TWENTY-FOUR MILLION DEAD birds on over 120 farms across 13 states. US poultry banned in at least eight countries. Three governor-declared states of emergency. Right now, the United States is experiencing the worst avian influenza epidemic in its history, and all farmers can do about it, at least for the moment, is kill infected birds by the barn.
Government officials, to their credit, are looking beyond the present, scrambling to develop a vaccine that they hope can stop the virus in its tracks. But that may not be enough—and some experts, in fact, worry that vaccinating will only make things worse for the economic and physical health of America’s poultry industry.
The outbreaks of avian flu across the country are actually of two distinct varieties. The more virulent one, H5N2, emerged quietly, first showing up in a few backyard chickens near Boise, Idaho in January. But since March it has been throttling the Midwest, and on March 4 it was detected on a farm of 1.1 million birds in southern Minnesota. The USDA has been working on a vaccine for H5N2, and it will begin testing its effectiveness in live animals this month.
But bird flus mutate quickly—so quickly that they can outpace vaccines. Vaccines are de-clawed versions of viruses: harmless invaders that teach an immune system how to identify and attack the harmful virus. When that vaccine isn’t perfectly targeted, though, bits of virus can hang around. “When vaccinated birds do not have 100 percent immunity against a particular virus strain, the birds may still be able to infect others with the virus,” says Henry Wan, an influenza virologist at Mississippi State University.
A vaccinated chicken could even become a so-called silent carrier, able to pass along the virus without showing any symptoms. “Because it has some level of immunity, the bird will not show any clinical signs,” says Wan, “but it can still shed viruses.”
This becomes a bigger problem if the rate of vaccination isn’t high enough. If vaccinators don’t get enough of the poultry population, viral strains can get passed along into the environment. Endemic flus then become a persistent—and ever-evolving—threat to every new bird hatched or brought onto the farm. The viruses could become stronger and more diverse, turning vaccine development into a long-term game of whack-a-mole, in which the moles keep digging new holes, and each mallet only works once.
But flocks of vaccinated ghost carriers aren’t the only fear. There’s another, more economic problem: A vaccinated bird’s blood looks like an infected bird’s blood, at least to food safety officials in countries that are trade partners with the US. Without knowing for sure, nobody’s going to want to import the billions of American birds raised for overseas customers each year.
That problem arises because of the way vaccines work: Vaccines create the same antibodies as viruses. To a foreign quality control inspector doing a blood test, it makes it impossible to know whether a bird is infected or not. “You don’t want anything to mask the virus, so you can prove they are disease free,” says Carol Cardona, a veterinary viral disease specialist at the University of Minnesota.
This creates a catch-22. Which is better: A bird that’s unvaccinated? Or a vaccinated bird that foreign buyers don’t want because they can’t tell if it is vaccinated, or not yet showing symptoms for a deadly disease? Vaccines, in other words, could be worse for the poultry business than killing sick birds by the millions.
New vaccine methods could potentially circumvent both of these worries, though, says Cardona. Disease specialists can make vaccines that attack multiple viral strains. And administering the vaccines wouldn’t necessitate millions of needles going into chicken legs, little chicken band-aids, and mealworm-flavored suckers. Vaccines could be put into the water, feed, or even dusted onto a bird’s feathers. “Then the bird just ingests it when they preen,” says Cardona. As for the trade problem, novel vaccine methods are also capable of introducing marker proteins that can alert inspectors to a vaccinated—not viral—bird.
For now, though, there’s only one other way to stop a virus from spreading: Kill every last infected bird. (As humanely as possible. The American Veterinary Medical Association publishes guidelines on ethical animal euthanasia, aimed to reduce suffering.) Usually, the chickens or turkeys are gassed to death where they lived. “The idea is to keep them in that barn and, once the birds are dead, they compost the carcasses in that same building so they are reducing the spread,” says Cardona.
It’s a pretty symbiotic system: The decomposing bird bodies, turned over several times over the course of composting to even the rot, breed bacteria that kill off influenza viruses. Meanwhile, the barn is kept tightly locked, so foxes, flies, or rodents can’t sneak in for a meal and sneak out to spread the disease further.
That’s an OK system for now. Even though the mass cullings don’t seem to be slowing the spread of the virus between chickens, they’ll at least reduce exposure to humans—important, because even though the USDA says this bird flu outbreak poses no public health risk, that doesn’t mean people are immune. With enough exposure, H5N2 could evolve an affinity for humans, which is why farm workers who work closely with infected birds have been tested for disease markers and are being continuously monitored. In the absence of a vaccine, the USDA, state agriculture agencies, and individual farmers will continue to be exceptionally careful about keeping the virus contained. And if they fail? Well, the CDC is preparing a human vaccine, too.