Before this year, Ebola was a disease relegated to remote villages in Africa. Even public health officials did not worry about it spreading very far. Until recently, they would probably say that the virus typically burned out after ravaging only a handful of people. Then came 2014, a year that has, in many ways, rewritten the Ebola rulebook. We are in the middle of an unprecedented, nightmarish epidemic that has spread from a rural rainforest region in West Africa to large urban centers. Infected persons travelling from West Africa have now spread the disease to Europe and the US, inciting global concern. Tragically, politicians in the US are not working together to allay the public’s fears or collectively responding to Ebola by strengthening African laboratory facilities and sending staff with more expertise. Instead, the politicians have treated the Ebola outbreak and its potential to spread to the US as a political football. The press loves it and sadly, dogs have become the latest hot media issue.
Why dogs? The Spanish government, against the owner’s wishes recently euthanised a pet dog named Excalibur who belonged to an infected nurse. The nurse tested positive for Ebola virus after caring for an infected priest flown from the West African region for treatment in a Madrid hospital. The Madrid regional government obtained a court order to euthanise the pet dog, saying, “Available scientific information cannot rule out a risk of contagion.” The alternative of quarantine was not considered.
While media reports may be inflammatory and challenge pet ownership, there have been no scientific reports indicating that Ebola virus has been isolated from, or directly transmitted by dogs. As the virus inevitably spreads into more developed regions, we are likely to see increasing concern and media interest on the role of dogs in the transmission of this disease. Concern is so great among pet owners in the US that the Veterinary Information recently published a three-page Veterinary Considerations for Ebola Virus Outbreaks clinical use sheet so veterinarians could calm concerned owners(1).
The scientific evidence for dogs as a carrier of Ebola virus comes from a 2005 report(2) made during the 2001–2002 outbreak in Gabon. Several dogs were highly exposed to Ebola virus by eating infected dead animals. To examine whether these animals became infected, researchers sampled and screened 439 dogs for Ebola virus using specific immunoglobulin-G assay, antigen detection, and viral polymerase chain reaction amplification. Among dogs from villages with both infected animal carcasses and human cases, seroprevalence was 31.8%. The authors of the study suggested that Ebola virus can infect dogs and that the putative infection is symptomatic. However, no circulating Ebola antigens or viral DNA sequences (tested by PCR) were detected in either positive or negative serum specimens, and attempts to isolate virus from these samples failed. These findings indicated either old, transient Ebola infection of the tested dogs, or antigenic stimulation. Clinical signs did not develop in any of the dogs during the outbreak, a finding that tends to support antigenic stimulation, or very mild Ebola virus infection.
Reporters and some scientists are saying that although dogs can be asymptomatically infected, they may excrete infectious viral particles in urine, feces, and saliva for a short period before virus clearance, as observed experimentally in other animals. Given the frequency of contact between humans and domestic dogs, canine Ebola infection must be considered as a potential risk factor for human infection and virus spread. Human infection could occur through licking, biting, or grooming. Hence, dogs should be taken into consideration during the management of human Ebola outbreaks. But to confirm the potential human risk of Ebola virus–infected dogs, the mechanisms of viral excretion (i.e. body fluids and virus kinetics of excretion) must be investigated during experimental canine infection. Such research would also offer insights into the natural resistance of dogs. It is waiting to be done.
In times of public health crisis, authorities often feel pressured to take actions, whether or not they are evidence-based. In response to this cynophobia CDC Director Tom Frieden has stated, “There is one article in the medical literature that discusses the presence of antibodies to Ebola in dogs. Whether that was an accurate test and whether that was relevant we do not know” and “We have not identified this as a means of transmission,” although scientists do know that Ebola can infect mammals and the virus can spread that way(3). Michael San Filippo, senior media relations specialist for the AVMA has stated, “There are no documented cases of dogs passing the Ebola virus on to people – there is more concern about fruit bats and non-human primates.”
Some epidemiologists have suggested questioning whether the Personal Protective Equipment (PPE) guidelines are wrong, or reviewing the belief about fixed modes of transmission of Ebola. Although some doctors have assumed failures in donning and doffing of PPE as a cause of transmission to health workers(4), it is speculation and not based on evidence. Several American nurses reported that they followed strict protocols, yet contracted Ebola(5). The tragedy of Excalibur is that authorities did not even test him for Ebola before his euthanasia.
This is not the first time dogs have been used by authorities in a time of public health crisis. The Washington Post reported that in 1979, the worst recorded anthrax accident occurred in the Soviet bioweapons facility in Sverdlovsk. A failure to replace an air filter resulted in the accidental release of large quantities of weaponised anthrax into the nearby community, killing at least 66 people, probably more. In response, Soviet authorities blamed contaminated meat and dogs, closed down markets, and rounded up and shot stray dogs(6).
REFERENCES
1 Davis R, Weese JS. Veterinary considerations for Ebola virus outbreaks: Veterinary Information Network, 2014.
2 Allela L, Boury O, Pouillot R, et al. Ebola virus antibody prevalence in dogs and human risk. Emerg Infect Dis 2005;11:385-390.
3 CDC Newsroom. CDC Telebriefing: CDC update on first Ebola case diagnosed in the United States, 10-07-2014. Press Briefing Transcript: Centers for Disease Control and Prevention, 2014.
4 Cohen J. Infectious diseases. When Ebola protection fails. Science 2014;346:17-18.
5 Fischer WA, Hynes NA, Perl TM. Protecting health care workers from Ebola: Personal protective equipment is critical but is not enough. Ann Intern Med 2014.
6 Hoffman D. Wastes of war: A puzzle of epidemic proportions. The Washington Post. Dec 16 ed. Washington, D.C. Publisher: Graham, Donald E. 1998.