Epidemiology and Clinical Manifestation of West Nile Virus Infections of Equines in Hungary, 2007–2020

Abstract

West Nile virus (WNV) is an emerging pathogen in Hungary, causing severe outbreaks in equines and humans since 2007. The aim of our study was to provide a comprehensive report on the clinical signs of West Nile neuroinvasive disease (WNND) in horses in Hungary. Clinical details of 124 confirmed equine WNND cases were collected between 2007 and 2019. Data about the seasonal and geographical presentation, demographic data, clinical signs, treatment protocols, and disease progression were evaluated. Starting from an initial case originating from the area of possible virus introduction by migratory birds, the whole country became endemic with WNV over the subsequent 12 years. The transmission season did not expand significantly during the data collection period, but vaccination protocols should be always reviewed according to the recent observations. There was not any considerable relationship between the occurrence of WNND and age, breed, or gender. Ataxia was by far the most common neurologic sign related to the disease, but weakness, behavioral changes, and muscle fasciculation appeared frequently. Apart from recumbency combined with inappetence, no other clinical sign or treatment regime correlated with survival. The survival rate showed a moderate increase throughout the years, possibly due to the increased awareness of practitioners.

Comparison of West Nile Virus Disease in Humans and Horses: Exploiting Similarities for Enhancing Syndromic Surveillance

“…Age as a risk factor for neuroinvasive disease in horses, as well as a risk factor for severe disease and higher mortality, is unclear based on individual studies. In a selected group of publications that included four or more cases where age was provided, the average age of pooled data from 2891 horses with neuroinvasive disease was 8.5 years (ranging from 0.5 to 32 years) [ 21 , 24 , 116 , 126 , 127 , 128 , 129 , 130 , 131 , 132 , 133 , 134 , 135 , 136 ]. Although there was limited data in most publications regarding the age of the horses that died or were euthanized; in five of the aforementioned studies representing 637 horses, the average age of mortality was 10.37 years (current lifespan is 20–30 years) [ 24 , 116 , 127 , 130 , 135 ].…”

“…In two other studies, animals less than one year of age were more likely to die than in other age groups. [ 134 , 136 ] In another, all animals less than one year of age died [ 128 ].…”

“…In a study of 427 patients in Italy, the case-fatality rate was 22% [ 115 ], while the case-fatality rate was 8.8% in a cluster of 57 cases in a study from Romania [ 137 ]. The overall mortality was 28% in pooled data of 2993 horses from selected studies [ 9 , 22 , 24 , 116 , 126 , 127 , 128 , 129 , 130 , 131 , 132 , 134 , 135 , 136 , 138 , 139 , 140 ]. Mortality rates calculated using this same data were similar in horses infected with either L1a or L2 viruses, averaging 29% and 34%, respectively.…”

“…In human studies, men are typically considered more likely to develop WNV disease than women [ 95 , 115 , 141 ]. In equine studies, sex ratios vary between studies, with some demonstrating bias toward females [ 126 , 130 ] and in others, male horses [ 22 , 24 , 128 , 134 , 135 , 136 ]. However, the average of pooled data from 14 studies that included 2182 horses was 50.4% and 49.5% in males and females, respectively [ 24 , 116 , 126 , 128 , 129 , 130 , 132 , 136 , 139 , 140 ].…”

“…Changes in mentation can range from depression/obtundation to hyperexcitability. Approximately 30% of horses have some degree of decreased mentation or depression [ 10 , 22 , 116 , 126 , 128 , 129 , 134 , 135 , 136 , 140 ] to the point of stupor as well as narcolepsy [ 10 , 116 , 127 , 129 ]. Hyperexcitability has also been reported in approximately 30% of cases [ 9 , 22 , 24 , 116 , 128 , 129 , 133 , 134 , 135 , 136 , 140 ].…”