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Equine Infectious Anemia (EIA)

1.Disease information

Equine infectious anemia (EIA) is a noncontagious, infectious disease of horses and other Equidae. It is caused by an RNA virus classified in the Lentivirus genus, family Retroviridae. EIA can present as an acute, subacute, or chronic infection. On occasion, the virus can be a cause of significant morbidity and mortality. The most frequently encountered form of the disease is the inapparent, chronically infected carrier.

Under natural conditions, the most important mode of transmission of EIA is by the transfer of virus-infective blood by blood-feeding insects between horses in close proximity. The chance of transmission of EIA is directly proportional to the volume of blood retained on the mouthparts of the insect after feeding. In that respect, horse flies, deer flies, and to a lesser extent, stable flies are likely the most efficient vectors. Additionally, EIA can be readily transmitted iatrogenically through use of blood-contaminated syringes, needles, or surgical equipment, or by transfusion of infective blood or blood products. Infrequently, transplacental transmission can occur in infected mares that experience one or more clinical episodes during pregnancy.

Clinical Findings:

1. Acute sign

When horses are exposed to EIAV, they may develop severe, acute signs of disease and die within 2 to 3 weeks. This form of the disease is the most damaging and the most difficult to diagnose because the signs appear rapidly, and often only an elevated body temperature is noted. The clinical signs of the acute form of EIA are nonspecific; in mild cases, the initial fever may be short lived (often less than 24 hours). As a result, horse owners and veterinarians may not observe this initial sign when a horse is infected with EIAV. These infected horses often recover and continue to move freely in the population. The first indication that a horse was exposed to, and infected with, EIAV may well be a positive result on a routine annual test.

2. Chronic sign

If the horse survives this first acute bout, it may develop a recurring clinical disease with these signs:

                 • Fever: An infected horse’s temperature may rise suddenly to about 105 F or, rarely, as high as 108F. Then it may drop back to normal for an indeterminate period until the onset of another episode.

                 • Petechial hemorrhages: Minute blood-colored spots appear on the mucous membranes.

                 • Depression: The horse appears more or less dejected (head hangs low) and generally listless.

                 • Weight loss: The horse may refuse feed or may eat an inordinate amount but still continues on an obvious decline from normal weight.

                • Dependent edema: The horse may develop swelling, which is evidence of fluid collecting under the skin in the legs and under the chest and other underbody surfaces.

                • Anemia: The horse’s blood may experience a marked drop in its red corpuscle count and appear thin and watery. The animal may also have an irregular heartbeat, and a jugular pulse may become evident. The horse with chronic EIA is the classic “swamper” who has lost condition, is lethargic and anorexic, has a low hematocrit, and demonstrates a persistent decrease in the number of blood platelets, especially coincident with fever induced by EIAV.

 

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Figure 1 : Signs of Equine Infectious Anemia

3. Inapparent

By far the majority of horses are inapparent carriers. They show no overt clinical abnormalities as a result of infection. They survive as reservoirs of the infection for extended periods. Inapparent carriers have dramatically lower concentrations of EIAV in their blood than horses with active clinical signs of the disease. Only 1 horsefly out of 6 million is likely to pick up and transmit EIAV from this horse. All horses infected with EIAV are thought to remain virus carriers for life. The inapparent form may become chronic or acute due to severe stress, hard work, or the presence of other diseases.

Diagnosis:

A provisional clinical diagnosis of EIA must be confirmed by demonstration of antibodies to the virus in blood. 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 ELISA positive results must be confirmed by the Coggins test.

Treatment and Control:

No specific treatment or safe and effective vaccine is available. All horse shipped across province must be tested for EIA with a negative result within 12 months before transport. All horse sold, traded, or donated within a state must have tested negative for EIA no more than 12 month before change in ownership and, preferably, no more than 60–90 days. All horse entering horse auctions or sales markets are required to have a negative test before sale, or the horse must be held in quarantine until the test results are known.It is recommended that horse owners implement an EIA control plan for their premises. All horses should be tested every 12 months as part of a routine health program. More frequent testing may be indicated in areas that perennially have a high incidence of EIA. Owners of horse entering shows or competitive events should present proof to event officials of a negative EIA test. All new horse introduced to a herd should have a negative EIA test before entry or be isolated while tests are pending. Vector control practices, including application of insecticides and repellents and environmental insect control, should be implemented. Good hygiene and disinfection principles should be maintained to prevent iatrogenic infection of horses with contaminated needles, syringes, or equipment.

In 2016, 8 cases are positive. In 2017, 5 cases are positive.

2. Monitoring and Surveillance

The DLD has undertaken surveillance plan for equine disease called the declaration project to free from Equine Infectious Anemia. .  We set the numbering of sample by calculated from animal population from each province. There are totally about 2800 samples per year. The veterinarian officers collected blood samples. Moreover, the veterinarians officers will collect the samples from suspected cases for confirm disease status.

      The information of reference samples from control and operation by veterinarian institutions, or any nation coordination of equine disease from reporting system from 2014-2016 are presented following the table below:  

 

 Type /year  2014   2015 2016  2017
 Equine infectious anemia surveillance and prevention project   2500 samples    2716 samples   2800 samples   2815 samples 

 

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Figure 2: Blood collection for declaring project of EIA 

3.Emergency response

Apart from national notifiable diseases listed, there is animal disease notification system established, from an owner or a farmer in a village to DLD authority. In the line of command, up to the headquarters. Once the disease is suspected or outbreak reported, the local DLD authority has to conduct outbreak investigation as immediately as possible. The relevant investigative information will confirm appropriate intervention measures in order to eliminate the disease at source. When an outbreak occurs, control measures will be undertaken immediately to stop spread of the disease.

For Equine Infectious Anemia outbreak response plan is consist of

  1. Field veterinary of district/Provincial livestock office visits targeted horse farm and collected samples including infected horse and all of horse in the same herd of infected /suspected horse.
  2. Disease control by Field veterinary of district/Provincial livestock office
  • Improvement  of  biosecurity system in farm
  • Enhancement of disease surveillance
  • Cleaning and Disinfection
  • Isolation and quarantine
  • Animal movement control

      3.Provincial livestock office controls the disease in the outbreak area and report to Bureau of disease control and veterinary service in 24 hours after confirmation cases. Situation report every week until no case found.

     4. Because horse infected with EIA virus present the only known source of infection, antibody-positive animals should be kept at a safe distance (~200 m) from other horse. The seropositive horses must be placed under quarantine within 24 horse after the positive test results are known. The quarantine area must provide separation of at least 200 m. from all other horse.

     5. Reactor horses must be removed from the herd by euthanasia, slaughter, or quarantine at the premises of origin. After a reactor is detected in a herd, testing for EIA must be performed on all horses on the premises and repeated until all remaining horse on the premises test negative. These horses must be retested at 30- to 60-day intervals until no new cases are found. Quarantine on the premises is released when tests on the entire herd have been negative for at least 60 days after the reactor horse  have been removed.

  • Compensation about 75% of the price of the animal

     6. Public awareness and education