Bird flu primer
I recently got a mailing encouraging veterinarians to watch a made-for-TV movie about a fictional bird flu pandemic, in case it triggered questions from clients about avian influenza. I dunno. I'm not sure network television is where we should get our medical information, and for entertainment, I'd rather watch a West Wing rerun. Nonetheless, bird flu questions are rolling in. So here we go.
Avian influenza is an infection caused by avian (bird) influenza (flu) viruses that occur naturally in birds. It has been around in various forms for a long, long time. Wild birds carry and spread the viruses but usually do not get sick from them. When domesticated birds like chickens, ducks, and turkeys get infected, they may become very sick and die. Infected birds shed the highly contagious virus in saliva, nasal secretions, and feces. Susceptible birds contract the virus through direct contact with infected birds, or through contact with surfaces, such as cages or the ground, that have been contaminated by the virus-laden secretions, or through ingestion of contaminated water or feed.
Now let's learn some lingo. "Influenza A" viruses can infect lots of different animals, from ducks to pigs to whales to you and me. Subtypes are identified by surface proteins called hemagglutinin (HA) and neuraminidase (NA), which form various combinations. Certain subtypes are specific to certain species. For example, "human influenza," which infects people and passes directly human-to-human, has been caused by H1N1, H1N2, H2N2, and H3N2. Pigs? The bugs that typically get them are H1N1 and H3N2. Horses? H7N7 and H3N8. Birds are a different story. They can carry all subtypes. Where things get tricky is when a subtype normally found in one species hops to another species and causes illness. People who have direct contact with sick poultry (or virus-contaminated environs) have always had a risk of catching avian influenza. In 2003 during an outbreak of an H7N7 influenza in local poultry in the Netherlands, a Dutch veterinarian contracted the virus and died. Eighty-plus other people got sick (including four more vets), but most just got conjunctivitis or mild flu symptoms. The key safety net in these situations has been that although these variants of avian influenza occasionally infected people, they do not generally pass from one person directly to the next. In other words, when the chicken veterinarian came home sick with the bird flu, he didn't pass it on to his wife.
The current bird flu scare concerns the H5N1 subtype. Like many avian influenza viruses in the past, people in close contact with infected birds have contracted the disease. The fear is that, since flu viruses mutate all the time, H5N1 might mutate to a highly contagious form that spreads directly person-to-person. Since H5N1 is so different from the subtypes of flu people usually get, we will have little natural resistance. This is already evident in the high mortality rates noted in the small number of people who have contracted H5N1.
The good news? The New York Times recently reported that, at least in Southeast Asia where this scare began, the aggressive control methods being taken are working. The number of human cases in Asia is waning dramatically, and there is no evidence that H5N1 has reached North America either in birds or people. But many eminent health specialists still think it's only a matter of time.
Is there any risk to our pets or other animals? There have been documented cases in Asia and Europe of deaths in cats, both domestic kitties and large felines including tigers and leopards. It is thought that these cats got bird flu by eating raw infected poultry. (There is no risk from feeding cooked poultry or eggs, or eating it yourself, as the virus is easily killed by heating meat to 70 degrees C.) There is also evidence that cat-to-cat transmission is possible. Theoretically cats could carry and spread the disease. What about dogs? Tests done in Thailand suggest that canines may be susceptible to subclinical infection, if not outright disease. Pet birds are all at risk. So far cows and horses do not appear to be at risk A few pigs were found to have antibodies, but none showed clinical signs.
In countries with H5N1 outbreaks in the wild bird population, pet owners are being advised to keep cats indoors, dogs on leashes, and pet birds confined. The goal is to avoid contact with migrating waterfowl, poultry, contaminated environments, and water sources where wild birds congregate.
Other recommendations being made in H5N1 outbreak areas are actually reasonable precautions to take anywhere, to protect ourselves from diseases like tularemia, rabies, and West Nile virus. Here are a few things you can do. Report any evidence of significant sickness or death in birds, either wild or domestic. Don't call every time a goldfinch bumps his head on a window, but a few dead crows or a large number of sick or dead water fowl warrants a phone call. Limit your cat's contact with wild birds. If Tom brings in a dead bird or bunny, wear gloves and bag it in plastic for disposal. (In our area, we are not routinely testing these corpses for diseases. In H5N1 areas, they may be.) If the critter Tom nabs isn't dead, don't nurse it yourself. Don't let your kids play vet. Call a real vet. Call the animal control officer if appropriate. Do not touch or handle sick-looking or dead animals. If you do touch them, do not rub your eyes, eat, drink, or smoke until you wash your hands well with plenty of plain old soap and water. (You shouldn't be smoking anyway.) Hunters, the same goes for you. Don't handle or eat sick-looking game. Wear gloves when cleaning carcasses and do not eat, drink, rub your eyes, or smoke while handling them. (You shouldn't be smoking either.) Wash up well using soap and water, including all equipment.
To disinfect cages or other surfaces, you can kill flu viruses easily with diluted bleach. Blankets, towels, and clothing should be washed with laundry detergent and water. Then wash your hands again.
Now, I passed poultry medicine in vet school only because my professor liked me, and I'm not an epidemiologist. Maybe the risk of a pandemic has been blown out of proportion. Maybe not. It's good to be prepared, but not to panic. The U.S. department of Health and Human Services sponsors a great website at www.PandemicFlu.gov, which they call "One-stop access to U.S. Government avian flu and pandemic information." Another great site is www.cdc.gov/flu/avian/index.htm. Check these out if you want to learn more and decide for yourself...or in case you need material for a scary movie. Alfred Hitchcock, move over. Here comes The Bird Flu.