a large roundworm of man, one of the commonest human parasites (8 to 12 inches in length); various symptoms such as restlessness, fever, and sometimes diarrhea, are attributed to its presence, but usually it causes no definite symptoms; the similar species, Ascaris suum (or Ascaris lumbricoides suum) is very common in swine, but is not readily transmitted to man, and vice versa; the types are morphologically and immunologically similar but apparently are host-adapted types, considered distinct species or races.