AHEAD IN ANIMAL HEALTH
Mannheimia haemolytica serotype 2, apathogenic commensal or fatal primary pathogen? Jasper het Lam1; Thijs H.J. Derkman1; Evert van Garderen1; Remco Dijkman1; Erik van Engelen1 1 GD Animal Health, The Netherlands
Introduction • To further investigate the role of M. haemolytica in the pathogenesis of polyserositis in veal calves • M. haemolytica is part of the commensal flora of the upper respiratory tract in ruminants. • M. haemolytica is known to cause respiratory disease and polyserositis in calves. • Significantly increased incidence of fatal M. haemolytica infections in cattle in the Netherlands between 2004 and 2018 (Biesheuvel et al 2021) • M. haemolytica infections emerged in both dairy cows and veal calves. Since veal calves originate from dairy farms, were these infections caused by the same M. haemolytica genotype?
Materials and methods • Whole Genome Sequence(WGS) was performed on 96 M. haemolytica isolates. • These isolates were cultured from necropsied veal calves with fibrinous polyserositis (n=47) and dairy cows with fibrinous pleuropneumonia (n=38) due to M. haemolytica as the cause of death in the absence of pathogens that may cause similar lung pathology (Biesheuvel et al., 2021). • The animals were submitted for necropsy from 38 dairy farms and 35 veal farms between December 2018 and June 2020.
Results • M. haemolytica isolates from fibrinous pleuropneumonia (FPP) in dairy cows and fibrinous polyserositis (FPS) in veal calves appeared to be distinct serotypes. • Most strikingly, M. haemolytica serotype A2, commonly considered to be the commensal nonvirulent serotype in the nasopharynx of cattle, was associated with all fibrinous polyserositis cases in veal calves. • The majority of these A2 isolates contained antimicrobial resistance-genes for several groups of antibiotics, while these resistance-genes were virtually absent in isolates from FPP in cows, which were all (except one) serotype A1 of A6.
Figure 1 and 2. Circular unrooted phylogenetic single nucleotide polymorphism (SNP) tree based on 14052 informative SNPs from 96 M. haemolytica isolates and using M. haemolytica strain D153 as reference (NC_021743). Data were clustered using the neighbour joining method and the Jukes Cantor nucleotide substitution model. Dairy cow (DC) and veal calves (VC) are indicated, followed by the farm number and animal number. Samples originating from the same animal are indicated with a and b. Isolates belonging to distinct clusters are indicated with a black node (Cluster I) or grey node (Cluster II). Figure 1. Serotype A1 (yellow), A2 (purple) and A6 (green) are indicated in the outer ring.
Conclusions • An almost dichotomous distinction between serotype A2 and serotype A1 or A6 related to FPS and FPP, respectively. • The only two calves with FPP appeared to be infected with serotype A1 or A6. • Veal calves with FPS are born and raised for two to five weeks on dairy farms, where it seems plausible that they harbour the same M. haemolytica types as the remaining dairy youngstock. • Since FPS rarely occurs among dairy calves or dairy cows, it seems likely that the trigger for this disease, is present on veal farms and absent on dairy farms. • To identify this trigger, such as virulence of the bacterium, specific housing or management characteristics or Veal Calf with acute fibrinous pleuro-peritonitis (polyserositis) vulnerability of the host, further research is needed. caused by Mannheimia haemolytica
Figure 2. Antimicrobial resistance genes are indicated in the different coloured rings. Phenicol (yellow), sulphanomide (red), tetracycline (green), aminoglycoside (purple) and betalactam (blue) resistance genes are indicated in the outer rings.
Acute bovine fibrinous pleuropneumonia caused by Mannheimia haemolytica
Acknowledgements The findings resulted from a project that is financed by the producers organisation for dairy (ZuivelNL, The Hague, The Netherlands) and veal (SBK, Zeist, The Netherlands).
j.het.lam@gdanimalhealth.com www.gdanimalhealth.com
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