Response to Central Nervous System Signs in Domestic Geese and Ducks in West Nile Virus Endemic Areas

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This document outlines the current knowledge of the epidemiology and pathogenesis of WNV in domestic geese and to provide guidelines on how to manage situations when confronted with domestic geese displaying central nervous system (CNS) neurological signs.

Epidemiology and pathogenesis of West Nile Virus

Domestic geese: From the limited experience in the literature, it appears that geese are most susceptible to WNV infection at a young age. Morbidity and mortality rates can be as a high as 30 to 40% in some flocks. The incubation period for WNV in geese is established to be two to three days, with most mortalities occurring 5 to 10 days post infection (PI). Transient viremia develops one to five days PI with peak virus titers 104-6 two days PI. This level of viremia is of sufficient magnitude to infect mosquitos, meaning the geese can serve as a reservoir and amplifying host for WNV. WNV was isolated from the brain, heart, kidney, and intestine during 5 to 10 days PI, and from the oropharyngeal swabs of clinically ill birds. The viremic stage in geese coincides with the manifestation of clinical signs of infection. Infected geese will show signs of depression, weight loss, torticollis, opisthotonous, and rhythmic side-to-side movement of the head. These clinical signs cannot be distinguished from Newcastle disease (ND) and highly pathogenic avian influenza (HPAI) - both reportable diseases of poultry. The WNV titer of infected geese is declining by 10 days PI, with no WNV isolated from plasma or tissues from goslings 21 days PI, which also corresponds with the disappearance of clinical signs.

Ducks may become infected with WNV; however, limited data indicate that ducks have a low to moderate viremia of short duration. The pathogenesis of WNV infection in ducks is unknown at this time. However, there is no scientific evidence that domestic ducks could pose a threat of WNV infection to humans when handled at slaughter.

Flock Investigation

Geese flocks that exhibit any neurological signs must be reported to the Canadian Food Inspection Agency (CFIA) for investigation. A CFIA veterinarian will examine the flock to rule out ND and HPAI, in accordance with Foreign Animal Disease Strategy protocols established for these two diseases. Once the ND and HPAI have been ruled out, the quarantine will be released, and the owner and the attending private or provincial veterinarian may pursue confirmation of WNV diagnosis. The District veterinarian will notify the owner in writing of the necessity that his/her geese be free of neurological signs for 30 days before scheduled slaughter in registered establishments in Canada, or 90 days before being eligible for export. Prior to shipment for slaughter to a federally registered establishment, geese that originate from flocks with confirmed or suspected WNV will require certification by a licensed veterinarian, stating that they have been free of clinical signs for 30 days. An attestation by the producer, must be submitted to the slaughtering establishment prior to shipment of the affected flock.

ND and Avian influenza (AI) in geese and ducks, and WNV infection in geese are potentially pathogenic to humans, and thus any suspicion of these diseases must be communicated to the provincial health authorities, as well as the Provincial Department of Agriculture.

Note: WNV is an immediately notifiable disease under the Health of Animals Regulations. All persons involved in the handling of these animals should follow occupational health and safety standards for handling slaughter animal species, as recommended in the document West Nile Virus - Protect Yourself! by Public Health Agency of Canada.

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