S. Gallinarum Biovar Pullorum¶

At a Glance


Antigenic Formula	`1,9,12:-:-`
Serogroup	O:9 (D1)
NCBI Pathogen Detection	View isolates

Background Information¶

Salmonella enterica subsp. enterica serovar Gallinarum (antigenic formula 1,9,12:–:–) is a serovar of the O:9 (D₁) serogroup. This serovar has two biovars: Gallinarum, and Pullorum. Biovar Pullorum has been found to exhibit host specificity for aquatic birds, and poultry and is mainly associated with Pullorum disease (PD), which, in its acute form, is almost exclusively a septicemic disease affecting young chickens. PD is mainly egg-transmitted and can result in high death loss in the young birds. Transmission of PD can also occur through direct or indirect contact with infected birds, as well as through contaminated feed, water, litter, or respiratory exposure. Vaccines for PD were not developed until the 21st century, with a sipC mutant recently identified as a promising vaccine candidate for chickens. However, the National Poultry Improvement Plan (NPIP), established in the early 1930s to reduce the spread of PD and fowl typhoid, has achieved great success in the U.S. In 1967, all commercial chicken hatcheries involved in the NPIP were fully free of PD caused by Salmonella Gallinarum.

The NCBI PD link for biovar Pullorum is unavailable because SeqSero2, the in silico serotyping tool used by NCBI PD, cannot differentiate: i) between serovars Enteritidis and Gallinarum, and ii) at the biovar level.

Genetic Characteristics¶

Studies have found that isolates from biovar Pullorum can be multidrug-resistant. Cui et al. analyzed a total of 114 Pullorum isolates from China and revealed that almost all Pullorum isolates (94.74%, n = 108) showed resistance to at least one class of antimicrobial, with 35.96% of the isolates being classified as multidrug-resistant. Another Chinese study examined 652 Pullorum isolates and found ampicillin–tetracycline–nalidixic acid (13.6%) was the most common multidrug-resistant pattern observed. They also concluded that strains resistant to six different classes of antibiotics began emerging and have remained prevalent after 2008. In 2014, an isolate resistant to seven antibiotics (ampicillin–cefazolin–streptomycin–tetracycline–sulphonamides–nalidixic acid–nitrofurantoin) was found. Sun et al. stated that 71.9% of isolates exhibited resistance to nalidixic acid, while no resistance (0%) was observed for cefotaxime, amikacin, gentamicin, fosfomycin, meropenem, and polymyxin.

Animal Reservoir¶

Biovar Pullorum can be found in almost all species of birds. However, clinical signs have been only observed in chickens, turkeys, guinea fowl, quail, and pheasant.

Geographical Distribution¶

Biovar Pullorum has been reported worldwide.

Animal outbreaks: There have been multiple outbreaks in chickens associated with biovar Pullorum. Examples are shown below:

Year	Location	Breed	Number of cases
2019	France	Quail	1,920¹
1990	Zambia	Broiler	1,000²

¹ The flock size is 12,000, and 1,920 birds died.

²The flock size is 1,500, and 1,000 birds died.

Border Rejections¶

There have been no recent border rejections linked to this biovar.

Recalls¶

There have been no recent recalls linked to this biovar.