Leonidas Zimarinda has watched over Rwanda's gorillas for almost 30 years. "I track them until I find them and then keep an eye on them". Protecting these endangered animals has become high priority since the government realised just how lucrative eco-tourism could be. "The worth of gorilla permits is probably $33 million a year", states Rosette Rugamba from Rwanda's tourist authority. In recent years, sales of permits have doubled. But not everyone with money is welcome. As gorillas share 98% of our DNA, they are vulnerable to our diseases. Anyone with a cold is turned away.