When encountering this creature make sure to stay a distance, same goes for taming, Megalania carry mega rabies, this will spread to your tames and tribe mates, so if by chance it does bite you, stay away from your teammates and tames until you get cured.
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.