West Nile Virus Infection

Description

West Nile Virus (WNV) is a mosquito borne virus belonging to the genus Flavivirus. Subtypes of WNV, previously known as Kunjin virus (WNV_KUN) are endemic in parts of Australia and has been present for many years. These are infrequently associated with disease in humans.

Horses, people and a variety of other animals, especially birds, may become infected through a bite from an infected mosquito. Like most other arboviral infections the disease is expected to occur during late summer and autumn. In Australia, disease has been limited to horses, although several cases have been suspected (though not confirmed) in dogs and alpacas. Most animals infected with WNV do not develop any clinical signs. Unlike strains of WNV found in the Northern hemisphere, Australian strains of WNV have not caused disease in birds.

In 2011, there was a large outbreak of neurological disease in horses in south-east Australia caused by a variant of the Australian strain WNV_KUN.

The initial signs of disease can be non-specific and may be mistaken for colic as horses appear depressed and reluctant to move, however these signs are soon followed by neurological signs. The most commonly encountered signs are those of ataxia (including stumbling, staggering, wobbly gait, or incoordination) but a range of other CNS signs may also be observed. Most affected horses recover uneventfully within a few days to weeks; however the disease is fatal in about 10% of cases.

It is important to differentiate the illness from Hendra virus infection particularly in areas where flying foxes are abundant and to take appropriate precautions.

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Diagnosis and tests available

Diagnosis

Diagnosis in horses and domestic non-avian species is based on the history, clinical signs, serology and other diagnostic tests where appropriate.

Tests available

¹ Turnaround times are provided as a guide only. For specific information about your submission please contact Customer Service.

²The WNV IgM ELISA is only suitable for equine samples and is the preferred test for blood samples collected from horses within 2 weeks of the onset of clinical signs. The first sample should be collected as soon as possible after clinical signs have been observed.

³Collection of paired clotted blood samples in the acute and convalescent phases of the illness (approximately 3-4 weeks apart) is recommended to confirm recent infection in mammalian non-equine species.

Note

• The risk of Hendra virus should be considered prior to tissue collection

Additional Information