RABIES
It belongs to the family
Rhabdoviridiae, genus: lyssa virus and the species rabies lyssavirus. It is
rod or bullet shaped enveloped virus. it is a single stranded RNA virus.
usually it affects all warm blooded animals, especially foxes, dogs, jackals,
wolves, rabbits and bats are highly susceptible to this infection. However, man
has been often infected by dog bite. As it affects neuron it is called
neurotropic virus. its transmission mainly occurs through saliva of animals but
rarely through contact with human saliva.
Morphology: The virus consists
of envelope and nucleocapsid.
Envelope: It is an outer layer
comprising with lipids, it contains peplomers
or spikes with the size of 10nm length. Obviously the spikes play a
vital role in attachment of virus to the host cell. Moreover, envelope is lined
by a layer of matrix proteins.
Nucleocapsid: It is an internal structure, which
has been found to be shown with single stranded negative sense RNA, this
measure approximately about 60nm X 1sent in 80nm. RNA polymerase enzyme also
present in RNA.
Genome: Viral genome encodes the protein are
associated with either ribonucleic protein complex or viral envelope.
Resistance : This virus is sensitive to ethanol,
chloroform, acetone, phenol,formalin, UV rays and sunlight. It dies at room
temperature it is also inactivated by heat at 60o C for one hour. It is
resistant to dryness cold and decay.
Antigenic properties: Glycoprotein-G provides antigen
properties, it includes complement fixing antibodies.
Nucleoprotein : Also it has hem agglutinating
activity. It is used in preparation of vaccine
it induces antibody.
Pathogenesis:-
Source : infected dogs (saliva)
Infected animal and human
being
Mode of transmission :-
Dog
bite: Virus is being
transmitted by dog bite
Licking: Even licking by
dog is enough to initiate the infection, virus can transmit through minute
pores on the skin.
Pathogenesis; sequential events
Rabid Dog bite
Introduce small amount of saliva
Penetration of virus and its entry
due to endocytosis through endosome transport pathway. Inside the endosome low
ph. Value induces the membrane fusion virus starts replication. Multiplication
of virus at inoculated site of muscle and connective tissue.
Virus then binds on receptors of
neuromuscular junction.
Centripetal spread of virus along the
peripheral nerve.
Virus travels on axon.
Reaches to dorsal root ganglia of spinal cord.
Ascending towards central nervous
system
Once it reaches CNG, disseminates
into hippocampus cerebellum.
From CNG-centrifugal spread takes
place.
Reaches to salivary
gland by means of sensory and autonomic nerves.
Spread to vital organ, kidney, heart,
retina, and crania.
Viremia does not occur.
Shedding of Virus in saliva.
Clinical Symptoms : Fever, headache, excess salivation ,
muscle spasms, paralysis and mental confusion are the symptoms can be found,
apart from this dizziness, fatigue, loss of appetite are also characterized
Gastro intestinal symptoms such as nausea or vomiting resulted.
Hydrophobia: it is otherwise as fear of water. It
is the clinical condition in which the patient cannot drink water due to spasm
of throat muscle; it develops , when the function of brain steam respiratory
neurons are arrested due to the infections of rabies.
Lab
diagnosis:-
Sample
collection- Blood, Wound swab, saliva CSF and Biopsy
Culture
:- Chick embryo is used for cultivation
of viruses. Inoculate the sample into yolk sac then observe the growth
Tissue
culture:- it is
performed in chick embryo fibroblast, hamster kidney cells.
Immunofluorescence
test: Viral antigen is taken, (it could be specimen
) add anti rabies Abs tagged with isothiocyanate if fluorescence developed that
indicates positive if not, the test
result in negative.
Demonstration
of negri body: in this, following stain can be used
H and E stain
Sellers stain (basic fuschin and
methylene blue in methanol)
Negri bodies appear as round,
purplish pink color with basophilic inner granules.
Viral
RNA detection : RT-PCR can be used to amplify the
genes of rabies virus RNA from the brain tissue. It is the most appropriate
method employed in detection of virus.
Prevention rabies vaccine:- Vaccine are effective in human and other animals to prevent
infection pet animal and dog must be vaccinated in preventing the spread of
rabies to humans.
Rabies vaccine may be safely used in
all age groups. Human rabies- specific immunoglobulin (HRIG ) is available and
is derived from the plasma of immunized human donors for passive immunization.
HRIG is used after high-risk exposure to rabies and is given at the same time
as rabies vaccine (at a different site) to give rapid protection until the
rabies vaccine becomes effective. It is infiltrated in and around the cleansed
wound, or intramuscularly into the antero-lateral thigh. It can be given for
the up to seven days after starting the vaccination course (active
immunisatiob). The dose is HRIG 20 IU/kg body weight.
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