Although it is less than comforting to think about, all viruses mutate. Some - like influenza viruses - just do it faster than others.
So we shouldn’t be terribly surprised to learn that a rabid skunk that bit a woman in New Mexico last April turns out to have carried a new strain of rabies, likely acquired from a bat.
First the statement from the New Mexico Department of Health, after which I’ll return with a bit more on the diversity of rabies viruses in North America and around the world.
The New Mexico Department of Health (NMDOH) announced today that a rabid fox from Lincoln County that bit a woman on April 20 had a strain of rabies that has never before been identified. The genetic sequencing of the virus was done in the Rabies Laboratory at the Centers for Disease Control and Prevention (CDC) in Atlanta. The woman received a series of rabies vaccinations that has prevented her from developing rabies, which is usually fatal.
The “Fox Involved in Attack Tests Positive for Rabies” press release went out after initial testing on the fox at the NMDOH’s rabies laboratory was positive.
“We are working with the New Mexico Department of Game and Fish (NMDGF) and the CDC to increase surveillance in Lincoln County,” said Department of Health Cabinet Secretary Retta Ward, MPH. “We’ll be collecting dead foxes and bats found on the ground in Lincoln County and testing them for rabies. This new strain is related to other rabies strains found in bats.”
Children should be reminded that they should never touch a bat or other wild animal and that they should always report any contact with bats to their parents immediately. Rabies is fatal in humans but if you have been exposed to a rabid animal, it can be prevented with immediate treatment.
Although only one or two people die each year in the United States due to rabies, it remains a major killer around the globe, with the World Health Organization estimating that:
- Infection causes tens of thousands of deaths every year, mostly in Asia and Africa.
- 40% of people who are bitten by suspect rabid animals are children under 15 years of age.
- Dogs are the source of the vast majority of human rabies deaths.
- Immediate wound cleansing and immunization within a few hours after contact with a suspect rabid animal can prevent the onset of rabies and death.
- Every year, more than 15 million people worldwide receive a post-exposure vaccination to prevent the disease – this is estimated to prevent hundreds of thousands of rabies deaths annually.
With aggressive pet vaccination in the United States, dogs are no longer the most common route for exposure here. Instead, in the Eastern United States raccoons are the biggest risk, while in the Southwestern states skunks, foxes, coyotes are more likely to carry the virus.
Medscape’s excellent overview of Rabies by Sandra G Gompf, MD, FACP, FIDSA further explains:
The only rodent in the United States that can carry rabies long enough to transmit it to humans is the groundhog. Other small rodents (eg, squirrels, chipmunks, rats, mice) and lagomorphs (eg, rabbits, hares) usually die before being able to transmit rabies virus to humans, and human disease has not been documented from these mammals.
A bit surprisingly, American opossums are considered to be at low risk for carrying rabies, as their lower body temperatures inhibit virus replication. Who knew? The article also addresses the ability of the rabies virus to mutate and adapt:
Rabies continues to adapt to new hosts and evolve transmissibility in previously “dead-end” hosts. In Arizona 2001, a mutated bat strain was confirmed to have developed both pathogenicity and transmissibility in both foxes and skunks, which previously were not seriously affected or contagious upon infection. Human encroachments into natural areas, as in suburban development, have been associated with the spread of rabies strains in the past.
Rabies was undetected in terrestrial wildlife of northern Arizona until 2001, when rabies was diagnosed in 19 rabid skunks in Flagstaff. Laboratory analyses showed causative rabies viruses associated with bats, which indicated cross-species transmission of unprecedented magnitude. Public health infrastructure must be maintained to address emerging zoonotic diseases.
In 2009, 8 years after its discovery, the National Geographic carried a report (see New, Fast-Evolving Rabies Virus Found -- And Spreading) was still spreading passively among the skunk population in Flagstaff.
For more on all of this, including steps you can take to protect yourself and your pets, the Humane Society maintains an excellent resource on rabies (see Understanding Rabies), as does the CDC, which maintains an extensive Rabies Information Website.