Rabies Etiology, transmission, epidemiology, source of infection, pathogenesis, control and prevention

1. Faculty of Veterinary Medicine & Animal Husbandry
Somali National University
Mogadishu, Gaheyr Campus
Sep. 07. 2019
INFECTIOUS DISEASES II (Viral Diseases)
ANIMAL RABIES

2. Rabies virus belongs to the Rhabdoviridae family,
which includes at least three genera of animal
viruses,
Lyssavirus
Ephemerovirus
Vesiculovirus.

3. The genus Lyssavirus includes rabies virus, Lagos bat,
Mokola virus, Duvenhage virus, European bat virus 1 & 2
and Australian bat virus.

4.  Rhabdoviruses have nonsegmented, negative-
stranded RNA genomes.
 The virions have a distinctive bullet-shaped
morphology, and possess a lipid-containing
bilayer envelope.

5. Rabies virus causes acute encephalitis in all
warm-blooded hosts, including humans, and
the outcome is almost always fatal.

6. Survey by OIE in 2013 found that there were more than
150 countries and regions infected by rabies, and over 55
000 people died of rabies every year, most in developing
countries in Asia and Africa.

7. Map: Rabies Infection Distribution 2019.
Geographic Distribution

8. Species Affected
It is probable that all species are
susceptible Rabies including domestic
animals, poultry and wild animals.
mainly dogs and cats.

9. Dogs: the main carrier of rabies
More than 95% of human cases of rabies are due to
bites from infected dogs. Controlling and eradicating
rabies therefore means combating it at its animal source.

10. Transmission
Transmission of the disease is almost invariably
through the bite of a rabid animal although infection
through abraded surfaces or the conjunctiva
contaminated with infected saliva can occur and
aerosol infection in caves inhabited by rabid bats has
been demonstrated.

11. Pathogenesis
The virus travels along the nerve fibres from the point
of introduction to the cerebro-spinal cord and then to
the brain, followed by centrifugal spread throughout
the peripheral and central nervous systems.

12. It is at this stage, before the first symptoms appear that
spread may occur to the salivary glands and the saliva be-
come infective.
It is therefore essential that when an animal is suspected of
being rabid all human and animal contacts during the two
to three days preceding the onset of symptoms should be
traced and appropriate action taken.

14. Sick dog
wolves
bat
cat
rat
Rabies is a natural epidemic disease, wild animals are
the main natural host of rabies virus.
Source of Infection

15. Clinical Features
The clinical features of rabies are similar in most
species, but there is great variation between
individuals. Following the bite of a rabid animal the
incubation period is usually between 14 and 90 days,
but may be considerably longer.

16. An incubation period of 2 years has been reported in a
cat, and four human cases have been described with
incubation periods proven to be from at least 11 months
to at least 6 years.

17. A dog which is normally quiet may suddenly appear
very friendly, and one normally docile may without
warning become short tempered, may refuse
interference, and tend to hide in corners.

18. Dog rabies is characterized by clinical manifestations,
including changes to normal behavior, such as:
Biting without provocation
Eating abnormal items such as sticks, nails, feces, etc.
Running for no apparent reason
Vocal changes (e.g. hoarse barking and growling) or
inability to produce sounds
Excessive salivation or foaming from the mouth

19. There is a prodromal (preclinical) phase prior to
overt clinical disease, which often is overlooked in
animals or is reported as a change in temperament.

20. Two clinical forms of the disease are recognized:
 furious
 dumb or paralytic.
In the furious form, an affected animal frequently
exhibits restlessness and hyperesthesia to noise
and strong light, and will stare or bark at
something that is not apparent to the observer. It
may bite itself and snap as if at imaginary flies.

21. A symptom which can be a useful aid to clinical
diagnosis is the watchful `apprehensive' expression of the
eyes, as though the dog was fully aware that is was being
subjected to some paranormal strain but was puzzled as to
its origin.

22.  Non-domestic carnivora lose their fear of man and
will enter his habitations and attack without
provocation.
 Cats become aggressive.
 Cattle touch the ground and make short runs, tossing
their heads, as though about to charge.
 Horses may exhibit signs of excitement that can
readily be mistaken for colic.

23.  A depraved appetite is common in the dog but
not hydrophobia.
 A dog which is unable to swallow may
however attempt to seize the water bowl in its
teeth and try to tear it.

24.  Somewhat similarly, a rabid goat may either
spill the water bowl by `butting it', or stamp on
it in a frenzy with its fore feet.

25. A change of voice is also a common feature in many
species, giving rise to the characteristic `rabies
howl' in the dog and a change in the `bellow' of
cattle.

26.  The furious stage is followed by dullness and depression
and a progressive muscular paralysis. The term dumb
rabies denotes this later stage which may or may not
have been preceded by the furious excitable stage.
Paralysis of the tongue and lower jaw (dropped jaw) and
profuse salivation are common, and death may follow.

27.  Changes are mainly confined to the central
nervous system.
 The meninges of the brain are usually congested
and cerebral edema may be present.
 The only other gross macroscopic finding likely to
be encountered is a collection of foreign bodies
such as sticks, stones, pieces of metal, etc., in a
rabid dog's stomach.
Pathology

28.  Microscopically, the pathognomonic
cytoplasmic inclusion bodies (Negri bodies) are
seen in nerve cells.

29. They pant and cough. Serous nasal and lachrymal
secretions increase in volume and induce sneezing but
soon become mucopurulent. The nasal discharges tend
to encrust and block the nasal passages, causing oral
breathing.

31.  Rapid and accurate laboratory diagnosis of rabies
in humans and other animals are essential for
early postexposure prophylaxis.
 In addition, laboratory identification of positive
rabies cases may aid in defining current
epidemiologic patterns of disease and provide
appropriate information for the development of
rabies control programs.
Diagnosis

32.  The standard test for rabies testing is direct FA(dFA).
 This test is the most rapid and reliable of all the tests
available for routine use.
 Other tests for diagnosis and research, such as
electron microscopy (EM), histologic examination,
immunohistochemistry (IHC), RT-PCR, and isolation
in cell culture are useful tools for studying the virus
structure, histopathology, molecular typing, and
virulence of rabies viruses.

33. Pathological analysis:brain
soft membrane swelling,
congestion and bleeding,
the fourth ventricle with
yellow or pink liquid.
Histological
diagnosis:detecting the
within the base body
Electron microscopy:
bullet or baculovirus
Particles, one end flat, the
other end of blunt.

34. 1 to 2-day-old suckling mice were injected with 10% brain
suspension treated with penicillin and streptomycin. 5 to 8
days after inoculation, neonatal rabies clinical symptoms:
hind limbs and esophageal palsy, 8 to 9 days of death.
Autopsy findings: intestinal mucosal congestion, bladder
filling, increased 5 to 8 times. Brain images and tissue
sections can be observed in the Niger body, the accuracy of
up to 100%.

35. Fluorescent Antibody test (FAT)
• ‘Gold-standard’ test
• Antigen detection
• Brain smear
• Apple green staining
• time <2 hours
• Fresh tissue should be
examined, whenever
possible
• Sensitivity 90 – 100%
Negative dFAPositive dFA

36. Prevention & Control
The control of rabies in different countries of the world
poses very different problems, depending on whether
they are free of the disease, whether they are
industrialized or developing countries, and whether
vampire bat rabies is a problem.

37. Rabies-free Areas:
Rigidly enforced quarantine of dogs and cats for 6
months has been effectively used to exclude rabies
from Australia, Japan, New Zealand, Hawaii, and
several other islands.

38. Endemic Areas:
(1) Stray dog and cat elimination and control of the
movement of pets (quarantine may be called for in
emergencies); (2) immunization of dogs and cats, so as to
break the chains of virus transmission;
(3) laboratory diagnosis, to confirm clinical observations
and obtain accurate incidence data; (4) surveillance, to
measure the effectiveness of all control measures; and (5)
public education programs to assure cooperation.

39. Historically, rabies control in wildlife has been based on
animal population reduction by trapping and poisoning,
but in the past few years, fox immunization, by the
distribution of baits containing an attenuated live-virus
rabies vaccine, appears to have been highly successful in
reducing transmission.

40. Vaccination:
Animal rabies vaccines, produced in cultured cells as
inactivated or in some countries as attenuated live-
virus vaccines, are efficacious and safe.
Veterinarians and other individuals
occupationally or otherwise at risk of rabies should
be prophylactically immunized.

41. Thanks!