rabies_smt7.ppt

7/27/2019 Rabies_Smt7.ppt

1/50


2/50


3/50

Rabies has been around forcenturies; described as early as2300 B.C.

Transmission is direct, primarily

via inoculation by bite, withinfectious virus present in saliva.

The reservoir for rabies is theanimal pool that circulates rabies

virus (diverse species of mammalseach with a specific strain).

Rabies is >99% fatal oncesymptoms occur

Rabies The Disease


4/50

Rabies is caused by a virus

Family Rhabdoviridae

bullet shaped

Genus Lyssavirus

Rabies Lagos bat strain

Mokola

Duvenhage

EBL-1

EBL-2

ABLV Picture from Centers for Disease Control and Preventionwww.cdc.gov/ncidod/dvrd/rabies


5/50

Bullet Shaped Morphology

Helical RNP Core

RNA Structure And Organization

Five proteins Ribonucleoprotein (RNP) Core:

Nucleocapsid protein (N)

Nucleocapsidphosphoprotein (NS or P)

RNA polymerase (L)

Matrix protein (M)

Glycoprotein (G)

G proteinM proteinEnvelope

RNP core

RNA

M protein

Envelope(membrane

bilayer)

RNP

Cross Sectional

Illustrations from Centers for Disease Control and Preventionwww.cdc.gov/ncidod/dvrd/rabies

G protein

Rabies Virus


6/50

How is rabies contracted

Rabies is most commonly spread by bitecontact between the rabid animal andthe recipient animal or human

In rabies infection, the virus present inthe CNS and other organs

Average incubation period(the timebetween an initial exposure to the virusand the development of symptoms ofdisease) is 4 weeks


7/50

Map from Centers for Disease Control and Preventionwww.cdc.gov/ncidod/dvrd/rabies

2 main ecologic cycles:

Batall over U.S. except Hawaii

Terrestrial (ground animals) raccoon,

skunk, fox, coyote


8/50

Rabies Infection

Virus-laden saliva or other infectious materialfrom the rabid animal must be introducedthrough a break in skin (bite) or onto mucous

membranes

Virus binds to a nerve cell & migrates to spinal

cord to brain (centripetal spread), then viralreplication occurs & produces encephalitis


9/50


10/50

Transmission/Pathogenesis

Viral particles travel out from brain (centrifugalspread) via nerve cells to salivary glands, wherefurther replication occurs & secretion in saliva,

rendering the person or animal to be infectious

At the time it gets to the salivary glands, this is theend stage of the disease, and death usually occurs

shortly thereafter within several days

Incubation period: Usually 4 weeks; can range from10 days to a year or more (??)


11/50

Infection Cycle

1. Attachment to host cell

- Main site of attachment

is at the neuromuscular

junction site of nervecells

- Main receptor is the

nicotine acetylcholine

receptor

- These receptors have a

high affinity for the viral

G-protein

Nerve terminal

www.bris.ac.uk/depts/physiology

Lewis 2000


12/50

2. Penetration via endocytosis

-the viral membrane attaches to the host cellular

membrane and enters into acidic endosomes by

endoycytosis

3. Uncoating of the viral envelope-uncoating separates the nucleic acid from the

envelope and nucleocapsid

-this step is necessary before transcription and

replication can take place

-takes place in the cytoplasm

Gaudin 2000


13/50

4) Transcription

-each gene is transcribed, separately, into its

complementary mRNA

5) Translation

-the five viral proteins are synthesized


14/50

6. Replication

-the RNA polymerase binds to mRNA and begins synthesis of

the complementary positive strand-the newly synthesized N-protein binds to the termination

synthesis of each mRNA so that a complete strand can besynthesized

-the full-length positive RNA strand then serves as a templatefor the synthesis of the negative viral genome

7. Assembly

-the N,L, and P-protein form the nucleocapsid aroundthe RNA strand and attaches to the cell membrane

6. Budding

-Virus buds from the cell membrane, taking some of theglycoprotein from the host to form the envelope

Wagner 1996


15/50

Diagnostic Techniques

1. Histological examination for Negri bodies

-negri bodies are cytoplasmic masses of viral nucleocapsidsfound in the brain tissue

-problem is that negri bodies are only present in 50-80% of

rabies cases

2. Direct flourescent antibody test

-uses tissue from suspected host and labeled antibodies,specific to the viral antigen

-if the rabies antigen is present, the antibodies will attach;monitored by flourescent microscope

-the technique poses the risk of infection to technician, but isa quick diagnosis

Jogai 2002


16/50


17/50

3. Immunohistochemical technique

-confers the presence of viral antigens in organs

outside the NS (GI-tract, heart, etc.)-biopsies are stained with immunoperoxidase, to

expose antigens, and treated w/ labeled rabies-specific antibodies to detect antigens

-benefits

reduces risk to technician because tissue sample areembedded in formalin-fixed paraffin

can examine the spread of the virus in organs outside ofthe nervous system

Jogai 2000


18/50

4. Mouse inoculation test

-brain material from the patient in question is inoculated into

mice to see if it leads to fatality

-this procedure takes at least a week

5. RT-PCR

-Reverse Transcriptase-Polymerase Chain Reaction

-can make a DNA copy of the viral genome and use PCR, with

a primer specific to the rabies genome, to determine its

presence

Meslin 1996


19/50

Headache, fever, sore throat

Nervousness, confusion

Pain or tingling at the site of the bite

Hallucinations

Seeing things that are not really there

Hydrophobia

Fear of water" due to spasms in the throat

Paralysis

Unable to move parts of the body

Coma and death

Symptoms


20/50

Rabies Human Deaths

Annual human deaths worldwide areapproximately 55,000; every 15 minutes apatient dies of rabies.

40-70% rabies victioms are children under 15years of age

Modern cell culture vaccines and animal controlmeasures in developed countries have reduced

the incidence of rabies deaths. In the United States, there has been a mean of 3

deaths per year since 1990.


21/50

Prevention steps after an animal

bite:

Wash the wound

well with soap

and water

Have the animal tested

for rabies

See a Doctor, even if

the bite is very small.

Contact your local health

department and animal

control officer.


22/50

Should Anti-Rabies Prophylaxis

be Administered?

CONSIDERATIONS:

High or lower risk animal?

Was there an exposure?

Likelihood & timing for animalcapture for confinement ortesting?


23/50

High Risk Animals

Raccoon

Skunk Groundhog

Fox

Bat

free-roaming cats


24/50

Intermediate Risk Animals

Dogs

Cats vaccinated or non-roaming

Livestockhorses, cattle, pigs

Other non-rodent wild animalspecies

i.e, opossum, bear, deer, coyote,etc


25/50

Low Risk Animal

Squirrels, chipmunks

Rats Mice, voles

Indoor small caged pet rodents

Logomorphs


26/50

WHO Definition of Exposure

Category Type of contact Type of

exposure

Recommended treatment

I Touching or feeding of animals;

Licks on intact skin;

None None if reliable history is

taken

II Nibbling of uncovered skin

Minor scratches or abrasions

without bleeding

Minor Administer vaccine

immediately; Stop

treatment if animal remains

healthy for of 10 days or ifanimal is proven to be

negative for rabies by a

reliable laboratory using

appropriate diagnostic

techniques

III Single or multiple transdermal

bites or scratches, licks on

broken skin; Contamination of

mucous membrane with saliva

(i.e. licks); Exposures to bats

Severe Administer RIG and

vaccine immediately. Stop

if animal remains healthy for

10 days or if animal is

negative for rabies


27/50

Was There An Exposure?

A bite (penetration of the skin by teeth) from aknown or suspect rabid animal

Scratches, abrasions, open wounds (bleedingwithin 24 hrs), or mucous membranes (eyes)

contaminated with saliva or other potentiallyinfectious material from a known or suspectrabid animal

Other contact - such as petting an animal orcontact with urine, feces or skunk spray - doesNOT constitute an exposure


28/50

Can The Biting Animal Be

Confined & Observed?

Healthy dogs, cats, ferrets and livestock may be

confined and observed for 10 14 days

Raccoons, skunks, fox, groundhogs and other

wildlife may excrete rabies virus while

asymptomatic for extended periods and cannot

be safely confined & observed. Testing of theanimal - or prophylaxis of bite victim - is always

recommended


29/50

10 Day Confinement &

Observation Period

In domestic animals the virus usually appearsin the saliva at the onset of clinical signs so ifanimal healthy, probably not rabid

Rarely, the virus can appear in the saliva 1 to 3days prior to onset of illness, so thus anobservation period created

Clinical course usually less than 7 days -animal dead before end of 10 days


30/50

Rabies Vaccination Status Of

Animal

Lower risk if animal has been regularly

vaccinated

But NO vaccine is 100% effective

Put as much weight on animal behavior

& health status


31/50

Animal Behavior/Health Risk

Factors To Consider

Was the bite or exposure provoked?

Did the animal escape in a normal manner?

Rabies is characterized by abnormal

behavior with neurologic impairment.

There is often a period of aggression thatprogresses to paralysis, although

aggression may not always occur


32/50

Rabies Virus Survival

If saliva or other material potentially containingthe rabies virus is dry to the touch, the virus canbe considered noninfectious.

Stability of the virus in the environment

Strong soaps, detergents, acids and alkalis allinactivate the virus

Heat inactivates the virus

Radiation destroys the virus

Lipid solvents inactivate the virus


33/50

Pre- and Post-exposure

Prophylaxis


34/50

WHO Recommended

Post-exposure prophylaxis

1. Immediate flushing and washing of the woundwith soap and water, or other detergent

If soap or detergent are not available, flushextensively with water

2. Passive immunization: Administration ofRabies immune globulin for Category III

contacts/exposures3. Active immunization: Administration of tissueculture vaccine according to one of WHOregimens


35/50

Rabies Postexposure (PEP)

Two biologics are administered:

Human Rabies Immunoglobulin (HRIG) confers

immediate protection with antibodies vs rabies

Rabies Vaccine - patient develops antibodies over

a 2 to 4 week period


36/50

Standard intramuscular regimen. One

dose into deltoidon each of days:

Essen intramuscular Regimen

WHO Recommended PEP

Schedule

5 vials

5 visitsday 0 3 7 14 28

Rabies immunoglobulin


37/50

Pre-exposure Prevention

1. Avoid contact with wild animals

2. Do not handle dead animals

3. People that work with wild or domestic

animals should be vaccinated

4. Vaccination of domestic and reservoir wild

animals


38/50

Preexposure Vaccination

Recommended for veterinarians, veterinarytechnicians, animal control officers, animal shelterworkers, rabies lab personnel and person workingwith wildlife.

Provides protection from unapparent exposures andwhen treatment is delayed

Also recommended for persons spending 1 month ormore in countries with endemic dog rabies and inwhich PEP would likely be significantly delayed togeographic distances/ lack of medical infrastructure


39/50

Pre-exposure Vaccination Protocol

Three doses of vaccine administered on days

0, 7 and 21 or 28

Dosage: 1.0 ml administered IM in the upper

deltoid

Test serum every 2 years to determine if an

adequate antibody level persists. If absent,

administer booster


40/50

WHO Recommended Pre-exposure

3-dose series intramuscular or intradermal

regimen

Pre-exposure

Exposure: No Rabies

immunoglobulin needed

day 0 7 21 or 28 day 0 3


41/50

What is an Effective vaccine?

One that increases the number of antibodies specific

to the viral antigen

Antigens are expressed on the cell surface and bind with

antibody

The antibody acts by neutralizing the antigen, decreasing

its pathogenic ability

Acts as an inhibitor for adsorption and/or replicationof the virus

Is high in G- or N-viral proteins


42/50

http://www.niaid.nih.gov/publications/autoimmune/work.html


43/50

Main Types of Vaccines

1. Brain-tissue vaccine

-synthesized from infected brain tissue originally by Pasteur

-use both adult and suckling mammal brain tissue (SMB)

-causes neural complications associated with immune response to neural antigens and foreign

proteins contained in the vaccine

these complications are lower in SMB vaccine

relatively cost-effective

90% of human vaccination still uses this

Koprowski 1996


44/50

2. Cell-culture vaccine

-prepared from supernatant of virus-infected cells

-two main typesa. chicken-embryo

major neurological complications due to embryo

antigens

not generally used in U.S. for this reason

b. human-diploid cell vaccine

virion preparations grown in human diploid cells

requires fewer doses and causes fewer complications

used as standard for preparation of other vaccinesvery costly

Meslin 1996

ll


45/50

3. Genetically engineered vaccines

-the goal is to conserve the antigenic structure of the G-

protein, while reducing its pathogenic ability

-the recombinant G-protein is modified in such a way that:

it is almost identically similar to challenge virus

it decreases viral uptake, and/or prevents budding, and/or

stimulates high expression of the G-protein

-induces high levels of neutralizing antibodies, allowingprotection against several rabies strands

-safe, potent, cost-effective

-but through recombinant processes in body, wild-type virus

could be regenerated

Morimoto 2001


46/50

Post-exposure Prophylaxis

1. Wash bite wound thoroughly with soap and water

2. Isolate the animal if possible

3. Seek post-exposure treatment

-same vaccines above are also used in post-exposuretreatment to stimulate the development of antibodies

-can also use lectins or neurotoxins that are specific to thenAchR to inhibit viral infection

these will successfully compete with the receptor, decreasing viral

uptake

Marchetti 1995 and Voyles 1993


47/50

Monitoring Post-exposure Vaccines

Why?

Efficacy of the vaccine varies with individual

The generation of high amounts of rabies antibodies in ashort time is imperative for survival

Methods to monitor vaccine efficacy

1. Mouse Neutralization test (MNT)

Virus/serum mix at several dilutions are inoculated in mice and

the mortality/survival rate is measured

Time-consuming, expensive, and need constant supply of rabiesconjugate


48/50

2. Rapid Flourescent Focus Inhibition Test

-mix dilute serum with constant dose of CVS

-stain with flourescent antibody to detect presence of non-neutralized virus

-time-consuming, expensive, and need constant supply of rabies

conjugate

3.ELISA-dilutions of sera are added to wells coated with G-or N-protein

-detection of rabies antibodies specific to viral protein by

monitoring absorbance

-expensive and equipment may not be readily available


49/50

4. Latex agglutination test

-new technique that is less expensive, less time-consuming, and less

laborous

-serum of treated patient is tested on beads that have been coated with

purified glycoprotein of the rabies virus

-amount of agglutination is a direct measure of the efficiency of the

vaccine


50/50

Thank You!!!!!!

rabies_smt7.ppt

Documents