Compositions and methods for treating or reducing the severity or likelihood of occurrence of a parasitic worm or helminth infection in a subject are described. The methods include administering to the subject a therapeutically effective amount of a recombinant bacterium expressing a crystal protein such as a Bacillus thuringiensis crystal protein (Cry). The crystal proteins may be full length, truncated, variant, or sub-variant Cry proteins. Examples of crystal proteins include Cry5B, Cry21, Cry14A, Cry6A, and Cry13A. The recombinant bacterium may be, for example, a Bacillus subtilis or other Gram-positive bacterium, for instance, a lactic acid fermenting bacterium such as Lactococcus or Lactobacillus. Related compositions and recombinant microorganisms are also described.