The second half of the 20th Century was an exciting time for developments in livestock parasite control. The 1960s saw the introduction of a vaccine to protect cattle against lungworm infection. Developed by Jimmy Armour and colleagues at the University of Glasgow Veterinary School, the vaccine was (and is) based on oral delivery of irradiated lungworm larvae to calves. It provided a very good level of protection against subsequent challenge. Surely more vaccines for other worms would follow?
Then in 1981, the introduction of ivermectin heralded in a brave new world of endectocides, deliverable in novel ways, including pour-on formulations.
Innovation in anti-parasitic drug delivery has continued. However, the early promise of anti-parasite vaccines has been relatively slow to deliver.
There have been some notable exceptions. The Paracox series of vaccines, developed by scientists at the Institute for Animal Health, evolved from painstaking work to understand how “precocious” strains of the single-celled parasite responsible could protect poultry from re-infection, while themselves not causing disease in vaccinated birds. A vaccine against tapeworms, developed at the University of Melbourne, could protect sheep very effectively against infection – although there was not much commercial potential in that particular vaccine, similar vaccines are now being developed to protect pigs against tapeworms that are important pathogens of man.
Numerous other efforts to produce vaccines against worm parasites of livestock, for example, have stalled. Many of the barriers are technological – in order to be able to produce enough parasite proteins reliably for batch production – recombinant technology – producing the proteins in bacteria – is used. However, the proteins produced by these means may differ in subtle ways from the “native” proteins in the parasite itself – which limits their vaccine effectiveness. In an attempt to side-step this barrier, a group of scientists from the Moredun Institute have reverted to using purified proteins – isolated by a complicated but precise process from the worms themselves – to produce an effective vaccine to protect sheep against a gut worm – the Barber’s Pole Worm (Haemonchus contortus) that has dramatically affected sheep production in the Southern Hemisphere, and in particular Australia. (www.barbervax.com.au).
Parasites also, unlike the many bacteria and viruses for which effective vaccines have already been developed – have developed pretty sophisticated methods themselves for short-circuiting and confusing the hosts immune response – making the task of the vaccinologist even more difficult.
Despite these considerable hurdles to be overcome, the interest in developing parasite vaccines has been considerable. The EU Commission, for example, has invested almost 25 million Euro over 10 years in three successive, multinational large-scale parasite vaccine projects. The latest of these is PARAGONE.
Notwithstanding the success of Barbervax, the consensus if that for most parasites, the future for parasite vaccines will be in the use of recombinant proteins. Led by Professor Jacqui Matthews from the Moredun Institute,
The PARAGONE project is striving to produce effective vaccines for several major parasitic disease of livestock including:
- Sheep Scab
- Gut worms of sheep and cattle
- Liver fluke affecting sheep and cattle
- Red mite of Poultry
The work involves scientists from ten Universities and Research Institutes, together with five commercial partners, from across Europe as well as South America
But so what? Why has the EU and other funding agencies put so much money into this research? How will this benefit society – farmers, consumers, animals?
We are now at the stage that this EU funded project is likely to be instrumental in delivering at least one vaccine for an important parasitic disease of livestock. The scientific advances and breakthroughs being made are at the stage when they are knocking at the door of overcoming the many challenges associated with producing vaccines effective against these complex parasites. This means that it is reasonably safe to predict that instead of relying only on dosing as a control method, we will also be able to vaccinate against – prevent instead of treating – these parasitic infections.
For farmers, the advantages are obvious. Whereas drug-based control methods have become more convenient with the advent of spot on formulations, long-acting compounds etc., the cost per animal over a grazing season is still considerable. Worryingly also, drugs are losing their effect as with constant use, parasite populations become resistant to them. Routine use of drugs to control disease in livestock is also bad for the environment – as residues may effect ecosystems, and potentially also for consumers if withdrawal periods are not strictly observed.
With three years to go on the project – this is one to keep an eye on in terms of real life outcomes of EU investment in cutting-edge research. Watch this space!