Equine Infectious Anemia Control Requires Active Surveillance & Awareness
ACVIM 2008
Charles J. Issel, DVM, PhD, DACVM
Lexington, KY, USA

The Status of EIA in the US

In 2008 equine infectious anemia (EIA) is essentially eradicated in the United States. That statement must be further defined to indicate that of the approximately 2 million horses sampled each year, only 303 cases have been found over the last 24 months (0.008%), and 66 of those were on one premises. Thus in the mobile and tested population, the risk of encountering EIA is essentially zero today. It is very rare today to find a veterinarian in the United States that has ever seen an active clinical case of EIA. We are in an enviable position but we are at risk of becoming too complacent about EIA because we consider it "eradicated" from our spheres of influence.

To get a true sense of EIA in the United States we must take into account the numbers of horses and other equids that have never been tested for this infection. The number is unknown, but the rate of infection with EIAV would be expected to differ from the rate seen today and to be closer to the rates found when testing for EIA was first possible (in the early 1970s) when thousands of cases were found each year. In many areas, even where annual testing requirements are in place, a relatively high percentage of the population remains untested, and is conservatively estimated nationally at 50%.

The challenge for the veterinary profession in regards to EIA today can be summarized under two major headings: 1) increase efforts to maximize the return on the investments owners have made to test their horses (>$55,000,000 in 2007); and 2) adopt methods of infection control so that we do not risk transmitting EIAV between horses in practice situations. These two areas are discussed below.

Changing the Strategy: "Smarter Testing" for EIA

When a critical eye is placed on testing for EIA in the United States, it is clear that we are essentially testing the same horses each year in response to requirements for entry, competition, housing, and so forth. For the most part, the horses that are tested annually are not at risk of acquiring EIA because they reside on premises/in areas where only test-negative horses are found. Little is being done in an organized manner to find the remaining pockets of infection where horses have eluded testing to date.

In essence, we are penalizing owners of tested horses for doing the right thing. One way we could reward these owners who test their horses is to change the interval of testing in this mobile and tested population. In most states today a 12 month interval is used for import requirements. The state of New Jersey recognized over 10 years ago that the risk of EIA was so low that a test of resident horses every 24 months was sufficient for surveillance. They have had excellent compliance and results. Analysis of testing results by the National Surveillance Unit of the USDA from statistics compiled from states by the USDA indicate a similar expected risk of acquiring EIA in the majority of states (based on test results from prior years and estimates of expected infection rates in untested horses). Thus it is possible for states to regionalize control strategies for EIA with no expected increase of new cases of EIA, even with a change in testing interval from 12 to 24 months. The expected savings to owners with uniform testing requirements for entry into or movement within the regionalized zone is estimated at more than $10 million each year from regionalization alone and more than $10 million by changing the intervals for testing. The Infectious Diseases of Horses Committee of the US Animal Health Association has recommended such changes as a high priority.

One of the best ways to protect owners and to find new cases of EIA, especially in previously untested horses, is to require a test for change of ownership. In states where this requirement was introduced within the last 10 years, viz. Arkansas and Texas, it has been a most productive method to find new cases, both in the primary case and potentially in previously untested horses on the same and/or adjacent premises.

Increased Awareness of EIA in Clinical Settings

The recent outbreak of EIA in Ireland in 2006 was an excellent reminder about the risk potential for EIA transmission. Because Ireland and its veterinary profession had never experienced EIA, they never considered methods to reduce the human impact on transmission of this blood-borne pathogen. They considered themselves free of EIA, similar to our earlier statement that in the US today we are virtually free of EIA. As most veterinarians in the US today have never encountered clinical EIA, I would suggest that to most practicing veterinarians EIA control does not enter their psyche as they do rounds or deal with their hospitalized patients. The risks are real and the risks are manageable, if we keep the threat of EIA in mind and in perspective.

Let me briefly summarize the events which led to a virtual shutdown of equine activities in Ireland from June 2006 until the lifting of restrictions in late December 2006.

EIA appears to have been introduced into Ireland in equine-origin plasma products.

The first cases of EIA (March 2006) were not diagnosed clinically, in laboratory examinations or in post-mortem examinations of foals that had received the tainted plasma.

Mares on the farm with the infected foals became ill and one was transported to a veterinary hospital where it was treated for liver failure. The mare experienced heavy bleeding and, after 2 days of unsuccessful treatments in hospital, was euthanatized.

EIA was not suspected until the veterinary hospital staff heard rumors from veterinarians on the farm of origin about an outbreak of EIA in 2006 in Italy, possibly the country of origin for the plasma used on the farm.

Once the possibility of EIA surfaced, testing of samples from the mare and samples collected earlier from the foals were confirmed positive for antibodies against EIA 2 days later.

A thorough analysis by the Irish Department of Agriculture of events in the hospital and on the multitude of equine facilities throughout Ireland suggest that the majority of the 28 diagnosed cases of EIA in 2006 were in some way mediated by man; 16 occurred in a common exposure at the hospital where the mare was treated. Only 2 of the cases were thought to be transmitted by biting flies (Tabanids--horseflies and deer flies), even though biting flies were present and relatively numerous on most at-risk premises during the peak of the outbreak.

What lessons should we learn from the experiences in Ireland?

First and foremost, freedom from disease requires active surveillance. Although the risk is negligible today, failure to address the risk invites unwanted consequences.

Second, cleaning and disinfection do not adequately address the risk that EIA poses in clinical situations. The outbreak of EIA in the veterinary hospital, where disinfection followed cleaning of blood spills, demonstrated that in veterinary medicine we should adopt universal precautions for preventing the spread of blood-borne pathogens in facilities under our control. In veterinary practices, this involves testing patients on entry, treating each patient as if they are infected with EIA, containing blood spills and adequately disinfecting them before the usual cleaning and disinfection, and using separate protective gloves as well as disposable needles and syringes on each patient.

The potential for human transmission of EIA virus between horses is thousands of times higher than that of insect vectors. The example I find useful is that when you are collecting a jugular blood sample from a horse with fever and unknown status for EIA and use your finger or thumb to clean up the area, the one drop of blood you may become contaminated with may contain more than 100,000 horse infective doses of EIA virus! In Ireland, each practitioner using such techniques without protective gloves on an acute case of EIA had the potential to infect every horse in Ireland. With care and attention, the risk of human transmission of EIAV between horses can be reduced to zero.

Infection Control in a Broader Perspective

Unfortunately, the majority of veterinary hospitals throughout the world were not designed to be high security isolation facilities to contain highly infective agents in individual enclosures. Veterinary medicine has been victimized in recent years by hospital outbreaks of a number of serious diseases; even the most careful and proactive programs have not been immune to these events. The best approach to minimize these outbreaks appears to include:

 Establish and follow guidelines for monitoring and containing infective agents

 Apprise clients of the potential risks of hospitalization and your control plan

 Monitor individual patients for selected agents throughout their stay

 Pray....and know that your faith in science is sound but realize that science is fallible

For more detailed information, including recommendations for specific organisms, the reader is referred to the Vet Clinics of NA monograph and AAEP web sites.1,2 Additionally, standard precautions for veterinary practices have been recently promulgated by the National Association of State Public Health Veterinarians and are available on their web site.

References

1.  Advances in Diagnosis and Management of Infection. 2006. Vet Clinics of North America 22(2):279-661. Southwood, LL, editor. Elsevier Press.

2.  Equine Infectious Disease Outbreak: AAEP Control Guidelines. 2006. Developed by the AAEP Infectious Disease Task Force. (available online to members at https://www.aaep.org/control_guidelines_intro.htm).

3.  The National Association of State Public Health Veterinarians in 2006 published a Veterinary Standard Precautions Compendium and a Model Infection Control Plan for Veterinary Practices http://nasphv.org/documentsCompendia.html which are available on their web site.

Speaker Information
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Charles Issel, DVM, PhD, DACVM
University of Kentucky
Lexington, KY


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