i have never dealt with these worms before, but have dealt with numerous parasites in gars. combining the info we have here and the brief search i did on those worms, it seems like Levamisole is the best treatment for the worms...HOWEVER, i have not used it before. for most parasites i use jungle parasite clear or prazipro, both of which use praziquantel as the active ingredient and this works on all major parasite groups (roundworms, fish lice, anchor worm, etc). i have found that about half the dosage works well with gars and other primitive fishes; i've used a full dose on a couple occasions and that seemed to be ok too.
i would recommend going with a half dose of this levamisole and see how that works; if you can get a hold of something with praziquantel, that is also advisable as that is proven to work with gars. keep us posted and good luck. if you are feeding live you may also want to treat your feeder tank as they are likely a good host for the worms.--
--solomon