Examining Horizontal Transmission of Nippostrongylus brasiliensis in Mice to Assess Biosecurity Risks

Nippostrongylus brasiliensis (Nb) infected mice are commonly used to study immune responses. There is no consensus regarding the biosecurity measures that should be employed when housing Nb-infected mice and rats. Transmission is reported to not occur when infected mice are co-housed with naive mice. We sought to determine what conditions, if any, favor horizontal transmission. Female NOD.Cg- Prkdc scid Il2rg tm1Wjl /Sz (NSG; n=12) and C57BL/6J (B6; n=12) mice inoculated with 750 Nb L3 larvae were cohoused with naïve NSG (n=24) and B6 (n=24) mice at a ratio of 1 infected:2 naïve mice per cage for 28 days within static microsiolator (MI) cages changed on a 14-day interval. We also assessed whether larval development to the L3 stage could occur when Nb egg-containing fecal pellets are maintained under 4 different environmental conditions (dry, moist, soiled bedding, and control) and whether infection results when naïve NSG mice (n=9) are housed in MI cages with infective L3 larvae-spiked (10,000/cage) soiled bedding. NSG mice (n=3) were also gavaged with Nb eggs to model the potential for infection to occur following coprophagy. Both naïve NSG (9 of 24) and B6 (10 of 24) mice cohoused with an infected cagemate passed Nb eggs in feces as early as 1 day and intermittently for varying periods following cohousing, presumably a result of coprophagy as adult worms were not detected at euthanasia. While eggs were able to develop into L3 larvae under 2 environmental conditions (moist and control), none of the NSG mice housed in cages with L3-spiked bedding or gavaged with eggs became infected with Nb. Findings demonstrate that horizontal transmission does not occur when mice are housed with Nb-shedding cagemates in static MI cages with a 14-day cage changing interval. Results from this study can be used to inform biosecurity practices when working with the Nb-infected mouse model. ### Competing Interest Statement The authors have declared no competing interest. * Nb : Nippostrongylus brasiliensis L3 : Infective larvae (3rd stage) L5 : Adult worms DPI : Days post inoculation DPH : Days post cohousing EPG : Eggs per gram of feces AAM : Alternatively activated macrophages