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:.
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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 FALSE Highly contagious between horses A deadly disease with a high mortality rate FALSE Associated with poor management/hygiene practices FALSE TRUE Incurable
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 Inapparent .01 viruses/ml ≤ 416 viruses/horse Acute Max. 1,000,000 viruses/ml Chronic ≤ 10,000 viruses/ml • 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: • Viral burden of infected horses • Vector concentration/type • Size of mouthparts = amount of blood residue • Proximity of susceptible and infected horses • Interrupted feeding distance to new host ≤ 50 yds • 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 • 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
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 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 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 your horse being hit by lightning Greater chance of you and your horse being hit by lightning during a snow storm Greater chance of you and your horse being hit by lightning
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 ?