wildlife, zoo and aquatic assay data sheet

Betanodavirus PCR test

Test code: S0275 - Ultrasensitive qualitative detection of betanodavirus by reverse transcription coupled real time PCR

Betanodavirus, also known as nervous necrosis virus or NNV, is a genus of non-enveloped, positive-sense single-stranded RNA viruses belonging to the family Nodaviridae. These small icosahedral viruses measure 20 to 30 nm in diameter. Their genome consists of two RNA segments: RNA1, which is approximately 3.1 kilobases long and encodes the RNA-dependent RNA polymerase as well as the non-structural protein B2 that suppresses the host’s RNA silencing defenses; and RNA2, which is about 1.4 kilobases in length and codes for the capsid protein.

The genus is divided into four main genotypes: red-spotted grouper nervous necrosis virus (RGNNV), which tends to occur in warmer waters, barfin flounder nervous necrosis virus (BFNNV), which prefers colder environments, tiger puffer nervous necrosis virus (TPNNV), and striped jack nervous necrosis virus (SJNNV). These genotypes differ in their temperature preferences and host ranges.

Betanodaviruses cause viral nervous necrosis (VNN), also called viral encephalopathy and retinopathy (VER), a serious disease that primarily affects the central nervous system, including the brain and retina, of fish. Infected fish typically show abnormal spiral swimming, erratic behavior, loss of coordination, darkened body color, reduced appetite, and buoyancy problems. The virus is particularly destructive in larval and juvenile fish, where mortality rates can approach 100 percent, although it can also affect larger individuals. It impacts more than 50 species of marine fish and some freshwater fish, with common hosts including groupers, sea bass, sea bream, barramundi, and flounder. Outbreaks frequently result in major economic losses in aquaculture operations worldwide, spanning Asia, Europe, Australia, and the Americas.

The virus spreads both horizontally through contaminated water and vertically from infected broodstock to offspring. It is highly stable in the environment, which contributes to its persistence in farming systems. While primarily a pathogen of fish, it has been rarely detected in non-fish hosts such as sea turtles. No specific antiviral treatments are available, so control relies on strict biosecurity measures, screening of broodstock, disinfection protocols, ongoing development of vaccines, and selective breeding for resistant fish stocks. Betanodavirus is one of the most significant viral threats in global fish farming because of its devastating impact on the nervous system of young fish and its widespread effects on aquaculture production.

Diagnosis by cell culture or histopathological examination is slow and often non-specific, therefore PCR is preferred due to its speed, high sensitivity and specificity (Dalla Valle et al., 2005; Panzarin et al., 2010).

Preferred specimens: Filter media, or biofilm swab, or 0.2 ml fresh or frozen tissue.

Contact Zoologix if advice is needed to determine an appropriate specimen type for a specific diagnostic application. For specimen types not listed here, please contact Zoologix to confirm specimen acceptability and shipping instructions.

For all specimen types, if there will be a delay in shipping, or during very warm weather, refrigerate specimens until shipped and ship with a cold pack unless more stringent shipping requirements are specified. Frozen specimens should be shipped so as to remain frozen in transit. See shipping instructions for more information.

Turnaround time: 2 business days

Methodology: Qualitative reverse transcription coupled real time PCR

Normal range: Nondetected