Author: Kurt Treftz, Cascade Pest Control
A recent finding in Riverside County indicates that rats may indeed be playing a role in spreading the bird flu virus. In late January 2025, the US Department of Agriculture confirmed the presence of the H5N1 avian influenza in four black rats found in Riverside County, CA, which has recently experienced a bird flu outbreak.
Avian influenza viruses have been known to infect not only domestic and wild birds but also non-avian species. In fact, the recent outbreak of the bird flu virus in the United States has been found in over 50 North American mammals, including skunks, cats, dolphins, harbor seals, foxes, mountain lions, and coyotes.
The current outbreak of H5N1 has affected approximately 148 million poultry birds since 2022, causing the price of eggs to skyrocket. It has also spread to dairy cattle, with 973 confirmed cases across 17 states. Human cases have also been reported among dairy and poultry workers.
Significance of Infected Rats
Adding rats to the list of mammals that have contracted the H5N1 virus can have a significant impact for several reasons.
Transmission Risk
Because rats, like the common black and Norway species, are often found in urban environments, they have ample opportunity to spread the virus. They have multiple pathways, including dropping, urine, blood, and saliva, to transmit the infection.
Mobility
Rats are highly mobile and venture freely between farms, homes, and warehouses. This active lifestyle could accelerate the spread of the virus and expose humans and pets to the infection.
Mechanical Vector
Even rats that aren’t symptomatic can carry the virus. They act as mechanical vectors, transmitting the virus on their coat from contaminated areas.
Active Viral Shedding
Another danger from rats is that the avain influenza virus can replicate without adaption in rodents. This means that the virus in the rats often has high viral titers and transmits easily to other animals.
In areas with a high concentration of rats, there is an elevated risk of them being a vector for any number of infectious organisms. Currently, rats are not considered the primary cause of H5N1, but they represent a potentially significant risk factor in the spread of this debilitating virus.
Mitigating the Risk of Infected Rats
To reduce the impact of infected rats, it is important to be proactive and fight back.
- Rodent-proof poultry houses. One immediate and essential step is ensuring that rodents do not have access to birds. Keep rats away, whether it is a commercial farm or a backyard coop.
- Repel rats. Make sure that your home or business is not attractive to rodents. Seal up holes, block entry points, and reduce attractants like food/water.
- Implement control measures. Keep rats away with natural methods as well. Choose to plant items that discourage rodents from making a home. Set traps if there is concern of an active rodent invasion. Hire professional rat control services.
- Report sick rodents. If you see evidence of sick rats, make sure to report it so that the USDA and state extension services can work to get ahead of outbreaks. They use a combination of surveillance, containment, and prevention to try to monitor and protect poultry, livestock, and public health. You can be part of the solution.
The fight against the current H5N1 avian influenza outbreak is far from over. As the situation continues to evolve, we can all play a part in stopping the spread. Staying aware and preventing rodents from gaining a foothold could be a small step in the right direction.
