Prevention and control of equine infectious anemia in horse

10/10/2022

Control of equine infectious anemia
Vector control practices should be a part of any EIA prevention and control program. These should include routine application of insecticides and repellants as well as the implementation of insect control measures.
Any control program for EIA must emphasize awareness of how readily the causal virus can be transmitted indirectly from an infected individual to other equids on a premises through the re-use of contaminated needles, syringes, surgical or dental instruments, or other equipment. Strict observance of the principles of good hygiene and disinfection is essential if iatrogenic transmission of EIA is to be prevented.
Specific measures to prevent/control EIA can be summarized as follows:
Infected horses become lifelong carriers and pose a risk of infection to other horses. Management options for an EIA-positive horse are euthanasia or lifetime quarantine, with permanent isolation at least 200 yards away from noninfected horses.
Prevention is key to stopping the spread of EIA.
Use a sterile needle, syringe, and IV set for all injections or treatments.
Disinfect dental, tattoo, surgical equipment, lip chains, and bits thoroughly between horses. Remove all debris and blood with soap and water before disinfection.
Only administer commercially licensed blood or blood products.
Keep open wounds clean and covered, if possible.
Use a sterile needle and syringe each time when puncturing a multidose medication bottle.
Use sterile technique when drawing up and administering medications.
Require proof of a recent negative EIA test upon introduction of a horse onto a premises for the first time.
Practice good fly control by regular mucking out of stalls, proper disposal of manure away from horse stabling areas, and using fly sprays or natural predators to minimize fly presence.

10/10/2022

Prevention of equine infectious anemia
prophylactic vaccination, it is recommended that horse owners implement an EIA control plan for their premises. An integral part of such a program should be annual testing of all horses. More frequent testing may be indicated in areas that previously experienced a high incidence of EIA. All equines introduced to a herd should have a negative EIA test before arrival or be isolated while tests are pending. Horses competing in shows or performance events should be accompanied by proof that they have been tested for EIA within a specific period of time.

10/10/2022

Diagnosis is based on serologic tests
The clinical signs of acute equine infectious anemia are often nonspecific and not definitive of the disease. Accordingly, a provisional clinical diagnosis must be confirmed by demonstration of antibodies to the virus in blood. Laboratory confirmation of a suspect case of EIA needs to be pursued without delay. A wide range of infectious and noninfectious diseases can clinically resemble and be confused with EIA. These include:
equine viral arteritis
purpura hemorrhagica
piroplasmosis
leptospirosis
severe strongyliasis or fascioliasis
phenothiazine toxicity
autoimmune hemolytic anemia
Although the internationally accepted serologic test is the agar gel immunodiffusion or Coggins test, there is increasing acceptance of a variety of ELISA tests, either competitive or synthetic antigen-based, because they can provide rapid results. Because ELISA tests can give a higher rate of false positives, all positive ELISA results must be confirmed by the Coggins test. When used in combination, ELISA and agar gel immunodiffusion tests provide the highest level of sensitivity combined with specificity. The Western blot is a supplemental test that can be resorted to in cases of conflicting results with other diagnostic tests.
A problem with available serologic tests is that they can give negative results when testing sera collected within the first 10–14 days of infection. Whereas the vast majority of horses infected with EIA virus will have seroconverted by 45 days, there have been exceptional cases in which the interval has been ≥90 days.
Virus detection assays such as reverse transcription PCR are not routinely used to diagnose EIA. Notwithstanding their sensitivity, they may not detect virus in carrier horses with very low viral loads. Although the animal inoculation test is highly sensitive for detection of EIA virus, for logistic and economic reasons, it is no longer in vogue as a means of diagnosis of EIA.

10/10/2022

Clinical Findings of Equine Infectious Anemia
The clinical findings and course of infection with equine infectious anemia virus are variable, depending on the virulence of the virus strain, viral dose, and susceptibility of the horse. After an incubation period of 15–45 days or longer in naturally acquired cases of infection, classic cases of the disease have been described as progressing through three clinical phases. An initial or acute episode lasting 1–3 days is characterized by fever, depression, and thrombocytopenia. Because these signs can be mild and transitory, they are often overlooked or misdiagnosed. Typically, this initial phase is followed by a prolonged period associated with:
recurring episodes of fever
depression
thrombocytopenia
increased heart and respiration rates
anemia
jaundice
petechiation on mucous membranes
epistaxis
dependent edema
muscle weakness
loss of condition
The interval between episodes can range from days to weeks or months. In most cases, the episodes of clinical disease subside within a year, and infected horses become inapparent carriers and reservoirs of EIA virus. Many of these horses remain clinically normal. However, some chronically infected horses may continue to experience recurrent episodes varying from fever and thrombocytopenia to many of the extensive range of clinical signs that have been described. Such episodes are frequently associated with intercurrent infections and other sources of stress.
Although the foregoing represents the most commonly described clinical course of the disease, some outbreaks of EIA can be associated with peracute infection in which the primary viral infection is uncontrolled; this can result in a very high fever, severely reduced platelet counts, and infrequently acute depression and epistaxis leading to death. In view of the wide variation in response seen in natural cases of infection, it is not possible to confirm a diagnosis of EIA based solely on clinical grounds.
Although clinical signs can differ in range and severity between individuals, cases of EIA can present with many or most of the following:
fever
depression
low platelet count
anemia
increased heart and respiration rates
jaundice
hemorrhages on mucous membranes
epistaxis
dependent edema
muscle weakness
muscle atrophy

10/10/2022

Epidemiology and Transmission of Equine Infectious Anemia
All equids infected with EIA virus remain lifelong carriers. Such individuals constitute the natural reservoir of the virus and ensure its perpetuation in equid populations over time. The combination of frequent carriers and mechanical transmission by blood-feeding insects explains why EIA is found in equine populations in a wide range of climatic zones and countries around the world.
Although EIA is usually considered a blood-borne infection, all body fluids and tissues should be regarded as potentially infectious, especially during febrile episodes when viral levels are high. Evidence of EIA virus has even been found in nasal swabs and in swabs taken from the buccal cavity and genitalia. There are limited data to suggest that infectious virus can be present in milk. EIA virus can also be passed to foals in utero. Evidence in support of venereal transmission is questionable; it is unlikely to occur unless semen is contaminated with blood in the case of an infected stallion.
There is circumstantial evidence suggesting that EIA virus may, under exceptional circumstances, also be transmitted via the respiratory route through aerosolization of blood when an infected horse is bleeding from the nostrils.
Transmission of EIA by biting flies is purely mechanical; the virus does not replicate in the insect. The chances of transmission of EIA among horses in close proximity to one another has been shown to be directly proportional to the volume of blood retained on the mouthparts of an insect after feeding. Based on this, horse flies, deer flies, and to a lesser extent, stable flies, are the most efficient vectors of the virus. It is also because the bites are irritating and trigger host defensive behavior that interrupts the flies' feeding routine and results in their seeking out another susceptible host to complete their blood meal.
EIA transmission is influenced by the number and species of flies, density of the horse population, level of viremia in the host, and quantity of blood transferred. Infections are especially common in hot, humid countries of the world with very large biting fly populations. Symptomatic, febrile horses are more likely to transmit the disease than animals with inapparent infections.
Aside from the ral transmission of EIA by blood-feeding insects, the disease can also be readily transmitted iatrogenically through the re-use of blood-contaminated syringes and needles, surgical instruments, dental equipment, and IV sets and by the transfusion of infective blood or blood products. The virus is purported to persist for up to 96 hours on contaminated hypodermic needles. The importance of iatrogenic spread of EIA cannot be overstated. It has become increasingly common in some countries among a certain element of the equine industry that is indifferent to the inherent risks involved and the potential for dissemination of the virus.

10/10/2022

Etiology and Pathogenesis of Equine Infectious Anemia
The causal agent of equine infectious anemia is an RNA virus, classified in the Lentivirus genus, family Retroviridae. The virus is readily inactivated by most common disinfectants, such as bleach, ethanol, iodophore disinfectants, phenolic compounds, glutaraldehyde, and formalin. Because bleach-based and ethanol disinfectants are readily inactivated in the presence of organic material, for example manure or soil, contaminated surfaces must first be cleaned thoroughly of such matter using soap and water before treating with a disinfectant. Pressure washing of a soiled surface is contraindicated because of the risk of aerosolization of potentially infectious blood or other body fluids on wall or floor surfaces.
In equids infected with EIA virus, there is a very close relationship between the development of overt signs of disease and the amount of virus present. Virus is found free in plasma or associated with monocytes and macrophages in infected animals. Virus burdens reach their highest levels during febrile episodes, after which they decline. It has been shown that the concentration of EIA virus in tissues must reach a threshold level to trigger a clinical response. The potential of a viral strain to induce disease is largely due to its replicative capacity or pathogenicity in the infected host.
The pathology of EIA-mediated disease is a consequence of macrophage infection that in turn interferes with host-cell gene expression; this leads to increased production of pro-inflammatory mediators or cytokines, in particular TNF-alpha, IL-1, IL-6, and transforming growth factor beta. Aside from the latter activating the arachidonic pathway that results in increased production of prostaglandin E2 and the induction of a febrile response, these cytokines may also cause thrombocytopenia. Increased production of TNF-alpha may also be partly responsible for the anemia that develops in EIA virus-infected equids by virtue of its ability to inhibit erythropoiesis.
Aside from the foregoing role that pro-inflammatory cytokines play in the pathogenesis of EIA, adaptive immune responses are also involved in the pathology of the disease. Platelets from infected horses have significant amounts of bound IgG or IgM, which result in their immune-mediated destruction, contributing to both splenomegaly and hepatomegaly.
There is reason to believe that cell-mediated and not humoral immune responses are responsible for initial control of EIA virus infection. Once acute viral infection has been controlled, the infected individual will remain free of overt signs of disease until a variant virus emerges that can evade the host’s immune system.

10/10/2022

Equine infectious anemia (EIA) is a noncontagious infectious disease of equids caused by a virus of the same name. Clinical outcomes range from subclinical to a range of signs of variable severity, including fever, depression, muscle weakness, thrombocytopenia, anemia, jaundice, increased heart and respiration rates, hemorrhages on mucous membranes, epistaxis, collapse, and death in a small percentage of cases. Diagnosis of EIA is based on serologic testing and demonstration of antibodies to the virus in blood. There are no treatments or vaccines.

27/05/2022

Equine infectious anaemia (EIA) is a viral infectious disease that causes anaemia and is associated with recurrent periods of fever.
Equine infectious anaemia occurs in horses, mules and donkeys, and is transmitted by bloodsucking insects. The foetus can also become infected in pregnant animals. The equine infectious anaemia virus (EIAV) is a lentivirus and belongs to the same family as the maedi-visna virus in sheep and HIV (cause of the disease AIDS) in humans. Once a horse has become infected, the animal may remain infectious for other horses for life. Humans cannot be infected with the EIA virus (EIAV).
Equine infectious anaemia is a notifiable animal disease. If the disease is suspected, the NVWA must be informed. It is often difficult to distinguish EIA from other diseases associated with fever. It can only be done through laboratory testing.
Clinical signs equine infectious anaemia
There are various stages in EIA. Horses may survive the infection without evident clinical symptoms, an acute phase may be observed, or the disease may have a chronic progression. The incubation period, before clinical symptoms can be observed, is 3-30 days, but may also be much longer. All animals infected with the EIA virus remain carriers for life and form a potential source of infection.
Acute
The disease often starts with acute symptoms that are potentially, but not often, fatal. In this acute phase, making a diagnosis is difficult, because the symptoms appear rapidly, and often only an elevated body temperature is found. Apart from fever, however, lethargy, anaemia, bleeding and reduced appetite may also be observed. During this phase of the disease, the blood contains extremely high concentrations of the virus, and the risk of transmission is relatively high.
Chronic
If the animal does not die during the acute phase of the disease, it may become chronic. The horse will then have periods of fever (with intervening periods lasting weeks or even years), anaemia, weight loss and fluid retention (oedema) under the belly and on the legs.
Diagnostics equine infectious anaemia
Showing the presence of EIAV-specific antibodies using serologic testing is a reliable method for making an EIA diagnosis. Serologic testing can be conducted with an ELISA (enzyme-linked immunosorbent assay) or with an agar gel immunodiffusion test (AGIDT or Coggins test). The AGIDT is the gold standard and is used to make a definitive diagnosis.
Vaccine equine infectious anaemia
There is no vaccine or adequate treatment for the disease.
Prevention and control of equine infectious anaemia
Transmission of EIA usually occurs through the transfer of infected blood by blood-sucking insects, infected blood plasma, needles, syringes or other materials contaminated with blood.
Transmission of EIA by blood-sucking insects depends on the density of the horse population, the number of EIA-infected animals and the number, and behaviour of the insects (fly, horsefly and other large blood-sucking insects). The virus does not propagate in the insect, which transmits the virus only via the proboscis.
Transplacental infection can also occur (vertical transmission during the pregnancy of the infected horse to the foal) or when an infected stallion covers a mare.
The reuse of contaminated syringes and needles is a significant factor in transmitting EIA.
Limiting further transmission
In order to counter (further) transmission of EIAV, transmission via infected horses must in the first instance be minimised or ruled out.
Horses infected with EIA carry the virus for the rest of their lives. This results from the fact that the virus inserts its DNA into certain types of cell. If the animals find themselves under stress and/or are treated with corticosteroids, the virus may multiply again and make the animal ill. The animal is thus a constant "danger" to itself and to the horses around it.
As the Netherlands is free of this disease, it is important that non-infected horses are protected by placing an infected horse in quarantine (at a distance of at least 200 m from other horses) or by euthanising it.
Until every horse has been tested at a location, the assumption is that every horse at the location, or that has been there, is a potential EIAV reservoir. The NVWA will close off the location and let WBVR test all the other horses over a period of three months to check that they have not become infected.
Precautions for horse owners
The owners of horses can reduce the risk of infection with and spread of EIAV by taking a number of steps.
Use disposable syringes and needles. Follow the rule: a separate needle for each horse. Vets in the Netherlands always use disposable needles. They will also use blood products from donors that have been tested for EIA.
Clean and sterilise all instruments that could be contaminated with blood after each use.
Keep separate all horses, mules and donkeys newly imported from abroad until they have been tested for EIA, or insist that a recent negative EIA test certificate is shown on import.
There is risk of transmission by insects, if an infected horse is present less than 200 metres away from the operation/farm. At a distance greater than 200 metres, the risk of infection via this route is small.
Contact the vet as soon as clinical symptoms are observed that could indicate infection with EIAV.

27/05/2022

28/04/2022

Equine infectious anaemia (EIA) is a viral infectious disease that causes anaemia and is associated with recurrent periods of fever.
Equine infectious anaemia occurs in horses, mules and donkeys, and is transmitted by bloodsucking insects. The foetus can also become infected in pregnant animals. The equine infectious anaemia virus (EIAV) is a lentivirus and belongs to the same family as the maedi-visna virus in sheep and HIV (cause of the disease AIDS) in humans. Once a horse has become infected, the animal may remain infectious for other horses for life. Humans cannot be infected with the EIA virus (EIAV).
Equine infectious anaemia is a notifiable animal disease. If the disease is suspected, the NVWA must be informed. It is often difficult to distinguish EIA from other diseases associated with fever. It can only be done through laboratory testing.

21/03/2022

Equine infectious anemia (EIA) is a viral disease caused by the equine infectious anemia virus. This virus belongs to the family of viruses that includes human immunodeficiency virus (HIV). The disease affects horses and ponies, but is not transmissible to humans. Donkeys and mules can contract EIA, but most do not develop severe clinical signs. Equine infectious anemia has been found worldwide and is a reportable disease in all U.S. states.
Blood-feeding flies (especially horse flies and deer flies), blood-contaminated needles, blood transfusions, and contaminated instruments can transmit the virus. Less common routes of infection include from mare to foal in utero, and in milk or semen. Infected horses can show no signs of disease or they may exhibit acute and/or chronic recurring clinical signs. The virus is present in white blood cells and plasma where levels can become elevated during periods of stress. EIA-positive horses that survive the acute stage of infection become lifelong carriers that can transmit the virus to other horses. There is currently no vaccine and no known treatment for EIA.
What are the clinical signs of equine infectious anemia?
Most horses remain asymptomatic. For those that do show clinical signs of EIA, these can be nonspecific, vary in severity, and classically progress through three stages after an initial incubation period of 15-45 (or more) days. The initial, acute episode, which lasts 1-3 days, is characterized by fever, a deficiency of platelets in the blood (thrombocytopenia), and lethargy. This is followed by a period of days to months in which clinical signs include recurring fever, thrombocytopenia, severe anemia (not enough red blood cells or hemoglobin in the blood), decreased appetite, and sudden death. Additional signs may include jaundice, rapid breathing, rapid heart rate, swelling of the limbs (edema), bleeding from the nose, red or purple spots on the mucous membranes, blood in the f***s and overall general weakness. It is impossible to differentiate EIA from other diseases that cause fever, edema and/or anemia based solely on clinical signs. Owners may not realize that a horse is infected unless it is tested.
The strain and dose of the virus, as well as the health of the animal, influence the severity of clinical signs and the morbidity rate. Many horses show no signs, or very mild signs, when they are first exposed to the virus. Those that survive the acute phase become lifelong carriers. These horses may develop recurrent flare-ups following periods of stress, exhibiting signs that vary from failure to thrive to fever, anemia, weight loss, lethargy, and swelling (edema) of the legs, chest, and abdomen.
How is equine infectious anemia diagnosed?
In the U.S., EIA testing must be performed by USDA-approved laboratories. Testing is performed by serology via the agar gel immunodiffusion (AGID) test, commonly known as the Coggins test (named after its developer Dr. Leroy Coggins), or enzyme-linked immunosorbent assay (ELISA).
A positive result using either test indicates the presence of EIA-specific antibodies in the blood. The AGID/Coggins test may not detect antibodies until 2 or 3 weeks after the horse has been infected. The ELISA can detect antibodies earlier and is more sensitive but has a higher rate of false positives.
Positive results on ELISA are usually confirmed by AGID/Coggins or immunoblotting (Western blotting). These tests can be supplemented with polymerase chain reaction (PCR) tests to confirm results, especially in cases where there are conflicting results. Reverse transcription polymerase chain reaction (RT-PCR) assays may also be used and are especially useful in foals born to infected mares as young animals may have maternal antibodies. A negative Coggins test, dated within the last 6-12 months (preferably within the last 60-90 days), is required when a horse is moved across state lines and is required in some states when a horse is sold, traded, or donated.
Testing laboratories must report positive EIA tests to local state or federal animal health officials within 24 hours. A regulatory veterinarian will then identify exposed horses, which will be placed under quarantine and tested for EIA. The USDA Animal and Plant Health Inspection Service maintains summary reports of confirmed EIA cases in the U.S.
The California Animal Health and Food Safety Laboratory offers both AGID and ELISA testing for the EIA virus.
How is equine infectious anemia treated?
There is no treatment or “cure” for EIA. If you suspect that your horse may be infected, call your veterinarian immediately, move the horse at least 200 yards away from other horses and reduce exposure to biting flies. Equine infectious anemia is a reportable disease. Positive cases must be reported by the testing laboratory to local state or federal animal health officials within two days of discovery.
What is the prognosis for equine infectious anemia?
In many cases, infected horses are clinically normal, or show nonspecific clinical signs. In severe cases, high fever, reduced platelet counts, and acute depression can lead to death. Regardless of the severity of clinical signs, infected animals are lifelong carriers. They must be permanently identified by tattoo, brand or microchip. Horses positive for EIA must be permanently isolated and quarantined at a minimum of 200 yards from all other horses or euthanized to prevent transmission of the disease.
How can equine infectious anemia be prevented?
Although EIA can result in serious outcomes, infections are rare. The rate of infection varies throughout the world based on location and is influenced by the number and species of flies, their habitats and the density of the horse population. The virus itself does not persist in the environment and cannot survive in soil or water. It is infective for up to 96 hours on contaminated needles and stays viable on the mouthparts of biting flies for less than 4 hours. It can be destroyed by most common disinfectants, such as bleach or alcohol (follow manufacturer’s recommendations and label instructions).
Since there is no vaccine available in the U.S., surveillance and testing are the best methods of prevention.
To reduce your horse’s chance of becoming infected with EIA:
Reduce exposure to biting flies through proactive management and insect control.
Never reuse needles or syringes; only use sterile needles and licensed blood products.
Use a sterile needle each time you puncture a multi-dose medication bottle.
Thoroughly disinfect surgical and dental equipment, bits and lip chains between horses.
Ensure that blood transfusions are only performed by licensed veterinarians using blood from confirmed EIA-negative donor horses.
Clean and cover open wounds.
Test every horse at least annually.
Separate horses with fevers, inappetence and/or lethargy from other horses and contact your veterinarian.
Require proof of a recent negative EIA test for new horses entering the premises or when purchasing a new horse.

16/03/2022

Equine Infectious Anemia - causes, pathophysiology, clinical signs, diagnosis, treatment, prevention

16/03/2022

14/07/2021

Prevalence
Equine infectious anemia is a worldwide disease of Equidae, including horses, ponies, donkeys, mules, and zebras. Because EIAV is most commonly transmitted by insect vectors, the prevalence is higher in regions with warm climates. In Brazil, for example, the infection rate in certain horse herds has been as high as 50%.7 Infection with EIAV is reportable in the United States and to the World Organization for Animal Health (OIE).9 In the United States, the highest percentage of positive testing horses historically occurs in the Gulf Coast region, which has a favorable climate for vector transmission. Since a reliable serologic test for EIA was developed in the early 1970s10,11 and identification of reactors and culling of positive horses became possible, the percentage of horses testing positive for EIA in the United States has declined from almost 4% in 1972 to less than 0.003% in 2010.12,13 Nonetheless, these figures do not necessarily reflect EIA prevalence in the general horse population because they are biased by repeated testing of high-quality horses competing in events that require negative test results. Testing is only required for horses that are entering exhibitions or competitive events, being moved interstate, changing ownership, being imported, or entering auctions or sales markets. The American Horse Council estimates the U.S. horse population at 9.2 million,14 and according to the U.S. Department of Agriculture Animal and Plant Health Inspection Service (USDA-APHIS), between 1.5 and 2 million horses are tested each year.12,13 Based on this information, approximately 22% of the U.S. horse population is tested annually. This figure is likely an overestimate because the tests performed in a given year include repetitive testing of an undisclosed number of horses. The USDA National Animal Health Monitoring System Equine 2005 study evaluated 3349 equine operations in 28 states and found that 54.1% of these operations tested at least one horse for EIA during the year and that overall, 37.6% of the horses on all operations were tested.15 In summary, a large percentage of horses in the United States are not tested and the true EIA prevalence is not precisely known. Annual U.S. EIA testing reports
In Europe, EIA is endemic in Italy and Romania.16-18 In Ireland, an EIA outbreak occurred in 2006, and more recently, cases have been reported in France, Germany, and Great Britain.16-19 The 2006 outbreak in Ireland involved 38 horses and was the first outbreak in Ireland with evidence of trans­mission.17,19 The initial cases comprised four foals that were infected iatrogenically by the administration of infected plasma imported without license from Italy.17 Transmission to the other 34 horses occurred by a combination of iatrogenic means, probable insect vector-borne transmission, and possibly via aerosol.17,19 The potential aerosol transmission involved 13 horses sharing hospital airspace with an infected mare that had ongoing epistaxis and snorting for 13 hours prior to euthanasia.19 All infected horses either died or were euthanized, and no further EIA-positive horses have been detected in Ireland since December 2006.18,20 Government costs associated with control of the outbreak and the successful EIA eradication effort in Ireland have been conservatively estimated to exceed €1 million.20 At the time of this writing, three EIA cases had occurred in Great Britain since January 2010, and all three infected horses were of Romanian or suspected Romanian origin.16 The endemic status of persistently EIA-infected horses in countries such as Italy and Romania represents a continual threat for uninfected horses from nonendemic regions traveling in Europe, especially those traveling for competition purposes on 10-day health certificates. Despite the calculated low risk of a horse traveling from an EIA-free country, such as the United Kingdom,16 to an endemic region and returning to the country of origin and instigating of an outbreak, naïve horses may become infected and pose a risk of transmission because of the time frame of reentry testing. By contrast, in Romania, the EIA threat has likely improved because of European Commission control measures implemented in 2010; these include microchipping horses for trade, requiring health certificates for travel, holding at a premises with no other horses within 200 m (219 yards) for 90 days prior to travel, and requiring premovement EIA testing (twice 90 days apart) and 30 days of isolation postmovement with testing at the final destination.16 Current EIA information for countries throughout the world can be obtained