WEST NILE VIRUS OUTBREAK IN ITALY: CLINICAL FINDINGS IN 10 HORSES G.

In the past ten years, West Nile Disease (WND) has reemerged as an important cause of disease in horses and human. Particularly, USA outbreak caused substantial damage in human, equine and avian population. In the late summer 2008 an outbreak of West Nile Disease was reported in Northern Italy. By March 2009, the epidemiological data documented 563 horses serologically positive for WNV, 32 out of them showing neurological signs. 5 horses died or were euthanized due to the severity of the clinical signs. Many outbreaks have been documented worldwide, but only a percentage of papers describes accurately the clinical signs of horses affected by WNV encephalomyelitis. The purpose of this report is to describe the neurologic signs, and clinicopathologic abnormalities in 10 horses affected by WNV encephalomyelitis, referred to the Veterinary Clinical Department of the Faculty of Veterinary Medicine of the University of Bologna during the Italian outbreak in 2008. All horses had video recorded neurological examination, documenting the clinical signs. Diagnosis of WND in all horses was made considering the course of the disease and the positive result of the ELISA test for the detection of antibodies (IgG) against WNV. All the horses underwent general physical and neurological examination, as well as haematobiochemical evaluation. In two more severely affected horses, cerebrospinal fluid (CSF) was analyzed and, after euthanasia, brain and spinal cord were removed for neuropathologic evaluation. Age ranged from 24 to 84 months (median: 62 months). The most frequently affected breed was the standardbred (5 cases). All the horses lived in an environment severely infested by mosquitoes and they all had an acute onset of generalized illness consisting mainly in anorexia and depression. Fever was not consistently reported by the referring veterinarians. Neurologic signs varied markedly in severity from the onset to the time of the examination. Affected horses had different patterns of Central Nervous System (CNS) signs related either to the degree of severity and to the different neuroanatomical involvement. The most striking signs were related to gait abnormalities, recorded in all horses. The two more severely affected horses had both severe tetraparesis, in one case not ambulatory and leading to permanent recumbency. The second horse frequently showed spontaneous dorsoflexion of the right front limb. The less severily affected cases (eight horses) had various degrees of spinal ataxia and paraparesis, defined as marked in two horses and mild in five, and central vestibular involvement in one case. Lateralized signs were recorded in three horses. Gait deficits were exacerbated when horses were led in tight circles or after backing. The sway test was abnormal in most cases, showing weakness and incoordination. Left head tilt was recorded in the horse with vestibular ataxia. Besides the recumbent horse, showing bilaterally absent menace reaction and ventral strabismus, cranial nerves tests were otherwise normal in all horses. Change in behaviour was noticed in 5 cases and consisted mainly in hyperexcitability, depression and aggressiveness. Different protocols of symptomatic anti-inflammatory therapy were performed in all cases (including Flunixin meglumine; corticosteroids and DMSO administration). Treatment was maintained for not more than one week. All the horses with mild to moderate signs had a positive response to treatment, improving dramatically in few days and recovering without consequences. Conversely, the two more severely affected horses, despite treatment, worsened to permanent recumbency and were euthanized for humane reasons due to their poor neurologic status. The CSF analysis revealed in both cases a moderate mononuclear pleocytosis (respectively: 190 cell/?l 97% mononuclear and 272 cell/?l, 84% mononuclear). Haematobiochemical tests, including determination of acute phase protei...