Efficacy of antimicrobial treatments and vaccination regimens for control of porcine reproductive and respiratory syndrome virus and Streptococcus suis coinfection of nursery pigs

Seventy-six, crossbred, porcine reproductive and respiratory syndrome virus (PRRSV)-free pigs were weaned at 12 days of age and randomly assigned to s even groups of 10 to 11 pigs each, Pigs in group 1 served as unchallenged c ontrols. Pigs in groups 2 to 7 were challenged intranasally with 2 mi of hi gh-virulence PRRSV isolate VR-2385 (10(4.47) 50% tissue culture infective d oses per 2 mi) on day 0 of the study (30 days of age). Seven days after PRR SV challenge, pigs in groups 2 to 7 were challenged intranasally with 2 mi of Streptococcus suis serotype 2 (10(8.30) CFU/2 mi), Group 2 pigs served a s untreated positive controls. Antimicrobial treatments included daily intr amuscular injection with 66,000 IU of procaine penicillin G per kg of body weight on days 8 to 10 (group 3), drinking water medication with 23.1 mg of tiamulin per kg during days 8 to 10 (group 4), and daily intramuscular inj ection of 5.0 mg of ceftiofur hydrochloride per kg on days 8 to 10 (group 5 ), Vaccination regimens included two intramuscular doses of an autogenous k illed S, suis vaccine (group 6) prior to S, suis challenge or a single 2-ml intramuscular dose of an attenuated live PRRSV vaccine (group 7) 2 weeks p rior to PRRSV challenge. Mortality was 0, 63, 45, 54, 9, 40, and 81% in gro ups 1 to 7, respectively, Ceftiofur treatment was the only regimen that sig nificantly (P < 0.05) reduced mortality associated with PRRSV and S, suis c oinfection, The other treatments and vaccinations were less effective. We c onclude that ceftiofur administered by injection for three consecutive days following S, suis challenge was the most effective regimen for minimizing disease associated with PRRSV and S, suis coinfection.