1. Rabies: effect, mechanism, and treatment
By: Avinash Sankar, Julia White, Cameron Ho, and Victoria Trinh
PHM142
October 1, 2019
PHM Fall 2019
Instructor: Chesa Dojo Soeandy
Coordinator: Jeffrey Henderson

2. What is Rabies?
An infection caused by the rabies virus transmitted zoonotically
It is transmitted through direct contact with saliva or CNS tissue from an infected animal
It affects the brain and spinal cord of mammals, including humans
It is nearly always deadly if not treated before symptoms begin
Cameron
Rabies is an infection caused by the rabies virus transmitted zoonotically, meaning it is transmitted by animals
The rabies virus is transmitted through direct contact (through broken skin or mucous membranes in the eyes, nose, or mouth) with saliva or brain/nervous system tissue from an infected animal.
It affects the brain and spinal cord (the CNS) of mammals, including humans which will be the main focus of this lecture
It is nearly always deadly if not treated before symptoms begin
People usually get rabies when a rabid animal bites them. People in Canada and the U.S. are most likely to get rabies from bats
Also a neat fact: rabies is referred to as hydrophobia as those infected are scared of water

3. Structure of the Rabies Virus
Cameron
The rabies virus is a rod-shaped, single-stranded, enveloped RNA virus. The virus genome encodes five proteins: G, L, M, N, and P protein.
Source-h-t-t-p-s-d-o-k-u-w-i-k-i_fig2_
Pal, 2017

4. Stages of Rabies Progression
Incubation
Prodrome
Acute neurologic period
Coma
Death
Cameron
There are 5 stages of the progression of the rabies disease: incubation, prodrome, acute neurologic period, coma, and death.

5. Avinash

6. Incubation
Long duration (~2 months)and high variability (week to years)
Dependence on various factors such as location of bite relative to
CNS, amount of virus inoculated and innervation of bite site
Pain around site
General symptoms (fever, headache, numbness and tingling sensations)
Avinash
The incubation period of the virus, which is the time it takes between exposure to the virus and the first symptoms of the disease, is quite long. On average, it is about two months but it could take up to several years, the virus will normally enter the muscle first before travelling through the nervous system. If you are bitten by an animal in the incubation stage there is no infection.
All dependent on when the virus can travel from the bite site, bypassing peripheral nerves reaching its ultimate target in the brain
1-2 cm/day
Shorter incubation period if bitten closer to the CNS
Dependence on factors such as how close the bite is to the CNS and the severity determined by degree of innervation and amount of virus
General symptoms such as fever, headache, tingling around the bite area, pain as initial symptoms

7. Prodromal Phase and Symptoms
First presence of clinical symptoms
Fatigue, malaise, vomiting, diarrhea, nausea, insomnia among others
Indicates it is too late for any rabies vaccinations
Virus has migrated from the muscles of the injury site to peripheral nerves and toward CNS (spinal cord and brain)
Avinash
These symptoms are often nonspecific (general malaise, fever, and fatigue) or suggest involvement of the respiratory system (sore throat, cough, and dyspnea), gastrointestinal system (anorexia, dysphagia, nausea, vomiting, abdominal pain, and diarrhea), or central nervous systems (headache, vertigo, anxiety, apprehension, irritability, and nervousness). More remarkable abnormalities (agitation, photophobia, priapism, increased libido, insomnia, nightmares, and depression) may also occur, suggesting encephalitis, psychiatric disturbances, or brain conditions.
Presence of clinical symptoms, nonspecific
Virus has infiltrated areas of the CNS such as the spinal cord and more importantly the brain
Lasts a little over a week
General symptoms such as fatigue, malaise, vomiting, diarrhea, insomnia, nausea, anxiety
Once the clinical symptoms appear, it is too late for vaccination
Pain or paresthesia at site of bite

8. Acute Neurological Period
CNS Dysfunction
“Furious Rabies” - 80% of cases characterized by hyperactivity, aggressive behavior, hypersalivation, hyperventilation, seizure activity
“Paralytic Rabies” - starting from bite location, progressive muscle weakness and paralysis is spread over the body
Hydrophobia - inability to swallow fluids resulting in fear of drinking
Major brain inflammation resulting in irregular breathing and coma
Inevitable death by cardiac or respiratory arrest
Avinash
CNS Dysfunction, Ends in coma and subsequent death, Hyperactivity, excessive salivation
Hydrophobia, inability to swallow and afraid of drinking fluids
Infects neurons used in respiration and swallowing, which affects the respiratory and pre swallowing cycle
Affects the central pattern generator neural network
Photophobia, hallucinations, seizures, aggression, hyperventilation
Spasms of the muscles in the throat and larynx occur because rabies affects the area in the brain that controls swallowing, speaking, and breathing
Furious Rabies
80% of cases
Hyperstimulation, hyperactivity, violent physical symptoms
Come and go effect, instances of calmness between these furious episodes
Paralytic Rabies
20 percent of individuals
Gradually weakened muscles especially around area of the bite, Starts from location of bite and gradual paralysis ensues
Develops over much longer timeframe
Coma and Death
Late in the disease, after the virus has reached the brain and multiplied there to cause an inflammation of the brain, it moves from the brain to the salivary glands and saliva.
Rabies virus eventually concludes with severe inflammation in the brain and Rapid and shallow breathing
Results in death usually by respiratory or cardiac arrest

9. Robertson K, Johnson K, et al. 2012
Virus is transmitted through the saliva of a rabies infected animal mostly via bite
The virus can then either move directly to peripheral nerves or replicate in the nearby skeletal muscle and move through the
NMJ to gain access to the peripheral nerves
It can then move retrogradely up the axons in the spinal cord until it replicates and infects the ventral horn neurons or the dorsal root ganglia
From here it will rapidly spread to the CNS and brain causing rapid nervous system dysfunction and spreading to peripheral sites such as
The salivary glands by the cranial nerves
The rabies antigen is localized to areas with rich cholinergic innervation, such as cerebral cortex and limbic structures, including amygdala, hippocampus, thalamus, hypothalamus, and basal ganglia, as seen in in vivo studies in experimental animals, confirms its cholinergic affinity.
Robertson K, Johnson K, et al. 2012

10. Mechanism: Biochemistry
The virus will replicate locally then move through the neuromuscular junction to the unmyelinated nerve.
The nicotinic acetylcholine receptors (nAChR) play a major role in the uptake of rabies into the nerve.
Julia
Rabies virus will then undergo axoplasmic transport towards the cell body. Then it gets into the cell body and replicates.
Historically, the nAChR was the first-identified receptor for viral entry at the neuromuscular junctions. Antagonist of the nAChR are points of interest of research into preventing the rabies virus spread. Travel to the CNS via the peripheral axons occurs at a fairly constant rate of 12 to 24 mm per day
Rabies may also enter by binding to p75NTR which results in both being taken into the body of the nerve
Fisher C., et al. 2018

11. CDC 2019
The virus attaches to the cell using G protein coupled receptors. After adsorption, the virus penetrates the host cell and enters the cytoplasm by pinocytosis Then the primary transcription of five complementary messenger proteins. After viral proteins have been synthesized, replication of the genomic RNA continues with the synthesis of full length, positive-stranded RNA, which acts as a template for the production of negative-stranded RNA.

12. Diagnosis General diagnosis
If there is a history of an animal bite, and signs and symptoms have appeared, then diagnosis is simple
However, rabies’ symptoms are very general and are similar to other infectious and noninfectious disease
Laboratory diagnosis
Perform a direct immunofluorescence test on a skip biopsy for evidence of the rabies antigen
Isolate the virus from saliva after inoculation of neuroblastoma cells
Perform a rapid fluorescent focus inhibition test (RFFIT) in the serum of an unvaccinated person
Diagnosis of a person with rabies is very important since, as mentioned previously, once symptoms appear the result is most likely death.
Diagnosis is only simple if the patient is aware that they were bitten.
However, early on in the progression, rabies mimics other infectious or non-infectious diseases, and therefore it is a bit harder and may require a laboratory test
One option is to use a direct immunofluorescence test on a skin biopsy from the nape of the neck for evidence of rabies antigen. This is the most sensitive and specific method of detecting rabies antigen in skin
Another option is to isolate the virus from saliva after inoculation of neuroblastoma cells. This method is usually the most successful during the first 2 to 3 weeks of contraction
And finally, you may also perform the rapid fluorescent focus inhibition test (RFFIT) in the serum of unvaccinated individuals to detect the rabies virus-neutralizing antibody,

13. Pre-exposure Treatment
Only those who are at high risk of exposure
Laboratory workers
Animal handlers
Veterinarians
Spelunkers (cave explorers)
People travelling to parts of the world where exposure to rabies is likely
3 doses of the rabies vaccine are given:
2nd is given 7 days after the first dose
3rd is given days after the first dose
The rabies vaccine is unique in that it is most often used after exposure to the disease.
The only people who typically get vaccinated as a preventive measure (before exposure) are those who are at high risk for exposure
These include Laboratory workers, Animal handlers, Veterinarians, Spelunkers (cave explorers), and People travelling to parts of the world where exposure to rabies is likely
For these people three doses of vaccine are given; the second is given seven days after the first dose and the third 21 to 28 days after the first dose.

14. Post-exposure Prophylaxis (PEP) Treatment: 2 stages
1: Rabies immune globulin (RabIg)
Immediate, short-term protection against the virus via antibodies
One dose is injected in or around the the wound
2: Rabies vaccine
Long lasting protection, helps the immune system to make antibodies
Four doses are given over 14 days in the shoulder: Day 1, 3, 7, and 14
However, in the cases where someone is exposed to rabies, the treatment is considered to be post-exposure prophylaxis (PEP)
You must first clean the wound and then start with the treatment
There are two stages, the first being one dose of rabies immune globulin
this is a preparation of serum obtained from people who have high levels of rabies-specific antibodies in their blood.
Rabies immune globulin should be injected in or around the wound to prevent attachment of the rabies virus to the nervous system.
It is an immediate, short-term protection against the virus
The second step is the vaccine, which is given to prevent the progressive fatal disease
a total of four shots are given in the shoulder muscle
The first shot is given immediately after exposure to a rabid animal, then again three days later, seven days later, and 14 days later.

15. Types of Immunity Passive Immunity
Given the antibodies rather than the body producing its own
Provides rapid protection
Not long lasting
Active Immunity
Gained through exposure of the disease which would trigger the immune system response to produce antibodies (natural immunity)
Or through vaccine of weakened form of the disease (vaccine induced immunity)
Long lasting
The Vaccines’ goal is to create immunity there are 2 types that are achieved in the case of rabies treatment → passive and active immunity.
Rabies immune globulin is passive immunity, it introduces rabies antibodies to the immune system as it takes time for the immune system to produce their own antibodies for rabies.
The Rabies vaccine is active immunity where a weakened strain of rabies is given to the immune system to trigger it to produce its own antibodies.
In general, we give rabies immunoglobulin for immediate effects and rabies vaccine to get the immune system to produce its own antibodies for rabies

16. Summary Rabies is a viral infection that is transmitted zoonotically
Stages: Incubation, Prodromal, Acute Neurological, Coma, and Death
Symptoms: fatigue, malaise, vomiting, diarrhea, nausea, insomnia, and ultimately death
Infection travels from the muscle to the neuromuscular junction into the central nervous system to exert effects
Nicotinic acetylcholine receptor allows for uptake into the neuromuscular junction
2 stages of post-exposure prophylaxis (PEP) treatment:
1. Rabies Immune Globulin - immediate, short-term protection
2. Rabies Vaccine - long-lasting protection
Cameron
Rabies is an viral infection that is transmitted zoonotically
Stages: Incubation, Prodromal, Acute Neurological, Coma, and Death
Symptoms: fatigue, malaise, vomiting, diarrhea, nausea, insomnia, and ultimately death
Infection travels from the muscle to the neuromuscular junction into the central nervous system to exert effects
Nicotinic acetylcholine receptor allows for uptake into the neuromuscular junction
2 stages of post-exposure prophylaxis (PEP) treatment:
1. Rabies Immune Globulin - immediate, short-term protection
2. Rabies Vaccine - long-lasting protection

17. Works Cited
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