1. Understanding protective immunity to Haemonchus contortus to aid development of a recombinant vaccine Eve Hanks1, Alexa Brett Roberts1, David Smith2, George FJ Newlands2, David P Knox2, Alasdair J Nisbet2, Tom N McNeilly2, Collette Britton Institute of Biodiversity Animal Health and Comparative Medicine, University of Glasgow 2 Moredun Research Institute, Edinburgh
Introduction Haemonchus contortus is a blood feeding gastrointestinal parasite of small ruminants. Infection with this nematode leads to high production losses and up to 50% mortality in lambs. Anthelmintic resistance is an increasing problem and there is an urgent need for vaccination. Previous studies have shown some success following vaccination with H. contortus larval surface antigens, resulting in 61% reduction in faecal egg count (FEC) (Piedrafita, et al. 2012). Excretory/secretory (ES) products released by H. contortus can also induce protective immunity, with FEC reduced by 88.5% (Bassetto & Amarante, 2015). However, gut membrane proteins isolated from adult worms show most success and a native gut membrane protein vaccine is now sold commercially as Barbervax in Australia ( ; Bassetto & Amarante, 2015). This vaccine is enriched in proteases H11 and H-gal-GP complex. We recently initiated a study aiming to identify correlates of protective immunity that will help in developing a recombinant vaccine. Here we compare the antibody responses of sheep vaccinated with Barbervax with those vaccinated with C. elegans-expressed recombinant H. contortus proteases, including H11.
Table 1: protection results of trial
Barbervax group
Recombinant group
Group
Vaccination
Protection 1
Barbervax
90% 2
Recombinant C. elegans expressed proteases 0% 3
Adjuvant only challenge control
Figure 4: ELISA antibody detection from individual sheep. Note sheep
in Barbervax group have a higher response overall. Sheep 24 in the
recombinant group has the best response and was most protected
Results
Western blot analysis was undertaken to determine patterns of
antibody recognition to Barbervax protein antigens. The
Barbervax vaccine group had the earliest response to H11 and
HgalGP proteins. The best protected sheep with the lowest
FECs in this group showed response at Day 28 as shown (Fig.2).
In the recombinant vaccine group, sheep 24 showed the earliest
appropriate response to vaccination (Fig. 3). Antibody titre for
each group was detected by ELISA (Fig. 4) and this was highest in
the Barbervax vaccine group. Again, sheep 24 from the
recombinant group showed a marked antibody response to
vaccination and this sheep had the lowest FEC of the group.
Discussion
This trial demonstrated that Barbervax vaccinated
sheep recognise protective proteins earlier (Day 28) than
recombinant vaccinated sheep and mount a stronger
immune response overall. One Sheep (24) from the
recombinant group has displayed signs of a protective
response and there is a statistically significant reduction of
37% between the FEC of the challenge control group and
the recombinant vaccinated group at Day 27 post challenge
( p value ). This is encouraging for recombinant vaccine
development although further work is needed.
Figure 1: Trial design
Barbervax vaccinated group (1)
Recombinant vaccinated group (2)
Challenge control group (3)
Figure 1: Haemonchus contortus
Figure 2: DAY 28 – Antibody response of individual sheep showing early recognition of protein. Best protected indicated by stars
Figure 5: FEC graph
250
150
100 50 37
Barbervax Group
250
150
100 50 37
Recombinant Group
H11
HgalGP 1 2 3
Three groups of crossbred lambs were divided
into groups of 7 and vaccinated subcutaneously
at Day 0 and Day 28 of the trial with either
Barbervax vaccine (1); recombinant vaccine (2)
or adjuvant only, Quil A (3). The lambs were
challenged with larvae at Day 28 and sera and FECs
taken regularly throughout the trial until Day 55
when post morten was completed.
Figure 3: DAY 35 – Significantly increased response of Barbervax group & recognition of H11 by sheep 24 in the recombinant group (arrows)
References
Bassetto, C.C. & Amarante, A.F.T. (2015) Vaccination of sheep and cattle against haemonchosis. Journal of Helminthology,
89,
Piedrafita, D.P., De Veer, M.J., Sherrard, J., Kraska, T., Elhay, M. & Meeusen, E.N. (2012) Field vaccination of sheep with a
larval-specific antigen of the gastrointestinal nematode Haemonchus contortus confers significant protection against an
experimental challenge infection. Vaccine, 30,
Acknowledgements
With thanks to British Society of Parasitologists for the travel award funding
Funded by University of Glasgow Industrial Parternship PhD scheme with Moredun Scientific
250
150
100 50 37
Barbervax Group
250
150
100 50 37
Recombinant Group
H11
HgalGP