Vaccines; a new weapon in the arsenal to fight against the worms that turned?

Researchers at the Moredun Research Institute write about their recent work to develop a vaccine strategy against infection with the helminth pathogen of sheep, Teladorsagia circumcincta

By Alasdair J Nisbet, Tom N. McNeilly and Jacqueline B Matthews, Moredun Research Institute, Edinburgh

Worm infections cause global disease

Gastrointestinal helminths cause substantial production-limiting disease in livestock worldwide.  Indeed, parasitic diseases are viewed as the major cause of economic loss in UK sheep flocks (Learmont et al., 2016). Increasing levels of anthelmintic resistance are a massive threat in sheep parasitic nematodes, so alternative methods for control of these worms is sought.  One obvious alternative is the development of protective vaccines.  

Vaccines can help protect against Teladorsagia circumcincta infection

In 2013 we published a paper, in the journal Vaccine, describing efficacy of a recombinant sub-unit vaccine to protect lambs against infection with the abomasal nematode, Teladorsagia circumcincta (Nisbet et al., 2013). The results were encouraging in that the 6 month-old lambs included in these experiments were significantly protected against challenge infection compared to adjuvant-only recipient animals.

However, it is important that this vaccine is also proven to be effective in younger lambs (the most susceptible class of stock on farms) and in ewes, to reduce the natural increase in worm egg shedding observed in these animals around the time of lambing.

Immunisation in young lambs

As a first to step to address these issues, we immunised ewes just before and during pregnancy to test if prior immunisation with the recombinant vaccine could reduce contamination of pasture due to the periparturient reduction in immunity normally observed around lambing. Reducing egg shedding in ewes would then have a substantial impact on downstream levels of pasture infectivity for lambs when they start grazing with a concomitant positive effect on their growth and finishing time.

Two-pronged approach to increasing health and welfare in sheep

The experiments described in our latest paper (Nisbet et al., 2016) demonstrated that, during late gestation and early lactation, when ewe natural immunity to T. circumcincta wanes, prior immunisation with the sub-unit vaccine reduced egg shedding from ewes by approximately 45%. Such reductions in shedding would have a major effect on subsequent pasture infectivity.

The next step is to examine vaccine-induced stimulation of immunity in young lambs, thus taking a two-pronged strategy to reducing the production losses and health and welfare impact of this important pathogen of sheep.

References

  • Learmount J, Stephens N, Boughtflower V, Barrecheguren A, Rickell K, Massei G, Taylor M. Three-year evaluation of best practice guidelines for nematode control on commercial sheep farms in the UK. Vet Parasitol. 2016;226:116-23.
  • Nisbet AJ, McNeilly TN, Wildblood LA, Morrison AA, Bartley DJ, Bartley Y, Longhi C, McKendrick IJ, Palarea-Albaladejo J, Matthews JB.  Successful immunization against a parasitic nematode by vaccination with recombinant proteins. Vaccine. 2013;31:4017-23.
  • Nisbet AJ, McNeilly TN, Greer AW, Bartley Y, Oliver EM, Smith S, Palarea-Albaladejo J, Matthews JB. Protection of ewes against Teladorsagia circumcincta infection in the periparturient period by vaccination with recombinant antigen Vet. Parasitol. 2016;228:130-36.

Funding: This research was funded by Benchmark Animal Health. AJN, TNMcN and JBM are also funded by Scottish Government RESAS.

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