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Research article2014Peer reviewedOpen access

Spatial and temporal distribution of incidence of acquired equine polyneuropathy in Norway and Sweden, 1995-2012

Wolff, Cecilia; Egenvall, Agneta; Hanche-Olsen, Siv; Gröndahl, Gittan

Abstract

Acquired equine polyneuropathy (AEP) is an emerging disease in horses in Sweden, Norway andFinland since 1995. Affected horses show bilateral pelvic limb knuckling and weakness, sometimes progressing torecumbency and euthanasia. The aetiology is unknown but is thought to be non-infectious and non-genetic,though possibly toxic or toxico-infectious. The objectives of this study were to describe the spatial, temporal andspatio-temporal features of AEP in Norway and Sweden for the period of 1995 to 2012. Data from all documentedcase farms (n = 136) were used. Space-time interaction clustering of case farms was investigated with a retrospectivespace-time scan statistic with a space-time permutation model, the space-time K-function and the Jacquez k nearestneighbour (kNN) test.Results:There was a clear seasonality in disease occurrence, as 123 case farms presented their first case fromJanuary to May. However, there was large variation in the number of case farms between years. Case farms weremore numerous in certain regions. Despite the larger horse population in Sweden, 120 of the case farms were inNorway. Space-time clustering was supported by the K-function and partly by the space-time scan, but not by theJacquez k nearest neighbour (kNN) test.Conclusions:The results suggest an aetiology for AEP where the exposure is not consistent in time, but variesduring and between years, assuming that the incubation period does not vary greatly. The results further suggestthat the exposure varies between regions as well. Two out of three different analytical methods supportedspatio-temporal clustering of case farms, which renderedinconclusive results. The negative result in the kNN testmight be explained by lack of power, which is due to the small number of outbreaks in relation to the size ofthe study area and length of the study period, and further by the low to moderate power of methods to detectspace-time clustering when the background population is unknown. Further research is needed to study howmanagement, meteorological variables and other factors with local or regional differences may explain outbreaksof AEP.Keywords:Acquired equine polyneuropathy, Knuckling, Horse, Space-time scan statistics, Space-time K-function,Jacquez k nearest neighbour test

Published in

BMC Veterinary Research
2014, Volume: 10, article number: 265