The emergence of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2), the virus responsible for COVID-19, raised concerns about its ability to infect species beyond humans. This led to questions about the vulnerability of common food sources. Understanding the biological requirements for infection is necessary to determine if teleost fish, the most common type of fish, are susceptible to this coronavirus.
The Necessary Mechanism for Infection
Successful viral infection depends on a precise molecular interaction between the virus and a host cell. SARS-CoV-2 uses its surface spike (S) protein to initiate entry. This spike protein must bind to a specific receptor found on the host cell, functioning much like a molecular “key” fitting into a “lock.”
For SARS-CoV-2, the cellular lock is the Angiotensin-Converting Enzyme 2 (ACE2) receptor. The virus’s spike protein attaches firmly to this receptor, which is widely expressed in human and mammalian tissues. This binding triggers a process that allows the virus to fuse with the cell membrane and release its genetic material, leading to replication and infection. The presence of a compatible ACE2 receptor is a prerequisite for a species to be biologically vulnerable to SARS-CoV-2.
Are Fish Susceptible to SARS-CoV-2?
The question of fish susceptibility is addressed by examining the compatibility of their ACE2 receptors with the SARS-CoV-2 spike protein. Teleost fish, which include the majority of species like salmon and cod, possess an ACE2-like receptor on their cells. However, the structure and genetic sequence of the fish receptor are significantly different from the human or mammalian versions.
Scientific analysis shows that the amino acid sequence of the ACE2 binding site in fish is poorly conserved compared to humans. Only 25% to 45% of the residues at the critical contact points are shared between human and fish ACE2. This substantial difference in molecular structure prevents the SARS-CoV-2 spike protein from achieving the high-affinity binding required for cell entry and viral replication.
Experimental studies using cell lines from various teleost species, such as fathead minnows and silver carp, have consistently demonstrated they cannot be infected by SARS-CoV-2. Researchers confirmed the virus is unable to use the fish ACE2 to enter the cells, effectively blocking the infection process. Therefore, fish are not biologically susceptible to infection due to the lack of a suitable cellular entry point.
Food Safety and Environmental Transmission Risk
Since teleost fish cannot be infected with SARS-CoV-2, the risk of transmission through fish consumption is extremely low. The virus is not considered a foodborne pathogen, meaning it does not cause illness through ingestion of contaminated food. Eating raw or cooked fish does not pose a risk of catching COVID-19 because the virus cannot replicate inside the fish.
Concerns have arisen when viral traces were detected on the surfaces of frozen food, including fish and their packaging, during cold-chain transport. This represents surface contamination from human handling, not an internal infection of the fish itself. The virus can survive for a period on cold surfaces, but this non-replicating viral load poses a risk of surface-to-hand transmission, not a risk from the fish as a host.
SARS-CoV-2 RNA has also been found in aquatic environments, primarily due to the discharge of wastewater containing viral particles from infected individuals. While the virus is present in sewage, this environmental presence represents non-viable or non-replicating viral material. The aquatic environment does not support the replication of SARS-CoV-2, and the virus does not infect fish or pose a transmission risk back to humans.