Ebola, animals and emerging disease

It’s never good when the day’s big news stories are about an infectious disease. Of course, lately that disease has been Ebola. Ebola has not only killed a lot of people in West Africa, it’s contributed to the breakdown of healthcare and social structures there.

For all we hear about Ebola, we don’t hear much about where it came from in the first place. In reality, we’ll probably never know how the first Ebola victim became infected. Experts say the outbreak likely started from an animal-to-human encounter. The term for this is “zoonotic transmission”: disease transfer between animals and people. Like people, gorillas and chimpanzees can catch and die from Ebola. When people contact these diseased animals – such as using these animals for food – the virus can jump from one species to the other.

But if the chimps and gorillas die from Ebola, too, they really can’t be the reservoir (dependable source) for the virus. After all, if a virus kills all of its victims, it’s going to die out, too. In order for a nasty virus like Ebola to ensure its own survival, it needs to infect an animal in which it can survive long enough to be passed on. For Ebola, it appears that species is the fruit bat. Fruit bats are good “bridges” between species for several nasty animal and human diseases. They leave their viruses behind when they feed on fruit, and other animals become infected when they eat the leftovers.

The Ebola outbreak has shined a bright light on medical care disparities among the world’s countries. Our health care system and attention to infection control will prevent widespread transmission of the Ebola virus in our country. That’s important, because as long as there’s a large outbreak somewhere, we can expect cases from travelers to show up here.

This bleed over of Ebola into developed countries has demonstrated another interesting connection between the disease and animals. Last week, a nurse in Spain came down with Ebola after returning from West Africa. Immediately, her close contacts were placed under observation. But she had another important contact while she was sick – her pet dog. Health authorities put the dog to sleep due to the possibility that the dog might serve as a source of Ebola for other people.

Now it’s getting serious!

For animal rights activists, anyway. The outcry over the dog’s death sentence in some ways exceeded the concern for human Ebola victims. More than twice as many people signed an online petition to save the dog than signed one calling for fast-tracking a human Ebola vaccine!

It’s fascinating that a disease that started in wild animals in Africa has implications for a pet dog in Madrid – albeit with critical human implications connecting the two. It validates the idea that animal diseases are something we need to pay attention to.

There was no conclusive reason to put the dog to sleep, but it’s understandable that the authorities weren’t going to take any chances. We don’t know much about how Ebola might affect domestic animals. The only real study out there determined that about 25% of dogs found in the area of a previous outbreak had antibodies against Ebola. The dogs probably encountered the virus through eating wildlife that had died from Ebola, or potentially from licking body fluids that came from sick people.

Finding Ebola antibodies in a dog doesn’t mean the virus is still in the animal, however. Researchers did not find the Ebola virus in the dogs, nor were the dogs sick. One could argue that these positive-testing dogs successfully fought off the infection – something that most people can’t do.

These big knowledge gaps will persist. Understandably, Ebola in domestic animals would be problematic to research. SDSU likely will not have any “Ebola in cattle” experiments running any time soon!

No less than 75 percent of emerging human diseases originate in animals. Ebola is one of them. In our country we are fortunate to have a strong infrastructure of veterinarians and veterinary diagnostic labs, such as the one here at SDSU. We are better able than most to detect emerging issues in animals that could spill over into people. It’s critical that those resources stay ready and updated to nip the next big outbreak in the bud.

Russ Daly, DVM, is the Extension Veterinarian at South Dakota State University. He can be reached via e-mail at russell.daly@sdstate.edu or at 605-688-5171.