Evaluation of the efficacy of two different tulathromycin treatments in weaned piglets infected intratracheally with Haemophilus parasuis serovar 5

Once viewed as an infrequent disease of young pigs, Glässer’s
disease has emerged as a major pathogen affecting naïve swine
herds. Current trends recognize Haemophilus parasuis (HPS)serovar 5
as one of the most virulent and most prevalent serovars capable of
eliciting sudden death and systemic Glässer's disease in swine. The
prudent use of antimicrobials is considered to be an important
component in the control of the septicemic spread of a HPS
infection within a pig. Tulathromycin, a triamilide antibiotica, is
an approved antimicrobial in many countries however its efficacy
against HPS has not been completely examined. The objective of this
study was to evaluate the efficacy of two different tulathromycin
treatments in commercially weaned piglets challenged
intratracheally with HPS serovar 5. A total of 27 piglets were
infected with 5 x 10 (8) CFU HPS serovar 5. Eighteen of these
piglets were administed two tulathromycin treatments at different
times (7 days, 4 days)prior to infection and nine piglets served as
controls. After challenge, severe clinical signs, pathological and
histopathological lesions indicative of Glässer’s disease were seen
in all pigs infected with HPS. Furthermore, pyelitis was observed
in seven challenged pigs. This is the first study which reports the
findings of these lesions in HPS infected pigs and further studies
are required to confirm these findings. Based on the results of the
clinical examinations, gross and histopathological lesions, the
administration of the two tulathromycin treatments 4 and 7 days
prior to the experimental HPS infection did not appear to have a
significant antimicrobial effect against the infection dose and
serovar used in this study. Factors such as unsuitable application
times or the high challenge inoculum dose may have contributed to
these findings. Further studies examining the efficacy of
tulathromycin taking these changes into consideration are
necessary.