Equine Infectious Anemia Equine Infectious Anemia and Coggins Testingand Coggins Testing

Facts, Fable, Reaction and Reality

Director of Equine StudiesDirector of Equine StudiesSouthern Illinois University CarbondaleSouthern Illinois University Carbondale

President,President,HorsemenHorsemen’’s Council of Illinoiss Council of Illinois

Sheryl S. King, Ph.D, PASSheryl S. King, Ph.D, PAS

How Much Do How Much Do You You Know Know About EIA?About EIA?

Incurable

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

TRUE

• 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

USDA Survey on Equine USDA Survey on Equine Infectious Anemia KnowledgeInfectious Anemia Knowledge

National Animal Health Monitoring System 1998 survey:

Equine Infectious Anemia VirusEquine Infectious Anemia Virus• Retrovirus

Lentivirus subfamily is in the same family as HIV

• Shape-shifter rapid mutational changes to its outer coat evade antibody neutralization

• 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

EIAV can reproduce in the face of a strong immune response

• 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

EIA Virus (EIAV) PersistenceEIA Virus (EIAV) Persistence

• 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 StatesThree 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

Most effective method= humans (iatrogenic)

Blood on horsefly mouthparts = .00001 mlAcute reactor = 1,000,000 viruses/ml

= 10 virus particles/acute reactor/fly biteVirus survival time on mouthparts ≤ 30 min

Spot of blood from needle stick = .1 mlAcute reactor = 1,000,000 viruses/ml

= 100,000 virus particles/acute reactor/needle stickVirus survival time in syringe ≥ 96 hr

transmission decreased with one horse-one needle practice

EIAV Transmission by Direct Blood MixingEIAV Transmission by Direct Blood Mixing

Natural transmission by interrupted feeding of biting flies

• 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.

• 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

• The majority (95%) of horses found to be positive on serologic tests are inapparent carriers

Symptom Severity Symptom Severity Viral Load Viral Load Transmissibility Transmissibility

AcuteMax. 1,000,000 viruses/ml

Chronic≤ 10,000 viruses/ml

Inapparent.01 viruses/ml

≤ 416 viruses/horse

• Even in acute cases, mortality in natural infections is very low, and most convert to inapparent within 30 days

Natural Transmission Depends on:Natural Transmission Depends on:

1. Viral burden of infected horses

2. Vector concentration/typeSize of mouthparts = amount of blood residue

3. Proximity of susceptible and infected horsesInterrupted feeding distance to new host ≤ 50 yds

4. Defensive behavior of horsesIndividual tolerance, degree of pain inflicted by bite, number of flies feedingOlder, infirm horses defend less but distance themselves from others more

5. Tabanid behaviorFeeding persistenceProximity to alternate hostViral survival on mouthpartsPrefer dark colored horses

Field Results From 40 Years of Data Field Results From 40 Years of Data at F.R.I.E.N.D.Sat 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?”

Severe stress can revert inapparent carrier into symptomatic transmitter

Immunosuppression Lifts Immunosuppression Lifts Immune Control Immune Control

Testing For EIATesting For EIA*Coggins Test = AGID

“gold standard” for EIA antibody tests

*ELISA = Rapid color-change enzyme testcan produce false positivesshows promise for “stall-side” rapid testing

Western Blot = Tests for virus proteins, not antibodiesConfirming test for equivocal results; detect EIAV before antibodies are formed but is not quantitative

SID (sideroleucocyte) testAntibody + horses can test 0 (-) for virus using a SID test

Q-PCR = Tests for EIA pro-viral DNA in macrophageSensitive before antibodies are formedCan indicate actual viral load, can test foal exposure

EIA Testing Laws in IllinoisEIA 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 ReactorsFate of EIA Positive Reactors

Traditional EIA Traditional EIA ““Hot ZonesHot Zones””

National EIA Testing Results National EIA Testing Results 1972 - 20051972 - 2005

2009-10 National EIA Testing2009-10 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 TestingNational 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?

# EIA+ horses versus # EIA+ horses versus # tested horses# tested horses

< 30< 30¢ ¢ versus versus $10,000$10,000

Rate of IncidenceRate of Incidence

=

EIA Testing in IllinoisEIA Testing in Illinois

0 positives since 2006 from >250,000 tests

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 ~$400,000-$500,000/yr

Are we spending our resources wisely?

Year Total Tests

Positives % Positive

1995 NA 11

1996 NA 23

1997 34,221 19 0.055

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

Chances of Your Horse Contracting Chances of Your Horse Contracting the EIA Virus in Illinoisthe EIA Virus in Illinois

Much greater chance of you being hit by lightning Greater chance of your horse being hit by lightning

Greater chance of you and 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+ Arkansas Reports 40 EIA+ Horses on a Single FarmHorses on a Single Farm

80 resident horses on farmno complete herd test in 4-5 years

40 EIA(+) horses (50% of resident population)required 60 day retest for remaining EIA(-) horses = one EIA(+)

Closed herd – no horses leaving farm since 2004newest herd addition in 2011 EIA(-) as well as farm of origin

No EIA(+) in surrounding farms (within ¼ mile)

Two acute reactors died; 39 EIA(+) euthanized

Unusually severe vector year in 2011

48 EIA(+) on 5 premises; ~65,000 tests = .07% incidence

Are Current EIA Testing Laws Are Current EIA Testing Laws Effective?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

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

OrOr ??

Should Illinois Consider Should Illinois Consider Revision of EIA Regulations?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 BarriersEffective Barriers