indicate that parvovirus IHHNV should be delisted as a notifiable shrimp disease

The main purpose of this report is to provide hard evidence that the shrimp parvovirus IHHNV has not resulted "in significant consequences e.g. production losses, morbidity or mortality at a zone or country level" in Thailand since at least 2010. It also reveals that no single PCR test is sufficient to identify IHHNV-infected shrimp. It presents historical evidence and new evidence from 11 commercial ponds cultivating the giant tiger shrimp Penaeus monodon in Thailand. These ponds were selected because they were the ponds that gave positive PCR test results for IHHNV using 2 methods recommended for IHHNV diagnosis by WOAH. However, an additional in-house "IHHNV Long-Amp method" (IHHNV-LA) was also used to amplify 90% of the 4 kb IHHNV genome sequence, and it also gave false-positive test results with 2 of the 11 ponds. Further tests using normal histopathological analysis for the presence of pathognomonic Cowdry A type inclusions (CAI), in situ hybridization (ISH) and immunohistochemistry (IHC) could confirm IHHNV infections in only 2 of the 4 ponds PCR-positive using all 3 PCR methods. In addition, positive detection of CAI alone was equivalent to ISH or IHC in confirming IHHNV infection after a positive test with any of the PCR methods used. In summary, the recommended WOAH PCR methods gave false positive test results for IHHNV infection with 9/11 ponds (82%). All 11 ponds gave profitable harvests despite the confirmation of IHHNV in 2 ponds, where it was accompanied by various additional pathogens. Unfortunately, according to current practice, positive PCR test results with the WOAH methods alone sometimes leads to rejection of traded shrimp products without assurance that the test results are not false positive results that may arise from endogenous viral elements (EVE).

zoology↗