Beyond the Birds: Avian Flu Infects Other Animals
Avian flu is not just for the birds; cases have been reported in the United States in dairy cows, as well as types of cats, a fox, a seal, and most recently, rats and domestic indoor cats, according to the latest data from the US Department of Agriculture (USDA)’s Animal and Plant Health Inspection Service (APHIS).
In the United States, > 500 cases of H1N1 have been identified in a range of mammal species since 2022, according to APHIS.
The current list of detections in mammals has expanded to include rats. Avian flu had previously been in mice on farms affected by avian flu. Of the recent rat detections, four involved black rats that were sampled in late January in Riverside County, California, where recent poultry outbreaks also have been confirmed, according to APHIS.
Other reported infections in mammals include a fox in North Dakota, a bobcat in Washington state, a mountain lion in Wisconsin, and a harbor seal in Massachusetts.
Several cases of avian flu also have been reported in domestic cats. A report published in the Centers for Disease Control and Prevention (CDC)’s Morbidity and Mortality Weekly Report (MMWR) outlined cases of H5N1 detected in two indoor domestic cats in Michigan. While these cases are the first reported in indoor cats, cases of H5N1 have been reported in outdoor cats on US dairy farms.
The indoor cats lived in the homes of dairy workers but had no known direct exposure to H5N1-affected farms, according to the report. The cats developed respiratory and neurologic symptoms; one was euthanized and one died. The cats’ human owners who were dairy farm workers declined influenza A (H5) testing; other household members tested negative.
“Given the potential for fomite contamination, farmworkers are encouraged to consider removing clothing and footwear and to rinse off any animal byproduct residue (including milk and feces) before entering households,” the MMWR authors wrote.
Jump to Mammals Not Surprising
Influenza A viruses are shared, and interspecies transmission has always existed, said Marie Culhane, DVM, PhD, professor at the College of Veterinary Medicine, University of Minnesota, St. Paul, Minnesota, in an interview.
“The more virus there is in our shared ecosystem, the more opportunities exist for other mammals and birds to get infected,” Culhane said.
The recent report of avian flu in domestic cats may not immediately impact guidance for preventing disease transmission, said Culhane, who was not involved in the MMWR report. “I am always hopeful that science will inform policies and guidance; unfortunately, science literacy levels of policy and guidance makers vary widely,” she said.
For clinicians, the takeaway regarding avian flu in other animals is to continue to test patients for flu, Culhane told Medscape Medical News.
A flu diagnosis is straightforward, and requires only a swab or swabs of nasal, oral, pharyngeal, or conjunctival mucosa and polymerase chain reaction test for influenza A virus, with subtyping to determine H5, she said. “If the symptoms have cleared, a serum antibody test for H5 flu can be done to demonstrate prior exposure to the virus,” she noted. Clinicians will miss the H5 flu diagnosis without a test, “and you won’t understand how the virus moves if you don’t get a history from the human patient regarding their exposure to animals and animal products,” Culhane emphasized.
Animals mean mammals and birds, she said. “By animal products, I mean raw (unpasteurized) milk, uncooked/raw meat, nest-run eggs (which are eggs that are unwashed, ungraded, and unmarked as to grade and size), feces, urine, saliva, nasal discharges, and blood,” she said. “The United States currently has one of the best public health systems in the world; reach out to the experts and find out the best approaches for the diagnosis and management of flu in humans as a clinician,” she said.
If patients are concerned about exposure through their pets or other animals, remind them to wash their hands after handling any pets with outdoor access, or pets that are fed raw foods, said Culhane. “Don’t feed your pets raw food or raw milk,” Culhane added.
The avian flu also appears to be evolving, based on another recent report of an oseltamivir-resistant strain among poultry in Canada, although the implications for spread to other species remain unclear.
USDA Emphasizes Avoidance First, Then Handwashing
“The finding of HPAI [highly pathogenic avian influenza] in mammals is not unexpected, given that many species are susceptible to influenza viruses and wildlife often come into direct contact with wild birds,” a USDA spokesperson told Medscape Medical News in an interview. “Many of these species were likely infected after consuming dead birds that were infected with HPAI,” the spokesperson said.
Most mammals do not appear to spread HPAI; however, APHIS does not recommend touching or collecting sick or dead animals, according to the spokesperson.
APHIS recommends immediate handwashing with soap and water for at least 20 seconds in cases of potential exposure, including having direct contact with animals, animal food, or supplies, and animal waste or feces; cleaning up after animals, including body fluids or waste; and after leaving areas where animals are housed, “even if you did not touch the animal,” the USDA spokesperson told Medscape Medical News.
An ongoing list of detections of HPAI in mammals in the United States is available on the APHIS website.
Several authors on the MMWR report disclosed support from the USDA. Culhane had no financial conflicts to disclose.
