Image: microscopic view of the rabies virus
Rabies: Rabies Virus is a zoonotic Lyssavirus, transmitted when the saliva of an infected mammal comes in direct contact with another mammal. Typically a scratch or a bite, but can also be via mucous membranes in the eyes, nose, or mouth (Center for Disease Control and Prevention, 2019). Prior to 1960, the most common reservoir was canines, but now in the U.S. it is mostly found in different wildlife species, including bats, raccoons, skunks and foxes. However, outside of the U.S. many dogs still carry the disease (Pieracci, E. G., Pearson, C. M., Wallace, R. M., Blanton, J. D., Whitehouse, E.R., Xiaoyue Ma, Stauffer, K., Chipman, R. B., Olson, V., & Ma, X. 2019).
Right Image: Infected dog bite
The Viral Pathway: The virus first infects muscle, then moves via the nerves to the spinal cord and brain. During this time, called the incubation period, the mammal will not show symptoms and it could range from weeks to months, often depending on the strain of the virus, any prior immunity, and the location of the exposure site. Once the virus reaches the brain, it multiplies and causes in inflammation, this is when symptoms appear. The virus then moves from the brain to the salivary glands and saliva. At this point, symptoms continue, worsen, and the mammal is now a threat to others because the virus is in their saliva and can be transmitted. Three or five days after the inflammation begins, the virus has typically caused enough brain damage that the signs of rabies are obvious. The infected mammal typically dies after about seven days of being ill (Center for Disease Control and Prevention 2019).
Image: Scientists studying images of the rabies virus
Symptoms: In the first couple of days after the incubation period for a human, the symptoms may seem like those of the flu, such as headache, general weakness, discomfort, or fever. Other symptoms include itching, discomfort, or a prickling sensation at the exposure site and eventually more neurological symptoms that are associated with cerebral dysfunction. These include anxiety, confusion, and agitation. Eventually, the person will experience delirium, hallucinations, hydrophobia, and insomnia (Center for Disease Control and Prevention 2019)
Image: An infected patient
Mortality: Rabies causes about 59,000 deaths worldwide, including about two in the U.S. every year. The canine rabies virus variant was responsible for 98% of these cases. Major outbreaks of this virus are rare and the canine rabies virus variant (CRVV) was eliminated, but Rabies is so fast acting and deadly that it has 99% mortality rate. Once symptoms begin to appear, there is no known successful treatment. The only treatment available for Rabies is post exposure prophylaxis (PEP), which must be administered quickly after contact in order to be effective (Pieracci, E. G., Pearson, C. M., Wallace, R. M., Blanton, J. D., Whitehouse, E.R., Xiaoyue Ma, Stauffer, K., Chipman, R. B., Olson, V., & Ma, X. 2019). As of 2019, there were only 20 documented cases of human survival from clinical rabies, and very few survived with no form of prophylaxis (Center for Disease Control and Prevention 2019).
Image: An infected patient
Vaccines: The first attempt at immunization for rabies was done by Pierre- Victor Galtier, who experimented with intravenous inoculation of the rabies virus on dogs. Louis Pasteur, however, who tested the us of an attenuated version of the virus for vaccination purposes on rabbits. The original version of the vaccine involved daily injections to the spinal cord. This resulted in difficult maintenance of spinal cords at different times of desiccation, and the occasional paralysis as a result of the high concentration of myelin. In addition there were incidences where vaccine recipients developed rabies (Tsiang, H. 1998). The vaccine was then tested on dogs and eventually humans in 1885, first with Joseph Meister, a nine-year-old boy, during the incubation period after he was bit by a rabid dog (Offord 2016). The original version of the vaccine involved daily injections to the spinal cord. This resulted in difficult maintenance of spinal cords at different times of desiccation, and the occasional paralysis as a result of the high concentration of myelin. In addition there were incidences where vaccine recipients developed rabies (Tsiang, H. 1998).
Image: The Pasteur Institute in India during the production of the rabies vaccine: caged rabbits showing symptoms after inoculation
Prevention: During the early 20th century CRVV was enzootic in the U.S. Government intervention began in 1947 with the introduction of animal vaccination and leash control laws. Rates of CRVV continued to fall throughout the 20th century, and in 2004, CRVV was eliminated with the help of new parenteral and oral rabies vaccines. With proper precautions, funding, and education, people are better equipped to protect themselves from the virus and seek out and access treatment when necessary. From 1960 to 2018, there was only 125 reported cases of rabies in humans in the U.S. (Pieracci, E. G., Pearson, C. M., Wallace, R. M., Blanton, J. D., Whitehouse, E.R., Xiaoyue Ma, Stauffer, K., Chipman, R. B., Olson, V., & Ma, X. 2019).
Image: Rabid dog barking
Threat Level: Rabies Virus remains a threat to humans because of its increasing presence in wildlife, especially during travel. Rabies in raccoons spread from Alabama to Maine beginning in the late 1970s, this spread caused the largest epizootic of animal rabies in U.S. history and increased human exposure. An oral rabies vaccine has helped to limit the spread of raccoon rabies. However, in areas without oral vaccination, 75% of rabies cases in mammals in the U.S. are in raccoons. In areas where both raccoon and bat rabies occur, human rabies exposures are 6 times more common (Pieracci, E. G., Pearson, C. M., Wallace, R. M., Blanton, J. D., Whitehouse, E.R., Xiaoyue Ma, Stauffer, K., Chipman, R. B., Olson, V., & Ma, X. 2019). Rabies is also more common in rural and poor communities, with about half of all cases being in children younger than 15 (Rabies: Epidemiology and burden of disease 2020).
International Presence: Canine rabies is no longer present in Western Europe, Canada, the U.S., Japan, and some Latin American countries, and it was never found in Australia and many pacific island nations. On the other hand, approximately 95% of the annual cases occurs in Africa and Asia. Asia has an estimated 35,172 human deaths per year, India alone being responsible for 35% of international deaths, and Africa has around 21,476 human deaths per year due to canine rabies. However, it is likely that these numbers are inaccurate due to underreporting (Rabies: Epidemiology and burden of disease 2020).
Top Image: number of human deaths from dog-transmitted rabies
Bottom Image: deaths per capita from dog-transmitted rabies
Credits:
Photo credits can be found on the attached References page.