Bartonella (formerly known as Rochalimaea) is a genus of Gram-negative bacteria. Facultative intracellular parasites, Bartonella species can infect healthy people but are considered especially important as opportunistic pathogens. Bartonella are transmitted by insect vectors such as ticks, fleas, sand flies and mosquitoes. At least eight Bartonella species or subspecies are known to infect humans. In June 2007, a new species of the genus, called Bartonella melophagi, was discovered.[citation needed] This is the sixth species known to infect humans, and the ninth species and subspecies, overall, known to infect humans.