Submitted to: Vaccine
Publication Type: Peer reviewed journal
Publication Acceptance Date: 6/11/2009
Publication Date: 7/12/2009
Citation: Steenhard, N., Jungersen, G., Kokotovic, B., Beshah, E., Dawson, H.D., Urban Jr, J.F., Roepstorff, A., Thamsborg, S. 2009. Ascaris suum infection negatively affects the response to a Mycoplasma hyopneumoniae vaccination and subsequent challenge infection in pigs. Vaccine. 27:5161-5169. Interpretive Summary: Since their first introduction more than a century ago, vaccines have become one of the most cost-effective tools to prevent and manage infectious diseases in human and animal populations. The consequences of incidental worm infection in livestock and humans have not been adequately studied in the context of a bacterial challenge infection following vaccination. This is particularly important in areas of the world where worm infections are prevalent. The current study focused on a vaccination protocol where pigs were experimentally infected with the low numbers of eggs from the common round worm Ascaris suum and subsequently vaccinated with a commercial vaccine against Mycoplasma hyopneumonia. These pigs were then challenged in the lungs with an aerosol containing live Mycoplasma hyopneumonia and vaccine efficacy and response to the challenge infection were evaluated. There was a negative impact of the worm infection on the titer and class of antibodies induced by the vaccination and the severity of lung infection was increased. These results indicate a need for further work in this area, and for controlled field studies to assess the impact of other similar scenarios on both livestock and humans.
Technical Abstract: It is vital to understand the possible mechanisms that may impair optimal vaccine efficacy. The hypothesis posed in this study was that a concurrent Ascaris suum infection of pigs vaccinated with a Mycoplasma hyopneumoniae (Mh) vaccine would modulate the protective immune response to a subsequent challenge infection. Four groups of pigs were either 1) untreated (group C), 2) vaccinated against Mh three weeks after the start of the study (group V), 3) given a trickle infection with A. suum throughout the study (group A), or 4) given a trickle infection with A. suum and vaccinated against Mh (group AV). All pigs were subsequently inoculated with live Mh bacteria four weeks after the Mh vaccination and necropsied after another four weeks. All pigs in group V sero-converted three weeks after vaccination (100%), as opposed to only 33% of group AV pigs that were Mh-vaccinated and given A. suum. Only 78% of pigs in group AV eventually sero-converted during the study. Pigs in group AV had a higher mean percentage of lung pathology and the variation was significantly higher in these pigs compared to pigs in group V. The pattern of gene expression in the lungs and draining lymph nodes indicated a local Th2-skewed response induced by A. suum. Our study indicated that A. suum significantly compromised the effect of Mh vaccination. The impact of reduced vaccine efficacy caused by a common gastrointestinal helminth emphasises the importance of parasite control. More focus should be put into this area of research to outline the practical consequences of this interaction, and to be able to predict, prevent, and correct negative interactions.