Equine Infectious Anemia
and Coggins Testing
Facts, Fable, Reaction and Reality
Sheryl S. King, Ph.D, PAS
Director of Equine Studies
Southern Illinois University Carbondale
President,
Horsemen’s Council of Illinois
How Much Do You Know
About EIA?
Equine Infectious Anemia is:
Otherwise known as Coggin’s disease
FALSE
A relatively new disease – emerging within the last 50 years
FALSE
Common, affecting a significant number of horses in the US
FALSE
Highly contagious between horses
FALSE
A deadly disease with a high mortality rate
FALSE
Associated with poor management/hygiene practices
FALSE
Incurable
TRUE
USDA Survey on Equine
Infectious Anemia Knowledge
National Animal Health Monitoring System 1998 survey:
• 30.3% of horse operations had never heard of EIA
• 16.3% recognized the name, but not much else
• 22.5% knew some basics
• 30.9% were really knowledgeable about EIA
Equine Infectious Anemia Virus
• Retrovirus
Lentivirus subfamily is in the same family as HIV
• Attaches to blood cells (platelets and red blood cells)
Infected blood cells are destroyed by the horse’s own immune system,
causing clotting problems and anemia
• Shape-shifter
rapid mutational changes to its outer coat evade antibody neutralization
EIAV can reproduce in the
face of a strong immune
response
EIA Virus (EIAV) Persistence
• EIAV incorporates its genetic code into macrophage DNA
EIA virus can reproduce in macrophage
viral reproduction kills macrophage – horse antibodies kill virus; steady
state is eventually achieved with very low virus counts
• Disease can go “dormant” for prolonged periods, or lifetime
EIAV infection may be controlled by the infected horse but it cannot
be eliminated
Three EIA Disease States
Acute/Sub-Acute
• Fever and anemia - sometimes severe
• First reaction to infection, especially to large amounts of virus transfer
• Initial clinical disease state lasts 3-20 days
• Mortality from natural infection is rare
Chronic
• Intermittent fever and anemia bouts
•General wasting and slow decline
Inapparent
• Healthy - no fever or anemia
• 95% of current EIA+ population
EIAV Transmission by Direct Blood Mixing
Most effective method= humans (iatrogenic)
Spot of blood from needle stick = .1 ml
Acute reactor = 1,000,000 viruses/ml
= 100,000 virus particles/acute reactor/needle stick
Virus survival time in syringe ≥ 96 hr
transmission decreased with one horse-one needle practice
Natural transmission by interrupted feeding of biting flies
Blood on horsefly mouthparts = .00001 ml
Acute reactor = 1,000,000 viruses/ml
= 10 virus particles/acute reactor/fly bite
Virus survival time on mouthparts ≤ 30
min
Symptom Severity = Viral Load = Transmissibility
Acute
Chronic
Inapparent
Max. 1,000,000 viruses/ml
≤ 10,000 viruses/ml
.01 viruses/ml
≤ 416 viruses/horse
• The acute response is rarely seen in natural situations, where blood-feeding
insects transmit low doses of virus
85-90% present as subclinical with no observable signs of the disease
• Even in acute cases, mortality in natural infections is very low, and most convert
to inapparent within 30 days
• The majority (95%) of horses found to be positive on serologic tests are
inapparent carriers
• After visiting an asymptomatic carrier, only one out of every 6 million flies is likely
to become a vector; requiring over 10,000 fly bites/hr for transmission.
Natural Transmission Depends on:
1. Viral burden of infected horses
2. Vector concentration/type
Size of mouthparts = amount of blood residue
3. Proximity of susceptible and infected horses
Interrupted feeding distance to new host ≤ 50 yds
4. Defensive behavior of horses
Individual tolerance, degree of pain inflicted by bite, number of flies feeding
Older, infirm horses defend less but distance themselves from others more
5. Tabanid behavior
Feeding persistence
Proximity to alternate host
Viral survival on mouthparts
Prefer dark colored horses
Field Results From 40 Years of Data
at F.R.I.E.N.D.S
No acute or chronic cases since
early 1970’s
EIA+ horses run at pasture with EIA- horses:
0 cases of EIA- horses becoming EIA+
“Are we losing horses to EIA or to the Coggins test?”
Immunosuppression Lifts
Immune Control
Severe stress can revert inapparent carrier into symptomatic transmitter
Testing For EIA
*Coggins Test = AGID
“gold standard” for EIA antibody tests
*ELISA = Rapid color-change enzyme test
can produce false positives
shows promise for “stall-side” rapid testing
Western Blot = Tests for virus proteins, not antibodies
Confirming test for equivocal results; detect EIAV before
antibodies are formed but is not quantitative
SID (sideroleucocyte) test
Antibody + horses can test 0 (-) for virus using a SID test
Q-PCR = Tests for EIA pro-viral DNA in macrophage
Sensitive before antibodies are formed
Can indicate actual viral load, can test foal exposure
EIA Testing Laws in Illinois
Proof of negative test performed within one
year for equids over 12 months old for:
• Entry into Illinois from any state or foreign country
•Participation in any publicly advertised event involving
horses
• Change of ownership – public or private
Fate of EIA Positive Reactors
Quarantine, Confirmed Testing and Retesting Possible
Exposed Horses, Permanent Branding
• Euthanasia
• Quarantine for life – screened stall, 200 yards from nearest equine
• Transport in sealed trailer to approved/state inspected horse slaughter
facility for immediate slaughter (no longer an option due to slaughter
ban)
• Donation to approved research facility, approved sanctuary
Traditional EIA “Hot Zones”
National EIA Testing Results
1972 - 2005
2009-10 National EIA Testing
37 positives on 30 premises from
~2,000,000 tests
47 positives on 30 premises from
1,681,570 tests
National EIA Testing
USDA estimates incidence = .001 - .008%
Multiple cases on single farm are rare
Cost estimate for testing = $30,000,000 to US horse
owners; $6,000,000 for testing labs
Are we expending our efforts and funds efficiently?
Rate of Incidence
# EIA+ horses versus
# tested horses
=
< 30¢ versus
$10,000
EIA Testing in Illinois
Year
Total Tests
Positives
% Positive
0 positives since 2006
from >250,000 tests
1995
NA
11
1996
NA
23
1997
34,221
19
1998
NA
6
1999
48,872
24
0.049
2000
51,167
8
0.016
2001
52,718
4
0.008
2002
40,538
0
0.000
2003
55,314
2
0.004
2004
55,518
2
0.004
2005
56,122
2
0.003
2006
54,903
0
0.000
2007
49,725
0
0.000
2008
27,991
0
0.000
2009
45,296
0
0.000
2010
49,539
0
0.000
0.055
Cost estimate IDOA:
>$100,000 per year
Cost to IL horse owners:
2010 increase from $0/test
to $8 - $10/test
~$400,000-$500,000/yr
Are we spending our
resources wisely?
Chances of Your Horse Contracting
the EIA Virus in Illinois
Much greater chance of you being hit by lightning
Greater chance of you and your horse being hit
by lightning
Greater chance of your horse being hit by lightning
Greater chance of you and your horse being hit
by lightning during a snow storm
Arkansas Reports 40 EIA+
Horses on a Single Farm
80 resident horses on farm
no complete herd test in 4-5 years
Closed herd – no horses leaving farm since 2004
newest herd addition in 2011 EIA(-) as well as farm of origin
40 EIA(+) horses (50% of resident population)
required 60 day retest for remaining EIA(-) horses = one EIA(+)
Two acute reactors died; 39 EIA(+) euthanized
Unusually severe vector year in 2011
No EIA(+) in surrounding farms (within ¼ mile)
48 EIA(+) on 5 premises; ~65,000 tests = .07% incidence
Are Current EIA Testing Laws
Effective?
Current regulations act to repeatedly retest the same
negative horses –targeting those horses who will never
come in contact with the disease
Argument for continued aggressive testing suggest
“reservoirs” of affected horses on untested premises
USDA EIA premises data do not show patterns of “reservoirs” of EIA+
horses
EIA cannot be passed from inapparent carrier to healthy horse – there is
time to identify carriers without indiscriminate yearly testing
EIA will not be transmitted between horses separated by 200 yards –
isolated, untested reservoirs will remain isolated
Or
?
USDA recommends focused testing of at-risk populations
and regional state-coordinated testing
“One of the most effective ways to find new
cases of EIA appears to be a required test at
change of ownership.”
USDA
Promote/fund development of veterinary
stall-side testing kits
Should Illinois Consider
Revision of EIA Regulations?
• Negative Coggins 1x/5 yr for mobile Illinois horse population
• Regional equine “passports” designating horse from “EIA-free
farm”?
• Entire population of farm tested negative; no pasture mingling with untested
horses; all newcomers tested
• Allow free movement of horses from such farms within the region without
additional (yearly) testing
• Negative test for all incoming equids
• Negative test to accompany all horses changing ownership
• Mandatory testing of any horse with nonspecific fever and/or anemia
• Q-PCR testing EIA(+) inapparent carriers rather than euthanasia ?
Effective Barriers