In many parts of Australia, registration fees for cat ownership are also common. Some of the species are to be found nowhere else in the world. Cats also represent a danger because they can carry a variety of diseases which can harm native animals. They have been known to carry rabies, toxoplasmosis, sarcosporidiosis, and ringworm. Birds and the small mammals hunted by cats are particularly susceptible to these diseases, many of whom may be transmitted by a mere scratch.
Human beings are also at risk.
The exact effect that feral cats have on the environment is hard to gauge. Most experts agree however, that it is fairly sizable. However, it has been estimated by one expert that cars may actually be a greater threat to Australia's fauna. He argues that if one multiplies the amount of animals killed on one mile of road during one year by the number of miles of paved road in the country, the amount far surpasses the amount of animals killed by cats. In addition, if some of the more elevated claims of how many animals cats kill per year were correct, there would be no small native animals left today.