Francisella noatunensis subsp. Noatunensis is the causative agent of the disease Francisellosis, which affects both farmed
and wild Atlantic cod (Gadus morhua). Francisella noatunensis is resistant to commonly utilized antibiotics, therefore, the
need for a more effective treatment or the development of preventative measures is essential. The bacterium is listed as a
category F disease. F-listed diseases do not pose a threat in the EU/EØS but can cause great risk in Norway. The bacteria can
cause high mortality rates and, therefore, threaten both fish welfare and an economic threat to cod aquaculture.
Francisellosis does not currently have any preventative nor curative measures.
This study analyses the effects of three potential live attenuated vaccine candidates produced by allelic recombination of a
single virulence gene in F. noatunensis, including clpB, iglC, and pilD. The vaccine candidates were administered both nasally
and peritoneally, in high and low doses. The trial tests the efficiency of the various vaccine candidates to determine which
vaccine, concentration, and administration route provides the best protection against F. noatunensis in Atlantic cod. The
infected fish presented with characteristic pathologies related to infection by F. noatunensis, including, but not limited to,
granulomatous development and inflammation.
Up- and down-regulations in expression of antimicrobial peptides, pro-inflammatory, and anti-inflammatory cytokines in
combination with less severe histopathological findings of head kidney samples indicate that vaccination with the F.n.n. clpB
mutant shows great potential in providing protection against F. noatunensis in Atlantic cod.