Dietary Enterococcus faecium NCIMB 10415 and Zinc Oxide Stimulate Immune
Reactions to Trivalent Influenza Vaccination in Pigs but Do Not Affect
Virological Response upon Challenge Infection
Swine influenza viruses (SIV) regularly cause significant disease in pigs
worldwide. Since there is no causative treatment of SIV, we tested if
probiotic Enterococcus (E.) faecium NCIMB 10415 or zinc (Zn) oxide as feed
supplements provide beneficial effects upon SIV infection in piglets. Seventy-
two weaned piglets were fed three different diets containing either E. faecium
or different levels of Zn (2500 ppm, Zn(high); 50 ppm, Zn(low)). Half of the
piglets were vaccinated intramuscularly (VAC) twice with an inactivated
trivalent SIV vaccine, while all piglets were then infected intranasally with
H3N2 SIV. Significantly higher weekly weight gains were observed in the E.
faecium group before virus infection, and piglets in Zn(high) and E. faecium
groups gained weight after infection while those in the control group
(Zn(low)) lost weight. Using ELISA, we found significantly higher
H3N2-specific antibody levels in the E. faecium+VAC group 2 days before and at
the day of challenge infection as well as at 4 and 6 days after challenge
infection. Higher hemagglutination inhibition (HI) titers were also observed
in the Zn(high)+VAC and E. faecium+VAC groups at 0, 1 and 4 days after
infection. However, there were no significant differences in virus shedding
and lung lesions between the dietary groups. Using flow cytometry analysis
significantly higher activated T helper cells and cytotoxic T lymphocyte
percentages in the PBMCs were detected in the Zn(high) and E. faecium groups
at single time points after infection compared to the Zn(low) control group,
but no prolonged effect was found. In the BAL cells no influence of dietary
supplementation on immune cell percentages could be detected. Our results
suggest that feeding high doses of zinc oxide and particularly E. faecium
could beneficially influence humoral immune responses after vaccination and
recovery from SIV infection, but not affect virus shedding and lung pathology