Quantitative Evaluation for the Surveillance Strategies of Equine Infectious Anemia in Japan

Abstract

Equine infectious anemia (EIA) has not been detected since 1993 by the nation-wide surveillance testing at least every five years, therefore it is believed that this disease has been eradicated from Japan. For the purpose of considering effective and efficient surveillance to be adopted under the current EIA situation, we evaluated several surveillance strategies using a transmission model of EIA among non-racehorse. The model incorporated horse movements for generating the spread of between and within four independent sectors, that constitute non-racehorse population, namely, the equestrian sector, private owner sector, exhibition sector and fattening sector.The number of infected horses and farms after one year from introduction of an infected horse was estimated 14 heads (90%CI : 2-72 heads) and 2 farms (90%CI : 1-8 farms) in the baseline model. Under the current surveillance model, it was estimated that an infected horse was first detected 13 weeks (90%CI : 4-56 weeks) after the disease introduction, the number of horses and farms that have been infected before the detection were estimated 5 head (90%CI : 1-17 heads) and 1 farm (90%CI : 1-2 farms), respectively. A surveillance strategy testing horses in the equestrian sector and private owner sector annually as well as horses for movement detected infected horses earlier than the current surveillance model. However, it increased the number of horses to be inspected per year. Lengthening testing interval from once a year to once every 3 years or every 5years, reduce the number of horses to be tested up to 30-40% with almost equivalent effectiveness of the current surveillance strategy. Using the transmission model of EIA, we could evaluate various surveillance strategies for early detection from the viewpoint of effectiveness and efficiency.Further refinement of the model, such as incorporating temporary movements of horses or reflecting potential risk of racehorses and imported horses, may provide more useful information for considering applicable surveillance strategies.