Equine Viral Arteritis (+ssRNA, Arteriviridae, Equarterivirus): Molecular diagnosis (RT-PCR).
Information 02-01-2012

Equine viral arteritis (EVA) is a contagious disease affecting the respiratory tract of horses, named for the characteristic inflammatory lesions induced by causative virus in the smaller blood vessels, particularly arterioles animal with acute infection. The EVA is produced by equine arteritis virus
is a small RNA virus, which is the prototype enveloped virus of the genus Arterivirus, family Arteriviridae, Nidovirales order. Based on their genetic structure and replication strategy, three other viruses have been classified in the same genus and family, increaser virus lactic dehydrogenase mice, the virus simian hemorrhagic fever and most importantly, virus porcine reproductive and respiratory syndrome; that produces large economic losses in pig populations in North America, Europe and elsewhere. All the accumulated evidence would indicate that natural infection with EVA is restricted to members of the family Equidae.

The virus
is not transmitted to humans. The equine arteritis virus is not a particularly resistant virus outside the body and is rapidly inactivated by a range of physicochemical conditions. It is sensitive to sunlight, high temperatures, low humidity and various disinfectants and lipid solvents. However, the viability of the virus is kept in refrigeration or freezing temperatures. The equine arteritis virus can remain infective in frozen for long periods of time semen, even for many years

Based on outbreaks of EVA and the results of serological studies, the EVA is distributed in many horse populations throughout the world. Japan and Iceland are notable exceptions. Studies of different horse populations have shown that the prevalence of infection EAV can vary widely among horse breeds both in the same country and between countries. Importantly
, the widespread dissemination of EVA can occur both at racetracks and breeding farms. Because many cases of primary infection are asymptomatic EVA, the absence of clinical evidence of EVA is no guarantee absence of virus in any equine population.

Factors of the virus, host and are involved in environmental epidemiology EVA. These have been identified as important: the variation in pathogenicity strains of natural outbreaks AVE, transmission routes chronic infection acute phase and persistence of the virus in the stallion and the nature of acquired immunity the infection.

Horses in acute stage of infection eliminate EAV for a limited period of time in various body secretions and excretions. The highest concentration of virus
is usually eliminated via the respiratory tract; the spread of the virus can last up to 16 days. Aerosol transmission is the most significant means of disseminating EAV either breeding farms or wherever horses are in intimate contact with each other , for example, racecourses, samples, sales or veterinary clinics. An additional important route of transmission of the virus in breeding farms is sexually transmitted by acutely infected stallion. EAV transmission may also occur by congenital route, producing abortion or the birth of a congenitally infected and alive but sick foal. On such occasions, the placenta, amniotic fluid and fetus are abundant sources of virus. In the case of carrier stallion, EAV transmission occurs only route venereal

Even a degree of confusion about the actual clinical significance of EVA persists. This mainly derives from the misconception that the EVA is a serious disease with a mortality rate of 40 to 60%. The reality is that most natural infections are subclinical pictures EVA. Exposure to
the virus can result in clinical or inapparent infections depending on the strain involved, the dose of virus, age and physical condition of the infected animal and various environmental factors. The morbidity rate may differ significantly between outbreaks EVA, with higher rates in large concentrations of horses, for example, at racetracks. The horses kept in these circumstances are often stressed by the demands of training and competition.

The onset of clinical signs is preceded by an incubation period of 3 to 14 days vary by route of infection. It is shorter in the case of aerosol exposure and longer if transmission occurs by the venereal route.

Typical cases of the disease may present all or any combination of the following symptoms:
  • Fever to 41 ° C which can last from 2 to 9 days
  • Varying degrees of anorexia and depression
  • leukopenia
  • Edema members mainly seen in the bottom of hindlegs but may involve the four members
  • Nasal discharge serous-mucoid associated with a variable degree of rhinitis
  • Edema periorbital or supraorbital
  • Conjunctivitis of varying severity, usually called "pink eye"
  • Epifora may be unilateral or bilateral
  • Photophobia, very frequently observed in cases with severe conjunctivitis;
  • Edema involving the scrotum and foreskin in foals / sires and mammary glands in the mare
  • Urticaria rash that can occur as generalized lesions localized, small, discrete, usually on the cheeks, sides of the neck or chest region, or, as a maculopapular rash in most body
  • Abortion in the mare
  • Pneumoenteritis interstitial pneumonia or fatal in young foals

Other clinical signs observed less frequently include:
  • Swellings in edematous adventitious intermandibular space below the sternum, the shoulder region or other body parts;
  • Respiratory distress, even with dyspnea and tachypnea, especially in young foals;
  • Cough
  • Diarrhea
  • Paresis and ataxia hindquarter
  • submandibular lymphadenopathy
  • Papular eruptions in the mucous membrane of the upper lip; normally they found associated with skin rash
  • Gingiva and oral erosions

In general, the severity of the EVA tends
to be higher in the very young or old horses in debilitated individuals and horses who are physically stressed. It is important to emphasize that with very few exceptions, horses affected with this disease recover completely, even in the absence of any symptomatic treatment. Horses in training may experience a period of slower performance during acute and convalescent early stages of infection. Natural mortality EVA infections occur, but are rare in infants congenitally infected usually with the virus; they succumb fulminant interstitial pneumonia within 48 to 96 hours of birth. Deaths have also been reported in foals a few weeks to months to develop a rapidly progressive pneumoenteritis.
Exposed pregnant mares may abort the EVA in late acute or early convalescent phase of infection rather
than months after viral exposure, as some might believe. The abortion may or may not be preceded by clinical signs in infected mare EVA. There have been cases of abortion natural or experimental infection of EAV from 3 to 10 months of gestation. The percentage of abortions in mares susceptible may vary widely from less than 10% to 50 and 60%. Exposure of pregnant mares EAV in late gestation periods can not produce abortion but the birth of a congenitally infected with the virus colt. These foals invariably succumb rapidly progressive interstitial pneumonia within the first 3-4 days of life. Mares aborting because EAV seem to suffer no adverse effects on fertility.
In contrast, affected EVA stallions may suffer a short period of subfertility. It is believed that this is the result of increased testicular temperature caused by pyrexia and severe scrotal swelling that can occur in acute infections stallion.

Given the clinical similarities between this disease and other infectious and noninfectious diseases in equines, a provisional diagnosis of EVA can be confirmed by providing an adequate sample to evaluate in the laboratory. When suspected acute infection of EVA, confirmation of diagnosis is based on virus isolation, nucleic acid detection of viral antigen or the demonstration of a specific antibody response by a paired test (acute and convalescent) serum harvested 3 or 4 weeks apart.

The most suitable for testing in the acute phase of the disease and nasopharyngeal samples include conjunctival secretions and blood sample preserved with EDTA. To optimize the detection of virus, samples should be collected as soon as possible after the peak fever is suspected or when signs of an infection by this virus. Secretions should be transferred to a viral transport medium and shipped refrigerated or frozen in a container suitable for the laboratory. Blood samples must be sent to
the laboratory refrigerated but not frozen.

When suspected of abortions, detection and virus isolation should be done with fluids and tissues of the placenta, lung, liver and lymphoreticular tissues of the fetus. The suspect cases of death or old horses ponies, most tissues including lymph nodes associated
with the respiratory and digestive tract, should be collected for laboratory examination.

EVA infection is confirmed serologically by demonstrating seroconversion or a significant increase (4 times or more) of antibody titers to
the virus. When researching on a possible horse carrier state, it is important first of all, be determined individually if serologically positive or negative for antibodies to the EAV. As the carrier state has never been diagnosed in a seronegative stallion sires with only titers of 1: 4 or higher of the virus, without a proper and certified medical history EAV vaccination, it is considered a carrier. The carrier state can be confirmed by virus isolation or detection of viral nucleic acid in a sample of semen.

In IVAMI we perform laboratory diagnostics detecting the RNA genome of the virus followed by a transcription amplification (RT-PCR).