A virus found in shrimp and fish may cause an eye disease in humans, according to a recent study that marks the first known case of a pathogen from aquatic animals infecting people.
Those “who handle dissected aquatic animals daily without adequate protection or eat raw aquatic animals daily are at high risk” of being exposed to the virus, the researchers cautioned in their recently published paper.
They advised taking protective measures, such as wearing gloves, when handling such animals at home.
“To date, no virus originating from aquatic animals has been shown to infect humans and directly cause disease,” they wrote, adding that they found “this emerging human eye disease is associated with cross-species infection by an aquatic virus”.
The researchers from the Chinese Academy of Fishery Sciences, Qingdao Eye Hospital of Shandong First Medical University, the University of Melbourne and Duke-NUS Medical School in Singapore published their findings in Nature Microbiology in late March.
Called covert mortality nodavirus (CMNV), the virus was first identified in farmed shrimp in 2014. Its discovery helped explain a disease that had caused serious losses to China’s shrimp industry since 2009.
A survey of 523 animal samples collected worldwide found the virus to be widespread in wild and farmed aquatic species across Antarctica, Africa, the Americas and Asia.
The virus isolated from Antarctic krill was “evolutionarily the most ancient, suggesting it may represent the initial known host”, the team wrote, adding that the species lives in near-freezing seawater and possibly acts as a reservoir for the virus.
“In aquaculture, CMNV-infected shrimp typically remain asymptomatic under stable, suitable water temperature,” they explained.
“But shrimp infected with CMNV experience gradual, uninterrupted mortality when the water temperature exceeds 28 degrees Celsius (82.4 degrees Fahrenheit) or environmental conditions fluctuate rapidly.”
“The spillover of such viruses poses new biosecurity risks to both aquaculture and human health,” they added.
According to the study, more than 20 aquatic species can be infected, including shrimp, crabs, molluscs (clams, mussels, oysters and scallops), cephalopods (octopus, cuttlefish and squid) and other species, such as spoon worms.
The eye condition, known as persistent ocular hypertensive viral anterior uveitis (POH-VAU), leads to recurrent inflammation and extremely high pressure inside the eye.
If left untreated, hypertension can lead to irreversible optic nerve damage and severe vision impairment.
While most viral eye infections are caused by known viruses like herpes or cytomegalovirus, patients with the new condition tested negative for these viruses. Instead, the team found CMNV in the patients’ eye tissue.
Looking into how patients were infected, the team found that “frequent unprotected processing of aquatic animals and consumption of raw aquatic animals were commonly reported exposure events”, together accounting for 71 per cent of the investigated cases.
Those at high risk include home-based handlers of seafood, people who eat raw aquatic products and those who have suffered “puncture wounds from aquatic animal appendages”, such as live or frozen fish and shrimp.
Beyond direct handling, the study raised the possibility of “interfamilial transmission” within households through “shared utensils or other close contact at home”.
The researchers observed cases among young people who had no direct contact with seafood but lived with family members who did.
“Their family members had severe or frequent exposure to CMNV risks associated with hand injuries during the unprotected handling of aquatic animals,” the team wrote, while adding that further validation was needed.
In laboratory tests, the team found that infected mice developed progressively increased intraocular pressure and pathological damage to ocular tissue, mirroring the symptoms seen in human patients.
The virus was also shown in lab tests to be capable of infecting mammalian cells.
An analysis of patients from different regions in China showed that the eye disease was much more common in the country’s main fish-farming areas.
The six provinces that produced more than 10 million tonnes of farmed seafood from 2022 to 2024 had a 77 per cent higher proportion of POH-VAU cases among ophthalmic patients than the 11 provinces whose production was below 1 million tonnes.
“Higher aquaculture production may be associated with an increased risk of disease,” the researchers wrote.
Climate change, natural resource exploration and expanding human fishery activities were bringing people into closer contact with previously isolated marine wildlife, they added.
The researchers cautioned that the increased interaction raised the risk of viruses leaping from the sea to humans.