By Mary Ann Lieser
Small-scale farmers who are thinking about diversifying by adding poultry should know about Infectious Bursal Disease (IBD). Sometimes called Gumboro Disease because it was first identified in Gumboro, Delaware in the 1960s, IBD is now present throughout the U.S., as well as many other parts of the world.
“There are hundreds of thousands of cases in this country every year. It’s present in nearly every large commercial poultry operation,” says Dr. Daral Jackwood, of The Ohio State University, Ohio Agricultural Research and Development Center in Wooster, Ohio. Dr. Jackwood is at the helm of the Jackwood Laboratory, which is dedicated to the control and prevention of IBD.
Those large-scale producers are prepared to manage the disease and they consider the price of vaccinations a part of their operation’s overhead costs. But IBD has shown up in backyard flocks as well, and most of those cases could have been prevented had the owners known the best practices for establishing a small flock and acquiring stock.
IBD is caused by a virus, and there are lots of strains, some more virulent than others. Very virulent strains are currently a bigger problem in Europe than in the U.S., but there is a reservoir of highly virulent IBD in the western U.S., especially in California and Washington.
The virus is extremely easy to transmit, and difficult to eliminate once a site has been contaminated. So prevention is vitally important. And the biggest element in prevention is taking care when acquiring stock. It’s best not to accept chicks from a friend, or purchase chicks from a facility that hasn’t kept good records. Rather, purchase from hatcheries that will share their vaccination records. Once you have chicks, don’t sell or trade birds under eighteen weeks of age, and don’t transport young birds to fairs, shows or auctions. Minimize traffic to and from areas where the chicks are housed.
“A small, isolated flock with no exposure to other poultry or equipment should be fine, but if your neighbor works at a commercial poultry farm your birds will eventually be exposed to IBD,” says Dr. Jackwood. And then a vaccine regimen, which inoculates breeding hens and follows up with the chicks, will become necessary.
Chicks are most susceptible to IBD between three and six weeks after hatching, when any maternal-derived immunity will have waned. Depending on the strain of virus, a chick that age with IBD may not show any signs of disease while other strains of the disease can cause birds to be unmistakably sick. Symptoms may include ruffled feathers, watery diarrhea, soiled vents, dehydration, unsteady gait, listlessness and a bedraggled appearance. There is no treatment for sick birds, but supportive care, a clean environment and easy access to food and water can help to reduce mortality. If a chick is cold or stressed, it’s more likely to succumb; mortality rates range widely depending on the virulence of the strain and the breed of poultry, but can be over 50 percent for the very virulent strains of the virus. More layers than broilers die, and white leghorns and Araucana chickens are particularly susceptible.
The birds that recover can go on to do fine, with no lingering effects, but the facility where the birds are housed will be contaminated. Large amounts of the virus are excreted in fecal material for anywhere from one to three weeks when birds are sick. The virus is stable, resistant to disinfectants, and easily spread via surfaces, insects and rodents. There are cases of IBD infections traced to contaminated manure that was spread on fields adjoining a chicken owner’s property, or traced to the bottom of a shoe belonging to a visitor who spent only a brief time on a chicken owner’s property. Even wild birds can spread IBD, which does infect other birds although it only causes disease in poultry. Researchers aren’t certain how long the virus can remain viable, and advise that it’s best to store poultry manure at least six months, if possible, before spreading, and to protect manure heaps from wildlife.
“It’s nearly impossible to get rid of IBD virus,” says Dr. Jackwood, and once a site is contaminated it can cause increasing problems in subsequent generations of chicks. Chickens infected prior to three weeks of age will have subclinical cases of IBD. While they show no symptoms, those birds can go on to suffer from immunosuppression for the rest of their lives, making them predisposed to other infections — Newcastle disease, Marek’s disease, E. coli, infectious bronchitis, coccidiosis, inclusion body hepatitis (IBH), gangrenous dermatitis or Chronic Respiratory Disease (CRD). And the immunosuppressed chickens don’t respond well to any vaccines. Owners will see economic impacts because those immunosuppressed birds will take longer to reach market size and will not perform well.
When a chick is first infected, the virus lodges in cells in the bird’s bursa of Fabricius, located near the cloaca, which is the single posterior opening for the digestive, urinary, and reproductive systems. The bursa of Fabricius is the location for B lymphocyte production; when B cell production is hampered before three weeks of age, that chick won’t have adequate immune function even after it recovers from the disease.
IBD can be diagnosed by having a veterinarian examine the bird’s cloaca and bursa. In addition, many vets will send tissue samples to a laboratory for genetic sequencing so that mutated strains of the virus can be tracked. Dr. Jackwood’s lab routinely sequences the virus’ RNA from poultry all over the world, which helps pharmaceutical companies develop vaccines. Much like the influenza vaccine that U.S. residents are encouraged to receive annually, and which changes from year to year in response to the evolving flu strains that are in circulation, multiple IBD vaccines are available.
“There are a number of variant vaccines,” says Dr. Jackwood. “A vaccine that’s used in Georgia won’t necessarily be effective in Ohio. And it’s something researchers and pharmaceutical companies have to stay on top of, because mutations in the variant viruses cause enormous challenges to sustain the effectiveness of vaccines.”
Because the virus is so easy to spread, and so difficult to eradicate once present in a location, maternal immunity through vaccination is the central component of nationwide efforts to control IBD. For a small-scale producer, awareness and prevention are critical. By acquiring chicks only from facilities with vaccination records, being aware of the movements of people and machinery on the property, and being willing to partner with a veterinarian for a vaccination program should that become necessary, we can all benefit by keeping the damage caused by IBD to a minimum.