Clinical scoring is the most sensitive biomarker detecting developing sepsis in newborn mice

Newborn individuals are highly susceptible to infectious diseases. For better insights into age-specific host-pathogen interactions infection models are increasingly employed in neonatal mice. However, for newborn mice no measures are available to objectify the clinical disease state, particularly not in a longitudinal manner, to meet legal animal welfare requirements. We developed a scoring system for newborn mice that relies on observational and examination-based parameters and validated it by applying a Staphylococcus aureus-induced infection model in two different mouse strains. The scoring results strongly correlated with the death kinetics independent of which mouse strain was used. A score above 7 predicted fatality. While the score values increased already at early sepsis stages the large majority of plasma cytokine levels remained comparable to those in uninfected control neonates. The levels of interleukin (Il)-6, chemokine C-C motif ligand 5, Il-1α and tumor necrosis factor α were not increased before 24 hours after infection and correlated only at this late stage of sepsis with the scored disease state. We propose the first clinical scoring system that serves as important research tool to evaluate the clinical course of sepsis in newborn mice. It detects health impairments of newborn pups in a highly sensitive and longitudinal manner, providing information about the disease severity as well as prognosis.