Megalania giving you a bad time? This toxic bite sounds like what modern Komodo Dragons have. They bite with a mix of venom and bacteria. This giant lizard is essentially Komodo’s great great great granddaddy.. They likely had a similar trait if you are all feeling sick after encountering one.
I have personally had trouble finding these guys on single player, but I found a tip that will help you guys! All you have to do is eat rare flowers and everything will aggro on you including these guys. They spawn in the redwood cave, carnivore Island cave the artifact of the hunter cave and the lava cave.