2. INTRODUCTION
Rabies is a zoonotic viral disease that affects the CNS
Caused by a virus of the family Rhabdoviridae, genus Lyssavirus, subgroup rabies
virus
Rabies is present on all continents except Antartica, with over 95% of human
death occurring in Asia and Africa
It is one of the neglected tropical disease that predominantly affects already
marginalized, poor and vulnerable populations
Once clinical symptoms appear, rabies is virtually 100% fatal.
3.
4. TRANSMISION
Through deep bite or scratch from an animal with rabies, usually a dog
Transmission can also occur if saliva of infected animals comes into direct contact
with mucosa (e.g eyes or mouth) or fresh skin wounds.
Wildlife vectors and / or reservoirs include cats, wolves, foxes, jackals, skunks,
mongooses, raccoons, vampire bats, and fruit and insect eating bats.
Human to human transmission has been documented only through infected
corneal and solid organ grafts from unsuspected rabies infected donors.
5. PATHOPHYSIOLOGY
Inoculation into muscle
Endogenous muscle micro-RNA bind to viral transcripts and limit both replication
and viral protein production , such that the virus is able to evade detection by
antigen presenting cells
Once enough virus replicates, it binds motor neuron junctions at postsynaptic
nicotinic acetylcholine receptors, which initiates uptake into the motor endplate.
The virus then rapidly propagates across motor axons and chemical synapses in
retrograde fashion toward the ganglia and nerve roots.
The rabies virus travels along these axons at a rate of 12-24mm/day to enter the
spinal ganglion.
At this point the prodromal symptoms of neuralgia and hypoesthesia may begin,
in addition to fever and flulike illness
6. Once reaching the CNS, it spreads throughout
Anterograde spread of rabies virus via sensory and autonomic pathways from CNS
to salivary glands and other viscera
Throughout propagation of the virus along motor pathways, the virus elicits little
inflammation
Rabies does not damage neurons
Neuronal morphology and lifespan is normal throughout the cause of the
Death occurs from global neurotransmitter blockade and widespread
dysfunction
7. The virion acts in the synaptic space, where homology in amino acid sequences
between neurotransmitter receptors for acetylcholine, GABA, and glycine may
afford a mechanism for viral binding of these receptors. Thus its action is
neurotoxic rather than cytotoxic
Characterized by the presence of negri
9. INCUBATION PERIOD
Average duration of incubation is 20-90 days
In more than 90% of cases, incubation is less than 1year
A person whose inoculum occurs with a scratch on the hand may take longer to
develop symptoms of rabies than a person who receives a bite to the head
The incubation period is less than 50days if the patient is bitten on the head or
neck or if a heavy inoculum is transferred through multiple bites, deep wounds, or
large wounds.
Infected patients may not recall exposure because of the prolonged incubation
period
10. CLINICAL FEATURES
Two forms of rabies
- Furious rabies
- Paralytic rabies
FURIOUS RABIES
Most common presentation and the duration of this period is 2-10days
Headache
Fevers, flu like symptoms
Confusion
Fluctuating periods of excitement with hallucinations
Hydrophobia
11. Insomnia
Depression
Diarrhea and vomiting
Pain or intense itching at the inoculation site
-After several hours to days, this becomes episodic and interspersed with calm,
cooperative, lucid periods
-Furious episodes last less than 5min
Episodes may be triggered by visual, auditory or tactile stimuli or may be
spontaneous
- This phase may end in cardiorespiratory arrest or may progress to paralysis
12. PARALYTIC RABIES
-Associated with objective signs of developing CNS disease, however consciousness
remains unaffected until the onset of coma.
-Patient is relatively quiet compared with a person with the furious form.
-The duration is 2-7days.
Muscle fasciculation
Priapism
Focal or generalized convulsions
Paralysis (ascending paralysis)
13. INVESTIGATIONS
Viral cultures and polymerase chain reaction (PCR) assay;
- Saliva
- CSF
- Brain tissue
Blood gas analysis
FBC/DC
CXR
EEG,ECG
Skin biopsy (most reliable test of rabies infection during the first week)
14. MANAGEMENT
Wound should be cleaned immediately with soap and water, flushing it thoroughly
to remove saliva.
Debridement and careful exploration for foreign body
Leave wounds to heal by secondary intention to permit drainage of wound fluids
and prevent infection
Antibiotic prophylaxis
Anti rabies on day 0,3,7,14 and 28
15. REFERENCES
Zandi F, Goshadrou F, Meyfour A, Vaziri B. Rabies Infection: An Overview of
Lyssavirus-Host Protein Interactions. Iran Biomed J. 2021 Jul 1. 25 (4):226-42
WHO. Rabies. World Health Organization. Available at
http://www.who.int/mediacentre/factsheets/fs099/en/. 21 May 2019; Accessed: 1
Jun 2019.
Liu C, Cahill JD. Epidemiology of Rabies and Current US Vaccine Guidelines. R I
Med J (2013). 2020 Aug 3. 103 (6):51-53.
