Graphical Abstract Illustration of the principal sources and routes of transmission in chickens of the two biovars (Pullorum and Gallinarum) of Salmonella enterica serovar Gallinarum. Note that the labels indicate the typical biovar transmitted by a given route, but they do not exclude the other biovar. Abstract Salmonella serovar Gallinarum has two distinct biovars, Pullorum and Gallinarum. They are host-adapted avian pathogens that infect a number of wild and domesticated species but they pose a particular threat to farmed and backyard chickens and turkeys. Both biovars cause invasive and septicaemic disease, often resulting in high mortality. Pullorum is transmitted in eggs and typically affects birds soon after hatch. Gallinarum may cause disease in any age of bird, which often progresses through mature flocks. The establishment of clean breeding stock has resulted in freedom from the pathogens in many countries although even in these territories sporadic incursions still occur.