Listeria is an opportunistic pathogen: It is most prevalent in the elderly, pregnant mothers, and AIDS patients. With improved healthcare leading to a growing elderly population and extended life expectancies for AIDS patients, physicians are more likely to encounter this otherwise-rare infection (only 7 per 1,000,000 healthy people are infected with virulent listeria each year).^[6] Better understanding the cell biology of Listeria infections, including relevant virulence factors, may lead to better treatments for listeriosis and other intracytoplasmic parasite infections. Researchers are now investigating the use of listeria as a cancer vaccine, taking advantage of its "ability to induce potent innate and adaptive immunity.