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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.

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

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1. https://pmc.ncbi.nlm.nih.gov/articles/PMC10812584/#:~:text=Salmonella%20enterica%20subsp.,disease%20(PD)%2C%20respectively
2. https://www.woah.org/en/disease/pullorum-disease/#:~:text=Pullorum%20disease%20of%20chickens%20is,septicaemic%20disease%20of%20young%20chickens.
3. https://www.merckvetmanual.com/poultry/salmonelloses-in-poultry/pullorum-disease-in-poultry#Epidemiology_v3342829
4. https://www.sciencedirect.com/science/article/pii/S0378113513005476
5. https://www.poultryimprovement.org/
6. https://pubmed.ncbi.nlm.nih.gov/34412452/
7. https://bmcmicrobiol.biomedcentral.com/articles/10.1186/s12866-024-03296-3
8. https://pmc.ncbi.nlm.nih.gov/articles/PMC7936142/
9. https://www.sciencedirect.com/science/article/pii/S0032579120309457
10. https://www.sciencedirect.com/science/article/pii/B9780444525123001832
11. https://www.nature.com/articles/s41597-022-01605-x
12. https://pmc.ncbi.nlm.nih.gov/articles/PMC7823777/#:~:text=An%20outbreak%20of%20pullorum%20disease,quail%20farm%20in%20western%20France.
13. https://www.jstor.org/stable/1592212?seq=3