AcIV-E in sturgeon: surveillance for an elusive virus

Loss of appetite, abnormal swimming and mortality among young sturgeon demand a prompt investigation, but they do not identify a cause on their own. One agent to consider is Acipenser European iridovirus, usually abbreviated AcIV-E, a large DNA virus detected in several European countries. A 2024 report from eight northern Italian farms illustrates both its significance and the limitations of diagnosis when no clinical sign is specific and routine virus isolation is unavailable.

A virus with unresolved biology and nomenclature

AcIV-E belongs to a group of nucleocytoplasmic large DNA viruses described in sturgeon. Its taxonomy and relationship to other sturgeon viruses remain under discussion because genomic information is incomplete and historical names overlap. This uncertainty does not make the health problem less real, but it does require careful terminology and transparent reporting of the diagnostic target.

The virus was definitively identified in Europe during the past decade, with disease events reported in countries including Italy and Sweden. Published detections involve Russian, Siberian, Adriatic and stellate sturgeon, sterlet and other acipenserids. Differences between species have been observed, but current evidence is not sufficient to rank susceptibility confidently across all production settings.

Evidence from clinically affected farms

Fabio Bondavalli and colleagues examined 482 sturgeon no older than twelve months, submitted from eight farms in the Po Valley between 2021 and 2023. All came from tanks experiencing health problems and mortality. Six Acipenser species and beluga, Huso huso, were represented.

Each fish underwent post-mortem examination, and gill tissue was tested using real-time PCR directed at the viral major capsid protein gene. AcIV-E DNA was detected in 204 fish, or 42.68% of the submitted animals. That figure is not the prevalence of AcIV-E across Italian sturgeon farms. The study sampled problem batches rather than a random cross-section of the farmed population, a limitation explicitly acknowledged by the authors.

Detection differed substantially among species in this dataset. Russian sturgeon (Acipenser gueldenstaedtii) accounted for 164 positive results among 257 tested fish, while 19 of 47 Adriatic sturgeon (A. naccarii) were positive. None of the 22 white sturgeon or 33 beluga tested positive. Those negative groups were small and selected through the same clinical submission process, so they do not establish resistance.

Warning signs are not diagnostic signs

Farm staff most often reported anorexia and superficial, slow or uncoordinated swimming. Some affected fish were passively carried towards tank screens by the current. Post-mortem findings could include abdominal distension, skin reddening, enlarged gills, splenomegaly and hepatic changes.

None of these findings is pathognomonic for AcIV-E. Water-quality disturbance, other viruses, opportunistic bacteria, parasites or multiple concurrent problems may produce a similar picture. PCR results therefore need to be interpreted with the batch history, lesions and investigation of alternative causes. Detection of a viral DNA target confirms that the target was present in the sample; it does not prove that AcIV-E alone caused every death.

Why molecular detection carries the diagnosis

For many fish viruses, growth in cell culture and observation of a cytopathic effect can support identification. AcIV-E has not been propagated reliably on the cell lines commonly tested. That prevents routine isolation and also constrains research into pathogenesis, immune responses and preventive tools.

Real-time PCR is therefore the principal diagnostic method described for AcIV-E. Gill tissue is a useful target because epithelial tropism has been reported, but sampling should be planned with the testing laboratory. The number and condition of fish, tissues collected, storage, transport and tests for potential co-infections all affect interpretation. Poorly preserved samples or an inadequate number of fish can weaken an otherwise appropriate investigation.

Prevention begins before fish arrive

There is no validated specific antiviral treatment that clears AcIV-E from a group of sturgeon. Control consequently focuses on avoiding introduction and limiting spread. Before juveniles or broodstock move, receiving farms need relevant health information: origin, recent mortality, laboratory results, contact with other populations and transport arrangements.

A genuinely separate quarantine area allows observation and risk-based testing before fish join established units. Water circuits, nets, tanks, vehicles and staff can connect groups that appear physically separate. A clean-to-higher-risk work sequence, dedicated equipment and validated sanitation procedures reduce those indirect routes.

If AcIV-E is suspected, pausing internal and external movements while the investigation proceeds helps contain uncertainty. Daily records of mortality, feed intake, behaviour, water temperature and interventions should be maintained by tank. This timeline guides the selection of fish and samples and makes laboratory results more meaningful.

Farm health and conservation are connected

Sturgeon production cycles are long, and the animals have considerable economic and conservation value. Some facilities also support restoration programmes. Moving an infected or potentially carrier fish to another farm or releasing it without health assessment could expose already vulnerable populations.

The Italian authors also identify farm effluent as a potential ecological concern, but their study did not directly demonstrate transmission to wild sturgeon. This distinction matters. The finding supports proportionate risk assessment, wastewater review and surveillance; it does not establish that a particular wild population has been infected by a farm. Coordination between producers, aquatic veterinarians, laboratories and conservation managers is essential where production and restoration overlap.

How Vetofish can help

Vetofish can support sturgeon farms during mortality investigations, from clinical review and sampling design to interpretation of molecular results and revision of biosecurity measures. Mapping the movement of animals, water, equipment and people often reveals where an apparently separate unit remains epidemiologically connected.

The goal is early detection without prematurely assigning a multifactorial event to one pathogen. A robust investigation combines daily observation, water-quality data, post-mortem examination, differential diagnosis, targeted PCR and documented movement decisions. For AcIV-E, the quality of this system is currently the strongest practical control available.

References

• Bondavalli F, Schleicherová D, Pastorino P, Mugetti D, Pedron C, Prearo M. “Detection of Acipenser European Iridovirus (AcIV-E) in Sturgeon Farms in Northern Italy between 2021–2023.” Viruses. 2024;16(3):465. doi:10.3390/v16030465.
• Mugetti D, Pastorino P, Menconi V, Pedron C, Prearo M. “The Old and the New on Viral Diseases in Sturgeon.” Pathogens. 2020;9(2):146. doi:10.3390/pathogens9020146.
• Bigarré L, Lesne M, Lautraite A, et al. “Two New Sturgeon Species are Susceptible to Acipenser Iridovirus European (AcIV-E) Infection.” Pathogens. 2020;9(3):156. doi:10.3390/pathogens9030156.
• Axén C, Vendramin N, Toffan A. “Outbreak of Mortality Associated with Acipenser Iridovirus European (AcIV-E) Detection in Siberian Sturgeon (Acipenser baerii) Farmed in Sweden.” Fishes. 2018;3(4):42. doi:10.3390/fishes3040042.