There are around 100 known but uncontacted tribes in the world, and the most recent to make contact was a sub-group of the Ayoreo-Totobiegosode peoples of the Chaco, a forest stretching from Paraguay to Bolivia and Argentina. In March 2004, a group of 17 Indians - five men, seven women and five children - were forced from the Paraguay forest after cattle ranchers forcibly colonized their territory and occupied their waterholes. The most recently discovered tribe yet to be contacted is a group of at least 21 Peruvian Indians spotted by aircraft on the shores of the Las Piedras river in Peru's south-eastern Amazon. First contact is a risky affair, as a tribe's lack of immunity to outsider's diseases can devastate a population; when the Murunahua Indians in south-eastern Peru were contacted for the first time, for example, more than half of them died.