If it is indeed something infectious (parasitic, bacterial, fungal or viral infection), then getting a fecal done at the vet would be a good start. Flagyl and Panacur (metronidazole and febendazole) are both specific to certain kinds of infections, so they may do something or nothing, and treating the snakes may be stressing them out for nothing before you find out what's causing the symptoms. I don't like treating an animal without knowing what's going on because of the stress factor, both psychological and physical.
If your Hondurans are strictly isolated from your other snakes, and/or you practice great hygiene, it makes sense that other animals you have are doing well. It's uncommon for pathogens to be super-specific to one species, or one family of animals.
Gastroenteric pathogens are transmitted by the fecal-oral route, meaning the pathogen is passed in the feces, then is transmitted into the mouth of another animal. This could be by tongue-flicking, tracking through feces then introducing them into the water dish, or having food touch feces then be eaten. I should clarify that by "feces," I don't mean physical stool, necessarily. If you clean up the stool, microscopic organisms can remain on the substrate. When you introduce the snakes together, they could have pathogens hanging out on their bodies that are introduced to the uninfected animal's enclosure.
Before the vet visit and until the problem is resolved, consider transferring the animals to a more sterile enclosure that still provides their basic needs (like temp. gradient, water and hides) but is much easier to clean and disinfect. I don't know what you're keeping them on now, but switching them to something disposable like paper towels or newsprint, and giving the enclosures a good, thorough disinfection will help reduce the spread of any pathogens. Treating the environment is as important as treating the animal, because a lot of these nasty bugs will hang out in the enclosure for a long time and can re-infect your animals.
If the fecal exam at the vet shows nothing, other diagnostics may be necessary, like blood tests to check out the general health of the animals. Blood will almost always shows signs of infection that may not be detectable by fecal exam. It wouldn't be a bad idea to have blood taken from one or two of the animals at the same time as the fecal to see what's going on in there, so that if nothing turns up on the fecal at least it will be one stressful vet visit for the snakes, not multiple.
Keep us posted!
Christina
www.herptiles.net
