Presentation on theme: "Equine Infectious Anemia and Coggins Testing Facts, Fable, Reaction and Reality Director of Equine Studies Southern Illinois University Carbondale President,"— Presentation transcript:
Equine Infectious Anemia and Coggins Testing Facts, Fable, Reaction and Reality Director of Equine Studies Southern Illinois University Carbondale President, Horsemen’s Council of Illinois Sheryl S. King, Ph.D, PAS
How Much Do You Know About EIA? Incurable Equine Infectious Anemia is: Otherwise known as Coggin’s diseaseFALSE 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 rateFALSE 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 Infectious Anemia Knowledge National Animal Health Monitoring System 1998 survey:
Equine 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) 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 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 ml Acute reactor = 1,000,000 viruses/ml = 10 virus particles/acute reactor/fly bite Virus survival time on mouthparts ≤ 30 min 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 EIAV 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 Viral Load Transmissibility Acute Max. 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: 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?”
Severe stress can revert inapparent carrier into symptomatic transmitter Immunosuppression Lifts Immune Control
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?
# EIA+ horses versus # tested horses < 30 ¢ versus $10,000 Rate of Incidence =
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? YearTotal TestsPositives% Positive 1995NA11 1996NA23 199734,221190.055 1998NA6 199948,872240.049 200051,16780.016 200152,71840.008 200240,53800.000 200355,31420.004 200455,51820.004 200556,12220.003 200654,90300.000 200749,72500.000 200827,99100.000 200945,29600.000 201049,53900.000
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 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 40 EIA(+) horses (50% of resident population) required 60 day retest for remaining EIA(-) horses = one EIA(+) Closed herd – no horses leaving farm since 2004 newest 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 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 Or ?
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 ?