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Wednesday, February 20, 2013

Rabies virus: Properties, Mode of transmission, Pathogenesis, Types, Prevention, Vaccination, Lab diagnosis


Rabies virus

Properties of Rabies virus:

   1.            Rabies is a member of rhabdovirus family

   2.            Enveloped, RNA, single stranded virus

   3.            Bullet shaped, neurotropic virus

   4.            Attaches to the Ach receptor on the cell surface

   5.            Replicates in cytoplasm, killed by sunlight, heat or lipid solvent

   6.            If not treated, 100% mortality

   7.            Reservoir- Dogs, cats, bats, fox, raccoons, skunks, jackal, hyena, Mongoose


Structure of Rabies virus

Disease caused by Rabies virus:

Disease caused by Rabies virus is Rabies or Hydrophobia.


Transmission of Rabies virus:


   1.            The bite of a rabid animal (Dogs, cats, bats, fox, raccoons, skunks, jackal, hyena, Mongoose)

   2.            Aerosol of bat secretions containing rabies virus

   3.            Person to person by:
          a. Child biting to parents
          b. Cornea and organ transplantation


Pathogenesis of Rabies:

Pathogenesis of Rabies

Rabies: It is an acute highly fatal viral
infection caused by a rhabdovirus and primarily infects the CNS and salivary glands of a wide range of mammals and most frequently transmitted to man by saliva through bites of licks and produces fatal encephalitis in man

                           1.            Bite of rabid animal

                           2.            Rabies virus introduced into susceptible host

                           3.            Initially multiply in local immunity

                           4.            Infects the sensory neuron

                           5.            Moves by axonal transport to the CNS

                           6.            Start multiplication within the nerve cells

                           7.            Encephalitis developed with the death of neurons and demyelination

                           8.            Produce neurological sign and symptoms of rabies eg: Painful spasm of the throat muscle on swallowing, fever, anorexia, seizures, paralysis, coma, change in sensation in bite site

Neurotropic virus:

Neutropic viruses are those which preferentially infect nerve cells.

The neurotropic viruses are:
  1. Polio virus
  2. Rabies virus
  3. Echo virus
  4. Mumps virus
  5. Measles virus
  6. Herpes virus
  7. Coxsackie virus

Form of Rabies virus:

There are 2 forms of rabies virus:
1. Street virus:

          Freshly isolated virulent virus from infected man and animal are called street virus.

Criteria of street virus:


   1.            The virus is excreted in the saliva of affected animals

   2.            It is pathogenic to all mammals

   3.            It can multiply in the neuronal and extra-neuronal tissue (muscle)

   4.            They have long variable incubation period (10-90 days)

   5.            It forms “Negre bodies’


2. Fixed virus:

          Special brain to brain serial passages of a street virus in rabbits modifying the virus to form fixed virus

Criteria of fixed virus:


   1.            When in the virus is injected intra-cerebrally into the suitable animal, the virus shows, a fixed incubation period (4-6 days)

   2.            Direct injection to brain produces encephalitis

   3.            It can multiply in neuronal tissue but not in extra0neuronal tissue

   4.            Does not form negri bodies

   5.            It is used to produce anti-rabies vaccine

   6.            It is not-pathogenic, may be pathogenic if rabies vaccine is injected after inadequate inactivation of virus

Pre-exposure prophylaxis of Rabies:

Pre-exposure prophylaxis is required by those who handle potentially infected animal professionally, those who work with rabies virus in lab and those who live at special risk in rabies-endemic area.

Protection is afforded by active immunization by two intra-dermal injection of 0.1ml of HDC vaccine or two I/M injection of 1ml given 4 weeks apart followed by yearly boosters


Types of Rabies Vaccine:

   1.            Human diploid call vaccine (HDCV)
   2.            Nerve tissue vaccine (NTV)
   3.            DUCK embryo vaccine (DEV)
   4.            Rabies vaccine adsorbed
   5.            Purified chick embryo cell vaccine
   6.            Monkey lung vaccine


Post-prophylaxis of Rabies:


A. Wound management


   1.            Wound should be thoroughly cleaned with a Quaternary ammonium detergent or soap

   2.            Damaged tissue should be excised and the wound left unsutured.

   3.            Antibiotic and anti-tetanus measures should be taken.


B. Vaccination:


1.   Safest anti-rabies anti-serum is human rabies immunoglobin (dose is 200/kg bw, 1/2 is infiltrate around the bite and 1/2 is given I/M at a different site from the vaccine)
Hyperimmune animal serum dose is 200/kg. Common complication: Anaphylaxis (hypersensitivity reaction)

2.   Safest vaccine- is HDC strain vaccine 1.0 ml given intramuscularly on day “0”, 3, 7, 14, 30 and 90.
(In developing countries - 0.1 ml (HRG) of vaccine should be given intradermally into eight sites on day 1, with single boosters dose on 7 and 28.
  
 HDCV:   Slight risk - 2 ml X 7 days
                Moderate risk - 5 ml X 14 days
                Great risk - 10 ml X 14 days

Site: Ant. Abdominal wall (NTV), deltoid muscle (HDCV)

Rabies Patient


Lab Diagnosis of Rabies:


For humans:


1.   Isolation of virus from saliva, SF, Brain tissue

2.   Fluorescent-Ab staining of biopsy specimen

3.   Rise in titer of Ab

4.   Negri bodies is corneal scrapping and brain tissue


For animals:


The specimen is brain tissue. Tests done are:

1.   Fluorescent Ab to rabies virus

2.   Staining for Negri bodies

3.   Cell culture

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