The present invention relates to genetically modified ascomycetous filamentous fungi, particularly of the species Thermothelomyces heterothallica, having reduced activity or expression of KEX2 and/or ALP7, said filamentous fungi is capable of producing elevated amounts and stability of an exogenous protein.

Disclosed herein is a robust system for the reverse genetics generation of a Rift Valley fever (RVF) virus replicon particle (VRP.sub.RVF) vaccine candidate. VRP.sub.RVF can actively synthesize viral RNA and proteins, but lack structural glycoprotein genes, preventing spread within immunized individuals and reducing the risk of vaccine-induced pathogenicity. Is it disclosed herein that VRP.sub.RVF immunization is both safe and efficacious, resulting in a robust immune response that is protective against RVF virus challenge within 24 hours of immunization. Provided herein are VRP.sub.RVF, methods of producing VRP.sub.RVF, and method of using VRP.sub.RVF for immunization against RVF virus infection.