Re: Rabies

["Duncan Fletcher" <dfletche@gte.net>]

I have attached some e-mails that were originally collected by Barbara Peck.
She had a horse that consistently reacted to rabies vaccine the reactions
getting worse each year. These discuss the reliability of titers. The bottom
line appears to be that challenge studies indicate that titers are reliable
for rabies. But titers in general may not be reliable.

On a personal note, I do not vaccinate against rabies because there has only
been a single case of horse rabies in Washington in 40 years. There are no
documented cases of wild skunk, racoon, fox, cayote or possum rabies. On the
other hand, if I lived in other areas I would think it immoral to risk other
folks with non vaccination. In saying this, I realize there is no hard and
fast degree of risk that makes it immoral. But you do have to consider that
you are risking the lives of other people to protect your horse against what
is in most cases a minor risk.

From: atlhealth@mindspring.com
To: Barbara B. Peck
Sent: Wednesday, January 20, 1999 9:48 AM
Subject: Re: Rabies info Horses & Livestock

Barbara,
Yes, you can assume that any titer of >1:25 is a positive response to the
animal having sufficient antibody to be protected if bitten by a rabid
animal.  If a titer is < 0.5 IU or < 1:25 the animal needs to be
revaccinated.  Current vaccines for use in horses confer only a one year
duration of immunity.
In rabies, cell mediated response is not measured & challenge studies which
all of us have done in animals over the past 50 years allow us to say what I
just said about serum neutralizing antibody (humeral response).
Yes, you can forward my response to anyone you wish.  If they wish to call
me, fine.  At some point I'd like for such groups to talk to me by phone if
neccessary.
Thanks,
Keith Sikes, DVM, MPH

From: Sally Huber <shuber@salus.med.uvm.edu>
To: <bpeck@together.net>
Sent: Friday, January 22, 1999 10:12 AM
Subject: rabies


>Sarah Asked me to respond to your questions regarding the immunology of
>infectious agents.
>
>1. Most infections produce both cellular and humoral immunity, but both
>types of immunity are not usually equivalent in eliminating the agent.
>Generally, intracellular agents such as viruses and bacteria like Listeria
>are best controled by cellular immunity. Free-living organisms, such as
>most bacteria, are best controled by humoral immunity. This is a VERY broad
>generalization. In fact, what type of immunity controls an infection best
>can vary dramatically from agent to agent. Often, if the antibody titer is
>high enough, and if the antibody is a neutralizing antibody (some
>antibodies will bind to viruses but will fail to prevent the virus from
>infecting cells; these antibodies are largely useless in controling
>infection or could make the disease worse such as in Dengue fever), it can
>abort the infection early even when cellular immunity is the major line of
>defense in primary infections. This is the principal behind passive
>immunization in which the antibody is given to someone recently exposed to
>a pathogen.
>
>2. It is very difficult to measure cellular immunity but is easy to measure
>humoral immunity. Since cellular and humoral immunity often occur at the
>same time to any immunization, one could measure humoral immunity and
>assume that this gives an indication of the cellular response as well. This
>can be misleading, however, since humoral immunity can last much longer
>than cellular immunity. I would think that this will be a greater problem
>at low antibody titers. At an antibody titer of over 1:1000, I would feel
>quite confident that both cellular and humoral immunity exist. Cellular
>immunity might be measurable using skin tests. In these test, antigen is
>injected subcutaneously and the cellular response is measured 48 hrs later.
>Tuberculin testing is done this way. Usually, the amount of antigen given
>is insufficient to cause a systemic reaction even in highly reactive
>individuals.
>
>If you wish to forward this information, you are welcome to do so. I have a
>Ph.D. in Immunology from Duke University and have worked in viral
>immunology since 1978, first at Cornell University College of Medicine in
>New York City and then at the University of Vermont. I have over 100
>publications mostly on viral immunopathology and will gladly send a c.v. if
>anyone wants one.
>
>Good Luck to you.
>
>Sincerely,
>
>Sally Huber
>Sally A. Huber, Ph.D.
>Associate Professor
>Department of Pathology
>University of Vermont
>55A South Park Drive
>Colchester, VT 05446
>Ph. (802) 656-8944
>Fax. (802) 656-8965

From: atlhealth@mindspring.com
To: ridecamp@endurance.net
Cc: bpeck@together.net ; dfletche@gte.net
Sent: Monday, January 18, 1999 2:03 PM
Subject: Rabies info Horses & Livestock


This is to clarify a few points about rabies in general, and especially
about getting horses vaccinated.  Also about getting antibody titers done.
First, who am I to be giving advice?  I directed CDC's rabies program for
about 15 years, then was state public health veterinarian and state
epidemiologist in Georgia until 1990.  Since then, Mary Yager (SE AERC
member #14386) and I were asked to set up a rabies lab for testing human
serums for rabies antibody content in order to assist those companies
involved in making the human origin rabies immune globulin (HRIG).  We,
Atlanta Health Associates, Inc., as well as Kansas State University, test
individual human and animal sera for rabies antibody.
Rabies in horses is relatively rare, less than 50 cases/year in the United
States.  These result from exposures from rabid wild, carnivorous animals,
usually foxes, skunks, or raccoons.  While many other horses are obviously
exposed, they are protected from developing clinical rabies due to their
natural or acquired (vaccination) immunity.
The Compendium of Animal Rabies Control (1999) succinctly states "All
species of livestock are susceptible to rabies; cattle and horses are the
most frequently infected."  As a practical measure the Compendium (which I
initiated in the 1960's and have helped update almost every year since then)
states, "It is neither economically feasible nor justified from a public
health standpoint to vaccinate all livestock against rabies.  However,
consideration  should be given to vaccination of horses and cows that are
particularly valuable, and/or may have frequent contact with humans.
There are three inactivated (safe and potent) rabies vaccines licensed by
USDA for use in horses which any veterinarian will have.
Anyone who would like a titer done on their horse could send 2 ml of serum
to KSU or to us at Atlanta Health Associates, Inc. Results will be faxed or
mailed to you within a week.  A titer (antibody/protection) will be
expressed in international units (IU) or in reciprocal dilution results.  A
blood containing >0.5 IU or >1:25 is considered a positive response
(protection) to vaccination.
If a horse who has been vaccinated and has a positive titer is subsequently
exposed to a rabid animal, the owner should have the animal revaccinated (1
dose of vaccine) and simply observed for 45 days.  If a horse is exposed and
was not vaccinated prior to the exposure, officials will recommend immediate
euthanasia of the animal or it must be kept in close quarantine for 6
months.
Sincerely,
Keith Sikes, DVM, MPH
Atlanta Health Associates, Inc.
309 Pirkle Ferry Road, Suite D300
Cumming, GA  30040
800-717-5612
770-205-9091




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