In older, >25-week infections, no significant differences in mf production per female worm were apparent between the different models (gerbil median absolute mf yield/animal = 850,000, range = 0–4,306,000; CB.17 SCID = 510,987, range = 61.3–938,925; BALB/c IL-4Rα-/-/IL-5-/- = 223,000, range = 39,000–5,200,000). This evidence concerns the gene IL5 and infection.