Nonsense. I have a LOT of conversations about what people consider to be an animal, because I’m vegan. Other than the occasional moron who asks if I eat fish, everyone considers all non-plant, non-fungus critters “animals.”
Schistosomes, liver flukes, tapeworms, guinea worms, trichinae and other parasites have certainly wreaked plenty of havoc over the centuries too.
Except meat and saturated fat doesn’t lead to heart diseases.
Taking animal as a species:
Killing as being responsible for:
Mosquitoes
Killing as killing directly:
Snakes
Taking animal as a single animal:
Killing as being responsible for:
Possibly a rat that introduced a disease to a city.
Killings as killing directly:
Possibly a specific tiger.
If humans are not excluded, they would top every category.