Next... Equine Viral Arteritis
This is mainly a disease that causes abortion, but it can also cause respiratory signs. It was first isolated from horses in 1953 in Ohio. Clinical signs are very similar to those seen with equine influenza and EHV-1 and 4.
| Do you think this is the likely problem? |
Infectious agent: Equine arteritis virus (EAV), an RNA virus in the Ramily Flaviviridae, Genus Arterivirus.
History: Outbreaks are associated with movement of horses; it's found most often at racetracks and breeding farms, and is most prevalent in STANDARDBREDS. Morbidity is generally low, but can reach up to 60%.
Clinical Signs: May be asymptomatic (scary!) or so mild that signs are not noticed (most horses fall into this group). May resemble other respiratory diseases like equine influenza, equine herpesivurs, equine infectious anemia, African horse sickness, purpura hemorrhagica and urticaria. Mild fever, depression, inappetence, ocular and nasal discharge, conjunctivitis, rhinitis, stiff gait, limb edema (hind limbs most of time), periorbital and supraorbital edema, midventral edema of scrotum and prepuce in stallion and mammary glands of mare, urticarial rashes and edematous plaques. Less common signs include respiratory distress, coughing, diarrhea, ataxia, photophobia, corneal opacity. ABORTION MOST OFTEN OCCURS MID TO LATE GESTATION IN THE MARE, and acutely infected stallions show decreased libido and decreased sperm health and number. Transplacentally infected foals may develop a severe fulminating pneumonia and fibronecrotic enteritis.
Transmission: Venereal and through respiratory route (aerosol, respiratory secretions), FOMITES including tack and people. Venereal transmission appears to be most important, and this disease can be spread silently by persistently infected carrier stallions. The virus localizes in accessory sex glands of stallions and is shed in ejaculate. Infected stallions can infect 85-100% of seronegative mares to which they are bred!
Incubation Period: 3-14 days. Shed infective virus for 7 to 14 days after infection.
Pathogenesis: Virus replicates in alveolar macrophages then virus localizes to bronchial lymph nodes.
Within 3 days viremia leads to viral localization in many tissues and fluids. CHARACTERISTIC LESION IS VASCULITIS OF SMALL ARTERIES AND SOME SMALL VEINS. Initial lesions occur in vessels of lungs then vessels throughout the body may be affected. The virus also localizes in adrenal, seminiferous tubules, thyroid and liver. In most cases the virus can NOT BE FOUND in body fluids from 28 days after infection. However, the virus can live in places in the reproductive tract of stallions for months or years.
How do you diagnosis this?
| It's really tough to diagnose on clinical
signs alone, because they are minimal or look like other diseases. You can try to
isolate the virus from FLUIDS: nasopharyngeal or conjunctival swabs, semen, urine, buffy
coat cells from preservative free EDTA or heparin treated blood. In cases of
abortion, collect fluids, placenta, fetal tissues (especially lung) for virus
isolation. Serology can be used - the test is considered positive if there is a
4-fold increase in titer in samples taken 14 to 28 days apart. Consider seropositve males with a titer of 1:4 or greater as carriers. |
Treatment and Prevention: Symptomatic. Most horses recover spontaneously. Possible NSAIDS or diuretics for scrotal edema; antibiotics for secondary bacterial infections.
ISOLATE INFECTED ANIMALS FOR AT LEAST ONE MONTH. DO NOT BREED CARRIERS.
In case of outbreak, test all animals on site to determine seropositive individuals. TEST and isolate all new arrivals, especially from endemic countries. Test stallion semen. Castration is the only foolproof way to prevent venereal spread. Modified live vaccine is available, safe and effective for stallions and nonpregnant mares. Do not use in pregnant mares particularly during the last 2 months of gestation or in foals under 6 weeks. The vaccine offers 1 to 3 years of protection from the disease but does not prevent infection or shedding.