Key findings:

• Retrospective conclusion: high likelihood that at least 1 HPAI H5N1 cow from the USA entered Canada between Dec 1, 2023, and April 28, 2024, with moderate to high uncertainty
• Prospective conclusion: the likelihood and impact of HPAI H5N1 on 1 dairy farm in Canada between April 29 and Oct 31, 2024, from:
  •  Dairy cattle imported from the USA: very high, with moderate to high uncertainty
  •  Wild migratory birds from the USA: very low to low, with moderate uncertainty
  •  Cattle transport trucks from the USA: low, with high uncertainty
•  Moderate likelihood, with high uncertainty, that the infection of a dairy herd in Canada will result in spread within but not among the provinces
•  Importation is of higher concern compared to cattle transport trucks and wild migratory birds
•  Import conditions (i.e., a lactating cow must test negative for influenza A) will likely mitigate most of the risk identified for lactating cows
•  Residual risk with the importation of non-lactating dairy cattle
•  Information on the number and movements of cattle transport trucks between the US and Canada is needed to better assess risk

 Knowledge gaps: 

•  True prevalence of H5N1 in dairy cattle in the USA (incl. sub-clinically infected) in lactating vs non-lactating
•  Frequency and length of shedding virus in sub-clinical lactating cattle and clinic and sub-clinical non-lactating cattle
•  Modes of transmission within and among farms
•  Infectious dose
•  Number and types of herds that export dairy cattle to Canada