If you’re like me and watched Old Yeller on repeat as a child (and as in “repeat” I mean walk to the TV and take the 3 minutes to rewind the VCR tape to re-watch), then you learned two important lessons early in life: (1.) avoid wild hogs at all costs and (2.) rabies can be a real threat that is horrifying on many different levels.
In rural Texas in the 1860s where the movie plot is set, rabies was still a prominent threat in America. In several scenes throughout the movie, we note peoples’ various warnings of the “hydrophobia” epidemic in nearby wildlife and even watched as one of the family’s cows suffered from a rabies infection due to a wildlife encounter. The virus was, indeed, extensive throughout wildlife populations, thereby affecting humans and domesticated animals before prevention campaigns took place in the mid-20th century in America.
Rabies is characterized as an infectious, zoonotic (spread between animals and humans), viral pathogen that targets the central nervous system of the body and, if left untreated, is fatal in almost 100% of cases. Although rabies can infect all mammals, bats, raccoons, skunks, foxes, and even mongooses in Puerto Rico have been found to serve as key reservoirs of rabies variants. In warm-blooded hosts, rabies induces acute progressive encephalitis (without swift medical attention in humans), which is what will ultimately kill the host. The signs and symptoms may not appear for up to weeks or even months, with the incubation period of rabies varying greatly. There has even been one documented/confirmed case of a patient not exhibiting symptoms until 7 years after exposure to the virus!
Fig. 1 – The critters above (foxes, bats, skunks, and raccoons) all serve as primary reservoirs for slightly differentiated variants of the rabies virus. Although cross-species transmission certainly occurs (an example being raccoons rabies variant infecting canines) the variants are primarily transmitted within a single species that is the reservoir of that variant. cdc.gov
Symptoms of infection can be nonspecific in the beginning including lethargy, fever, vomiting, and anorexia in animals. However, within days the neurotropic virus progresses to cerebral dysfunction, cranial nerve dysfunction, ataxia, weakness, paralysis, seizures, difficulty breathing, difficulty swallowing, excessive salivation, abnormal behavior, aggression, and/or self-mutilation. I, personally, am astounded at the pathogenicity of the virus, ultimately compelling its host to spread the disease by modifying its behavior, becoming far more aggressive and fearless.
The virus is transmitted through direct contact from an infected animal. Examples of this direct contact include exposure through a bite or scratch from a rabid animal, or through mucous membranes or open wounds coming into contact with the saliva or nervous system tissue from an infected animal. The virus, however, cannot withstand exposure outside the body and is considered to be noninfectious after drying out or coming into contact with sunlight.
According to the CDC, wild animals account for 91% of reported rabies cases in 2017, with bats as the most frequently reported rabid animal having been reported in all states except Hawaii. Nevertheless, it should be noted that the vast majority of the bat population in America (94%) is uninfected.
Getting back to Old Yeller, the movie realistically depicted how before the mid-20th century rabies was a widespread concern for humans and their domesticated animals. It was common for dogs to transmit the disease from contact with rabid wild animals – that is until the early 1940s, when mass vaccination campaigns were employed in the U.S. and continued through to the 70s along with the implementation of strict leash laws for canine pets. Together, this yielded a significant decrease in dog and human rabies cases. Today, the U.S. is considered canine rabies virus variant free. This elimination is still considered one of the greatest public health achievements in the U.S. of the last century, only having 1-3 human cases of rabies per year as opposed to 30-50 human cases per year as seen in the early 20th century.
Although we have successfully observed a decrease in domestic animal rabies cases, wildlife rabies cases have reportedly increased significantly. However, this could be due to better detection capabilities (improved surveillance and laboratory testing) or perhaps, increased human contact with wild animals. Currently, one of the ongoing hurdles research scientists face concerning the study of rabies is that, despite the availability of numerous animal models, the findings seen in vitro with laboratory strains of the virus do not reflect in vivo findings with wild-type strain. Furthermore, widespread vaccination of some wild animals, such as bats, is currently not feasible. Although, in encouraging news, the CDC has recently developed a new rabies rapid test for animal and human cases, allowing potentially infected patients to forgo the usually necessary 4-week regiment of shots for people or euthanasia/isolation in negative animal cases. The LN34 test produces extremely accurate results that can be easily utilized with already existing testing platforms and even foreign countries without the need for specific training.
In, no doubt, one of the most heartbreaking and dramatic scenes in cinematic history (I will argue this with anyone), Old Yeller is bitten while protecting the family from a rabid wolf and isolated by the family to monitor if rabies symptoms arise. Sadly enough, Old Yeller began to exhibit symptoms of aggression and poor Travis realized he had no choice but to put down his beloved dog. Unfortunately, modern day treatment for pets (rabies post-exposure prophylactic is only for human use and very expensive) is not so different from what Travis was subjected to. Previously vaccinated pets can be re-vaccinated and observed for 45 days. However, animals already showing rabies symptoms must be euthanized immediately, reported, and tissues submitted for testing.
I’d like to end this on a positive note, though…and we have good reason to. Thankfully, due to the elimination efforts of the past century, rabies is already a considerably reduced concern for the wellbeing of ourselves, livestock, pets, and hopefully in the near future for wildlife populations. According to the USDA, “every year, federal, state, and local governments in our country distribute more than 10 million oral rabies vaccine (ORV) baits to reduce wildlife rabies and prevent disease transmission to humans, domestic animals, and pets”. These efforts to one day eliminate wildlife rabies variants is well worth the money being spent, with rabies associated costs totaling hundreds of millions of dollars in things like public health investigations, animal rabies tests, pre- or post-exposure prophylaxis, pet and livestock vaccinations, and public education efforts. Although America’s control of rabies is vastly improved, keep in mind that about 38,000 people still receive prophylactic treatments annually, resulting in over $150 million in health care costs.
So with all this information on rabies, I recommend you first, make sure all your pets are vaccinated, then watch *and sing along to* the best theme song to any movie ever made.
Sources and Supplemental Information
Berger, Franck & Desplanches, Noëlle & Baillargeaux, Sylvie & Joubert, Michel & Miller, Manuelle & Ribadeau Dumas, Florence & Spiegel, André & Bourhy, Hervé. (2013). Rabies Risk: Difficulties Encountered during Management of Grouped Cases of Bat Bites in 2 Isolated Villages in French Guiana. PLoS neglected tropical diseases. 7. e2258. 10.1371/journal.pntd.0002258.
Dyer, Jessie & Yager, Pamela & Orciari, Lillian & Greenberg, Lauren & Wallace, Ryan & Hanlon, Cathleen & Blanton, Jesse. (2014). Rabies surveillance in the United States during 2013. Journal of the American Veterinary Medical Association. 245. 1111-1123. 10.2460/javma.245.10.1111.
Mahadevan, Anita & Sukumaran, Suja & Mani, Reeta & Shankar, Susarala. (2016). Perspectives in Diagnosis and Treatment of Rabies Viral Encephalitis: Insights from Pathogenesis. Neurotherapeutics. 13. 10.1007/s13311-016-0452-4.
Velasco-Villa, Andrés & Mauldin, Matthew & Shi, Mang & Escobar, Luis E. & Gallardo-Romero, Nadia & Damon, Inger & Olson, Victoria & Streicker, Daniel & Emerson, Ginny. (2017).
https://www.cdc.gov/rabies/index.html
Thank you, science 