What is refugia?

In agriculture, there is a large range of pests which can reduce the profitability and/or viability of an enterprise. For many of these pests we are reliant on chemicals to kill the pests, thereby reducing their negative impact on production. In sheep production systems, internal nematode parasites, often referred to as "worms" cause substantial production loss and even death. According to http://www.wormboss.com.au/worms/roundworms/the-cost-of-roundworms.php, worms are the highest animal health cost in the Australian sheep industry. These worms have been successfully controlled by chemicals in the form of drenches since about the 1970's when very safe and highly effective drenches started to be invented. However, it wasn't long until the worms evolved "resistance" to these drenches and new drenches were invented to continue the job. Over the years, the costs in developing drenches have increased while the value of agricultural commodities have remained relatively constant, or even declined in relative terms. It is clear that we cannot continue to develop new drenches, so it makes sense to prolong the use of existing drenches as long as possible. The use of refugia is a possible solution to prolong the use of existing drenches. It refers to the practice of leaving a portion of a population of a worm species (or any other pest species) unexposed to a chemical which would otherwise kill it. This allows any chemical resistant worms to be diluted amongst the genetically drench susceptible refugia, which results in a slowing of the development of resistance.

The Resurrect product has been shown to be extremely useful in not only slowing the development of drench resistance, but in largely reversing it. The problems with conventional refugia is that while you are slowing the development of resistance, the refugia is sourced on the same property as selection for resistance is happening, so in the end, resistance will develop albeit at a reduced rate. Furthermore, this utilization of "home grown refugia" is generally relatively unmeasured in that the undrenched sheep (at say, 2% of the mob) are at the mercy of whatever burden they happen to be carrying at the time of drenching, even if they are the healthier individuals. For this reason, this type of refugia will usually result in a small production loss, so even though we are prolonging the life of our drenches to save sheep from dying, this prolonged drench life is at the expense of productivity to some degree.

In addition to simple drench resistance, most people are unaware that by putting such strong selection pressure on the worms (and on pathogens in general), we are in fact breeding more virulent worms, the way in which this happens is a little involved, but it is very well described in Marek's disease in chickens http://journals.plos.org/plosbiology/article?id=10.1371/journal.pbio.1002198 .

Resurrect resolves almost every issue we have in terms on internal parasite management. Let me explain...

The Resurrect product is a quantified amount of H. contortus of a strain which is not only highly susceptible to MLs, BZs, Closantel and Levamisole (and of course Monepantel and adult H. contortus to Derquantel), but it is also much less virulent than most H. contortus on farms. In addition,  the Resurrect strain when used according to directions, has reliably increased ML and Levamizole susceptibility to greater than 95%, even if drenches were very ineffective initially. It also produces a marked increase in the efficacy of BZ drenches, but not to the same extent in a single application (about 85% effective). We have not managed to restore sustained action with Closantel right through to 4 weeks, but have boosted initial and sustained efficacy. Resurrect has also proven very good at restoring Moxidectin LA sustained activity at a high efficacy to 80 days in lactating ewes (which do not make label claim anyway due to Moxidectin stripping in the milk). Because the resurrect product is being replenished from stock which is not under selection pressure from drenches, it could in theory prolong the use of highly efficacious drenching indefinitely.

I will also throw in here that we have compared the production cost of inoculating with the Resurrect product with the use of an 80% effective drench. Over the 3 month inoculation period, sheep inoculated with the resurrect product (n=60) produced an average of 130g more wool than the sheep treated with an 80% effective Closantel (n=~600). So Resurrect, having the benefit of being a measured amount of parasites, can maximize refugia value while also minimizing production loss.

Back to the reduced virulence point of the Resurrect strain, this is not only important in reducing virulence we have accumulated in conventional "drenching for control" systems, but also where people are increasing immune action of the sheep either through breeding or the new Barbervax. Barbervax and breeding for worm resistance and resilience are fantastic innovations, however in every situation that we put survival pressure on the parasites, how they evolve to that pressure must be taken into account. By constantly killing worms with drenches and by stimulating a strong immune response in the host, we breed a worm that has a shorter life span, but lays bigger and more viable eggs and sucks a lot more blood per day so that here genes can persist in such a perilous environment. If you regularly migrate in "soft" refugia to the on farm population, you can reduce the impact that the parasites are having on your sheep before you even drench. We are currently undertaking trials to quantify the reduced virulence of the Resurrect strain compared with other barbers pole worms.

 

 

Resurrect can enhance any barbers pole control program - in a sustainable way!