1. A nucleic acid construct comprising a heterologous polynucleotide comprising a first nucleic acid sequence encoding a Toxoplasma secreted protein in frame fused upstream to a second nucleic acid sequence encoding a pharmaceutical polypeptide, wherein said Toxoplasma secreted protein is secreted to a host cell when infected by the Toxoplasma, wherein said heterologous polynucleotide is operably linked to a promoter for directing transcription of said heterologous polynucleotide in a Toxoplasma, wherein said promoter is selected from the group consisting of: a constitutive promoter, an inducible promoter, a latent period-specific promoter, and a Toxoplasma endogenous promoter with the proviso that said promoter is not a Toxofilin promoter.