Date of Graduation

5-2025

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Poultry Science (PhD)

Degree Level

Graduate

Department

Poultry Science

Advisor/Mentor

Hargis, Billy M.

Committee Member

Graham, Danielle

Second Committee Member

Johnson, Timothy J.

Third Committee Member

Lessner, Daniel J.

Fourth Committee Member

Robbins, Kabel M.

Fifth Committee Member

Latorre Cardenas, Juan D.

Keywords

Emerging pathogen; Neurological strain; pasteurianus; Streptococcosis; Streptococcus gallolyticus; Turkey poult

Abstract

During the past five years, there has been an increased occurrence of Streptococcus gallolyticus in young turkey poults. This emerging pathogen previously affected turkey flocks without any indication of disease prior to acute mortality. However, recently there has been two cases of neurological presentation associated with S. gallolyticus subsp. pasteurianus that are unique to traditional disease presentation in turkey poults. The objectives of the present dissertation were to compile data associated with the two neurological cases and compare different S. gallolyticus strains as well as pathogenic Enterococcus cecorum to the neurological strains. The two neurological cases occurred between July and August 2023 in a commercial turkey farm with recurrent S. gallolyticuss infection of subsequent flock. In both outbreaks, poults appeared to be in good flesh but were in lateral recumbency and displayed signs of depression as well as torticollis. Elevated mortality was observed in the first flock at 7 days of age, however, Avian Encephalomyelitis was initially suspected, so treatment to this flock was delayed until diagnosis from histopathology and bacterial culture. Downtime was shortened between outbreaks 1 and 2. There was only a downtime period of 12 days between outbreaks compared to the standard downtime for a single age brooder hub of 21 days. Genomic comparisons of the two outbreak strains revealed that they were identical and encoded for a putative collagen adhesin, a potential virulence factor. Outbreak occurrence in the southern portion of the United States is primarily confined to July and August in poults ranging in age between 1.5-2.5 weeks. Generally, there is less downtime during these months in preparation for Thanksgiving, creating ideal conditions for S. gallolyticus to persist in the environment. Moreover, S. gallolyticus recurrence on the same farms suggests that it could be found in the environment as a contaminant with poults serving as a reservoir. For this reason, cleaning and disinfection followed by increased downtime can eliminate S. gallolyticus from the environment. To evaluate strain comparisons, antibiotic sensitivity, API biochemical tests, and a turkey embryo lethality assay (ELA) were performed. The strains chosen for the ELA were based on their capsule type and subspecies to evaluate virulence capability. Embryos were inoculated with both a high and low dose of nine different strains into the allantoic cavity on 15 days of embryogenesis. The cumulative embryo mortality was highest in the neurological strain in both high and low doses and SGP4 in the low dose only. Macroscopic lesions were most prominent in the high dose on day one and two post inoculation with severe cranial hemorrhages, body hemorrhages, and congested organs. Histopathological examination revealed large amounts of coccoid bacteria in the brain, spleen, skeletal muscle, and liver. API RAPID ID 32 STREP was found to be better than API 20 STREP at identifying both S. gallolyticus and E. cecorum due to the inability of API 20 STREP to identify E. cecorum. High levels of bacteria recovered from the yolk suggest that it persists in the embryo and the poult will be infected upon hatch.

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