ARTERITIS VIRAL – Free download as Powerpoint Presentation . ppt), PDF File .pdf), Text File .txt) or view presentation slides online. Equine viral arteritis (EVA) is a contagious viral disease of equids caused by equine arteritis virus. (EAV), an RNA virus classified in the genus, Arterivirus, family. English Translation, Synonyms, Definitions and Usage Examples of Spanish Word ‘arteritis viral equina’.
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Equine viral arteritis
Equine viral arteritis is an infectious viral disease of horses that causes serious economic losses due to the presentation of abortions, respiratory disease and loss of performance. After the initial infection males can become persistently infected carriers scattering infection through semen, a situation that brings indirect economic losses by restrictions on international trade of horses and semen from breeding and from countries at risk of infection with the virus.
Outbreaks of infection have been reported in several American countries with which Colombia has active links of import and export of horses and semen. This article focuses on creating awareness of the key points of infection and on examples of how infection has been distributed in countries that have developed horse breeding, such as Argentina, a country aware of the origin and distribution of the infection.
Rev Colomb Cienc Pecu ; Based on their genetic structure and replication strategy, three additional viruses have been classified in the same genus and family. They are of great importance, one of them causing Porcine Reproductive and Respiratory Syndrome Plagemannand Moennig, Based on extensive comparative studies at the genomic and antigenic level of EAV, only one serotype has been detected, usually called the Bucyrus strain McCollum, However, temporal and geographic diversity among EAV isolates has been demonstrated Murphy et al.
There also exists some variability between the strains based on their pathogenicity, some strains being capable of causing a wide range of clinical symptoms, collectively referred to as EVA in susceptible horses, whereas others produce only a slight fever Balasuriya et al. Although through the years it has been recognized that EAV causes contagious abortion in pregnant mares Doll et al. However, from a practical standpoint, it is difficult to distinguish between EAV strains that can cause abortion and those which do not; additionally, there are no standard techniques to classify the strains based on their abortive properties.
Therefore, from a clinical point of view, all strains of the virus should be considered potentially abortigenic unless proved otherwise Timoney, However, the virus can rapidly be inactivated by low humidity, sunlight, and the use of lipid solvents, or by using common inactivating detergents Burky,Shirai et al.
Yet, since virus viability upon refrigeration or freezing is high, EAV can remain infective in frozen semen for long periods of time, even years Timoney, More than a century ago, reports were published in the European veterinary literature concerning a horse disease whose clinical features were consistent with those described for EVA. The most important outbreak of EVA in America occurred inwhen the disease struck many racing thoroughbred farms in Kentucky. This outbreak led to two very important findings regarding the EVA: The fear that a highly pathogenic strain had emerged, joined with the belief that most horse populations are susceptible to the virus, led to an increased evaluation of the importance of the disease worldwide, imposing severe restrictions on the movement of horses with positive titers of antibodies against the virus Timoney and McCollum, a.
These measures were subsequently gradually decreased, with today a greater emphasis on controlling the international trade of carrier stallions and infected semen, which have frequently been implicated in the spread of the virus within and between countries Timoney, b.
According to the World Animal Health Organization-OIE, a carrier stallion has serological positive for antibodies to the virus using the virus neutralisation test or an appropriately validated enzyme-linked immunosorbent assay ELISA and also positive virus isolation from the semen Timoney, EVA is primarily a respiratory disease, transmitted through inhalation of viral particles between horses during the acute stage of infection mainly during transport of the animals for trade, exhibition or racing.
The virus can be excreted by nasal secretions until 16 days post-infection, and this is a source of infection for horses that are in closecontact McCollum, However, unlike other respiratory diseases, EAV can also be transmitted as a venereal disease during insemination, either by natural mating or artificial insemination, because the virus may be excreted in the semen, which is a major source of infection Figure 1.
When a mare, a gelding or a sexually immature colt catches the disease, the animal excretes the virus through respiratory airways and develops a strong immunity to re-infection Fukunaga et al.
In contrast, adult males are very likely to become carriers of the virus for long periods of time and can transmit the virus to mares during mating Neu et al.
Although the mare easily eliminates the virus, a pregnant EAV-infected mare cantransmit the virus tothe fetus.
Vertical transmission can occur by the congenital route, and depending on how advanced the pregnancy is, the fetus can become infected, die and be aborted between 9 and 30 days after infection.
At times a live but congenitally infected and sick foal is born Vaala et al. There are considerable variations in the clinical symptoms and in severity of infection, and although many horses infected with EAV do not show symptoms, it has been demonstrated that experimental infection can be fatal Glaser et al.
As in most infectious diseases, certain host factors determine the severity of the disease, such as age, immune status, sex which determines the possibility of being a potential carrier, etc.
Other factors depend on the agent such as the route of exposure, viral strain and infective dose. Urticaria that may be localized in the face and neck or generalized in most of the body is also common Timoney andMcCollum, b. Another symptom of infection in pregnant mares is abortion, that is not preceded by any characteristic or premonitory sign and may occur either at the end of the acute phase of illness or when the recovery phase begins Coignoul and Cheville, ; Vaala et al.
These changes persist for about 16 weeks, at which time the horse returns to its normal seminal parameters Neu et al. Additionally, carrier stallions can excrete virus in the semen and exhibit a normal semen quality Timoney et al. As for other members of the Equidae family, outbreaks have not been reported among donkeys or mules, and although antibodies have been identified, there is little information on the clinical signs observed in these species Timoney and McCollum, b.
Two days after aerosol infection, EAV spreads rapidly to the bronchial and pulmonary lymph nodes, reaching the bloodstream and spreading throughout the body. It is therefore possible to isolate the virus in a wide variety of tissues and body fluids, making isolation of the virus possible 2 days post-infection in nasopharyngeal swab samples, 19 days in white cells, and up to 9 days in serum or plasma Figure 2.
Virus clearance coincides with the development of specific neutralizing antibodies against EAV Timoney and McCollum, b. During primary viremia, EAV infects and replicates in endothelial cells causing strong multi-vessel damage to the endothelium, the subsequent internal elastic lamina and affecting the middle muscular layer of the vessels. Vasculitis is characterized by fibrinoid necrosis of small arteries with extravasation of red blood cells and proteinaceous material. Experimentally, it has become clear that abortion is primarily the result of fetal infection, other than myometritis or damage to the placenta, leading to expulsion of the fetus; in addition, there is evidence that the tissues of the aborted fetus tissues have higher viral titers compared to the mother, stressing the high level of virus replication in the fetus MacLachlan et al.
The natural reservoir of EAV infection is the carrier stallion, which ensures the permanence of the infection in equine populations. The carrier state has been identified only in the stallion, not in mares, geldings or sexually immature foals Timoney et al.
Virus can persist in the stallion for weeks, months or years, even for life in some individuals. In the persistently infected stallion, EAV is located in the accessory sexual glands and establishment and persistence of the carrier state is testosteronedependent Little et al.
Carrier stallions constantly eliminate the virus in the semen and consequently the risk of transmission of infection is limited to the time of mating.
A lesser percentage of long-term carrier stallions can clear the virus spontaneously from the reproductive tracts and do not show risk for transmission of infection Timoney and McCollum, However it has been shown that carrier stallions are the natural source of genetic and phenotypic diversity of the virus, creating new risks of emergence of viral variants with new pathogenic potential Balasuriya et al.
Given the clinical similarity of EVA with other equine infectious and non-infectious diseases, any presumptive diagnosis should always be confirmed by laboratory tests Holyoak et al. The presence of EVA must be suspected if respiratory symptoms are accompanied by abortions. Virus isolates can be obtained from nasopharyngeal swabs or washes, conjunctival swabs, samples of ejaculates, essentially the sperm-rich fraction, placentas, fetal fluids and tissues of aborted fetuses, such as lung, spleen and lymph nodes, and through blood samples with EDTAas anticoagulant.
The most widely used method for diagnosis is the evaluation of neutralizing antibodies, although the presence of such antibodies does not indicate active infection, but rather that the animal has been exposed to EAV. An active infection is diagnosed when high levels of antibodies in a single sample are found or when an increase in antibody titers occurs in two paired blood samples, obtained days apart Holyoak et al.
Although several types of immunoassays ELISAs have been developed, given the high specificity of the virus neutralization test to detect individuals with low serum antibody titers, this test has been established by the World Animal Health Organization-OIE as the gold standard for international transport of horses Timoney, Since there is no specific treatment for EVA, once the infection is confirmed clinical management should include rest, fluids and in some cases, broadspectrum antibiotics to reduce the risk of secondary bacterial infections.
Adult horses fully recover from the disease, leaving only the recovered stallions as carriers and sources ofinfection. Although in Colombia, EVA is an exotic disease, some prevention and control measures have been widely reported, that can make infection a manageable disease, and most importantly, can reduce the direct economic losses produced by disease outbreaks.
The combination of vaccination with the use of isolation measures of unvaccinated animals can prevent the transmission of EAV. Since EAV-negative and properly immunized stallions cannot be carriers, every negative foal under 9 months of age should be vaccinated. In addition, vaccination has been successfully used as a tool to control the spread of the disease during an outbreak, controlling the spread of infection and the severity of the symptoms Timoney, It is necessary to mention that due to EVA is an exotic disease, vaccinations are not recommended in our country yet.
In breeders and sites dedicated to reproduction, it is necessary to perform bleeding and serological assays of all horses prior to mating; viral isolation should also be attempted on imported semen before use. It is very important to maintain strict hygiene and disinfection of instruments and equipment to minimize the risk of transmission of the virus. EAVnegative mares should mate only with semen from EAV-seronegative stallions, but not with semen from carriers that could be infected.
If the results of blood tests are positive for a stallion, but there is no official documentation of a negative state prior to vaccination, the stallion should be analyzed to determine its possible carrier state.
Virus isolation should be attempted using semen of two separate ejaculations, or mating two EAV-negative mares with the same stallion. Twenty-eight days after mating, serological surveys should be performed on the mares to determine if neutralizing antibodies against EAV have developed Holyoak et al.
Carrier stallions should mate only with EAVpositive or properly vaccinated mares.
When a carrier stallion is paired with a positive mare or with a vaccinated mare, both mares should be isolated for 24 hours after mating to prevent mechanical transmission of the virus through traces of semen. If it is the first time that the mare has been paired with a carrier stallion, the mare should be isolated from other horses for 21 days due to the possibility of virus dispersion trough traces of semen.
All vaccinated horses should receive yearly boosters to protect them against infection and in the case of stallions, to prevent the development of the carrier state.
Epidemiological status in America. In America, the presence of EAV has been reported in different countries of South, Central and North America, mainly in Argentina, the United States and Canada where the virus has caused substantial economic losses and is today one of the main pathogens of veterinary importance Figure 3. EAV distribution in America. In light grey, countries with positive serology. Dark grey, country with the most recent EAV outbreak.
Crossfilled, EAV positive result by surveillance in borders, no cases reported in the country. The prevalence of EAV varies significantly among horse breeds. Breed-related differences in seroprevalence might be due to genetic differences, but eqhina are more likely to be caused by different management practices USDA-APHIS, In experimentally infected horses, the breed arteditis no apparent effect on susceptibility to infection or the establishment of carriers Neu et al.
On the other hand, the virus was never isolated in Chile, but the border surveillance program detected the presence of two positive animals Figure 3one of which was killed and the other returned to its country of origin Berrios, Inusing neutralization assays, out of artetitis, equine serum samples taken from 5 different states of Venezuela, 2. The case of Argentine has been largely discussed and documented in the scientific and technical literature, as it is the South American country with the agteritis number of reported cases.
Untilthere were no reported cases of the disease in Argentina and the virus had never been isolated in samples from nasal swabs or abortions in horses suffering from respiratory or reproductive disorders. In parallel with the approval of the import of horses from EVA-infected countries, Argentina initiated serological monitoring of imported horses and semen as part of the EVA Epidemiological Surveillance Program; this revealed one positive sample of semen imported in Apriland led to the destruction of the entire lot of semen, and to official intervention of the two farms involved in the import and use of the semen.
In paired samples carried out in all of the horses existing in the two farms, no infection was found,andthisdeterminedtheriseofhealthactivities and restrictive measures in the movement of horses movementrestriction DelaSota et al.
In Octoberof three stallions imported to Argentina, one was seropositive, so that the farm was restricted and required sanitation. In this site and during the implementation of these health activities a high serological prevalence was detected and the two other stallions were confirmed by biological assays as virus reservoirs and were consequently castrated to prevent the spread of the infection Dela Sota et al.
There have been different serological tests, to try to assess the presence of infection in different areas and horse populations fromArgentina, most of them yielding negative results, such as in breeders that had imported horses to Argentina sinceand aarteritis in horses present in farms adjacent in a radius of 10 km to the first farm in which the infection was first detected De la Sota et al. Three year later, in Octoberthe requirement to diagnose EVA in native, imported horses or seminal material was established.
Out of the samples included in this study, Of these, 10 were zrteritis imported from the U.
Equine Viral Arteritis: epidemiological and intervention perspectives
InJunetwo farms epidemiologically related with the initial outbreak of EVA were evaluated by virus neutralization. Bleeding was performed on all the horses in order to detect possible cases of seroconversion. As a result of positive serological diagnoses, interventions were conducted in six establishments. Serological surveys were conducted in all the horses, two serial diagnostic tests with an interval of 14 days, to verify the absence of viral activity.
Of a total of equines sampled in nine farms,