[Equine Infectious Anaemia - a review from an official veterinary perspective]. / Die Equine Infektiöse Anämie ­ eine Besprechung aus amtstierärztlicher Sicht.

INTRODUCTION: Equine infectious anaemia (EIA) is a sporadic viral disease in many countries. Every single case has, however, a dramatic impact: infected animals have to be put down, and quarantine restrictions on horse movements lasting three months lead to substantial economic losses. In Switzerland, the mandatory notification was introduced in 1994 in order to facilitate international traffic. A year later, the "new" Ordinance on epizootics of 1995 classified EIA as a "disease to be eradicated". An infected polo horse in the canton of Argovia in summer 2017 thus represented Switzerland's first official case. It served as a starting point to review the legal frameworks of the EU and Switzerland. Recent publications suggest that there might be some potential to optimize the current diagnostic protocols. EIA is transmitted by virus-containing blood and blood products. Introductions in previously disease-free regions are mostly due to human activities, while blood feeding insects as horse flies or other biting flies act as mechanical vectors only locally within some 100 meters. As before, the new EU Regulations governing animal health do not prescribe national monitoring and control plans, allowing member states to shape them according to their particular situation. However, they have to ensure that equids intended for intracommunity movements comply with specific guarantees. In this context, a fine-tuning of current international standards seems conceivable. Mandatory testing preceding each movement would not be a proportionate option even for the future. Regardless their final wording, it would be a great step for all the actors involved in animal traffic if it were possible to adopt rules that are accepted and uniformly implemented by all competent authorities at national, regional and local level. However, the official system will never be able to guarantee absolute safety. Since there are neither effective vaccines nor treatment protocols, it is crucial that all owners, stablehands, veterinarians, associations, and organizers of horse contests are aware of the disease risks, minimizing them as far as possible by adequate biosecurity measures.

INTRODUCTION: L'anémie infectieuse des équidés (AIE) est une maladie virale sporadique dans de nombreux pays. Chaque cas a pourtant de graves conséquences: les animaux infectés doivent être éliminés, et les interdictions de mouvements d'équidés pendant trois mois causent des pertes économiques substantielles. En Suisse, la notification obligatoire a été introduite en 1994 pour faciliter les échanges transfrontaliers. En 1995, la «nouvelle¼ ordonnance sur les épizooties a ensuite classé l'AIE dans la catégorie des «épizooties à éradiquer¼. Le cheval de polo infecté, qui a été découvert durant l'été 2017 dans le canton d'Argovie, représente donc le premier cas officiel d'AIE en Suisse. Il a servi de point de départ pour une appréciation de la réglementation de l'UE et du droit suisse. Des études récentes indiquent qu'il existerait un potentiel d'optimisation des protocoles de diagnostic. L'AIE est transmise par le sang et les produits sanguins contenant l'agent infectieux. L'introduction de la maladie dans une région indemne est souvent liée à des activités humaines, les insectes hématophages, comme les taons ou les mouches piquantes, peuvent servir de vecteurs mécaniques au niveau local, dans un rayon ne dépassant pas quelques centaines de mètres. Comme l'actuelle, la nouvelle réglementation de l'UE régissant la santé animale ne prescrira pas aux États membres une stratégie nationale de surveillance ou de lutte, qu'ils peuvent en conséquence adapter en fonction de leur situation particulière. Ils doivent toutefois assurer que les équidés destinés aux mouvements intracommunautaires remplissent des conditions spécifiées. A cet égard, un «ajustage¼ des normes internationales parait envisageable, mais comme c'est déjà le cas actuellement, un examen de laboratoire avant tout déplacement ne sera pas exigé. Indépendamment de leur formulation finale, des conditions de déplacement d'équidés généralement acceptées et appliquées uniformément par toutes les autorités compétentes aux échelles nationales, régionales et locales signifieraient un grand progrès pour tous les acteurs impliqués dans le trafic d'animaux. Les législations ne pourront jamais garantir une sécurité absolue. Considérant qu'il n'existe ni vaccination efficace ni traitement, il est crucial que les détenteurs, palefreniers, vétérinaires, associations et organisateurs de manifestations équestres soient conscients du danger d'épizootie, et qu'ils le réduisent autant que possible par des mesures de biosécurité adéquates.

Evolution of equine infectious anaemia in naturally infected mules with different serological reactivity patterns prior and after immune suppression.

Information on equine infectious anaemia (EIA) in mules, including those with an equivocal reaction in agar gel immunodiffusion test (AGIDT), is scarce. For this, a study was conducted to evaluate the clinical, viral loads and pathological findings of two groups of naturally infected asymptomatic mules, respectively with a negative/equivocal and positive AGIDT reactivity, which were subjected to pharmacological immune suppression (IS). A non-infected control was included in the study that remained negative during the observation period. Throughout the whole study, even repeated episodes of recrudescence of EIA were observed in 9 infected mules, independently from their AGIDT reactivity. These events were generally characterised by mild, transient alterations, typical of the EIA acute form represented by hyperthermia and thrombocytopenia, in concomitance with viral RNA (vRNA) peaks that were higher in the Post-IS period, reaching values similar to those of horses during the clinical acute phase of EIA. Total tissue viral nucleic acid loads were greatest in animals with the major vRNA activity and in particular in those with negative/equivocal AGIDT reactivity. vRNA replication levels were around 10-1000 times lower than those reported in horses, with the animals still presenting typical alterations of EIA reactivation. Macroscopic lesions were absent in all the infected animals while histological alterations were characterised by lymphomonocyte infiltrates and moderate hemosiderosis in the cytoplasm of macrophages. On the basis of the above results, even mules with an equivocal/negative AGIDT reaction may act as EIAV reservoirs. Moreover, such animals could escape detection due to the low AGIDT sensitivity and therefore contribute to the maintenance and spread of the infection.

Equine infectious anaemia and mechanical transmission: man and the wee beasties.

There is no credible evidence that the lentivirus that causes equine infectious anaemia (EIA) replicates in invertebrates. The virus persistently infects its equid hosts and is often present in blood in significant quantities. Blood-feeding arthropods thus have the potential to transfer the virus between hosts, especially if their feeding on the first host is interrupted and immediately continued on a second host. The general details and dynamics of mechanical transmission are included in this paper, as this agent presents an excellent model. Mechanical transmission can be effectively controlled if the dynamics and interactions of the host, virus and vector populations are understood. Efficient transmission is proportional to the amount of agent found in the source material, the environmental survival of the agent, the number of vector feedings, the number of interrupted feedings, vector refeeding, the proximity of infected and naive hosts, host population density, and the length of time during which vectors and hosts are in contact. Establishing firm quantitative risk estimates for EIA is impossible, mainly because the virus content in blood can change exponentially from day to day. The EIA virus can be transmitted by horse flies for at least 30 minutes after feeding on a horse with acute signs of EIA, butthe probability of a horse fly being interrupted and completing its blood feeding on a second host at a distance of 50 m is very low, and the separation of infected and uninfected equids by 200 m breaks transmission. The statements above assume that human interactions are absent or do not contribute to the risk of virus transmission; however, the risk from human interventions, such as the too-often-used procedure of administering > 200 ml of plasma to foals, can easily be more than 10(7) times greater than the risk posed by a single horse fly. Controlling EIA depends upon the identification of persistently infected equids by serological testing because other methods of identifying infective virus orviral genetic material are less accurate or impractical.

Free-virus and cell-to-cell transmission in models of equine infectious anemia virus infection.

Equine infectious anemia virus (EIAV) is a lentivirus in the retrovirus family that infects horses and ponies. Two strains, referred to as the sensitive strain and the resistant strain, have been isolated from an experimentally-infected pony. The sensitive strain is vulnerable to neutralization by antibodies whereas the resistant strain is neutralization-insensitive. The sensitive strain mutates to the resistant strain. EIAV may infect healthy target cells via free virus or alternatively, directly from an infected target cell through cell-to-cell transfer. The proportion of transmission from free-virus or from cell-to-cell transmission is unknown. A system of ordinary differential equations (ODEs) is formulated for the virus-cell dynamics of EIAV. In addition, a Markov chain model and a branching process approximation near the infection-free equilibrium (IFE) are formulated. The basic reproduction number R0 is defined as the maximum of two reproduction numbers, R0s and R0r, one for the sensitive strain and one for the resistant strain. The IFE is shown to be globally asymptotically stable for the ODE model in a special case when the basic reproduction number is less than one. In addition, two endemic equilibria exist, a coexistence equilibrium and a resistant strain equilibrium. It is shown that if R0>1, the infection persists with at least one of the two strains. However, for small infectious doses, the sensitive strain and the resistant strain may not persist in the Markov chain model. Parameter values applicable to EIAV are used to illustrate the dynamics of the ODE and the Markov chain models. The examples highlight the importance of the proportion of cell-to-cell versus free-virus transmission that either leads to infection clearance or to infection persistence with either coexistence of both strains or to dominance by the resistant strain.

Equine infectious anemia and equine infectious anemia virus in 2013: a review.

A detailed description of equine infectious anemia virus and host responses to it are presented. Current control and eradication of the infection are discussed with suggestions for improvements to increase their effectiveness.

Is a diagnostic system based exclusively on agar gel immunodiffusion adequate for controlling the spread of equine infectious anaemia?

To improve the efficiency of the National equine infectious anaemia (EIA) surveillance program in Italy, a three-tiered diagnostic system has been adopted. This procedure involves initial screening by ELISA (Tier 1) with test-positive samples confirmed by the agar gel immunodiffusion test (AGIDT) (Tier 2) and, in the case of ELISA positive/AGIDT negative results, final determination by immunoblot (IB) (Tier 3). During this evaluation, 74,880 samples, principally collected from two Regions of Central Italy (Latium and Abruzzo) were examined, with 44 identified as negative in AGIDT but positive in both ELISA and IB. As the majority of these reactions occurred in mules, an observational study was conducted in this hybrid equid species to investigate if there is a correlation between plasma-associated viral loads and serological reactivity, to test the hypothesis that false-negative or very weak positive AGIDT results are associated with elite control of EIA virus (EIAV) replication accompanied by reduced transmission risks. The study animals consisted of 5 mules with positive AGIDT readings, along with another 5 giving negative or very weak positive results in this test. All mules were seropositive in Elisa and IB. Samples were collected routinely during an initial 56-day observation period, prior to dexamethasone treatment lasting 10 days, to determine the effect of immune suppression (IS) on clinical, humoral and virological responses. All mules were monitored for a further 28 days from day 0 of IS. None of the animals experienced relevant clinical responses before IS and there were no significant changes in antibody levels in ELISA, IB or AGIDT. However, plasma-associated viral-RNA (vRNA) loads, as determined using TaqMan(®) based RT-PCR, showed unexpectedly high sample to sample variation in all mules, demonstrating host-mediated control of viral replication is not constant over time. Furthermore, there was no apparent correlation between vRNA loads and antibody reactivity in serological tests. Analysis of PCR products established all mules were infected with viruses possessing nucleotide sequence similarity, varying from 77 to 96%, to previously identified European EIAV strains. Following IS, all mules showed increases in plasma-associated vRNA loads, suggesting control of EIAV replication is mediated by immune responses in this hybrid species. However, only three mules showed anamnestic humoral responses to rises in viral loads, as defined by at least a four-fold increase in ELISA titre, while two remained AGIDT-negative. This study demonstrates that viral loads in equids with consistent ELISA/IB positive-AGIDT negative to very weak positive test results (Group N) can be equivalent to those that produce clearly positive results in all three serologic tests (Group P). Therefore, such animals do not pose inherently lower risks for the transmission of EIAV. Consequently, the exclusive use of the AGIDT, as prescribed by the World Organization of Animal Health (OIE) for diagnosis of EIA prior to the international movement of horses, can report as negative some EIAV-infected equids. These results dramatically underscore the necessity of combining the specificity of AGIDT with tests with higher sensitivity, such as the ELISA and the power of the IB to enhance the accuracy of EIA diagnosis.

The risk of introduction of equine infectious anemia virus into USA via cloned horse embryos imported from Canada.

Deriving horse oocytes in the USA is hampered by the lack of abattoirs processing horse carcasses which could provide abundant quantities of ovaries from slaughtered mares. Therefore, several cloning industries in the USA are attempting to import cloned horse embryos from Canada. Like any agricultural commodity, cloned embryos pose a risk of introduction of exotic animal diseases into the importing country. Under such circumstances, risk assessment could provide an objective, transparent, and internationally accepted means for evaluating the risk. This quantitative risk assessment (QRA) was initiated to determine the risk of introduction of Equine infectious anemia virus (EIAV) into the USA via cloned horse embryos imported from Canada. In assessing the risk, a structured knowledge base regarding cloning in relation to Equine infectious anemia (EIA) was first developed. Based on the knowledge base, a scenario tree was developed to determine conditions (with mathematical probabilities) that could lead to the introduction and maintenance of EIAV along the cloning pathway. Parameters for the occurrence of the event at each node were estimated using published literature. Using @Risk software and setting Monte Carlo simulation at 50,000 iterations, the probability of importing an EIAV-infected cloned horse embryo was 1.8 × 10(-9) (R = 1.5 × 10(-12) to 2.9 × 10(-8)). Taking into account the current protocol for equine cloning and assuming the yield of 5 to 30 clones per year, the possible number of EIAV-infected cloned horse embryos ranged from 2.0 × 10(-10) to 9.1 × 10(-5) (Mean = 1.4×10(-6)) per year. Consequently, it would take up to 1.5 × 10(7) (R = 1.6 × 10(4) to 5.1 × 10(10)) years for EIAV to be introduced into the USA. Based on the knowledge base and our critical pathway analysis, the biological plausibility of introducing EIAV into USA via cloned horse embryos imported from Canada is extremely low.

Network simulation modeling of equine infectious anemia in the non-racehorse population in Japan.

An equine infectious anemia (EIA) transmission model was developed by constructing a network structure of horse movement patterns in a non-racehorse population. This model was then used to evaluate the effectiveness and efficiency of several EIA surveillance strategies. Because EIA had not been detected in Japan since 1993, it was appropriate to review the current surveillance strategy, which aims to eradicate EIA by intensive testing, and to consider alternative strategies suitable for the current EIA status in Japan. The non-racehorse population was divided into four sectors based on horse usage: the equestrian sector, private owner sector, exhibition sector, and fattening sector. To evaluate the risk of disease spread within and between sectors accompanied by horse movements, a stochastic individual-based network model was developed based on a previous survey of horse movement patterns. Surveillance parameters such as targeting sectors and frequency of testing were added into the model to compare surveillance strategies. The disease spread heterogeneously among sectors. Infection occurred mainly in the equestrian sector; the infection was less disseminated in other sectors. Therefore, we considered that the equestrian sector posed a higher risk of disease dissemination within and between sectors through horse movements. However, surveillance strategies targeting only the equestrian sector were not effective enough for early detection of the disease. Alternatively, targeting horses that moved permanently and those in the private owner sector in addition to the equestrian sector is recommended to achieve effectiveness equivalent to that of the current surveillance. In terms of surveillance efficacy, by increasing the testing interval (once yearly to once every 3 years), this testing scheme could reduce the number of tested horses to 44% of the current surveillance, while maintaining almost equivalent effectiveness. Intensive strategies targeting high-risk populations are considered to enhance effectiveness and efficiency of surveillance. The approach in this study may be helpful in the decision-making process that is involved in setting up strategies for risk-based surveillance.

Avaliação da nested PCR em comparação aos testes sorológicos IDGA e ELISA para o diagnóstico da anemia infecciosa equina / Evaluation of nested PCR compared with AGID and ELISA serological tests for equine infectious anemia diagnosis

Comparou-se a técnica nested PCR (nPCR) com os testes sorológicos IDGA e ELISA para o diagnóstico da anemia infecciosa equina. Amostras do DNA provenientes das células mononucleares do sangue periférico foram submetidas à amplificação do gene gag pela nPCR, que apresentou valores de sensibilidade e especificidade relativas de 90 por cento e 52,9 por cento, respectivamente, em relação à IDGA, e valores de 85,7 por cento e 49 por cento, respectivamente, em relação ao ELISA. Considerando-se os fatores referentes às limitações de cada técnica, pode ser sugerido o uso da nPCR como teste de diagnóstico complementar para AIE em amostras brasileiras.

The nested polymerase chain reaction (nPCR) technique was compared to AGID and ELISA serological tests for the diagnosis of Equine Infectious Anemia. DNA samples from the peripheral blood mononuclear cells were subjected to the amplification of the gag gene by nPCR, which showed relative sensibility and specificity values of 90.0 percent and 52.9 percent respectively, compared to the AGID and values of 85.7 percent and 49.0 percent, respectively, as compared to ELISA. Considering the factors concerning the limitations of each technique, the use of nPCR can be suggested as a complementary diagnostic test for EIA in Brazilian samples.

Risk of equine infectious disease transmission by non-race horse movements in Japan.

For determining surveillance programs or infectious disease countermeasures, risk evaluation approaches have been recently undertaken in the field of animal health. In the present study, to help establish efficient and effective surveillance and countermeasures for equine infectious diseases, we evaluated the potential risk of equine infectious disease transmission in non-race horses from the viewpoints of horse movements and health management practices by conducting a survey of non-race horse holdings. From the survey, the non-race horse population was classified into the following five sectors based on their purposes: the equestrian sector, private owner sector, exhibition sector, fattening sector and others. Our survey results showed that the equestrian and private owner sectors had the largest population sizes, and movements between and within these sectors occurred quite frequently, while there was little movement in the other sectors. Qualitative evaluation showed that the equestrian and private owner sectors had relatively high risks of equine infectious disease transmission through horse movements. Therefore, it would be effective to concentrate on these two sectors when implementing surveillance or preventative measures. Special priority should be given to the private owner sector because this sector has not implemented inspection and vaccination well compared with the equestrian sector, which possesses a high compliance rate for these practices. This qualitative risk evaluation focused on horse movements and health management practices could provide a basis for further risk evaluation to establish efficient and effective surveillance and countermeasures for equine infectious diseases.

Risk of equine infectious anemia virus disease transmission through in vitro embryo production using somatic cell nuclear transfer.

Prevention and regulation of equine infectious anemia virus (EIAV) disease transmission solely depend on identification, isolation, and elimination of infected animals because of lack of an effective vaccine. Embryo production via the somatic cell nuclear transfer (SCNT) technology uses oocytes collected mainly from untested animals, which creates a potential risk of EIAV transmission through infected embryos. The current review examines the risk of EIAV disease transmission through SCNT embryo production and transfer. Equine infectious anemia virus is a lentivirus from the family Retroviridae. Because of a lack of direct reports on this subject, relevant information gathered from close relatives of EIAV, such as human immunodeficiency virus (HIV), bovine immunodeficiency virus (BIV), feline immunodeficiency virus (FIV), and small ruminant lentiviruses (SRLVs), is summarized and used to predict the biological plausibility of EIAV disease transmission through transfers of the equine SCNT embryos. Based on published information regarding interaction of oocytes with lentiviruses and the sufficiency of oocyte and embryo washing procedures to prevent lentivirus transmission from in vitro-produced embryos of various species, we predicted the risk of EIAV transmission through SCNT embryo production and transfer to be very small or absent.

[Equine Infectious Anemia (EIA)]. / Equine Infektiöse Anämie (EIA).

Equine Infectious Anemia (EIA) is a reportable, eradicable epizootic disease caused by the equine lentivirus of the retrovirus family which affects equids only and occurs worldwide. The virus is transmitted by blood, mainly by sanguivorous insects. The main symptoms of the disease are pyrexia, apathy, loss of body condition and weight, anemia, edema and petechia. However, infected horses can also be inapparent carriers without any overt signs. The disease is diagnosed by serological tests like the Coggins test and ELISA tests. Presently, Switzerland is offi cially free from EIA. However, Switzerland is permanently at risk of introducing the virus as cases of EIA have recently been reported in different European countries.

Risk analysis of quarantine station performance: a case study of the importation of equine infectious anemia virus-infected horses into California.

We examined the risk of importing and mistakenly releasing equine infectious anemia virus (EIAV)-infected horses into California. A computer simulation model was constructed to evaluate current and alternative quarantine station procedures; 150,000 iterations were performed to simulate 15 different scenarios of 10,000 horses imported into the state over a 14-year period. Simulation results showed that under current conditions of low EIAV prevalence in exporting countries, increasing the quarantine period would not decrease the number of EIAV-infected horses mistakenly released from quarantine. In a worst case scenario of high EIAV prevalence in exporting countries, the model predicted 10 EIAV-infected horses would be imported, of these 1 or none would escape detection and would be released mistakenly if quarantine duration were 3 or 14 days, respectively. This model may be applied to other quarantine station situations for evaluating the importation risk for EIAV and other diseases.