CE Article #1 ) d t 0 L 6 4 s r e

e EquineViral Arteritis g h a s i p l , b 1 u P e r n u a g l i l DVM , PhD

i Julita Ramirez, F ( m c a University of Colorado, Denver M

ABSTRACT: Equine viral arteritis (EVA) is a reportable, highly contagious disease associated with sporadic outbreaks of acute respiratory disease and abortion in horses. EVA is a disease syndrome characterized by a wide variety of clinical signs. Although EVA is transmitted primarily by the respiratory route, the disease’s greatest economic impact is on the horse -breeding industry. Infection with the etiologic agent of the disease, equine arteritis , most commonly results in subclinical infection. Horses with clinical signs usually recover fully from the disease and gain immunity against reinfection. Proper vaccination of susceptible breeding stock can prevent spread of the disease. EVA is manageable through public and professional education that emphasizes prevention and control measures.

quine viral arteritis (EVA ) made headlines because of the impact of outbreaks on horse during the 2006 multistate outbreak, which owners. A solid understanding of the basics E resulted in shortages. 1 EVA has of EVA epidemiology, testing, prevention, and generated fear and controversy in the horse control strategies can help prepare practicing industry since a 1984 outbreak in the Kentucky veterinarians to address owners’ questions and Thoroughbred industry. Because outbreaks of concerns. Equine veterinarians should strive to this disease are uncommon and clinical signs actively educate horse owners to help prevent are nonspecific, many veterinarians do not the mass confusion that outbreaks can engender. include EVA in the differential diagnosis (Box 1) in appropriate situations and are unfamiliar EQUINE ARTERITIS VIRUS with effective prevention and control strategies. It is crucial to recognize the difference between Many horse owners are also uninformed about EVA and equine arteritis virus (EAV ) and to use the disease. The 1998 National Animal Health these terms properly. EVA is the disease syn - Monitoring Survey (NAHMS) conducted by drome characterized by a variety of clinical signs USDA-APHIS found that about 60% of sur - (Box 2), while EAV refers to the viral disease veyed horse operations were unaware of EVA, agent itself (Figure 1). EAV can cause sporadic and only 2.9 % of operations vaccinated one or outbreaks of respiratory disease and abortion in more horses against the virus. 2 In 2005, the horses worldwide. It is not a newly discovered number of operations vacci - organism; it was first isolated in 1953 from lung nating horses against EVA tissue of aborted fetuses during an outbreak of rose to 11.7%, indicating a respiratory disease and abortion on a Standard - •Take CE tests modest increase in public bred breeding farm in Bucyrus, Ohio. 3 The virus • See full-text articles awareness of the disease. It is infects equids only: ponies, horses, donkeys, and 4 CompendiumEquine.com especially important for veteri - mules are susceptible to natural infection. His - narians to understand EVA torically, the breeds of horse most affected in the

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Box 1. Primary Differential Diagnosis Box 2. Clinical Signs of Equine of EquineViral Arteritis a Viral Arteritis a • Equine herpesvirus 1 or 4 infection • Abortion • Equine influenza • Anorexia • Purpura hemorrhagica • Ataxia • Allergic reaction causing inflammation and urticaria • Conjunctivitis • Toxicosis due to a plant (e.g., hoary alyssum) • Depression • Equine infectious anemia • Edema (of the limbs, mammary glands, prepuce, • African horse sickness b scrotum, and ventral body wall as well as above or • Dourine b around the eyes ) • Getah virus infection b • Excessive lacrimation • Fever a Applicable differentials vary depending on the clinical signs. • Leukopenia A definitive diagnosis of EVA in clinically ill horses can be made only through diagnostic testing. • Petechial hemorrhage of mucous membranes bDiseases currently exotic to the United States. • Rhinitis and nasal discharge • Stiff gait • Urticaria (on the head and/or neck ; sometimes United States are the Standardbred, Thoroughbred, and generalized) Warmblood. The 1998 NAHMS study of US horses • Diarrhea found that 23.9% of unvaccinated Standardbreds, 4.5% of • Icterus Thoroughbreds, 3.6% of Warmbloods, and 0.6% of aAny or all of these signs may be present. No individual sign or Quarter Horses were seropositive for antibodies against set of signs is specific to the disease. However, if both respira - EAV. 5 In 2006, there was a significant outbreak of EVA tory disease and edema are present, EVA should be a top differ - ential. The most consistent clinical signs are fever, leukopenia, in the immunologically naive Quarter Horse population. and dependent limb edema. 9 Although the venereal route is better known, most EAV infections are transmitted via the res - piratory route. These dual routes of transmission make respiratory secretions from infected horses, may help the virus an economic threat to shows, sales and per - propagate an abortion storm in a herd of pregnant formance events, and the breeding industry. Mares mares. 8 Fetal tissues are often partially autolyzed, and infected by the venereal route develop viremia and can there are no pathognomonic lesions for EVA. 9 disseminate the virus to other susceptible horses through Most EAV infections are subclinical or result in mild respiratory secretions. There is no evidence to suggest clinical disease. Those that result in signs of disease gen - that mares exposed to semen from a carrier stallion will erally resolve in 1 to 2 weeks with simple supportive abort later in gestation .6 Pregnant mares abort 1 to 4 care. Mortality is rare , except in very young, old, immuno-

In 1998, approximately 60% of surveyed US horse operations were unaware of equine viral arteritis. weeks after respiratory infection, not as a result of being compromised, or debilitated horses. Mares infected late bred to a carrier stallion. Abortion can take place any in pregnancy may give birth to infected foals that can time between 3 and 10 months of gestation. EAV infec - die from interstitial pneumonia and/or enteritis. Ad- tion does not seem to affect the subsequent fertility of ministration of colostrum from immune mares has been mares, although stallions can have a transient decrease in found to attenuate or prevent infection in newborn the number of morphologically normal sperm cells due foals. 10 While EAV seroprevalence is fairly high in many to fever when they are first infected. 7 Many times, sus - horse populations worldwide, most equine abortions are ceptible pregnant mares abort without exhibiting signs of caused by other agents. disease. The aborted fetus and its associated tissues and Horses that are immunologically naive to EAV become fluids are infective to susceptible horses and, along with either subclinically or acutely clinically infected after

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Box 3. LaboratoriesThat ConductVirus NeutralizationTesting for EAV a • California Animal Health and Food Safety Laboratory System (University of California, Davis) • Clemson Veterinary Diagnostic Laboratory (Columbia, South Carolina) • Colorado State University (Fort Collins) • CS Roberts Veterinary Diagnostic Laboratory (Auburn, Alabama) • Kansas State University (Manhattan) • Kissimmee Diagnostic Laboratory (Kissimmee, Florida) • Murray State University (Breathitt, Kentucky) Figure 1. Rabbit Kidney –13 cells were infected with EAV • National Veterinary Services Laboratory (Ames, for 8 hours, and cryosections were labelled with anti-nsp2 followed Iowa) by protein-A –gold detection (bar = 0.1µm; reprinted by permission from Macmillan Publishers Ltd: Kirkegaard K, Taylor MP, Jackson • New Jersey Department of Agriculture (Trenton) WT. Nature Rev Microbiol 2:301-314 [April 2004; doi:10.1038/ • New York State Animal Health Diagnostic nrmicro865] ©2004). Laboratory (Ithaca) • Ohio Department of Agriculture (Reynoldsburg) • Oklahoma Animal Diagnostic Laboratory exposure to the virus. Mares, foals, and geldings stop (Stillwater) shedding the virus after recovering from infection and do • Oregon State University (Corvallis) not become permanent carriers . Stallions, however, can • Texas Veterinary Medical Diagnostic Laboratories become chronically infected without showing overt clini - (Amarillo and College Station) cal signs of infection and can continuously shed virus in • The University of Georgia Diagnostic Laboratory their semen for years while remaining apparently healthy. (Athens) Chronically infected stallions can spontaneously and per - • University of Illinois (Urbana) manently stop shedding the virus for unknown reasons. Castration of chronically infected stallions terminates • University of Kentucky Livestock Disease Diagnostic Center (Lexington) viral shedding, as testosterone is necessary to maintain the carrier state . Temporarily decreasing the testosterone level • Veterinary Diagnostic and Investigational Laboratory (Tifton, Georgia) has shown limited success as a therapy for reducing or eliminating viral shedding in the semen of carrier stal - • Washington Animal Disease Laboratory (Pullman) lions , although further studies of this method are aLaboratories approved by the USDA National Veterinary needed .6 Cooled and frozen semen from infected stal - Services Laboratory to conduct this testing . Accessed June lions is a well-known route of viral transmission because 2008 at www.ca.uky.edu/Gluck/ServEVA.asp . the virus can remain infective in frozen semen for years. A recent study found that the use of a two-stage process - ing technique involving density -gradient centrifugation followed by a “swim-up” step shows promise for removing nostic testing must be conducted to definitively diagnose the virus from infected semen. 11 EVA in sick horses because the clinical signs are indis - EAV primarily infects macrophages and vessel endo- tinguishable from those of other, more common infec - thelium throughout a horse’s body .12 The initial infection tious and noninfectious equine diseases. is followed by viral dissemination via the bloodstream, resulting in viremia. Clinical signs first appear 2 to 13 DIAGNOSTIC TESTING (average : 7 ) days after infection , and a fever may con - The most commonly used serologic test to detect EAV tinue for 2 to 9 days 5,8 (Box 2 ). Acutely infected horses antibodies is virus neutralization. Box 3 lists the veterinary shed the virus in nasal secretions for up to 16 days. Diag - laboratories that are approved by the USDA to conduct

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the virus neutralization test. Acute and convalescent blood samples should be collected for serology 3 to 4 weeks apart in red-top or serum-separator tubes. A fourfold or greater rise in antibody titers between paired serum samples indi - cates recent infection. 9 A titer of 1:4 or greater on a single sample is considered positive and indicates previous EAV exposure, exposure to natural infection, or vaccination. It is important to note that neutralized antibody titers can per - sist for several years after natural EAV infection .8 During the 2006 EVA outbreak, horses participating in sales events and shows in certain areas were required to test negative for EAV antibodies . Clients who are unfa - miliar with this disease may be confused or concerned about such regulations, so it is very important for veteri - narians to be familiar with the implications of different diagnostic tests. Horses that are clinically normal and serologically positive for EAV antibodies were either nat - urally exposed to the virus or vaccinated against it . These horses should be differentiated from acutely infected horses. Infection can be confirmed by viral isolation test - ing of nasopharyngeal or conjunctival swabs, unclotted blood, or semen . Reverse-transcription polymerase chain reaction (RT-PCR) testing is very useful as a rapid, sensi - tive method for detecting EAV . However, the World Organization for Animal Health (OIE) recommends using the RT-PCR assay in conjunction with viral isola - tion and not as an alternative to it, as existing RT-PCR testing must undergo further standardization and valida - tion. 13 Viral isolation and RT-PCR testing can be con - ducted on blood, semen, or tissue samples. Importantly, no currently available serologic test can distinguish past natural infection from past vaccination. During an outbreak, nasopharyngeal swabs, conjuncti - val swabs, or unclotted blood should be submitted for virus isolation to identify acutely infected horses. Blood samples for PCR or virus isolation testing should be collected in EDTA or citrate tubes because heparin interferes with these tests. Samples for virus isolation should be collected as early as possible in the course of infection. Blood samples should be refrigerated; other specimens should be chilled or, preferably, frozen. All samples should be sent via overnight shipping to a USDA-approved laboratory. An aborted fetus can be evaluated for EAV infection by submission of samples for virus isolation , PCR testing , and immunohistochem - istry. Appropriate tissues and fluid to submit for testing include placenta; fluid from body cavities; tissue from the spleen, lung, or liver; and lymph nodes associated with the respiratory and gastrointestinal systems. 5

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Attention! lions. A modified-live vaccine called Arvac (Fort Dodge Animal Health ) is the only commercial vaccine for pro - It is extremely important to ensure that clients have written, official certification of their horses’ negative tection against EAV infection in the United States. It serologic status based on virus neutralization testing at has been shown to be safe and effective for administra - an approved laboratory before initial vaccination against tion to nonpregnant horses. The vaccine is not recom - EVA and that a copy is retained for the medical record. mended for use in pregnant mares, especially during the Shows as well as sales and performance events last trimester, or foals younger than 6 weeks of age. Vac - sometimes require written documentation of a horse’s cination of pregnant mares in the last 2 months of ges - prevaccination seronegative status, as do other states or tation has led to a few instances of fetal invasion by the countries to which the horse might travel. vaccine virus. However, it may be beneficial to vaccinate pregnant mares in high-risk situations (when the risk of Up to 30% to 50% of stallions that test seropositive for exposure to EAV is high and the mare tests seronega - antibodies against EAV may be chronically infected with tive). Many hundreds of pregnant mares have been vac - the virus. Therefore, viral isolation should be conducted cinated without adverse effects. 14 The antibody response on the sperm-rich fraction of at least two semen samples generated by inoculation with this vaccine cannot be to determine whether a seropositive stallion is shedding serologically differentiated from natural infection. the virus .5 Antiseptic or disinfectant should not be used Therefore , it is extremely important to ensure that to clean the stallion’s external genitalia before collecting clients have written , official certification of their horses’ semen samples. It is important to disclose confirmed negative serologic status based on virus neutralization cases of EAV-shedding stallions to state authorities, as testing at an approved laboratory before initial vaccina -

In 2006 , a multistate outbreak of equine viral arteritis resulted in abortions, respiratory infections, neonatal foal death, and, in some areas, requirements for testing show, sale, and performance stock .

EVA is a reportable disease. The names and locations of tion against EVA and that a copy is retained for the state veterinary services are listed in Box 3 . medical record. Shows as well as sales and performance events sometimes require written documentation of a TREATMENT horse’s prevaccination seronegative status , as do other No specific antiviral treatment is available for EVA. states or countries to which the horse might travel. Supportive care, including stall rest , NSAID therapy, A recent study shows promise for future development and a diuretic to control edema, can help mitigate clini - of a live or modified-live virus vaccine that could enable cal signs in most patients. Most affected animals recover serologic differentiation between vaccinated and natu - completely. In some patients , antimicrobial therapy may rally infected horses. Castillo-Olivares et al 15 created an be warranted to prevent secondary bacterial infections avirulent viral strain without the major antigenic epitope or to treat pneumonia or cellulitis. Treatment of young of the naturally occurring virus. Inoculation with this foals with EAV-induced pneumonia and/or enteritis has mutant EAV protected ponies from experimental infec - been largely unsuccessful. 6 tion with a virulent EAV strain. A comprehensive EAV management program involves PREVENTION AND CONTROL vaccinating all colts 6 to 12 months of age that could be EVA can be controlled and is considered a manageable prospective breeding stallions to prevent the develop - disease. Educating horse owners about prevention and ment of the carrier state . In addition, all stallions should control strategies before an outbreak occurs is the best be vaccinated annually at least 4 weeks before the start method of avoiding confusion during an outbreak. Pre - of the breeding season. (The AAEP guidelines call for vention involves vaccination of susceptible horses and annual vaccination of seronegative mares before breed - avoidance of breeding susceptible mares to carrier stal - ing to carrier stallions. ) Seronegative mares should be

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vaccinated at least 3 weeks before being bred with a prevent the spread of EAV from voided semen, and all seropositive stallion and should be isolated from other potential fomites should be carefully disinfected. 16 seronegative horses during this time. On high-risk Horses that are vaccinated for the first time and subse - farms , clinicians should consider vaccinating all horses 6 quently exposed to EAV may experience a restricted months of age or older. A single intramuscular dose of reinfection cycle with short-term respiratory virus shed - vaccine is sufficient for protective antibody titers to ding . For example, when a mare is bred with a carrier develop. Vaccinated horses should receive an annual stallion after the mare’s first vaccination, she should be booster. New arrivals to breeding farms, including isolated from other horses for 3 weeks. 16 horses returning from other farms, shows, and race - Many countries do not allow importation of seroposi - tracks, should be isolated for 3 to 4 weeks to prevent the tive horses without proof of vaccination and seronegative spread of EVA and other infectious diseases. Pregnant prevaccination status. Some countries do not allow mares should be segregated from other horses. All seropositive stallions to be imported regardless of their unvaccinated breeding stallions should be serologically vaccination history. Therefore, it is very important to tested before the season starts . inform clients of the implications of vaccination for Virus isolation testing should be conducted on all international export before vaccinating their horses for semen that will be used to artificially inseminate suscep - the first time. Before having their horses vaccinated, tible mares. Regardless of whether breeding is by natural clients planning to export horses should check the cover or artificial insemination, carrier stallions should importation regulations of the country to which they be bred only to mares that test seropositive for EAV, plan to export . Carrier stallions (only those actively shed - including those that have been properly vaccinated. ding EAV) and their semen cannot be imported into any When carrier stallions are bred , precautions must be country other than the United States and Canada. taken to prevent spread of the virus. The stallion and The 2006 EVA outbreak was characterized by clinical mare should be isolated for 24 hours after breeding to signs of the disease along with abortions from 3 to 7 464 CE Equine Viral Arteritis

Resources forVeterinarians and Clients easily inactivated with exposure to heat, sunlight, des - iccation, or common disinfectants. Disinfection of • AAEP guidelines for breeding a mare to an EAV- shedding stallion ( www.aaep.org/images/files/ breeding phantoms (periodically or between uses ) is 2008%20MemDirEandPGuideFINAL.pd f) particularly important. The 2006 multistate EVA out - • AAEP EVA vaccination guidelines break was not confined to Quarter Horses because (www.aaep.org/eva.htm) horses of other breeds were exposed to the virus • Understanding Equine Viral Arteritis through contact with infected Quarter Horses. The Drs. Peter Timoney and William McCollum practice of keeping large numbers of animals in close (www.netpets.org/horses/healthspa/viral.html) physical contact greatly facilitates disease spread by • USDA Animal Health, Area Offices the respiratory route. During this outbreak , every (www.aphis.usda.gov/animal_health/area_offices) mare, stallion, and foal on the intensively managed • USDA guidelines on preventing and controlling index farm was infected. 17 EVA : Equine Viral Arteritis: Uniform Methods and Semen from imported stallions is another important Rules (www.aphis.usda.gov/vs/nahss/equine/eva/ potential route of infection, as Hullinger et al 18 showed in eva-umr.pdf) a 2001 study of horses in California (1.9% of resident • Equine Viral Arteritis: A Manageable Problem horses and 18.6% of imported horses surveyed were (www.aphis.usda.gov/vs/nahss/equine/eva/ seropositive for EAV) . This included 16.1% of imported eva_brochure_2001.pdf) To order an EVA video/booklet information packet, stallions. Even if no other methods of prevention are email Dr. Timothy R. Cordes, Senior Staff used, veterinarians should stress to clients who own Veterinarian, Equine Diseases, at breeding farms and mares the importance of testing stal - [email protected] . lions or semen that they plan on using before the start of • USDA International Animal Export Regulations the breeding season. (www.aphis.usda.gov/regulations/vs/iregs/animals) REFERENCES 1. Ryder E. EVA outbreak and vaccine shortage affecting western US. The Horse months of gestation. Several Quarter Horse stallions on online news . Article #7367 . Accessed October 2006 at www.thehorse.com . a large breeding farm in New Mexico were infected , 2. USDA APHIS NAHMS Equine 2005 Section III: Management and Health Changes in the U.S. Equine Industry, 1998-2005. Accessed July 2008 and several hundred mares were exposed by artificial at http://www.aphis.usda.gov/vs/ceah/ncahs/nahms/equine/equine05/ insemination with shipped semen or by visiting the equine05_report_part2_trends.pdf index premises during the outbreak. Nineteen states 3. Doll ER, Bryans JT, McCollum WH, Crowe ME. Isolation of a filterable received semen from the infected stallions and/or had agent causing arteritis of horses and abortion by mares ; its differentiation from the equine abortion (influenza) virus. Cornell Vet 1957;47(1):3-41. mares visit the index premises during this outbreak .17 4. Paweska JT, Binns MM, Woods PS, Chirnside ED. A survey for antibodies Ten states had confirmed cases of EVA or strong to equine arteritis virus in donkeys, mules, and zebra using virus neutraliza - circumstantial evidence of infection. 17 This outbreak tion (VN) and enzyme linked immunosorbent assay (ELISA). Equine Vet J 1997;29(1):40-43. demonstrates how quickly EAV can spread in an 5. Spickler AR, Roth JA , eds. Emerging and Exotic Diseases of Animals . Ames: immunologically naive equine population, especially Iowa State University College of Veterinary Medicine; 2006. when popular stallions are infected and untested or test 6. Timoney PJ. Equine viral arteritis: is the disease a cause for industry concern? results are not made public. Impulsion 2005:4-7,9-10. During an outbreak , the primary control strategy 7. Neu SM, Timoney PJ, Lowry SR. Changes in semen quality following exper - should be isolation of clinically affected horses from imental equine arteritis virus infection in the stallion. Theriogenology 1992; 37:407-443. susceptible animals and thorough disinfection of pos - 8. Timoney PJ, McCollum WH. Equine viral arteritis. Vet Clin North Am sible fomites. Vaccination of susceptible horses is also Equine Pract 1993;9:295-309. a good means of controlling an outbreak. Any facility 9. Holyoak GR, Balasuriya UBR, Broaddus CC, Timoney PJ. Equine viral experiencing an EVA outbreak should be quarantined arteritis: current status and prevention. Theriogenology 2008;70:403-414. for at least 3 weeks after all active infections have 10. McCollum WH. Studies of passive immunity in foals to equine viral arteritis. 2002;1:45-54. resolved. To control spread of the disease, contact of Vet Microbiol 11. Morrell JM, Geraghty RM. Effective removal of equine arteritis virus from susceptible animals with the secretions and excretions stallion semen. Equine Vet J 2006;38(3):224-229. of infected animals should be minimized or elimi - 12. Murphy FA, Gibbs EPJ, Horzinek MC, Studdert MJ . Veterinary . San nated and at-risk horses should be vaccinated. EAV is Diego : Academic Press ; 1999.

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13. OIE Manual of Diagnostic Tests and for Terrestrial Animals . 5 th 4. Which treatment is indicated for EVA? ed. 2004, chapter 2.5.10. Accessed July 2008 at http://www.oie.int/eng/ a. stall rest normes/en_mmanual.htm . b. administration of mannitol 14. McCue P . Equine Viral Arteritis [client information bulletin ]. Fort Collins : c. administration of amantidine Colorado State University ; 2006. Accessed June 2008 at www.cvmbs. colostate.edu/bms/ERL/evaupdate_f06.pdf . d. administration of EAV antiserum 15. Castillo-Olivares J, Wieringa R, Bakonyi T, et al . Generation of a candidate live marker vaccine for equine arteritis virus by deletion of the major virus 5. Samples that could be submitted for diagnosis of neutralization domain. J Virol 2003;77(15):8470-8480. EVA do not include 16. Equine Viral Arteritis [fact sheet ]. Accessed July 2008 at http://www. a. semen . c. cerebrospinal fluid . aphis.usda.gov/lpa/pubs/fsheet_faq_notice/fs_ahequineva.pdf . b. nasal secretions . d. blood . 17 . Timoney PJ, Creekmore L, Meade B, et al. 2006 multi-state occurrence of EVA. Accessed June 2008 at www.aphis.usda.gov/vs/nahss/equine/eva/ EVA_2006_Multistate_USAHA.pdf . 6. EAV infection primarily targets 18. Hullinger PJ , Gardner IA , Hietala SK , et al. Seroprevalence of antibodies a. T cells . against equine arteritis virus in horses residing in the United States and b. vessel endothelium . imported horses. JAVMA 2001;219(7):946-949. c. endometrium . d. erythrocytes . ARTICLE #1 CE TEST CE 7. After diagnosing EVA in a patient, a clinician The Auburn University College of Veterinary Medicine should not approves this article for 3 contact hours of continuing a. report the diagnosis to state authorities . education credit. Subscribers may take individual CE b. isolate the affected animal . tests or sign up for our annual CE program . Those c. begin aggressive treatment . who wish to apply this credit to fulfill state relicensure requirements should consult their respective state d. disinfect possible fomites . authorities regarding the applicability of this program. CE subscribers can take CE tests online and get real-time 8. Which of the following cannot be used to defini - scores at CompendiumEquine.com . tively diagnose EVA in a sick horse ? a. clinical signs b. virus isolation testing 1. The primary diagnostic differentials for EVA do c. RT-PCR testing not include d. paired serum samples a. purpura hemorrhagica . b. equine herpesvirus 1. 9. Which test can differentiate between a mare c. equine infectious anemia . that was vaccinated against EAV and one that d. equine protozoal myeloencephalitis . had past natural exposure to EAV? a. serologic testing 2. A(n) ______is most likely to be b. virus isolation testing seropositive for EAV . c. RT-PCR testing a. Thoroughbred c. Arabian d. none of the above b. Standardbred d. Akhal-Teke

3. Before vaccinating a horse against EAV for the 10. If an extremely valuable breeding stallion has first time , a clinician should tested positive for EAV by serology, what should a. conduct serologic testing and record the horse’s pre - the clinician recommend to the owner? vaccination titer. a. castration of the horse b. inform the owner that vaccination will result in a b. virus isolation testing on the semen to confirm EAV positive blood serum titer that may prevent the carrier status horse or its semen from being exported to certain c. public disclosure of the horse’s status and breeding countries. the horse with only seropositive or properly vacci - c. conduct virus isolation testing and record the horse’s nated mares using appropriate precautions to pre - prevaccination status. vent infection of susceptible horses d. a and b d. b and c

November/December 2008 COMPENDIUM EQUINE