Ebola: Dogs as Vectors

Animal lovers expressed outrage Oct. 8 as health officials in Spain made good on their pledge to euthanize the 12-year-old pet dog of a woman known to have the Ebola virus. They questioned whether a dog could spread the virus and accused the authorities of acting cruelly and irrationally.

But a research study published in Emerging Infectious Diseases in 2005 suggested that dog-to-human transmission could happen. The study documented that many dogs in Africa that lived in neighborhoods where Ebola was prevalent showed signs they were carrying the virus.

The CDC supplied the Ebola tests for that research.

Tom Frieden, MD director of the US Centers for Disease Control and Prevention (CDC) alluded to the study in a question-and-answer session held Oct.8 on Twitter.

Asked whether dogs could be vectors of the disease, Frieden said that while “There are no reports of dog to human transmission” the CDC is concerned about the possibility. The CDC is working with the American Veterinary Medicine Association and the US Department of Agriculture to set up guidelines, he said. There are currenly no rules on how potentially exposed pets should be treated and whether any recommendations on how to handle exposed pets should figure in disease-prevention strategies.

Along with Texas health authorities, the CDC is on high alert for new Ebola cases, following the death in a Dallas hospital Oct. 8 of Thomas Eric Duncan, a man from Monrovia, Liberia, who died in a Dallas hospital. His was the first documented case of Ebola developing in the US--though he was infected in Liberia

In the journal report, Lois Allela and colleagues in Gabon, with support from the French government, studied dogs living in the Gabon region during the 2001-2002 Ebola outbreak. They sampled 258 dogs and screened them by using an immunoglobulin G assay and viral polymerase chain reaction amplification.

Overall they found that in dogs from villages with both infected animal carcasses and human cases, 31.8% of the animals showed seroprevalence as did 15.4% of the dogs living in villages with human cases but no observed infected carcasses. (Testing of a control group of 102 dogs in France turned up two cases of seroprevalence but the researchers said those results were likely false positives.)

The team said the dogs in Gabon had likely acquired the virus by eating the carcasses of other animals that were infected.

“The dogs are not fed and have to scavenge for their food,” Allela wrote. Dogs might also have contracted Ebola by licking up the vomit of Ebola patients. The dogs that tested positive did not develop Ebola symptoms—unlike primates exposed to the virus. That suggests they had mild cases, Allela wrote.

Dog-to-human Ebola transmission was not directly documented, but could explain how some villagers who contracted the virus had no known contact with other patients, the researcher wrote.

“Dogs may excrete infectious viral particles in urine, feces, and saliva for a short period before virus clearance,” the team wrote, “canine Ebola infection must be considered as a potential risk factor for human infection and virus spread,” through pets’ typical interactions with their owners, like licking and grooming.

So far, in Dallas, animal transmission is not a big concern. According to Texas state health officials, the family Duncan was visiting in Dallas did not have a dog.

But the virus has been known to leap to humans from other species.

Belgian researchers who first documented Ebola in 1976 in what was then the Belgian Congo said it likely came from fruit bats. The virus is named after a river in the Democratic Republic of the Congo.