This disclosure describes a genetically-modified microbe that is a symbiont of an animal that is a vector organism for a pathogenic microbe, a paratransgenic organism that includes the genetically-modified microbe, and methods involving use of the genetically-modified microbe and/or the paratransgenic organism. Generally, the genetically-modified microbe includes a heterologous polynucleotide that encodes a heterologous polypeptide that reduces transmission of the pathogenic microbe.