Re: coggins
- From: Brian Whatcott <betwys1@xxxxxxxxxxxxx>
- Date: Sun, 21 Sep 2008 19:53:46 -0500
[the ***** asterisk strings in your text
are my underline method ******]
On Sun, 21 Sep 2008 22:23:04 GMT, una@xxxxxxx (Una) wrote:
... At
this time, two test methods are in wide use and accepted by most US
states for purposes of detecting EIA antibody: ELISA and AGID. The
Coggins test is an AGID test.
EIA is a retrovirus, like HIV, so once EIA has infected a horse's
cells, the horse is expected to remain infected for life.
***** However, the antibody tests are tests for exposure,
not infection. *****
There are tests for infection, but they are considerably
more expensive.
EIA is infectious, but it is not "highly" infectious. It is one of
the least infectious viruses known in horses.
Una
http://nsu.aphis.usda.gov/inventory/activity.faces?INVENTORY_NUMBER=61
http://www.aphis.usda.gov/animal_health/animal_diseases/eia/
I believe the basis for your position is given above in the second of
your referred URLs as follows:
http://www.aphis.usda.gov/animal_health/animal_diseases/eia/downloads/fs_eia.pdf
...or as a tinyurl:
http://tinyurl.com/3h944c
"Inapparent
By far the majority of horses are
inapparent carriers: they show no overt clinical
abnormalities as a result of infection. They survive
as reservoirs of the infection for extended periods.
Inapparent carriers have dramatically lower
concentrations of EIAV in their blood than horses with
active clinical signs of the disease. Only 1 horsefly
out of 6 million is likely to pick up and transmit EIAV
from this horse. All horses infected with EIAV are
thought to remain virus carriers for life. The inapparent
form may become chronic or acute due to severe
stress, hard work, or the presence of other diseases."
I will paraphrase the information provided there,
[in my understanding:]
(1)
EIA is transferred blood to blood as a virus by (typically)
flies.
(2)
If infected in this way, a horse will be a reservoir for life.
(3)
For the great majority of horses, for the great majority of
cross infection challenges (infected blood fly bites)
the bitten horse will not be infected.
(4)
Any infected horse can flair to the acute state, at which
time a fly bite containing its blood is highly potent
(the official datasheet uses the quaint measure of
"one millionth of one fifth of one teaspoonful"
of blood fluid as the infective dose)
(5)
If a horse IS infected, the fever may be transient or
be part of the lethal symptoms. Horses which do not die
may not be detected with symptoms during the acute
phase and thereafter be symptomless.
(6)
These asymptomatic horses are the life reservoirs
for onward transmission.
Una, your conclusion appears to rest on a consequence
of item (3) above.
That if a horse IS challenged, but NOT infected, it will
then develop antibodies, which will later be detected
by the AGID (Coggins) test.
Your references above do not explicitly support the
construction which you put on item (3).
It is instead possible that a titre
of serum from a chronic asymptomatic carrier which
does not infect another horse, also does not create
antibodies in it, and will provide a negative Coggins,
I can suppose.
Can you speak to the possibility of antibodies in the
uninfected horse as opposed to antibodies in the
symptomless passive carrier?
How would you tell the difference?
Brian W
.
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