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 (WNVKUN) 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 WNVKUN.

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

Test
Sample(s) required
Days of the week
test is conducted
Turnaround time1

West Nile Virus IgM ELISA2

Clotted blood (red top tube) or CSF

According to demand

7-10 days

West Nile Virus blocking Antibody ELISA3 Clotted blood (red top tube) or CSF According to demand 7-10 days
West Nile Virus Real–time PCR Fresh tissue (brain stem) and Cerebrospinal Fluid (CSF) According to demand 2-3 working days
Histopathology examination Fixed tissue Monday - Friday Up to 2 weeks for brain samples. Up to 5 days for other sample types.

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.

Specimen requirements

Blood (without anti-coagulant)

  • 10ml of blood into a plain red top tube
    • Submit chilled

Fresh tissue

  • Brain and upper cervical spinal cord
    • Submit brain cut in half longitudinally to ensure that all representative areas are available for virus detection. WNV is usually only detected in the brain stem and upper cervical spinal cord

Fixed tissue

  • Brain and upper cervical spinal cord
    • Submit fixed in neutral buffered formalin at a 10:1 ration of formalin: tissue

Cerebrospinal fluid

  • CSF collected into a sterile 5 ml vial or 10 ml plain red top tube
    • Submit chilled

Note