Recently, I fielded a question from a concerned cat owner about whether it was ok to feed her cats food containing eggs since she’d heard cats were dying from bird flu. I thought so, but realized I didn’t really know much about bird flu, cow flu, or cat flu. Dane County is home to many cats, dogs, people, horses, cows, bats, and backyard chickens. The commonality among these animals is that they all can be infected with influenza A. But what is influenza exactly? What’s with all those numbers and letters? Why are egg prices so high?
The influenza virus is a single-stranded RNA virus, and there are four types: A, B, C, and D. Influenza B only infects people and is the type most likely to cause a flu pandemic. Type C infections also only occur in humans and tend to cause mild illness. Type D primarily infects cattle and is one of the pathogens causing bovine respiratory disease (BRD), an often-fatal disease in calves. It can also infect horses, sheep, goats, poultry, pigs, and camels as well as humans. While type D can cause infection in humans, it’s unlikely to do so. Influenza type A, however, can be carried by or infect a lot of different animals, including birds, humans, and pigs.
Influenza viruses are further divided into subtypes based on two proteins found on the surface of the protein. There are 18 hemagglutinin (H) subtypes and 11 neuraminidase (N) subtypes. This is why scientists rattle off all those letters and numbers. There are also clades and subclades; thankfully, we don’t need to go into that much detail.
Two subtypes have only been found in bats common in Central and South America. The virus was found when screening healthy bats, so we don’t need to worry about congested, snotty bats flying around. Research suggests that bat influenza viruses would need to significantly change to become capable of infection and spread easily among people, so there’s no current risk to humans at this time.
Dogs can get influenza, and we’ve seen sporadic outbreaks across the United States. The most common brand of dog influenza is H3N2. Just to confuse matters, humans have an H3N2 subtype that causes seasonal influenza, but it’s not the same as the dog subtype. You can’t get influenza from your dog and vice versa. Dog influenza causes respiratory signs, like coughing, sneezing, discharge from the nose, lethargy, and a decreased appetite. Another subtype, H3N8, affected many racing greyhounds in 2005. There is a vaccine available for dogs that protects against both subtypes and is recommended for dogs that travel a lot or have compromised immune systems. H3N8 is also the subtype of horse flu. But again, not the same as the dog H3N8. Couldn’t we just give each subtype a name, like Orion? Equine influenza virus (EIV) causes the same symptoms in horses as we see in people and dogs: upper respiratory signs, fever, and fatigue.
Each of the dog and horse subtypes were originally found in birds and then spread to the other species. The first description of bird flu was in 1878 in northern Italy and referred to as “fowl plague” since it had a high death rate, much like the black plague. By definition, plague is caused by bacteria; scientists didn’t determine it was a virus until 1955. In 1981, the name was changed from fowl plague to avian influenza.
Birds have a lot of different subtypes and strains of influenza, so they’re classified as either low pathogenic avian influenza (LPAI) or highly pathogenic (HPAI). In the United States, most bird flu outbreaks have been due to LPAI strains, which cause only mild disease. If you raise chickens, you might notice some nasal discharge, decreased appetite, fewer eggs laid, diarrhea, and ruffled feathers, but most chickens recover. The highly pathogenic strains are the ones we worry about. Currently, the subtype is H5N1, making the full name HPAI A(H5N1). Infected birds may have nasal discharge, coughing, sneezing, diarrhea, reduced egg production or soft-shelled/misshapen eggs, purple discoloration of the skin, swelling of the head, tremors, incoordination, and sudden death. Rarely do chickens or other poultry recover from HPAI. When a flock is showing signs, the whole flock will be euthanized to contain the disease. Wild birds don’t get sick, but carry the virus and can pass it to other poultry in the area.
In March 2024, HPAI A(H5N1) was found in cows on many dairy farms over several states. Prior to this, bird flu viruses hadn’t been found in cows. HPAI can also infect other animals, including cats, dogs, and people. Lactating cows are most commonly affected, and clinical signs include a decreased appetite; reduced milk production; and a thickened, discolored appearance to the milk. Luckily, most affected dairy cows recover with supportive treatment.
Cats can become infected if they eat sick or dead infected birds, drink unpasteurized (raw) milk from infected cows, or eat undercooked or raw meat. Dogs also become infected in the same way as cats, but the incidence is lower. Signs of HPAI infection in cats and dogs include fever, lethargy, decreased appetite, reddened eyes, discharge from the eyes and nose, difficulty breathing, tremors, seizures, blindness, and incoordination.
How can you protect your pets? For cats and dogs, make sure you are feeding a cooked diet. Raw diets are not recommended, as they can be contaminated with bacteria as well as viruses and aren’t a healthier alternative to cooked diets. Avoid unpasteurized milk and raw eggs. If your pet shows signs of an upper respiratory disease or just doesn’t seem right, please contact your veterinarian for care. While human influenza vaccines don’t protect against HPAI, it’s always a good idea to get your yearly flu vaccine. We never know when one subtype may suddenly become much more severe.
