On 24 April, Ferret McDuff wrote:
 
>Your comments to Bob Martin, while watered down, seem to follow the
>standard party line you would expect from an epidemiologist.
 
I believe you have me confused with the enemy.  Does it matter that before I
began studying epidemiology I worked with cell and molecular biology and
molecular genetics?  Maybe some more information on the virology and
epidemiology would help.
 
>The main reason brain tissue testing is so widely used is simply because it
>is the "accepted" method.  It is the accepted method because it is widely
>used... circular logic.  There have been equal, if not greater results with
>other testing methods, yet they are not accepted.
 
Not so.  Brain tissue is used because rabies only infects nerve cells and
reproduces IN THE BRAIN.  Researchers have looked for rabies elsewhere and
cannot *reliably* find it.  The PCR method Bob Martin inquired about can,
under ideal circumstances, detect a single molecule of DNA...and *IT*
doesn't work.  Brain biopsy or dissection is the only truly reliable test
right now.  That's not a happy truth, but it *is* the truth.
 
>I thought the reason for testing the animal was to determine if it could
>have possibly infected the bite victim.  Therefore wouldn't it make sense
>that if there were no virus in the saliva at the time of testing then there
>was very likely none in the saliva at the time of the bite?
 
Yes.  I agree fully.  Unfortunately, the PCR studies done so far have not
reliably found the virus in saliva.  PCR is not perfect.  Inhibiting
substances exist in various tissues or fluids, and in the case of RNA (like
rabies virus) there are enzymes that break down RNA everywhere in the
environment, which makes the assay tricky and unreliable.  If someone can
get PCR to detect rabies in saliva with close to 100% sensitivity and
specificity then our worries will be over.  A simple saliva test and a
quarantine will be enough to rule out infection.
 
>We already have at least three studies, two of which were done by the same
>people, in the same labs, under the same conditions as were the tests which
>formed the basis for the quarantine in dogs.  How much more data do we need?
 
Unfortunately, some of the studies done lack what epidemiologists call
"external validity." One of the European studies used rabies from voles.
Rodents are not considered an efficient vector for rabies since in a contest
between a ferret/fox/dog/etc, the carnivore is likely to kill and devour the
rodent before it can be bitten badly enough to be infected.  From a
biological standpoint, that study was useful, but it was essentially
noninformative from a public health standpoint because ferrets aren't likely
to be infected by rabid voles and because the strains of rabies in Europe
differ from US strains.  For public health types to be fully satisfied, it
will probably require shedding studies on ferrets using North American
rabies strains from all of the major vectors for the disease: foxes,
raccoons, skunks and bats.
 
>The best strategy is to rebel against automatic kill and test policies,
>which are against the law in most states, and demand that public health
>officials do a reasonable case by case risk assesment...
 
I agree with this, too, but public health officials *everywhere* won't be
satisfied unless they know (1) the incubation period of all strains of
rabies in ferrets, and (2) whether ferrets can shed the virus in saliva
after being infected with any of the North American strains of the virus.
That information is not known yet.
 
There is a reason for this pig-headed attitude on the part of public health
officials.  Rabies is one of the few viral illnesses that is 100% fatal in
humans once symptoms develop.  (Well, OK, there are about five people in the
recorded history of humankind who have recovered, most of whom got the
"treat- ment" before symptoms set in, but that counts as 100% in my book.)
Even Ebola spares 15% of its victims.  If you are a public health director,
what do you say to a parent whose child has been bitten by a stray animal?
If the animal is rabid and the child does not receive prophylaxis, death is
certain.  The child can receive the prophylaxis without testing the animal,
but the series of injections costs about $1,000.  You and I know that
ferrets are a poor vector for the virus, that stray ferrets rarely live long
enough in the wild to incu- bate and transmit it, and that most of the
animals likely to transmit rabies to a ferret outdoors are much more likely
to kill the ferret rather than just bite it and let it go.  Despite all
that, public health officials are scared silly by rabies, and it will
require shedding studies as I described to convince them all.  For my part,
I am in contact with the rabies branch at CDC and trying to work with them
to convince state depts.  of health to change their practices.  (Rabies is
under the purview of local health depts--so we must convince 50 states, 10
provinces, 2 territories, and any other semi-autonomous district or
protectorate to agree to changes--a big task.) Because I work in
epidemiology, I can talk to these people easily and use their language to
convince them to change their ways.  If that's toeing the line, then I shall
toe--*behind* enemy lines--for all I'm worth.
--Jeff Johnston
[Posted in FML issue 1550]