Submitted by Darla K. McCrady 979-845-6656 - posted 1/29/07

Letter Submitted by Diane Fratessa - posted 1/11/05

WNV - West Nile Virus TAHC UPDATE - posted 7/10/02

• "Texas' Sees Its First Case of West Nile Virus (WNV) in a Horse Preliminary tests on a sick horse that was euthanized Saturday, June 29, near Katy in far west Harris County, indicate that the animal was infected with West Nile Virus (WNV), a form of "sleeping sickness" first detected in Texas in two dead blue jays June 18 on the northwest side of Houston. According to the Texas Department of Health (TDH), another 29 infected birds have since been found.
  
  
• ""We were notified today (July 3) that tests run on samples of the horses's blood and spinal fluid were positive for WNV. The tests were run both at the Texas Veterinary Medical Diagnostic Laboratory (TVMDL) in College Station, and at the National Veterinary Services Laboratory (NVSL) in Ames, Iowa," said Dr. Linda Logan, Texas' state veterinarian and executive director for the Texas Animal Health Commission (TAHC), the state's livestock health regulatory agency.
  
  
• ""The NVSL is running additional confirmation tests on the blood samples, but more than likely, we are seeing Texas' first case of West Nile Virus in a horse. Diagnosing WNV must be based on laboratory confirmation, as the signs of the disease, including staggering or the inability to rise, can mimic other diseases, including rabies, or other encepalitic diseases, such as Western Equine Encephalitis (WEE) and Eastern Equine Encephalitis (EEE)."
  
  
• "WNV was unheard of in North America until l999, when it was detected in birds in New York. The virus, which can cause brain swelling and severe illness in horses , previously had been confined to Africa, Europe, Asia, and the Middle East. WNV has spread to 20 US states, following the migratory flight patterns of birds along the Eastern Seaboard and west as far as Texas. In 2001, 738 horses, donkeys or other members of the equine family were diagnosed with the disease in the U.S., and about 20 percent of the animals had to be euthanized, due to the severity of their illness.
  
  
• ""Blue jays, crows and more than 70 other species of birds can carry the virus, but it is the mosquito that puts the disease cycle in motion," explained Dr. Logan. "After feeding on infected birds, mosquitoes ingest the virus, and about one percent of the pests then become infected and capable of spreading the virus to horses or humans. There have been no documented cases of animals or humans spreading the disease. Dogs and cats appear to be resistant to the disease."
  
  
• ""Home and stable owners should take precautions to prevent mosquito bites," said Dr. Joe Garrett, a veterinarian with the TDH's Zoonosis Control Division. "Get rid of stagnant water, drain flowerpots, keep bird baths clean and cut weeds down to discourage mosquito breeding grounds. Apply insect repellents, and put up screens to protect your home or stable from being 'invaded' by mosquitoes. There is no vaccine for people, but fortunately, human cases of WNV are extremely rare.
  
  
• "However, see your physician immediately if you develop signs of the disease, which include fever, headache, body aches and swollen lymph glands. More severe infection may be marked by headache, high fever, neck stiffness."
  
  
• ""We continue to work with other agencies to urge horse owners to have their animals vaccinated against WNV, and with the diagnosis of this disease in the Houston area, all possible preventive efforts are import to stop the spread of this disease," said Dr. Richard Ferris, area-veterinarian-in-charge for the U.S. Department of Agriculture's Veterinary Services in Texas. "We are investigating other potential cases in horses in Harris County and are awaiting test results. If you live in the Houston area, protect your horses from mosquitoes. While a vaccine is available for horses, the animal must receive two doses of WNV vaccine three to six weeks apart, and full protection does not begin until at least four to six weeks after the second dose of vaccine is administered," he said. "I'd urge owners to take action now to get horses protected."
  
  
• ""If your horse becomes ill and goes off feed, sways, develops head tremors, muscle twitches or cannot rise, contact your veterinarian, so he or she can collect and send in samples to us for diagnostic testing," said Dr. Lelve Gayle, executive director of the TVMDL. Laboratory confirmation of cases is particularly important for tracking the movement of WNV within the state.
  
  
• "Dr. Garrett said the TDH is continuing its WNV disease surveillance statewide, which includes testing mosquitoes, dead crows, blue jays, hawks and sampling zoo birds. Dead crows, blue jays or hawks can be submitted for laboratory examination, by calling the nearest regional Texas Department of Health office or the Texas Department of Health in Austin at 1-512-458-7255.
  
  
• ""If you are picking up a dead bird, wear gloves and wash your hands afterward," explained Dr. Garrett. "The bird could have had parasites of other illnesses, and it's always advisable to keep a barrier---like gloves--between you and the dead bird."
  
  
• "Dr. Logan reminded livestock owners that, as always, the TAHC operates a 24-hour hotline at 1-800-550-8242 for taking reports of unusual signs in livestock, including:
• 1. staggering, falling, or inability to rise
• 2. illness affecting a large percentage of animals
• 3. sudden death loss
• 4. blistering around an animal's lips, teats or hooves
• 5. unusual ticks or maggots
  
  
• "Additional information about WNV can be accessed onthe internet at: http://www.tdh.state.tx.us/zoonosis/diseases/arboviral/westnile/westnile.asp.
  
  
  

  EIA “The Facts and The Controversy” - posted 8/25/01

  
  
  

  Equine Infectious Anemia

  The Facts and The Controversy

  INTRODUCTION

  History

  Equine Infectious Anemia (EIA) is a potentially lethal disease of equids and causes chronic illness in some, but the majority of horses in the U.S. (85% to 95%) are asymptomatic with owners that are unaware of their infection.

  In 1966, a cyclical outbreak of EIA occurred among racehorses at U.S. tracks along the east coast. Other countries experiencing similar problems included several European nations, China, Japan and Latin America.^2,3,4,5 Consequently, concerned U.S. leaders from the Thoroughbred, Standardbred, and Quarterhorse industries gathered to form a united front to control the virus and encourage support for more research.³

  One result of this research was the development of the Coggins test in 1970, which detected EIA antibodies in equine blood samples.² In 1972, the U.S. Department of Agriculture (USDA) recognized the test as an official diagnostic test for EIA.² Individual states then imposed their own test and control regulations. The USDA regulates interstate and international movement of horses.⁶ Details on testing requirements varied but, in general, regulations required that horses that tested positive for ELA had to be euthanized, slaughtered, or permanently quarantined.

  The Controversy

  Regulations aroused controversy, primarily over the fate of horses that tested positive for EIA but were not sick. The following statements, taken from a 1978 review article in the Journal of Equine Medicine and Surgery,¹ represent the EIA controversy from 1972 to the present.

  • "A simple test for EIA made regulation superficially attractive."
  • • "EIA was not, in comparison with other diseases, an imminent danger to the horse industry."
    • "Until widespread testing was used, few suspected such a high percentage of infected horses would he asymptomatic; estimated to be somewhere from 85% to 95%."
    • "Some worried that unless certain controls were put in place, the asymptomatic animals would continue to be a threat."
    • "Some felt that contagiousness of EIA had been unjustifiably misrepresented, frightening misinformed horse owners into destroying more useful horses than the disease itself would.
    • "A disparity existed between opinions of a substantial portion of researchers and control programs purportedly based on those opinions. Researchers felt the scientific evidence did not justify universal quarantine or slaughter approach to EIA control;."

    THE VIRAL DISEASE

    The equine infectious anemia virus (EIA) is a lentivirus that uses its RNA (ribonucleic acid) to make a DNA (deoxyribonucleic acid) copy that can integrate into the horse’s own cellular DNA. This allows the virus to remain in the horse’s cells for its lifetime. The virus also evades the immune system by constantly mutating.⁷

    There are three main forms of the disease: acute, chronic, and asymptomatic (also called inapparent or subclinical).^2,7

    1. Acute symptoms -- fever (104 to 108 degrees F.), hemorrhage, edema (swelling), anemia, and death that usually occurs in three to four weeks. Antibodies may not be present for 1- to 45 days. Virus concentration is about 1 million infectious particles (ip) per milliliter (ml.) of blood.
    2. Chronic symptoms -- recurring bouts of fever, anemia and unthriftiness (chronically thin); this form is known as the "swamper," Virus concentration is about 1000 ip per mL of blood.
    3. Asymptomatic (subclinical) -- no symptoms of disease -- may have survived the acute or chronic form or may never have shown any symptoms. Virus concentration is about 0 to 10 ip per ml. of blood. The only evidence of the disease is the presence of antibodies in the blood, even if no infectious particles can be detected.

    Some strains of EIAV are lethal, others induce severe chronic disease, but many strains present today induce few to no overt clinical disease.^2,8 The EIAV strains with the greatest potential to induce severe disease have been selected against over the years by the test and slaughter methods.⁸ Federal regulators assume that all strains of EIAV have the genetic potential (a) to induce disease in equids and (b) to mutate and initiate epidemics.⁸ The genetic material of EIAV can be found persistently and sometimes in relatively high levels in test-positive asymptomatic cases.⁸

    Acutely and chronically infected horses are considered the most dangerous to uninfected horses.^2,7,9 The asymptomatic horse, except in certain circumstances, such as during a relapse, poses a very low threat to other horses. Monitoring the status of the asymptomatic horse is important because the horse may experience a low-grade fever that is not noticed by the owner.

    TRANSMISSION

    Transmission is mechanical

    The EIA virus is transmitted when the blood of an infected horse enters the blood of another horse mainly through the bites of large and small horseflies and deerflies.^7,10 These flies are abundant in wooded, swampy habitats that are suitable for breeding.⁷ Mosquitoes are not considered to be important vectors of EIAV.^7,10 Areas that offer suitable habitat to flies are more likely to have pockets of endemic EIA and a higher incidence of acute and chronic disease.

    USDA publications designate as EIA "hot spots" a number of states bordering the Gulf of Mexico and Mississippi River plus some adjacent states and some that harbor EIA-positive "free roaming" horses.^2,8 "Hot Spot" states are pressed by the USDA to institute more rigorous efforts to reduce EIA in endemic areas by mandatory testing and permanent identification of all equids.

    People can cause the transmission of EIAV to susceptible horses by using contaminated needles, syringes, instruments, and other equipment, as has been documented.^1,7,11 Unknown is the role that this type of transmission plays in the overall incidence of disease and in reported "outbreaks." However, most government reports emphasize the importance of transmission via human practices and educate against it.^7,12

    Transmission from asymptomatic horses has been documented

    The asymptomatic horse could theoretically transmit the virus if even if one infected cell is transferred.⁷ EIAV has been naturally transmitted by flies from asymptomatic horses during some experimental field studies; in others, transmission was difficult.^10,13

    Transmission is dose related

    Transmission is dose related and several factors increase the chance of transmitting the infection to the susceptible equid: (a) the amount of blood transferred, (b) the level of virus present in the blood, (c) close proximity of infected to uninfected horses, (d) close proximity of horses to horse flies and deer flies, and (e) interrupted feeding of flies (painful bites cause horses to repel flies while blood is still on the mouth parts). Some areas of dense horsefly populations resulted in over 1000 horsefly bites per hour.⁷

    The rate of transmission cannot be predicted accurately.

    Because of these variables, the rate of transmission cannot be predicted with accuracy. "If all infected horses have EIAV replication under control and the virus is present in only 1 infectious dose per mL of blood, then the predicted chance that any one fly that feeds on the horse would have a virus on its mouthparts is about 1 in 100,000. It’s a game of chance."⁷ Furthermore, only one horsefly out of 6 million is likely to pick up and transmit EIAV from the asymptomatic horse.¹⁴

    Statistically, an uninfected horse is safer 200 yards from an asymptomatic test-positive horse than in a herd of untested horses.^10,13

    Studies have shown that 99% of the horseflies, when interrupted in feeding, would be expected to return to the original host when separated by as much as about 50 yards from other horses.¹³ "There is an estimated million-fold greater risk of acquiring EIA by co-mingling with untested horses than being maintained 200 yards or more from quarantined test-positive aymptomatic carriers in areas of the country where infection is expected in 1 of 10,000 horses.".⁷

    Asymptomatic mares that test EIA-positive do not necessarily transmit the virus to foals.

    Foals of EIAV-positive dams with clinically asymptomatic infections have an excellent chance of being raised uninfected, even with high populations of bloodsucking flies.^9,10,15 The foal normally does receive Coggins-test-positive antibodies from the mare, but its own blood becomes negative, due to decay of maternal antibodies, in six to eight months. It is then safe for the foal to co-mingle with other EIAV-negative horses. ^9,10,15

    Some horses that test negative can transmit infection.

    Just as there are Coggins-positive animals that carry the EIA virus, there are also individuals that harbor the virus but are Coggins-negative.^16,17,18 Several horses that initially were reported Coggins positive later became Coggins negative, with some individuals remaining non-infectious while one is reported to have remained highly infectious.^16,17,18 It is also well known that the newly infected horse builds antibodies in 10 to 45 days postinfection, leaving a window of unknown contagion status before detectable antibodies are present in the blood.^2,8 For this reason, USDA recommends that when Coggins-positive horses have been found and removed from a group of horses, the remaining horses should be retested at 30- to 60-day intervals until new cases fail to appear⁷

    
    

    DIAGNOSTIC TESTS

    Several official laboratory diagnostic technologies are currently available to detect EIAV infection, not necessarily in an animal experiencing clinical disease. These tests include the AGID or Coggins, two types of ELISA (C-ELISA & SA-ELISA), and the western immnunoblot tests.^7,19 Two of these tests are practical, inexpensive, and very useful in the field to detect EIAV infection, because they require an easily obtained blood sample, results can be obtained quickly, and they are easily learned by laboratory personnel.

    The ELISA tests are very rapid and results are obtained on the same day of sample collection. One disadvantage is that the ELISA test is very sensitive and may give a false positive reading; therefore, ELISA tests have to be backed by the Coggins test.⁷ The Coggins test, which correlates well with the horse inoculation test, is also accurate (about 95%)¹⁹ and requires 24 hours for a reading. The western immunoblot test is expensive and requires greater technical expertise, but is useful when there is disparity among the other tests.⁷ Of course, in very unusual cases, the horse inoculation test (injection of blood from a suspect infected horse to a known negative horse) may be considered.

    As previously discussed, the Coggins test may result in false negatives in a few infected individuals that are virus shedders, but to date there is no remedy for this problem.

    For a more complete explanation of the EIA virus and diagnostic tests, see USDA-APHISEIA: A Status Report on Its Control (1996) and accompanying video.

    The ideal test would both detect and quantify the amount of virus present in the infected animal, but rapid, inexpensive, and acceptable tests are not available in the field to determine if an animal is infectious to others. Therefore, all horses diagnosed EIA-infected by the above tests, are considered a health hazard to EIA negative horses by the animal health regulatory agencies.^7,8

    Evaluating Disease Status

    There is great variability in how easily the EIA virus can be transmitted. Some research scientists have used the sideroleukocyte (SL) test to determine if an EIAV-infected horse is a threat to others.⁹ The SL test is not officially recognized by regulating agencies. However, the Japanese used and researched the SL test extensively as an official EIA diagnostic test for decades prior to the Coggins test.^4,20 The SL test has been used to help herd owners, who hope to save valuable genetic stock, manage EIA V-infected mares and raise EIA V-negative foals.⁹ It can help an owner of a quarantined EIA horse determine whether the horse is experiencing an EIA episode or an unrelated problem.

    The SL test measures iron uptake in phagocytes (a class of white blood cells) during a hemolytic crisis (breakdown of red blood cells) such as EIA, piroplasmosis (not present in the U.S.), strangles, and sometimes other conditions that affect red blood cells.²⁰ The SL test becomes positive (i.e., more than 2 sideroleukocytes per 10,000 cells) 2 to 3 days into the febrile period^4,9,20 and remains so generally 30 days but possibly longer.

    While the SL test is not recognized as an official test of EIAV infection, it is nevertheless clinically useful. For example, by way of analogy, physicians use the T-cell monitoring test to determine if/when an AIDS patient needs antiviral drug therapy. The same principle applies to monitoring the EIA V-infected horse. These tests are indicators of an active disease state which coincides with increased viral activity and ensuing tissue damage.

    VACCINE RESEARCH

    Research scientists have attempted to develop a vaccine that would be safe and effective to protect equids from EIAV infection. Early research (1970’s) with EIA vaccines internationally used the standard vaccine production techniques of the era.² Inactivated (killed) and modified-live (tamed) vaccines were produced to vaccinate horses and were tested by challenge with virulent (disease causing) EIAV. Results varied from good responses, as long as the animals were challenged with a homologous (same) strain to partial protection when killed products were used.² Enhanced clinical signs of disease were noted in animals that had been immunized with hyperimmune products² (serum containing EIA immune antibodies and other disease fighting blood components from a serially inoculated animal).

    Modern technology has brought forth vaccine strategies that include the study of subunit²¹ (parts of the EIA virus), recombinant²² (genetic material from the EIA virus inserted into the genetic structure of a non-disease producing virus), and inactivated EIA virus coated beads.²³ Inactivated and modified-live EIAV vaccines are also being studied.²⁴ Again, a variety of results have been reported depending on the type of vaccine used. Development of a safe and effective vaccine has been difficult because some of the vaccines used in the trials don’t stimulate a complete immune response and others, such as the modified-live vaccines, generally work the best only when the same EIAV strain is used as the challenge virus.² Enhancement of clinical signs continues to be a problem with some of the subunit and recombinant type vaccines.^21,22 In other words, these latter vaccines actually caused a worse disease condition in some of the animals when the vaccinated animals were challenged with virulent virus compared to the unvaccinated controls.^21,22

    In the mid 80’s, the Chinese claimed the successful development of a modified-live EIAV vaccine that has been used in the field to eliminate active disease (not the EIA virus) in their country.^5,25 This vaccine, after about 17 years of politics between the two countries, was approved in 2000 for study in the U.S. The vaccine has been through quarantine studies at Plum Island, N.Y. (an isolation facility for infectious disease organisms), and is currently being studied in a quarantine research laboratory in Boylestown, Mass.⁵

    Some research scientists have expressed their opinion that an EIA vaccine may become available to horse owners as soon as 2 to 3 years to as long as 10 years. Regulators maintain that vaccinating horses with modified-live vaccines would complicate current testing programs.²⁶ The Chinese vaccine is equipped with a marker and accompanying diagnostic test to differentiate the vaccine strain from a natural field strain.⁵ Advanced technological methods, available today, solve such problems so that modern vaccines need not interfere with EIA testing.

    REGULATIONS

    Federal law doesn’t require Coggins tests prior to the interstate movement of horses, but it prohibits the interstate movement of EIA reactors except to a slaughterhouse, research facility or return to its original home state.⁶ Federal law regulates international importation of equids.²⁷ Laws regulating EIA vary among the states, but most states require a health certificate and accompanying negative Coggins test for horses entering their state. The USDA is the guiding regulatory authority for the states and makes recommendations.

    State requirements, following USDA recommendations, range from a negative test in certain circumstances (e.g., intrastate transport of equids, private and commercial horse sales, admittance to equine events, anywhere equids assemble) to mandatory annual testing with permanent identification. The test and quarantine/slaughter law is followed by the states with each state enacting its own regulations regarding separation distances, quarantine time, identification of reactors, etc.

    In 1998, the USDA revised its recommendations with the intended goal of eradicating EIA. Two of the more important recommendations are a) annual testing of all equines and b) individual equine identification. Individual equine identification is critical to the control and surveillance of EIA and can be facilitated by using a uniform electronic identification standard.¹²

    A "good neighbor policy" law was enacted during the 1999 legislative session in Arkansas.⁸ This law enables a horse owner to obtain state verification of a neighbor’s compliance with the mandatory annual EIA test law. If there is no evidence of such compliance, the state is mandated to test such neighboring horses. The concept involving testing the 10% to 20% mobile equine population with trace back investigation has also been instituted in recent years to further reduce EIA infection rates.

    EFFECTIVENESS OF REGULATION

    EIA among tested animals has been reduced from more than 3% in 1972 to 0.046% in 2000 nationwide with a range of 0% to 0.28% among the states.²⁸ The figures for Texas are more than 13% in 1972 to 0.07% in 2000. In 1999 about 1.6 million of an estimated 6 to 7 million equids were tested.²⁸ Some representative figures for the incidence of EIA along with costs of testing are shown in Table 1.

    Table 1. Some Results and Costs of EIA Testing in the United States and Selected States (*Dollar estimates based on USDA estimates of $25/sample. **Use 90% based on estimated 85% to 95% asymptomatic)

    Horses Tested	Disease State	Cost to owners*
    United States (USDA 2000)28
    1,768,814	Total horses tested	$44,220,350
    813	Number of positive tests	$54,392/horse
    732	Estimated Asymptomatic**	$60,410/horse
    81	Estimated Symptomatic**	$545,930/horse
    Maine to Maryland (USDA, 1997 to 1998)8
    179,000	Total horses tested	$4,475,000
    3	Number of positive tests	$1,491,666/horse
    2.7	Estimated Asymptomatic**	$1,657,667/horse
    0.3	Estimated Symptomatic**	infinity
    Texas (USDA, 1999 to 2000)28
    247,035	Total horses tested	$6,175,875
    192	Number of positive tests	$32,166/horse
    173	Estimated Asymptomatic**	$35,699/horse
    19	Estimated Symptomatic**	$325,046/horse
    Kentucky (University of Kentucky, 1987 to 1996)29
    658,000	Total horses tested	$16,450,000
    338	Number of positive tests	$48,669/horse
    304	Estimated Asymptomatic**	$54,112/horse
    34	Estimated Symptomatic**	$483,823/horse

    In the left-hand column the table shows the total number of EIA tests performed and the number of tests that returned positive results in one year in the United States, in the northeast, and in Texas, and over ten years in Kentucky. The number of asymptomatic and symptomatic horses is then estimated assuming that 90% of positive horses are asymptomatic.

    On the right side of the table is the estimated cost of testing, based on $25 per sample. Then the total cost to all active horse owners to identify the horses that test positive is calculated along with the cost per horse to identify the symptomatic and asymptomatic horses. The dollar figures are estimates using averages found in various reports.

    Not included are the potential sale value and breeding potential that horse owners lose when their horses are destroyed because they tested positive for EIA. Owners receive no indemnification for the value of the horses lost, nor for euthanasia and disposal. An unknown cost to all taxpayers is the extra state spending for verification and costs to enforce each program.

    Not in the table are the estimated total EIA costs to horse owners just to test horses from 1972 to through 2000: roughly half a billion dollars.²⁸ In Kentucky alone in 2000 the cost was about 2.5 million dollars to find 4 reactors -- or about $640,000 per horse.²⁸

    Of the approximately 97,000 positive reactors identified in the United States from 1972 through 2000, about 87,000 asymptomatic animals were destroyed (using the estimate that 90% of test-positive horses are asymptomatic and assuming that the number of quarantined animals is insignificantly small).¹

    Note:  These figures were calculated using USDA totals for horses tested and total horses tested positive and & multiplying by the costs of the tests: $15/test from 1972-1985 and $25/test for 1986 - 2000.

    EIA ERADICATION - IS IT COST EFFECTIVE?

    Many people believe that EIA can be eradicated in the U.S. because equids are the sole hosts for EIAV. Others are skeptical because of the history of efforts to eradicate diseases that are more economically important and also transmissible to humans.

    An example is the program to eradicate bovine tuberculosis, which has resulted in a greatly reduced incidence of the disease, but eradication has proved elusive, despite more than eight decades of work and billions of dollars spent. The TB Eradication Division of the Bureau of Animal Industry originated in 1917.³⁰ Owners were indemnified with state and/or federal funds for loss of their condemned animals.³⁰ However, ground is being lost in the program to fight TB in cattle, as statements in a 1995 report³¹ illustrate: "These dairy herds (3,000 to 19,000 head) are so large and the cattle worth so much more than indemnity allows us that we can’t depopulate these herds; we don’t have the money so we have to live with the disease. When a disease is present in a population at a low prevalence, relatively speaking. it is expensive for the industry to require testing on every animal that changes ownership. (Emphasis added.) With low prevalence in the 1950’s and 1960’s, funds for developing improved diagnostic tests were not available. Today that trend continues."³¹

    The program to eradicate brucellosis in cattle, initiated in 1934,³⁰ also has yet to succeed. Both cattle diseases flourish in wildlife such as bison, elk, deer and coyotes, which can infect adjacent cattle. The incidence of both diseases has been greatly reduced and is considered eradicated in some places but not nationwide.

    If regulators don’t have the funds to eradicate TB or brucellosis in cattle nationwide, it is unlikely that funds will be available to eradicate EIA in horses. Of course, it is the horse-owning public, not governments, that continues to spend millions annually testing mostly the same horses. Unlike other agricultural eradication programs, efforts to control EIA do not cover the costs or losses to horse owners.

    EIA has been eradicated in Japan,³² an easier accomplishment there than elsewhere because Japan is an island nation, but only at great cost and the sacrifice of vast numbers of horses. In Japan, the horse population was progressively diminishing for other reasons and today there are relatively few horses in that country. In large regions of China, which has long borders with other countries, horses are economic necessities, not luxuries, for a great many people. Faced with outbreaks of virulent strains of EIA, Chinese scientists had no choice but to find methods of control which would reduce the incidence of serious disease without sacrificing useful animals.⁵

     

    QUARANTINE RANCHES/STABLES

    The concept of EIA quarantine ranches for asymptomatic carriers has not been widely considered or promoted in the U.S. perhaps because of cost issues or anxiety about potential transmission of the virus. A Florida facility has shown that these are not insurmountable obstacles. The Florida Research Institute for Equine Nurturing, Development, and Safety, Inc. (F.R.I.E.N.D.S) "a non-profit sponsor-a-horse program" has successfully maintained healthy asymptomatic horses for years without EIAV transmission to EIA V-negative equids in spite of a large horse fly population. At the same time, F.R.I.E.N.D.S provides affordable riding and other opportunities for enjoying horses to people who cannot or do not want to, own horses. For more information, link to eiahorses.org

    This EIA facility made lemonade out of lemons when in the 1970’s a family started the first EIA quarantine ranch; half of the ranch’s horses tested positive. At one point there were over 100 horses housed. By cooperating with Florida state regulators and using local veterinarians, the horses were and are monitored closely with much valuable research information being collected. The following was condensed from a letter from Debra Beye-Barwick, Chairman of the Board of the F.R.I.E.N.D.S., Inc. (2001).

    In the 1970’s, the facility had 2 stallions; 1 Coggins positive and 1 Coggins negative. They were bred frequently to the many registered mares of various breeds. All of the foals became Coggins negative after the maternal antibody waned. Many were sold, shown and never returned nor became Coggins positive. Over the last 30 years, 2 acute EIA cases were admitted to the ranch, in the late 1 9 70’s, that were very sick and died. All cases admitted since that time have been asymptomatic. These horses have experienced febrile episodes, but have been diagnosed with other conditions such as respiratory disease, colic or low grade infections. F.R.I.E.N.D.S. has never had a veterinarian attribute the cause of a death in their horse herd to EIA, other than the 2 mentioned acute cases. Most of the people that have donated horses to the ranch claim their horses weren’t sick and found it hard to believe that anything was wrong with them. The horses are ridden regularly and are housed across the road from the everglades (wetlands preservation property). A large horsefly population exists at the ranch yet none of their negative horses have ever tested positive. Eight horses testing negative in the last 9 years have never tested positive. Coggins tests are pulled on the negatives monthly. Each of these horses were different breeds and ages, some were ponies. The ranch currently houses 59 horses (soon to be 60), 2 miniature donkeys, 2 goats & 4 potbelly pigs. Of the 59 horses, 2 are negative "test horses," one of which originally tested positive on 12/22/93 and is now still testing negative; last test was done on 1/30/01. The ranch still has 2 horses from 1 973 and 1 974, now aged 33 yrs and 34 yrs. Many horse breeds are represented. The horse residing at the ranch the longest died at the age of 34 and he was still negative even after being among the herd for more than 1 5 years. The ranch had 2 horses sent to them that were test positive, both were freeze branded and among the herd for years before their retest was done. Of five horses tested that day, two were known to be Coggins negative and the other three test horses were expected to come back positive. Surprisingly, 2 of the 3 positives came back negative. They have been continually tested since 1 999 and they still test negative. One has died of old age, but the other is still alive.

    While research was a secondary benefit of the Florida quarantine ranch, an EIA herd was maintained primarily for scientific study at a University Research Facility with no transmission problems.⁹ This herd, which included about 100 chronic and asymptomatic EIAV carrier horses over a period of about 10 years, was co-mingled with sentinel horses (Coggins-negative horses within and/or adjacent to an EIA herd). Why transmission is high in some herds/stables and low to non-existent in others may be a matter of different EIAV strains infecting the horses and/or level of fly population present in the area.

    SUMMARY

    Equine Infectious Anemia is a disease that infects equids only. It is spread mechanically, primarily by biting flies but also by use of contaminated needles, syringes, etc. The disease can be (1) acute and often fatal, (2) chronic and debilitating, or (3) asymptomatic with no obvious effects. Since 1972 EIA has been diagnosed primarily by the Coggins test, which detects antibodies in blood samples but does not evaluate the quantity or virulence of EIA virus in the animal. It is estimated that the virus is not harmful to 85% to 95% of horses that test positive for EIA. Research has established a positive correlation between the amount of virus present and the degree of illness. Natural transmission from asymptomatic test-positive horses to test-negative horses is low in both field studies and in herds in which test-positive and test-negative animals co-mingle. Transmission and incidence of disease is highest where the environment is conducive to large and small horseflies and deerflies. There is no EIA treatment or preventive vaccine available in the United States. A vaccine has been widely used in China for many years with reported success in significantly reducing deaths and illness from EIA.

    The U.S. Department of Agriculture recommends regulations to the states and sets EIA testing requirements for importation and interstate transportation of horses and other equids. Regulations vary among the states but typically, animals that test positive for EIAV antibodies must be destroyed or quarantined. Because quarantine regulations are onerous, the vast majority of Coggins-positive horses are destroyed. Costs of testing, euthanasia, and disposal are borne by horse owners, who are not indemnified for their losses. Over the years, the incidence of EIA has been dramatically reduced among tested animals while the overall expenditures to identify Coggins-positive equids has increased. In 2000, the nationwide average cost to identify Coggins-positive equids was about $54,000 per positive animal, or about $500,000 per acutely or chronically ill animal.

    While there is little opposition to quarantine and humane slaughter of equids that are acutely or chronically ill with EIA, regulatory policies regarding asymptomatic horses have generated controversy over the years. On one side of the controversy are those who believe that EIA is a highly dangerous disease and that all equids that harbor the EIA virus, no matter how low the viral activity, are a potential threat to other equids. On the other side are those who believe that EIA has never been a major disease among horses, that only acute and chronically ill animals are realistic threats to uninfected animals, and that asymptomatic horses are very rarely a source of virulent EIA infection. Proponents of one view believe that current regulations are insufficient and that all untested horses should be tested and all that test positive should be destroyed. Proponents of the alternative view believe that current regulations are misguided in regard to asymptomatic animals and quarantine regulations should be relaxed.

     

     

    OBSERVATIONS AND OPINIONS

    1. EIA, a disease of equids, is treated differently from diseases in other livestock. EIAV is a lentivirus and is not a danger to humans or any animal other than equids. Lentiviruses in other livestock are not regulated at all. Agricultural animals that are infected by lentiviruses include cattle (bovine immunodeficiency virus), sheep (visna-maedi virus), and goats (caprine arthritis-encephalitis virus). Diseases in livestock that are a threat to humans, such as bovine tuberculosis and brucellosis, are regulated. Owners of livestock that must be destroyed to control those disease are indemnified. Owners of horses, on the other hand, must bear the costs and losses associated with EIA.
    2. The costs of EIA control are not just economic. The loss of a horse in which an owner has invested time, money, and emotional energy cannot be measured in dollars alone. The owner who has seen a well-loved useful previously healthy horse die of EIA may well believe that it is worthwhile to kill any number of otherwise healthy test-positive horses who might infect other horses, no matter how small the chances are of that happening. On the other hand, the owner of a well-loved useful healthy horse that has to be put down because it tests positive for EIA believes the loss of that one horse in no way protects any other horse and is an unfair unrecompensed taking of property by the government. No one can put up much argument against putting down a horse that is chronically or acutely ill from the equine infectious anemia virus. The issue is: How dangerous is an asymptomatic EIA-positive horse to other horses? Unfortunately there is not enough research to provide a definitive answer.
    3. The implementation of the test and slaughter-or-quarantine approach, with no satisfactory quarantine option, has had two unfortunate side effects: large numbers of untested animals that constitute a reservoir of the disease and reduced levels of research aimed at prevention and/or treatment. The reluctance of owners to risk losing their useful asymptomatic animals is understandable as is reluctance to support EIA research if all animals that harbor the virus are to be destroyed anyway. Of roughly 6 or 7 million equids nationwide, an estimated 80% of equids (about 5 million) have never been tested for EIA. Even in Louisiana, which requires that all equids be tested annually for EIA, compliance is estimated at 30% or, at best, 40%.
    4. In the early days of EIA testing, it was assumed that EIA was almost invariably a fatal or debilitating disease. How could anyone know otherwise? When early testing programs discovered many EIA-positive healthy horses, it was assumed that these horses had been sick in the past and would "relapse." Research evidence and practical experience over the years do not support these assumptions. In many transmission trials and in reports of "EIA Outbreaks" in the literature, very little has been reported about the disease status of the animals that test positive -- were they acutely, chronically, or asymptomatically affected? Evidence from research that did differentiate among the different forms of the disease and experience with herds of mixed test-positive and test-negative animals have shown that asymptomatic horses with low levels of EIAV rarely relapse and transmission of the virus is difficult. Regulations based on the assumption that anything is possible results in over-regulation.
    5. It is argued that asymptomatic animals are a threat to uninfected horses because (a) the virus mutates and could become more virulent, (b) just because a horse looks healthy doesn’t mean it can’t harbor a lot of active virus, (c) an EIAV-positive horse could relapse at any time, and (d) even if the viral activity is low, there is still a chance of transmission -- it’s "Russian roulette" to have a testpositive horse anywhere near uninfected horses. In Russian roulette, the chances of being struck by a bullet are 1 in 6, if the gun has six chambers. In the case of EIA, the chances of an uninfected horse getting a virus from a fly that has bitten an EIA-positive animals range from maybe 1 in 100,000 under circumstances that favor transmission to 1 in a few million, in most other circumstances. The Russian roulette argument works the other way as well -- there is a chance of transmitting the virus from a test-negative animal because (a) antibodies don’t appear for up to 45 days after EIAV infection and (b) a few animals harbor the virus and never produce a positive Coggins test. Again, the chances are very small.
    6. Just as there are endemic areas of EIA with an environment suitable for EIAV transmission, there are also areas with habitats that are not suitable for natural transmission. These areas should not be regulated with the same intensity that endemic areas require. The vast difference between the environments of east and west Texas is an example.
    7. Several lawsuits have been filed over the years by owners trying to save their Cogginspositive asymptomatic animals. Regulations to force testing of the untested 80% of the horse population might prompt class-action lawsuits. In addition, horse owners may push to have their horses declared companion animals. There is already a move in this direction. If the horse is removed from agriculture status, many of the advantages of this classification would be lost.³³
    8. Most of the horses testing positive for EIA today are asymptomatic. While several factors may explain this phenomenon, three stand out.

    a) Selection against the more virulent (disease causing) strains. Because they cause clinical illness, these strains are easier to identify and eliminate. b) The EIA virus may be adapting to its host. A virus can act like a parasite. To succeed, a parasite shouldn’t kill its host but rather adapt over time to live in harmony with it. As reported in 1978, 85 to 95% percent of horses that tested positive on the Coggins test were asymptomatic-- a finding that suggests virus adaptation. c) Through natural selection, the genetically resistant animal survives. Therefore, the ability of the EIA virus to reside silently in asymptomatic horses may also be due partly to the genetic resistance of the host animals. Ironically, the test-and-slaughter program may be selecting against the more genetically resistant individuals.

    RECOMMENDATIONS

    1. Continue those practices that are most effective. (a) Continue to require negative Coggins test for interstate and international importation of equids. (b) Continue to require negative Coggins tests at sales and other transactions so that the buyer is protected. (c) Continue to educate the horse-owning public about safe practices in handling needles, syringes, tack, barn equipment, etc. Provide information about effective fly control. Good stable management protects horses from many potential problems, not just EIA (which is actually exceedingly rare in most parts of the country). Provide facts about EIA without resorting to scare tactics or exaggeration.
    2. Provide for compensation or indemnification if an asymptomatic horse is to be put down because it tests EIAV positive. A reasonable quarantine option, without compensation should be offered.
    3. Quarantine farms or ranches, a more humane way to treat the asymptomatic EIA reactor, should be provided and financed by each state. This option to euthanasia could enable the asymptomatic horse to live until a vaccine or antiviral drug might possibly become available and accepted by the community. The facility would provide an excellent opportunity for research on the asymptomatic animal. Additionally, such a ranch could provide recreational and therapeutic opportunities to people who could enjoy the horses by paying a fee toward the support of the animals and the facility. Quarantine regulations should be based on research, not emotion. For example, it is unreasonable to require more than 200 yards between asymptomatic EIAV-positive horses and other horses because feeding flies have a propensity to stay with their host.
    4. Research is needed to understand the EIA virus, to develop treatments and preventive vaccines. To combat EIAV infections in "hot spot" areas, establish grants for universities programs to encourage EIA testing, establish quarantine farms for research, and compensate owners.
    5. If regulations require negative Coggins papers for activities such as horse racing, shows and rodeos, boarding stables, and other situations, then enforcement should be the responsibility of the regulators, not the private citizens. Organizations that sponsor equine activities should be encouraged, but not required, to check Coggins papers. Excessive paperwork builds resentment and resort to evasive tactics.

     

     

    REFERENCES CITED

    ¹ Crawford, T. & S.L. Kittleson, A Reappraisal of EIA Regulation, Journal of Equine Surgery & Medicine, Nov. 1978, p. 470-473 (1978)
    
    ² Johnson, A.W., Equine Infectious Anemia: The Literature 1966-1975, The Veterinary Bulletin, vol. 46, pp. 559-574 (1976)
    
    ³ Nolan, M.J., Statement by the American Horse Council, Equine Infectious Anemia: A National Review of Policies, Programs, and Future Objectives. AQHA, p. 11(1985)
    
    ⁴ Ishitani, R., Research in Japan on Control of Equine Infectious Anemia, Equine Infectious Diseases I: Proceedings of 1st International Conference on Equine Infectious Diseases, p. 1-2 (1966)
    
    ⁵ Tashjian, R.J., Progress report -- EIA Vaccine, ACVMF, 29 Prospect St., Boylestown, MA 01583, (April 1999)
    
    ⁶ Dawson, R.O., (Prof. of Law, U. of Texas), Your Horses, EIA, and the Law, Caution Horses, vol. 3, no. 3, (www.law.utexas.edu) Fall 1998
    
    ⁷ Cordes, T. & C. Issel, USDA-APHIS, EIA: A Status Report on Its Control, with accompanying video, (1996)
    
    ⁸ Cordes, T., Equine Infectious Anemia and EIA Brochure 2000, Center for Epidemiology and Animal Health, USDA--APHIS: VS attn NAHMS (NAHMS web@usda.gov; www.aphis.usda.gov/vs/ceah/cahm, (2000)
    
    ⁹ McConnell, S., and M. Katada, University Research Progress Reports and Projections on EIA, Equine Infectious Anemia: A National Review of Policies, Programs, and Future Objectives, AQHA, pp. 29-33, (1985)
    
    ¹⁰ Issel, C., Epidemiology and Insect Transmission, Equine Infectious Anemia: A National Review of Policies, Programs, and Future Objectives, AQHA, pp. 4 1-44, (1985)
    
    ¹¹ McConnell, S. Equine infectious anemia -- current research findings, Southwestern Veterinarian, vol. 25, no. 3, pp. 183-192. (1975)
    
    ¹² USDAAPHIS [91-55-037] Equine Infectious Anemia: Uniform Methods and Rules Effective January 1998, p. 12, (1998)
    
    ¹³ Foil, L.D., et al., Quantifying the Role of Horse Flies as Vectors of Equine Infectious Anemia, Equine Infectious Diseases V, Proceedings of the 5th International Conference,(D.G. Powell, Ed.), pp. 189-195, (1988)
    
    ¹⁴ USDAAPHIS Fact Sheet, Veterinary Services, Oct. 1996
    
    ¹⁵ Issel, C., Equine Disease Quarterly, Department of Veterinary Science, University of Kentucky, vol. 9, no. 2, (Jan. 2000)
    
    ¹⁶ McConnell, S., and M. Katada, Transmission of Equine Infectious Anemia Virus from a Horse Negative to Agar Gel Immunodiffusion testing, Equine Veterinary Journal, vol. 13, pp. 123-126, (1981)
    
    ¹⁷ McConnell et al. Occult Equine Infectious Anemia in an Immune Suppressed Serologically Negative Mare, Equine Practice vol. 5 pp. 30-39 (1983)
    
    ¹⁸ F.R.I.E.N.D.S., Florida Research Institute for Equine Nurturing, Development, and Safety, mc,. personal communication, (2001)
    
    ¹⁹ Sellon, D.C., Equine Infectious Anemia, Veterinary Clinics of North America -- Equine Practice, Update on Infectious Diseases, vol. 9, no. 2, pp. 32 1-336, (Aug. 1993)
    
    ²⁰ lshii, S., On the Histo-Pathological Studies of Infectious Anemia in Horses. On the Detection of Siderocytes in the Blood of Vena Jugularis arid Its Clinical Diagnostic Value, Japanese Journal of Veterinary Science, vol.2, pp. 531-557, (1940)
    
    ²¹ Issel, C., et al., Efficacy of Inactivated Whole Virus and Subunit Vaccines in Preventing Infection and Disease Caused by Equine Infectious Anemia Virus, Journal of Virology, vol. 66, pp. 3398-3408, (June 1992)
    
    ²² Raabe, M.L., et al., Immunization With a Recombinant Envelope Protein (rgp 90) of EIAV Produces a Spectrum of Vaccine Efficiency Ranging from Lack of Clinical Disease to Severe Enhancement, Virology vol. 245, pp., 151-162, (May 25, 1998)
    
    ²³ Issel, C., et al., A particulate Viral Protein Vaccine Reduces Viral Load and Delays Progression to Disease in Immunized Ponies Challenges with Equine Infectious Anemia, Virology, vol. 254, pp. 37-49, (1999)
    
    ²⁴ Hammond et al., Evaluation of Antibody Parameters as Potential Correlates of Protection or Enhancement by Experimental Vaccines to Equine Infectious Anemia Virus, Virology, vol. 262, no. 2, pp. 416-430, (Sept. 30, 1999)
    
    ²⁵ AVMA, Scientists To Pursue AIDS Vaccine Based on EIA Model, Journal of the American Veterinary Medical Association, vol. 211, p. 266, (Aug. 1, 1997)
    
    ²⁶ Johnson, J., EIA Debate, The Quarterhorse Journal, pp. 58-63, (Sept. 2000)
    
    ²⁷ USDA-APHIS, Veterinary Services, National Center for Import/Export, www.aphis.usda.gov/ncie 2001
    
    ²⁸ USDA [maps] National Animal Health Programs, USDA APHIS VS www.aphis.usda.gov/vs/eia/eia.html; www.aphis.usda.gov/vs/nahps/I,ages/eia-postest.jpg (1972- 2000)
    
    ²⁹ Ford,. R. Figure 1. EIA Surveillance Testing Equine Disease Quarterly vol. 5, no. 3, Department of Veterinary Science, University of Kentucky, (April 1997)
    
    ³⁰ Associates of the National Agricultural Library, Inc., Beltsville, MD., 100 years of Animal Health (1884-1984), Journal of National Agricultural Library Association, vol. 11, nos. 1/4, pp. 39-40, 42-44, (1987)
    
    ³¹ AVMA, Tuberculosis Persists in the U.S. Livestock, Journal of the American Veterinary Medical Association, vol. 209, pp. 1529-1530, (Nov. 1, 1995)
    
    ³² Nakajima et al. Equine Infectious Anemia: Research in Japan on the Virology, Immunology, Pathogenesis and Control The Guardian: Journal of Equine Science vol. 5. pp. 1-19 (1994)
    
    ³³ AAEP “Changing the Legal Status of Horses as Livestock” Revisited News and Notes from the American Association of Equine Practitioners (March 2001).
    
    
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