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micro
12/5
eisenberg


RABIES
two handouts - red and green


in addition to the material we got as part of the red handout, there are 
two articles called "supplemental reading" and one is a book chapter on 
rabies wihch is pretty good and fairly recent. there's also an article on 
prions. mostly on the BSE epidemic. those interested in the details of 
that can read the article.

"La Rage" - book cover of a french book - 
picture of a guy sticking a sword into a dog or wolf or something. La 
Rage is what they call rabies in France.
rabies was/is one of the most 
feared diseases in areas where it is not under control - in india there 
are over 20,000 human cases a year!

rabies is one of the oldest recorded 
human diseases; was written about in many old texts. one of the first 
diseases for which a vaccine was developed (by Pasteur). saliva was found 
to be infectious in 18004 by Zinke. Pasteur demonstrated the CNS as seat 
of infection (target organ). Pasteur developed what was called "fixed 
virus" - he used passage to create virus with fixed incubation time 
before clinical signs would appear. wild virus has a very variable 
incubation period - from a week to a year and a half. 
some guy Negri 
developed diagnostic test - took brain tissue and found characteristic 
intracytoplasmic inclusion bodies (Negri bodies) which are pathognomonic 
for rabies. these are arrays of viral particles in cytoplasm.

rabies is 
a rhabdovirus. all rhabdoviridae have a characteristic bullet shape. the 
nucleoprotein core has helical symmetry, but the matrix protein defines 
the bullet shape. these are -RNA, single strand, similar to 
paramyxoviruses in genome organization. there's a nuclear protein matrix 
surrounded by M protein (huh?) around whch is lipid envelope that virus 
gets from host cell as it buds out. as it buds out it aquires spike 
glycoprotein called G protein, which acts to attach to a host cell and to 
carry out the fusion step. G protein may have something to do with 
effects of virus on host although this isn't entirely clear. we're not 
sure what is involved in the effects on host. if you just put G protein 
gene into another virus G protein won't be toxic, won't cause neuro 
signs. but with rabies virus we think G protein may act neurotoxic.

so 
the virus comes into cell via receptor mediated endocytosis, there's - it 
brings in its own RNA polymerase, the L protein - so transcription 
happens in cytoplasm, a + strand RNA is made, and that's used as template 
for making mRNA to make protein and to make genomic -RNA for packaging. 
all this happens in cytoplasm, no nuclear involvement. the pieces you see 
as Negri bodies are accumulation of pieces of virus in cytoplasm of cell. 
it assembles and buds out and infects new cells. highly neurotropic 
virus. replication most abundant in CNS. this neurotropic virus is almost 
always transmitted by bite of rabid animal. there are a few documented 
cases of aerosol transmission - bat rabies from a cave full of bats did 
infect spelunkers who went into the cave - presumed aerosol transmission. 
there are a few cases of rabies a year where people get bat rabies and 
there is no known physical contact with bats - but some people think 
these do involve bites. incubation period is very variable. 
also, if 
there is a bite, if there is no intervention eg vaccination and passive 
immunization, the person will die of rabies. there are a few cases of 
animals surviving rabies infection but mortality is close to 100%. 


early symptoms:
nausea, vomiting, pain at bite site, anxiety. this used 
to be called prodrome.
late symptoms - when virus is in CNS:
spasms, 
confusion, inability to swallow, paralysis, death.
furious form: 
associated with aggressive canines and felines - become very aggressive.

dumb form, passive form: it's not really clear why an individual would 
get this vs furious form. probably depends which areas of the brain are 
infected first.

by the time early symptoms develop, it's too late to 
give prophylaxis. there is a time before the signs appear, and that's 
when you can intervene. 

exact sequence of events following a bite from 
an infected animal - there's a diagram in the handout. it depends to some 
extent where the bite occurs. the further from the brain, the better the 
chance of survival. there is a period following the bite during which 
there is virtually nothing going on. no clinical signs, you can find 
virus at the bite site but there's only very limited or no replication. 
virus really can't replicate in muscle. so clinical rabies depends on 
virus being able to enter a peripheral nerve and travel up it into the 
CNS. the variable incubation seems to depend on how long it takes virus 
to find peripheral nerve. if injected into the nerve it will get to the 
CNS in some kind of set time, I guess. first signs are on ipsilateral 
side (side of bite).
so it is hard to isolate virus at bite site after 
first 24 hrs. is there replication at bite site? not sure. virus spreads 
into peripheral nerve and becomes hard to detect. may take up to two 
weeks to get into CNS. once it gets there, spread in CNS is rapid. 
initially in neurons of doral root ganglia, ventral motor region. spreads 
into ipsilateral brain, then crosses over, moves to forebrain, then back 
to salivary glands, adrenals, kidney, and heart. must get into salivary 
glands to become infectious to new host. 

rabies diagnosis - can only 
occur either on basis of suspected exposure or after clinical signs 
develop (when it is too late). usually we go by suspected exposure. 
Fluorescent Ab and PCR are the best ways to detect it now. Also to figure 
out what strain of rabies you're dealing with.

Classically we've looked 
for negri bodies in thalamus, hypothalamus, pons, cerebral cortex, and 
dorsal horns of cord. it's most common to find them in neurons of the 
hippocampus of carnivores or the purkinje's cells of herbivores.
Negri 
bodies are about 80% accurate. the serologic/PCR tests are about 100% 
accurate. the negri bodies take time to develop, which accounts for the 
20% false negative rate.

first vaccine was made by pasteur, who 
developed a "fixed" virus using ground brains from rabbits infected with 
the fixed virus. he used that brain tissue as a vaccine. b/c the virus 
was in low quantity they would give these intraperitoneally following 
exposure. they were painful due to the high antigenicity of the brain 
protein. usually gave 20 or 21 shots over a few weeks and hopefully that 
person didn't get rabies. obviously this was postexposure treatment. in 
50s they made a duck embryo vaccine for people. 21 doses, allergic effect 
of egg. also animal vaccines came about here.
human diploid cell vaccine 
finally became available - whole virus vaccine - fewer shots required. it 
was hard to get a form of rabies to grow in human cells. this allowed use 
of vaccine in more rational way. now they only give 3 doses, IM or ID. 
what does the titer mean? there is experimental evidence that 
neutralizing Ab does play a role in preventing the virus from reaching 
CNS. so even though we don't understand the whole process of infection, 
we know that it works. antibody does mediate virus clearance from CNS. so 
they give the vaccine in two ways. to high risk individuals 
prophylactically, and post-exposure to people who have been exposed, in 
combination with immune globulin. there is a recommended regimen. 


reminder: wildlife vaccination uses recombinant vaccinia vaccine using G 
glycoprotein of rabies. 

rabies is seen worldwide except in island 
nations that can afford eradication programs. no rabies in UK, hawaii, 
japan. these places have strict quarantines. two cycles maintain the 
virus - urban and sylvatic. urban cycle mainly involves dogs and cats, 
and sylvatic cycle invovles skunks, raccoones, fox, bats, cattle, etc. 
can infect any warm blooded mammal. in europe, since 1945 it has been a 
problem - fox, wolves, badgers. in india they give as many as 200,000 
post exposure vaccinations/yr.

showing some charts.

although dog rabies 
has come down, and human rabies has come down, wild animal rabies has 
been increasing rather alarmingly. it hasn't affected the human cases. 
bats, raccoons, and skunks account for most rabies in this country. the 
rest are mainly cattle, dogs, and cats. cat vaccination is very 
important. in PA, farm cats are exempt from rabies vaccination 
requirements. *sigh*. farmers have a good lobby, i guess.

around here 
raccoon rabies is predominant. in the midwest, lots of skunk rabies. note 
that this strain got here by hunters moving rabid raccoons from the south 
into the north...*sigh*

how was this going to affect raccoon populations 
near humans? so far, no humans have been infected with the raccoon 
strains. why? CDC has some ideas. maybe because raccoons are large and 
easy to see, so anyone who sees and gets bitten by one will know, and 
will seek treatment. also because prophylaxis has been used effectively. 
also they think that they've eliminated the problem of cats and dogs 
getting infected by raccoons and then in turn infecting their people, due 
to vaccination of animals. also it could be that people aren't as 
susceptible to the raccoon strain - but we're not about to be able to 
prove that or anything. most of the human cases in this country have been 
associated with bat rabies, mostly one strain of bat rabies. that means 
we're probably very very sensitive to that strain, and it doesn't take 
much of it to infect us see handout.

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