Farming Magazine - June, 2009

COLUMNS

Small Livestock: What Do You Need to Know About Bird Flu?

By Diane Wells

Avian influenza (aka AI, avian flu, bird flu, fowl plague) is a contagious virus that expresses itself through a variety of subtypes. Each is characterized by its proteins and ability to produce disease, or pathogenicity. By way of different protein combinations, there are potentially 144 versions. Most are referred to as low pathogenic (LPAI), causing minimal to no clinical signs, while others as highly pathogenic (HPAI), killing 90 to 100 percent of infected birds. The Asian subtype HPAI H5N1 dominated headlines five years ago when it spread through eight Asian countries and more than 100 million birds were culled or died. Outbreaks are ongoing and, to date, 60 countries have reported its presence and over 250 million poultry and 256 humans have died. This subtype has not made it to the United States, but other subtypes are here and something for poultry farmers to keep in mind.

Photos courtesy of USDA/APHIS File Photo.
Birds with AI may exhibit a purple discoloration of wattles, combs and legs.

Waterfowl, shorebirds, terns and gulls are natural reservoirs for AI, carrying the virus in their intestines. An infected bird excretes the virus through its feces, and it is not uncommon for wild ducks to transmit LPAI to pastured poultry flocks when range is shared. Migratory birds are only one route for transmission, though. The smuggling of birds and poultry products is considered the primary means of transmission in other parts of the world and U.S. officials are regularly intercepting shipments of eggs, feet and birds from Asian countries. Humans and poultry equipment traveling to and from infected areas are also a potential route for transmission, along with newly acquired birds from not-so-trustworthy sources. Once a bird comes into contact with the virus, it spreads via nose, mouth and eye secretions. Flocks raised indoors can even transfer the virus by way of airborne secretions.

Detection of a low pathogenic subtype can be tricky, as its presence isn’t always evident to the naked eye, and when it is evident, signs are typically mild: a drop in the consumption of food and egg production and coughing and wheezing. Keep in mind that we’re talking about a flu virus and, just like with humans, some varieties can pack a wallop while others tread lightly on the system. Birds infected with a highly pathogenic subtype will show a lack of energy and appetite; decreased egg production; soft-shelled or misshapen eggs; swelling on the head, eyelids, comb, wattle and hocks; purple discoloration of the wattles, combs and legs; nasal discharge, coughing and sneezing; lack of coordination; and diarrhea.

In the interests of healthy poultry, it’s important that we not let AI slip off our radar screen. It is also in the interests of human health, as research has shown that certain low pathogenic subtypes have the potential to mutate into highly pathogenic subtypes. There is a strong species barrier (i.e., the virus does not easily jump from birds to humans), but pigs, horses, cats, ferrets and marine mammals have been shown to carry it. And, this is where it gets interesting: pigs can carry both human and avian flu strains and there is considerable concern that the two could combine and reassort to produce a strain capable of human-to-human transmission. It is in a virus’ nature to evolve over time, and influenza viruses mutate at a relatively high rate. Good for the virus, not so good for humans who want to control it.

To maintain a species barrier and keep your birds healthy, there are preventative measures you can take to minimize the risk of exposure. Vaccines are not considered effective in preventing poultry disease, cleanliness is. Keep a clean operation, and that includes you. Wash your hands before and after working with your birds. If you visit another farm or go to a live bird market or show, clean and disinfect your clothes, shoes, hands and equipment when you get home. A solution of equal parts bleach and water is an adequate disinfectant. There are also a number of products you can buy to do the job. If other farmers visit, restrict access to your facilities or offer them clean boots and coveralls. Remove dirt, litter, manure and other organic materials from poultry house surfaces and wash and disinfect regularly, including cages, tools, feeders and waterers. Keep in mind that, unless covered with polyurethane, wood surfaces are nearly impossible to sterilize. Clean and disinfect any poultry equipment you borrow or that is returned to you—better yet, do not borrow or lend equipment.

Swelling of the head, eyelids, wattles and hocks is a sign of AI.

The AI infection rate in migratory waterfowl is about 1 percent, and that number rises in late summer and early fall. If you let your birds range, do not let them coexist with wild ducks or geese or use any water source that the fowl could have contaminated. If a pond is your water source, disinfect that water before giving it to your birds. Ask your veterinarian for safe methods. When acquiring birds, get them from a reputable source that practices good disease control and keep these birds separate from the rest of the flock for 30 days. If you’ve shown birds at a fair, isolate them for at least two weeks after the show. Although Northeastern states have been clamping down on live bird markets and requiring the testing of flocks destined for them, you can never be too safe. Do not bring live birds back from these markets. Lastly, properly dispose of dead birds.

If you think your birds are showing signs of the flu, report it. Call the USDA Veterinary Services at 866-536-7593 or contact your state or local veterinarian. Cooperative extension agents are also good, knowledgeable people to turn to if you have questions or concerns. If you’re interested in reading more about avian influenza, visit the USDA’s avian influenza Web site, www.usda.gov/birdflu, or the USDA APHIS backyard biosecurity Web site, www.aphis.usda.gov/vs/birdbiosecurity. I also encourage you to do an Internet search to learn about ongoing surveillance efforts in your state.

The author, a brand new contributor to Farming, is a biologist who lives and farms in Vermont’s Northeast Kingdom.