Efficacy of Metarhizium spp. against gastrointestinal nematodes in goats and evidence of conidia infection through the integument.

The search for sustainable alternatives to manage gastrointestinal nematodes in small ruminants has intensified due to rising anthelmintic resistance. This study evaluated in vitro the efficacy of several Brazilian isolates of the genus Metarhizium spp. on gastrointestinal nematodes (GINs) of goats which were naturally infected with mixed populations predominantly composed of Haemonchus spp. (63%), Trichostrongylus spp. (35%), and Oesophagostomum spp. (2%). Biological assays were conducted using quantitative coproculture after 10 days of incubation, and SEM was performed after 72 h of fungus-larva interaction. Isolates LCM S05, LCM S10, LCM S11, LCM S13, LCM S14, and LCM S15 promoted larval reduction of: 50.24%, 43.29%, 44.99%, 55.45%, 52.52%, and 67.95%, respectively. Isolate LCM S15, which showed the greatest reduction in larvae, was tested at concentrations of 1.0 × 106, 1.0 × 107, and 1.0 × 108 conidia/mL, resulting in reductions in larvae of 36.90%, 50.17%, and 68.28%, respectively. In SEM, photomicrographs demonstrated that conidia adhered to and germinated on the nematode integument. This study demonstrates the potential of Brazilian isolates of Metarhizium spp. for the control of GINs in goats and highlights the route of fungal infection through the integument.