title: Comparison of transmission dynamics between Streptococcus uberis and Streptococcus agalactiae intramammary infections.
abstract: The objectives of study were to determine the transmission parameters (β), durations of infection, and basic reproductive numbers (R0) of both Streptococcus agalactiae and Streptococcus uberis as pathogens causing mastitis outbreaks in dairy herds. A 10-mo longitudinal study was performed using 2 smallholder dairy herds with mastitis outbreaks caused by Strep. agalactiae and Strep. uberis, respectively. Both herds had poor mastitis control management and did not change their milking management during the entire study period. Quarter milk samples were collected at monthly intervals from all lactating animals in each herd for bacteriological identification. The durations of infection for Strep. uberis intramammary infection (IMI) and Strep. agalactiae IMI were examined using Kaplan-Meier survival curves, and the Kaplan-Meier survival functions for Strep. uberis IMI and Strep. agalactiae IMI were compared using log rank survival-test. The spread of Strep. uberis and Strep. agalactiae through the population was determined by transmission parameter, β, the probability per unit of time that one infectious quarter will infect another quarter, assuming that all other quarters are susceptible. For the Strep. uberis outbreak herd (31 cows), 56 new infections and 28 quarters with spontaneous cure were observed. For the Strep. agalactiae outbreak herd (19 cows), 26 new infections and 9 quarters with spontaneous cure were observed. The duration of infection for Strep. agalactiae (mean=270.84 d) was significantly longer than the duration of infection for Strep. uberis (mean=187.88 d). The transmission parameters (β) estimated (including 95% confidence interval) for Strep. uberis IMI and Strep. agalactiae IMI were 0.0155 (0.0035-0.0693) and 0.0068 (0.0008-0.0606), respectively. The R0 (including 95% confidence interval) during the study were 2.91 (0.63-13.47) and 1.86 (0.21-16.61) for Strep. uberis IMI and Strep. agalactiae IMI, respectively. In conclusion, the transmission parameter and R0 values were not different between both pathogens; however, the duration of infection for Strep. agalactiae was longer than Strep. uberis. These suggest that Strep. uberis may have a different transmission dynamic compared with Strep. agalactiae.
authors.affiliation: Department of Food Animal Clinics, Faculty of Veterinary Medicine, Chiang Mai University, Mae Hea, Chiang Mai, Chiang Mai Province 50100, Thailand.
authors.forename: Kansuda
authors.initials: K
authors.lastname: Leelahapongsathon
authors.affiliation: Department of Population Medicine and Diagnostic Sciences, Cornell University, Ithaca, NY 14853; GD Animal Health, 7418EZ Deventer, the Netherlands.
authors.forename: Ynte Hein
authors.initials: YH
authors.lastname: Schukken
authors.affiliation: Department of Large Animal and Wild Life Clinical Sciences, Kasetsart University, Bangkok 10900, Thailand.
authors.forename: Tanu
authors.initials: T
authors.lastname: Pinyopummintr
authors.affiliation: Department of Food Animal Clinics, Faculty of Veterinary Medicine, Chiang Mai University, Mae Hea, Chiang Mai, Chiang Mai Province 50100, Thailand. Electronic address: Suriyasathaporn@hotmail.com.
authors.forename: Witaya
authors.initials: W
authors.lastname: Suriyasathaporn
mesh_terms: D000818:Animals; D002417:Cattle; D004196:Disease Outbreaks / Q000662:veterinary*; D005260:Female; D007774:Lactation; D008137:Longitudinal Studies; D008414:Mastitis, Bovine / Q000453:epidemiology* / Q000382:microbiology; D008892:Milk / Q000378:metabolism*; D013290:Streptococcal Infections / Q000382:microbiology / Q000635:transmission / Q000662:veterinary*; D013291:Streptococcus / Q000302:isolation & purification* / Q000502:physiology; D013292:Streptococcus agalactiae / Q000302:isolation & purification / Q000502:physiology
keywords: Streptococcus agalactiae; Streptococcus uberis; duration of infection; mastitis; outbreak