Suitability of the pre-nociceptive chicken embryo as a model for investigating Sporothrix spp. infection and inflammatory response

The use of alternative in vivo models, such as chicken embryos (CE), for studying Sporothrix spp. infection aligns with sustainable and ethical research practices but remains poorly explored. This study evaluated the suitability of the pre-nociceptive stage of the CE model for investigating Sporothrix brasiliensis and S. schenckii pathogenesis. S. schenckii, S. brasiliensis, and a feline field isolate of S. brasiliensis were inoculated on the chorioallantoic membrane at 8-day-old CE. Control groups included sterile saline and the probiotic Saccharomyces boulardii. By 3 days post-inoculation, mortality in Sporothrix-challenged groups ranged from 14.28% to 31.4%, with lesion frequencies between 9% and 18.2%. Primary macroscopic findings included greenish hepatic discoloration and hemorrhage. The combined incidence of morbidity and mortality was higher in the Sporothrix groups than in controls, this rate did not differentiate virulence levels among the tested fungal strains. Histopathological analysis of the liver showed no significant changes; however, cerebral inflammation was significantly more pronounced in both S. brasiliensis groups. Molecular analysis revealed no upregulation of IL-1β or IL-6, but an 11.8-fold increase in IL-8 transcripts was detected in embryos challenged with S. brasiliensis. These results demonstrate that Sporothrix brasiliensis, although not previously described as infecting chickens, infected and induced an inflammatory response in 11-day-old CE following experimental challenged with the yeast-like cells via the chorioallantoic membrane. Further studies using CE should be conducted to better understand the host-fungus relationship in experimental infection. Our findings reinforce the potential of the CE model for ethical, early-stage studies of sporotrichosis pathogenesis and the host immune response.