Does every animal have its own kind of flu, or is it just swine and birds?

Answers to your questions about the news.
April 27 2009 7:05 PM

Does Every Animal Have Its Own Kind of Flu?

No, but whales and seals do.

Click here to read more from Slate on the swine flu. 

Sick pets. Click image to expand.
Can all animals catch the flu?

The Department of Homeland Security has declared the swine flu a public-health emergency. Avian influenza remains active in Africa, Asia, and Europe. So pigs and birds each have their own form of influenza. Can all species get the flu?

Many other animals do contract influenza from time to time, but in most species it tends to die off quickly. Pigs, birds, humans, horses, and a few marine mammals like whales and seals have developed and sustained their own unique strains of the flu. In general, scientists won't label a strain as host-specific until most cases result from intraspecies transmission and the virus spans more than one generation of the host animal.

Advertisement

Birds are known to carry every single one of the 144 varieties of influenza virus, as defined by the shape of their surface proteins (ranging from the H1N1 strain to H16N9). For this reason, most scientists believe that all forms of the virus originated in birds and every flu is on some level a kind of bird flu.

Human, swine, and other host-specific strains are merely mutated avian strains that managed to infect a new kind of animal and spread across several generations. For the source virus to jump hosts, it would have to evolve a slightly different shape to its surface proteins, making them capable of binding to novel cell receptors. (This change usually does not represent an entirely different protein structure—i.e., the strain won't change from H1 to H2—but rather involves a shift of just a few molecules.)

Pigs happen to serve as efficient way stations for the transfer of influenza from birds to humans. That's because they have some bird-shaped cell receptors and some human-shaped cell receptors. An avian influenza strain can infect a pig without too much rearranging and then evolve the ability to infect humans. In addition, the same pig can harbor both human and avian flu. If the two strains exchange the right genetic information, they might produce a more versatile and dangerous offspring.

Mutation and infection alone are not sufficient to launch a species-specific strain of influenza. The new viral strain must be exposed to the new host species, and then it must keep spreading to more individuals before either the virus or host dies. For most species, those are pretty long odds. Avian influenza has infected cats, ferrets, and possibly dogs, but none of these mutant strains has survived long enough to be classified as a new, species-specific disease.

So why did the virus persist in humans, pigs, and birds? No one knows for sure, but humans and pigs tend to live in very close quarters. The survival of influenza among birds has two likely causes. First, most strains of avian influenza do not make their host sick, so the virus has plenty of time to evolve and be transmitted. Second, influenza survives quite well in cold water. When migratory birds settle briefly into small ponds, they leave the virus for the next set of travelers. Under these conditions, the disease spreads very easily.

Got a question about today's news? Ask the Explainer.

Explainer thanks David Swayne of the U.S. Department of Agriculture and Gary Whittaker of the Cornell University College of Veterinary Medicine.

TODAY IN SLATE

Jurisprudence

Scalia’s Liberal Streak

The conservative justice’s most brilliant—and surprisingly progressive—moments on the bench.

Colorado Is Ground Zero for the Fight Over Female Voters

There’s a Way to Keep Ex-Cons Out of Prison That Pays for Itself. Why Don’t More States Use It?

The NFL Explains How It Sees “the Role of the Female”

The Music Industry Is Ignoring Some of the Best Black Women Singing R&B

Culturebox

Theo’s Joint and Vanessa’s Whiskey

No sitcom did the “Very Special Episode” as well as The Cosby Show.

Television

The Other Huxtable Effect

Thirty years ago, The Cosby Show gave us one of TV’s great feminists.

Cliff Huxtable Explains the World: Five Lessons From TV’s Greatest Dad

Why Television Needs a New Cosby Show Right Now

  News & Politics
Weigel
Sept. 18 2014 8:20 PM A Clever Attempt at Explaining Away a Vote Against the Farm Bill
  Business
Moneybox
Sept. 18 2014 6:02 PM A Chinese Company Just Announced the Biggest IPO in U.S. History
  Life
The Slate Quiz
Sept. 18 2014 11:44 PM Play the Slate News Quiz With Jeopardy! superchampion Ken Jennings.
  Double X
Doublex
Sept. 18 2014 8:07 PM Crying Rape False rape accusations exist, and they are a serious problem.
  Slate Plus
Behind the Scenes
Sept. 18 2014 1:23 PM “It’s Not Every Day That You Can Beat the World Champion” An exclusive interview with chess grandmaster Fabiano Caruana.
  Arts
Brow Beat
Sept. 18 2014 4:33 PM The Top 5 Dadsplaining Moments From The Cosby Show
  Technology
Future Tense
Sept. 18 2014 6:48 PM By 2100 the World's Population Could Be 11 Billion
  Health & Science
Science
Sept. 18 2014 3:35 PM Do People Still Die of Rabies? And how do you know if an animal is rabid?
  Sports
Sports Nut
Sept. 18 2014 11:42 AM Grandmaster Clash One of the most amazing feats in chess history just happened, and no one noticed.