The causal agent is Salmonella Gallinarum. The incidence of fowl typhoid is low in the USA, Canada, and some European countries but is much higher in other countries. Although S Gallinarum is egg-transmitted and produces lesions in chicks and poults similar to those produced by S Pullorum, there is a much greater tendency to spread among growing or mature flocks. Mortality in young birds is similar to that seen in S Pullorum infection but may be higher in older birds.
The disease may be acute or chronic. Clinical signs and lesions in young birds are similar to those seen with S Pullorum infection. Older birds may be pale, dehydrated, and have diarrhea. Lesions in older birds may include a swollen, friable and often bile-stained liver, with or without necrotic foci; enlarged spleen and kidneys; anemia; and enteritis.
Treatment and control are as for pullorum disease (see Pullorum Disease in Poultry). There are no federally licensed vaccines in the USA. In other countries, vaccines (killed or modified live) made from a rough strain of S Gallinarum (9R) had variable results in controlling mortality. More recently, vaccines derived from outer membrane proteins, mutant strains, and a virulence-plasmid-cured derivative of S Gallinarum have shown promise in protecting birds against challenge. The standard serologic tests for pullorum disease are equally effective in detecting fowl typhoid.