Avian Flu: Cats Saved with Antivirals and a Combination of Treatments: A Study of Four Cases in California

It was June 2024 when researchers raised the alarm about the risks to domestic cats of the rapidly evolving H5N1 avian influenza virus . Experts then predicted a mortality rate of approximately 67% and urged feline families to remain vigilant. Now the same team returns to the topic, but with a hopeful outlook, in a new study just published on the case of four cats from a single household infected by the virus in California. The study, published by researchers at the University of Maryland, Cross Street Small Animal Veterinary Hospital, and the University of Texas Medical Branch (available as a preprint, not yet peer-reviewed), demonstrates that, "with timely supportive care and antiviral treatment, cats can survive H5N1 and can maintain high titers of neutralizing antibodies against H5N1 for at least 3–4 months after recovery."

The outbreak struck the family's feline colony, which lived near a dairy farm in Tulare, the epicenter of the H5N1 avian influenza epidemic in California, between late October and mid-November 2024. The authors' reconstruction begins precisely on October 31st with the arrival of cat number 2—a long-haired, neutered male, aged 1 year and 7 months—at a local veterinary hospital. "He's not well," the owner reports. Indeed, the cat is lethargic and refuses to move, despite not having a fever at the time. From the information gathered, it emerges that the feline, weighing over 4.6 kg and up to date with vaccinations, has access to both inside and outside the home. He is treated with subcutaneous fluids and a broad-spectrum antibiotic and shows minimal signs of improvement 24 hours later. He also receives an appetite stimulant, but dies just two days later.

During the visit, the family reported that another of their cats (Cat 1) had become seriously ill before him and had been taken to a different local veterinary clinic. A 1-year-and-5-month-old, neutered, short-haired male, Cat 1 lived alone indoors, with no outdoor access, and was vaccinated. He himself experienced a similar scenario: he suddenly became lethargic and was rushed to the local emergency room, where he underwent chest imaging and blood tests. The attending veterinarian suspected an upper respiratory infection, and after the owners brought him home, Cat 1 also died suddenly.

At the time of feline patient visits, several local cattle and poultry farms were experiencing outbreaks of highly pathogenic avian influenza (HPAI). The veterinarian treating cat 2, who also cares for these cattle, suspected a link to H5N1 because the family's home is less than a mile from these dairy farms, and the husband, a hay vendor, works in the sector and visits them frequently. The family was instructed on all possible precautions. However, on November 6, cat 3, a neutered long-haired male aged 1 year and 7 months and weighing over 5.1 kg, also became ill and came to medical attention. The vaccinated animal is living exclusively indoors. He too exhibits symptoms of lethargy and loss of appetite. He is also diagnosed with mental decline, dehydration, and a fever of 39°C. Doctors immediately treated him with injectable NSAIDs and subcutaneous fluid therapy and, suspecting H5N1, this time a dose of the antiviral oseltamivir (Tamiflu) was administered orally every 12 hours for 10 days.

On November 13th, Cat 3 was examined again. His appetite had improved, and his weight had risen to 5.6 kg. He was drinking normally, and his physical activity had returned to normal. He was also given antibiotic eye drops and discharged for follow-up. A happy ending also awaited Cat 4, a neutered short-haired male aged 4 years and 11 months, weighing 5.3 kg, vaccinated, and housed strictly indoors. He was taken into care by the doctors on November 7th. He also showed the same symptoms and signs of an upper respiratory infection. With a similar treatment regimen to that adopted for Cat 3 (subcutaneous solution, injectable NSAIDs, and oral oseltamivir), this feline is also on the road to recovery.

On February 26, 2025, the owner, contacted by veterinarians, confirmed that both cats had recovered and were back to normal. On March 13, blood samples were taken from the recovered cats during a follow-up visit. The result: both cats had high levels of neutralizing antibodies against the H5N1 avian influenza virus (2.3.4.4b). This outbreak, the authors conclude, "demonstrates that, with timely supportive care and antiviral treatment, H5N1 is a treatable disease in domestic cats."