The influence of Ascaridia galli development on cytokine gene expression and intestinal microbiota of infected chickens_abstract

The influence of Ascaridia galli development on cytokine gene expression and intestinal
microbiota of infected chickens
Maria Tereza Bethonico Terra 1 , Andrea Pietruska 2 , Ruediger Hauck 1,2
1 Department of Poultry Science, Auburn University, Auburn, Al 36849
2 Department of Pathobiology, Auburn University, Auburn, Al 36849
Ascaridia galli is an intestinal roundworm of chickens that affects the jejunum, can decrease egg
production, and negatively affect the intestinal microbiota decreasing the microbiota diversity. A.
galli infection is related to the Th2 immune response increasing the gene expression of IL-4 and
Il-13. However, there is still the need for a better understanding of the complete immune response
to early stages of these parasites. The aims of this study were to establish a timeline of the influence
of A. galli on the expression of cytokines and the composition and relative abundance of the
intestinal microbiota.
Fifty-six male layer type birds were kept in cages and randomly placed into the control and infected
group. The infected group was challenged with 500 embryonated A. galli eggs for three
consecutive days starting at 24 days of age. Three birds of each group were euthanized weekly
until the birds were 13-week-old, and the remaining birds were euthanized.
We were able to visualize larvae from week 1 to week 6 post infection in decreasing numbers and
between Week 4 and 5 there was an expressive reduction on numbers of larvae. At this time, adult
worms in the lumen and onset of egg shedding in the feces were expected. However, no worm
eggs were detected in the feces, and no adult worms were observed by the end of the experiment.
In the early stages of the infection before week five, the relative gene expression showed in most
weeks an upregulation of IL-13, a cytokine related to parasitic response, IL-8, a pro-inflammatory
cytokine and TGF-β4, an anti-inflammatory cytokine. INF-g, a Th1-response cytokine, was
downregulated. This response to the growth of the larvae in the intestinal wall was expected. In
week 5, all cytokines, including IL-10, another regulatory cytokine, whose expression had
remained unchanged before, were upregulated. In weeks 6 – 8, only TGF-b was upregulated once.
This suggest that this severe immune response in week five might be the reason of resolution of
the infection.
For the microbiota analysis, there were no significant differences in the diversity of Operational
Taxonomic Units (OTUs) within each sample (alpha diversity) between challenge and control
groups. The beta diversity analysis, i.e. the diversity between samples, showed that the age of the
birds was the most important variable explaining differences between samples.
A high infection dose and the fact that birds were fed with feed formulated for broilers, which is
more nutritionally dense, might have contributed to the birds’ immune system ability to clear the
infection before the worms were able to reach maturity.