Gene expression of Mx1 indicates exposure to ISAv and is commonly upregulated in vertebrates to orthomyxoviral exposure (part of the ‘influenza pathway’ [55, 56], but is not indicative of an appropriate ISAv immune response [53, 54, 57, 58], and can also be observed to be impacted under other viral or intracellular bacterial infections [59–61]. The gene discussed is MX1; the disease is influenza.