Rabies infection: Characteristics, Pathogenesis, Clincal features, Categories, Pre and Post exposure prophylaxis, management.

1. RABIES
DR.SRUTHY GNANASEKARAN
SENIOR RESIDENT
DEPARTMENT OF PEDIATRICS

2. INTRODUCTION
• Family: Rhabdoviridae
• Genus: Lyssavirus
• The classic rabies virus (genotype 1)
is distributed worldwide and naturally infects a large variety of animals.
• Each variant is specific to a particular animal reservoir,
although cross-species transmission can also occur.

3. EPIDERMIOLOGY
• Rabies is present on all continents except Antarctica.
• Predominantly afflicts underaged, poor, and geographically isolated populations.
• Approximately 50,000 cases of human rabies occur in Africa and Asia annually.
• Theoretically, rabies virus can infect any mammal which then can transmit disease to
humans.
• There have been 3 outbreaks of rabies associated with solid-organ and corneal
transplantations.

4. TRANSMISSION
• The infected saliva through a bite or scratch from a rabid mammal.
• ~ 35-50% of people bitten by a known rabies infected animal and receiving no PEP
contract rabies.
• The transmission rate is increased if the victim has suffered multiple bites and if the
inoculation occurs in highly innervated parts of the body such as the face and the hands.
• Infection does not occur after exposure of intact skin to infected secretions, but virus
may enter the body through intact mucous membranes.

5. PATHOGENESIS
Bite/Scratch
inoculation
rabies virus replicates slowly in muscle or skin
(long incubation period)
Enters the peripheral motor nerve
(nicotinic acetylcholine receptor)
In the nerve: the virus travels by fast axonal transport
(crossing synapses roughly every 12 hr)
Rapid dissemination in brain and spinal cord
Infection of the dorsal root ganglia = radiculitis
Infection concentrates in the brainstem = autonomic dysfunction & relative sparing of cognition
Enters the peripheral nervous system to all innervated organs.
It is through this route that the virus infects the salivary glands.
Many victims of rabies die from uncontrolled cardiac dysrhythmia.

6. HISTOPATHOLOGY
• Despite severe neurologic dysfunction with rabies, histopathology
reveals limited damage, inflammation, or apoptosis.
• The pathologic hallmark of rabies, the Negri body, is composed of clumped viral
nucleocapsids that create cytoplasmic inclusions on routine histology.
• Negri bodies can be absent in documented rabies virus infection.

7. CLINICAL FEATURES
• Incubation period for rabies is 1-3 months
• In the head: within 5 days after exposure, and occasionally the incubation period can
extend to longer than 6 months.
• Rabies has 2 principal clinical forms.
Encephalitic or “furious” rabies :
• Fever, sore throat, malaise, headache, nausea and vomiting, and weakness, paresthesia
and pruritus at or near the site of the bite that then extend along the affected limb.
• Encephalitis with agitation, depressed mentation, and seizures.
Paralytic or “dumb” rabies
• Fevers and ascending motor weakness affecting both the limbs and the cranial nerves.
• Encephalopathy

8. Phobias
• Rabies encephalitis initially have periods of lucidity alternating with periods of
profound encephalopathy.
• Hydrophobia and aerophobia are the cardinal signs of rabies; they are unique to humans
and are not universal or specific.
• Phobic spasms are manifested by agitation and fear created by being offered a drink or
fanning of air in the face, which in turn produce choking and aspiration through spasms
of the pharynx, neck, and diaphragm.

9. • The illness is relentlessly progressive.
• Dissociation of electrophysiologic or encephalographic activity with findings of
brainstem coma caused by anterograde denervation.
• Death almost always occurs within 1-2 days of hospitalization in developing countries
and by 18 days of hospitalization with intensive care.

10. DIAGNOSIS
• Reverse transcription polymerase chain reaction
• Rabies antigen is detected through immunofluorescence of saliva or biopsies of hairy skin
or brain.
• Rabies-specific antibody can be detected in serum or CSF samples
• Antirabies antibodies are present in the sera of patients who have received an incomplete
course of the rabies vaccine,
• Antibody in CSF is rarely detected after vaccination and is considered diagnostic of
rabies
• CSF abnormalities in cell count, glucose, and protein content are minimal and are not
diagnostic.
• MRI findings in the brain are late.

11. DIFFERENTIAL
DIAGNOSIS
• Severe cerebral infections,
• Tetanus
• Intoxications and envenomations.
• Autoimmune encephalitis, other infectious encephalitis,
• Psychiatric illness,
• Drug abuse,
• Conversion disorders.
• Paralytic rabies is most frequently confused with Guillain-Barré syndrome.

12. TREATMENT
• Rabies is generally fatal
• Rabies immunoglobulin (RIG)
• PEP
• Milwaukee Protocol (http://www.mcw.edu/rabies)

13. Algorithm for evaluating a child for
rabies postexposure prophylaxis

14. Post Exposure
Prophylaxis
Dogs, cats, and ferrets
1.Healthy and available for 10 days of observation = Prophylaxis only if animal
shows signs of rabies*
*(10-day observation period, at the first sign of rabies in the biting dog, cat, or
ferret, treatment of the exposed person with RIG (human) and vaccine
should be initiated. The animal should be euthanized immediately and tested.
Immunization is discontinued if immunofluorescent test result for the animal is
negative)
2.Rabid or suspected of being rabid: Immediate immunization and RIG
3.Unknown (escaped): Consult public health officials for advice

15. Post Exposure
Prophylaxis
Schedule:
MTVC (Modern Tissue Culture Vaccine) recommended for all category
II & III bites
Dose: 1.0 ml IM
• Day 0,3,7,14 & 30
• Day 0 being the day of commencement of vaccination
• A sixth dose on day 90 is optional & may be offered to patients with
severe debility or immunocompromised
• RIG + rabies vaccine in category III bites

16. PREVENTION
Primary prevention of rabies infection includes vaccination of domestic
animals and education to avoid wild animals, stray animals, and
animals with unusual behavior.

17. PRE EXPOSURE
PROPHYLAXIS
Killed rabies vaccine:
• Persons at high risk for exposure to wild-type virus
• Laboratory personnel working with rabies virus, veterinarians, and
• Others likely to be exposed to rabid animals as part of their occupation.
RIG or cell culture–based vaccine:
• Traveling to a rabies endemic region
Schedule:
• Preexposure prophylaxis schedule: On days 0, 7, and 21 or 28. IM
• PEP in the patient who has received preexposure prophylaxis or a prior full schedule of
PEP consists of 2 doses of vaccine (1 each on days 0 and 3) and does not require RIG.
• Requires boosting if the potential for exposure to rabid animals recurs.

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