EQUINE VIRAL ARTERITIS EQUINE VIRAL ARTERITIS EVA IS

EQUINE VIRAL ARTERITIS

EQUINE VIRAL ARTERITIS (EVA) IS A GLOBAL INFECTIOUS DISEASE OF HORSES AND IS CHARACTERIZED BY PANVASCULITIS INDUCING EDEMA, HEMORRHAGE, AND ABORTION IN PREGNANT MARES. EVA CAN CAUSE SEVERE ECONOMIC LOSSES FOR THE EQUINE INDUSTRY. THE VIRUS • EAV IS AN ENVELOPED, SPHERICAL, POSITIVE-STRANDED RNA VIRUS WITH A DIAMETER OF 50– 70 NM T. HE VIRION IS COMPRISED OF AN ISOMETRIC CORE SURROUNDED BY A LIPIDCONTAINING ENVELOPE FROM WHICH DELICATE SPIKES PROTRUDE. • EAV IS A NON-ARTHROPOD-BORNE VIRUS CLASSIFIED AS A MEMBER OF THE NEW ORDERNIDOVIRALES, INCLUDING ALSO THE BIGENERIC FAMILY CORONAVIRIDAE, WITHIN THE FAMILY ARTERIVIRIDAE WITH PORCINE RESPIRATORY AND REPRODUCTIVE SYNDROME VIRUS, SIMIAN HEMORRHAGIC FEVER VIRUS, AND LACTATE DEHYDROGENASE ELEVATING VIRUS.

CLINICAL SIGNS • CLINICAL FEATURES AND CARRIER STATE CLINICAL SIGNS MAY BE ABSENT OR MAY INCLUDE PYREXIA, DEPRESSION, ANOREXIA, LEUKOPENIA, LIMB EDEMA, STIFFNESS OF GAIT, RHYNORRHEA AND EPIPHORA, CONJUNCTIVITIS, AND RHINITIS. EDEMA OF THE PERIORBITAL AND SUPRAORBITAL AREAS, MIDVENTRAL REGIONS, SCROTUM, PREPUCE, AND MAMMARY GLAND, URTICARIAL RASH, AND ABORTION ALSO OCCUR. • LESS FREQUENTLY, SEVERE RESPIRATORY DISTRESS, ATAXIA, MUCOSAL PAPULAR ERUPTIONS, SUBMAXILLARY LYMPHADENOPATHY, AND INTERMANDIBULAR AND SHOULDER EDEMA MAY BE OBSERVED.

CLINICAL SIGNS • EAV CAN BE ASSOCIATED WITH EPIDEMIC ABORTION; IS OCCASIONALLY FATAL IN ADULTS AND MORE FREQUENTLY CAN BE FATAL FOR FOALS. • WHEN NEONATES ARE NOT PROTECTED BY PASSIVE MATERNAL IMMUNITY, THEY MAY PRESENT WITH SUDDEN DEATH OR SEVERE RESPIRATORY DISTRESS FOLLOWED BY DEATH. • AFFECTED INTACT MALES MAY BECOME LONG-TERM CARRIERS AND MAY SHED EAV IN THE SEMEN. • STALLIONS SHEDDING EAV IN THEIR SEMEN SERVE AS A RESERVOIR FOR THE VIRUS WITHIN THE EQUINE POPULATION. ADDITIONALLY, INFECTED STALLIONS AND SEMEN HAVE RESULTED IN RESTRICTIONS FOR INTERNATIONAL MOVEMENT OF HORSES AND SEMEN.

PATHOGENESIS IT IS POSSIBLE TO DETERMINE THE PATHOGENESIS OF EAV INFECTION IN HORSES BY FOLLOWING THE DISTRIBUTION OF VIRAL ANTIGEN AND LESIONS IN EXPERIMENTAL AND NATURAL INFECTIONS

PATHOGENESIS • CHORIONIC DETACHMENT AND EXPULSION OF AN INFECTED OR UNINFECTED FETUS MAY FOLLOW. • IN THE INFECTED FETUS, EAVAG CAN BE IDENTIFIED WITHIN THE TROPHOBLASTIC EPITHELIUM AND MESENCHYMA AND SHORTLY AFTER WITHIN PNEUMOCYTES, ALVEOLAR MACROPHAGES, THYMIC EPITHELIUM, AND ENTEROCYTES.

MACROSCOPIC LESIONS • GROSS LESIONS ARE THE EXPRESSION OF THE VASCULAR PATHOLOGIC CHANGES. • EDEMA, CONGESTION, AND HEMORRHAGE OF THE SUBCUTANEOUS TISSUES, LYMPH NODES, AND VISCERA ARE THE MOST FREQUENT GROSS LESIONS IN HORSES THAT DIE AFTER NATURAL OR EXPERIMENTAL EAV INFECTION. • THE BODY CAVITIES MAY CONTAIN MODERATE TO ABUNDANT AMOUNTS OF YELLOWISH CLEAR EXUDATE. • CONGESTION AND LYMPHADENOMEGALY, EDEMA, AND HEMORRHAGES CAN BE OBSERVED ALONG THE COURSE OF THE COLONIC AND CECAL VESSELS BUT ALSO ARE EVIDENT SYSTEMICALLY.

MACROSCOPIC LESIONS • ON THE CUT SURFACE OF LYMPH NODES, THERE MAY BE A PROMINENT SUBCAPSULAR SINUS AND DILATED MEDULLARY SINUSES. • LUNGS, ESPECIALLY THOSE OF INFECTED NEONATES, ARE WET AND INCREASED IN WEIGHT, WITH A PROMINENT LOBULAR PATTERN AND SOMETIMES CAN BE MULTIFOCALLY OR DIFFUSELY REDDISH BECAUSE OF CONGESTION AND HEMORRHAGE. • THE UTERINE ENDOMETRIAL SURFACE OF ABORTING MARES MAY BE SWOLLEN AND DIFFUSELY CONGESTED, SOMETIMES WITH HEMORRHAGES.

MICROSCOPIC LESIONS THE HISTOLOGIC LESIONS ARE OBSERVED IN VARIOUS SYSTEMS OF HORSES WITHEAV INFECTION. THE BLOOD VESSELS ARE THE PRINCIPAL TARGET. • Small muscular artery Fibrinoid necrosis of the tunica media and perivascular edema with lymphocytic infiltrate • Lung Interstitial pneumonia with hypertrophied type 2 pneumocytes containing intracytoplasmic EAV antigen.

MICROSCOPIC LESIONS • Small muscular artery Vascular intimal and medial necrosis with perivascular lymphocytic infiltrate and edema. EAV antigen is diffusing from the endothelium to the tunica media. • Kidney Severe diffuse interstitial lymphocytic nephritis with tubular necrosis and abundant EAV antigen contained in renal tubules and intraluminal casts.

MICROSCOPIC LESIONS • Chorioallantois A syncytial trophoblast cell contains abundant intracytoplasmic EAV antigen • Small arteries and necrosis and deposition of eosinophilic massin tunica media with cellular infiltration in adventitia

DIAGNOSIS • CLINICAL EQUINE VIRAL ARTERITIS SHOULD BE CONSIDERED WHEN THE CLINICAL SIGNS INCLUDE FEVER, DEPRESSION, EDEMA, CONJUNCTIVITIS, NASAL DISCHARGES AND ABORTIONS. THIS DISEASE IS DIFFICULT TO DIFFERENTIATE FROM OTHER SYSTEMIC AND RESPIRATORY ILLNESSES OF HORSES. • DIFFERENTIAL DIAGNOSIS THE DIFFERENTIAL DIAGNOSIS INCLUDES EQUINE INFLUENZA, EQUINE INFECTIOUS ANEMIA AND AFRICAN HORSE SICKNESS, AS WELL AS INFECTIONS WITH GETAH VIRUS, HENDRA VIRUS, EQUINE RHINITIS A AND B VIRUSES, EQUINE ADENOVIRUSES, AND EQUINE HERPESVIRUSES 1 AND 4.

LABORATORY TESTS EQUINE VIRAL ARTERITIS CAN BE DIAGNOSED BY VIRUS ISOLATION, THE DETECTION OF VIRAL ANTIGENS OR NUCLEIC ACIDS, AND SEROLOGY. In recently infected animals, equine arteritis virus may be recovered from: nasal secretions, blood and semen as well as from a number of tissues and fluids at necropsy. Carrier stallions can be identified by isolating the virus from semen; EAV is not found in the respiratory secretions, blood or urine of carriers. This virus can be isolated in rabbit, equine and monkey kidney cells or cell lines and rabbit kidney cells are the system of choice.

LABORATORY TESTS THE IDENTITY OF THE VIRUS CAN BE CONFIRMED USING: • SERUM NEUTRALIZATION, • REVERSE-TRANSCRIPTION PCR (RT-PCR) ASSAYS, • IMMUNOFLUORESCENCE OR IMMUNO-HISTOCHEMISTRY. SEROLOGICAL TESTS INCLUDE: • VIRUS NEUTRALIZATION, • COMPLEMENT FIXATION, • AGAR GEL IMMUNODIFFUSION, • INDIRECT FLUORESCENT ANTIBODY AND • ENZYME–LINKED IMMUNOSORBENT ASSAYS ELISA (ELISA).

PREVENTION AND CONTROL EFFECTIVE STRATEGIES FOR CONTROL AND PREVENTION CAN BE AND HAVE BEEN DESIGNED. THESE STRATEGIES INCLUDE: • MINIMIZING OR ELIMINATING DIRECT OR INDIRECT CONTACT OF SUSCEPTIBLE HORSES WITH THE SECRETIONS/EXCRETIONS OFEVA-INFECTED ANIMALS. • RESTRICTING SPREAD OF EAV IN BREEDING POPULATIONS, TO PREVENT OUTBREAKS OF VIRUS-RELATED ABORTION OR ILLNESS IN YOUNG FOALS, AND TO PREVENT THE ESTABLISHMENT OF THE CARRIER STATE IN STALLIONS AND POST-PUBERTAL COLTS. • DETERMINE SEROLOGIC AND VIROLOGIC STATUS OF ALL STALLIONS CONTRIBUTING SEMEN THAT WILL BE COOLSHIPPED OR CRYOPRESERVED.

VACCINE • THERE IS A SAFE AND EFFECTIVEEVA VACCINE (ARVAC 1, FORT DODGE ANIMAL HEALTH). • THIS VACCINE HAS BEEN SHOWN TO BE BOTH SAFE AND EFFECTIVE FOR USE IN STALLIONS, NON-PREGNANT MARES, GELDINGS, FILLIES, AND COLTS. • THERE IS NO EVIDENCE THAT A VACCINATED STALLION WILL DEVELOP THE CARRIER STATE WITH VACCINE VIRUS. • IS USED IN COLTS AFTER 6 MONTHS AND PRIOR TO 12 MONTH OF AGE.

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