• Anemia: The horse's blood may manifest 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. 



Inapparent — The majority of horses are inapparent carriers: they show no overt 

 clinical abnormalities as a result of infection. These animals survive as reservoirs 

 of the infection for extended periods. Inapparent carriers have dramatically lower 

 concentrations of ElAv in their blood than horses with active clinical signs of the 

 disease. Only 1 horse fly out of 6 million is likely to pick up and transmit EIAv from 

 such horses. All horses infected with EIAv are thought to remain virus carriers for life. 

 The inapparent form may become chronic or acute owing to severe stress, hard work, 

 or the presence of other diseases. 



Transmission 



EIA is a classic blood-borne infection. People have played an important role in EIAv 

 transmission over the years by using blood-contaminated materials on different 

 horses. But the EIAv is most often transmitted between horses in close proximity 

 by large biting insects such as horse flies or deer flies. The bites from these flies 

 stimulate defensive movement b\ the horse, which oltcn results in an interruption of 

 the bloodfeeding. When interrupted, the tl\- is moti\ated to complete the feeding as 

 soon as possible. It then attacks the same or a second host and feeds to repletion. Any 

 infective material from the blood of the first host present on the mouthparts of the 

 insect can be mechanicalK' transmitted to the second host. 



Insect transmission of EIAv is dependent on the number and habit of the insects, the 

 density of the horse population, the number of tunes the insect bites the same and 

 other horses, the amount of blood transferred between horses, and the level of virus 

 obtained in the blood meal. 



Prevention 



The AGID, or Coggins, test has been shown to correlate with horse inoculation test 

 results for EIAv and therefore can be used to identify EIAv carriers. Although other 

 serologic tests have been defined and approved for the diagnosis of EIA, the AGID test 

 is recognized internationally as the "gold standard" serologic test. The use of AGID 

 and additional tests has assisted in the control of EIA. Presently, USDA recognizes the 

 AGID and three ELISA formats for conducting official tests. 



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