Should We Euthanize Animals That May Have Ebola?

In Spain, when a nurse contracted Ebola, the authorities made the decision to euthanize her dog.

However, they did it based on this research paper, that has faulty reasoning in it. In it, the researchers tested the blood of a good sized sample of dogs for Ebola antigens (the things your body makes to fight a disease). They found that dogs do not show symptoms of Ebola but do produce antigens  - as do some other animals such as goats, horses, and guinea pigs. (Monkeys and pigs show symptoms.) They did this study because some humans had come down with Ebola without contacting a known source of it.

Here is where the reasoning is faulty: They concluded that because 27% of the infected village dogs (as compared to 22% of village dogs from areas without infection) had antigens they must be the source of infecting humans even though they do not show symptoms. To date, the only known animals that infected humans have been bats, pigs, and monkeys but others are suspected. These infected humans when the people came in contact with the blood of the animal - either by eating them, butchering them, or by dissecting them. If is also possible that humans can get Ebola from proximity - caring for infected caged, symptomatic animals on a daily basis, but exactly how much interaction is needed for infection is unknown.

The thing is - humans can also get Ebola and be asymptomatic. One small study found 45% of humans have antigens after being exposed to Ebola (another had a rate of 19%). (Ironically, the dog study researchers called this percentage "very rare.") In theory, that means these people get it but don't show signs of it. The dog study concluded that these humans could not be a source of Ebola for other humans, but the 5% increase in dogs in infected villages could be.

This study would have been more beneficial if the researchers had tested the humans for Ebola in the villages as well. If asymptomatic humans (those with antigens) were found to be in similar proportions in both villages - this could indicate that the increase in asymptomatic dogs was contributing to the outbreak. It would also have proven that a previous outbreak had visited the uninfected village. However, if more than 5% of the humans in the infected village had antigens - I would look at them as a source.

We know that humans who recover from the disease can still transmit it for 90 days in semen, breast milk, and blood- however, we have never tested asymptomatic patients to see if they shed the virus through any of these routes. In addition, the dog researchers never tested the dog's urine/ feces/ saliva to see if they shed the virus through these means.

In short - studying the dogs to see if, when, and how they excrete the virus would be far more beneficial than just killing them. More importantly, instead of just quarantining patients contacts and monitoring them for fever - they should also be asked to participate in studies. We need more accurate numbers of asymptomatic humans and we need to know if they are also infectious for 3 months. In the end, I think researchers will discover quarantine - not death - is an acceptable option.