Page 105 - August 2019
P. 105

                                 SOURCES OF IATROGENIC INFECTION
There are specific sources of iatrogenic infec- tion that are plaguing Quarter Horse racing and Bush Track racing horses:
• Re-use of needles and syringes on different
horses. Horse owners are advised to avoid shar-
ing of needles and syringes between horses.
• Contamination of multi-dose drug vials by inserting a used needle and/or syringe that
deposits blood (with virus) into the bottle. Infected blood contained within the hub of a used syringe or needle contaminates the drug vial, resulting in disease spread with subsequent drug administrations to additional horses.
• Re-use of intravenous (IV) tubing – invari- ably when using tubing to connect to an IV catheter, there is blowback of blood into the tube that cannot be cleaned out with just a rinse or even using antiseptic solutions.
• Improper cleaning and sterilization of lip tat- too equipment.
• Blood doping, particularly of Bush Track horses – this technique takes blood from one horse and gives it to another via IV transfusion.
• Possible use of unlicensed blood or plasma products illegally imported from other coun- tries, including Mexico or South America.
• The possibility of aerosol transmission subse- quent to power washing of facilities housing EIAV-positive horses, especially if a sick horse experiences hemorrhage and contaminates the floor or walls.
There are three phases of infection – acute, chronic, and an inapparent carrier. EIAV at- tains its highest blood-associated titers during clinical episodes, particularly when there is high fever. Following resolution of clinical signs, these levels drop significantly. During
a febrile episode, for example, viral titers can reach 1 million infectious particles per mil- liliter (ml) of blood; with resolution of fever, this drops to less than 100 infectious particles per ml.
Most infected horses develop some level
of anemia while still looking fit and fine and able to perform as intended. However, those that develop an acute crisis experience severe hemolytic anemia and are likely to die. Most infections, however, seem to progress to a rela- tive state of remission, yet these individuals still provide a reservoir for viral infection either via insect vectors and/or iatrogenic sources. And, the underlying anemia may decrease a horse’s resistance to contracting another blood-borne disease, like equine piroplasmosis. It is thought that stress of an inapparent carrier and/or age-related degeneration in the immune system causes that individual to be an active source of infection to others.
Lentiviruses such as EIAV do not stimulate natural, fully protective immunity. In part this
is because they have a high mutation rate, which is difficult for a vaccine to duplicate. This is why billions of dollars and many different vaccine ap- proaches against Lentiviruses, including HIV and EIAV, have mostly been unsuccessful. Because
of the difficulty in protecting against EIAV with immunization, the only successful approach is education about the importance of prevention
by eliminating potential contamination by blood products, and through surveillance and testing.
EIAV infection is limited to equids, so theo- retically it is possible to eliminate the virus from countries such as the United States where the incidence is comparatively low. However, the key factor is compliance, making this a political issue and not one strictly limited to science.
In regards to EIAV testing within the USA, most show horse disciplines test horses repeat- edly because the horses travel out of state, and
to clinics and shows where a negative Coggins test is required for entry. Such a clean population continues to be tested on an annual basis and so remains “clean.”
Racing practices are different than other equine disciplines. Where do racehorses go when they finish their racing career? Because these horses tend to be accomplished athletes, many go to jumping, Eventing, or barrel racing pursuits, as just a few examples. This results in an infected horse serving as a reservoir for horses in other disciplines that might otherwise be “clean.” Racing Quarter Horses exposed to EIAV at a young age that go undiag- nosed pose a risk once infiltrated into the rest of the equine population. Owners should be aware of this potential risk and consult their veterinarian to arrange appropriate testing prior to sale or purchase of a former racing Quarter Horse.
Each state oversees regulations on movement of horses into their state; most adhere to require- ments for EIAV testing every 12 months, and in some cases every 6 months. There has been discus- sion about codifying the 12-month requirement into a federal rule, but while states have specific testing requirements, for now there is no estab- lished national program of EIAV surveillance.
Another significant point is that Mexico
has no control program or testing for EIAV (or piroplasmosis). With that in mind, it is important to continue with routine EIAV testing in the USA due to the high risk of infection sources from south of the border.
Vigilance to control EIAV relies in part on each horse owner’s responsible care that includes routine surveillance testing. The increasing num- ber of positives each year is recently attributable to iatrogenic sources, which is preventable through educational efforts and routine testing.
Contamination of multi-dose drug vials occurs by inserting a used needle that deposits blood with virus into the bottle, resulting in disease spread with subsequent drug administrations to other horses.
When re-using intravenous tubing to connect to an IV catheter, there is blowback of blood into the tube that cannot be cleaned out and can result in EIAV transmission.
Improper cleaning and sterilization of lip tattoo equipment can transfer EIAV.
Blood doping – taking blood from one horse and giving it to another via IV transfusion – or the use of unlicensed blood or plasma products illegally imported from other countries, can spread EIAV.
Power washing equine facilities can increase the possibility of aerosol transmission of EIAV.
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