Midttun, H.L.E. et al. Sci Rep 10, 8083 (2020)

Laboratory animals can harbor certain pathogens without becoming overtly sick, but subclinical infections can nevertheless influence phenotypes in subtle ways. Health monitoring is routine rodents and becoming more frequent in increasingly popular lab animals, such as the zebrafish.

One pathogen, Pseudoloma neurophilia, is particularly prevalent in zebrafish facilities—over 50% will test positive in a given year. As such, researchers are increasingly studying how this microspordian parasite, which infects the hindbrain and spinal nerve roots without causing clinical illness, influences its host.

A new study from researchers at the Norwegian University of Life Sciences in Oslo reveals that P. neurophilia infection can, in sex- and context-specific manners, reduce locomotor activity and increase freezing. These results point to a potential—and potentially confounding—influence on anxiety-like behavior in P. neurophilia-infected fish.