New techniques keep disease on the back foot

Changing disease threats to UK livestock, as highlighted by the arrival of bluetongue last year, mean research into animal health problems is needed now more than ever, according to the Moredun Foundation’s honorary president, John Cameron.

“Present research topics include worm control – still one of the biggest costs to livestock producers – and Johne’s disease, widely regarded as the biggest health problem facing the cattle industry,” Mr Cameron told delegates at last week’s Moredun open day.

Worm vaccine

Farmers could soon have a new weapon in the ongoing battle against worms, according to Moredun researcher David Smith. “Ongoing work on a vaccine against haemonchus, the barber’s pole worm, is promising and could lead to the development of vaccines against a range of worms.”

“Although it is one of the most important parasites of sheep in the southern hemisphere, there are signs of increasing prevalence in the UK and it is thought this is in line with rising global temperatures,” said Prof Smith.

“Hopefully a vaccine will be in place before this worm becomes a real problem in the UK,” he said. “And by using this parasite as a pathfinder, we will be able to use this model to adapt to other parasites such as Ostertagia in cattle.”

Haemonchus attaches to the abomasum and sucks blood, resulting in anaemic sheep. Because this worm feeds on blood, the molecules on the microvilli membrane have become appropriate vaccination targets.

The vaccine had been trialled on Merinos in Australia, which have a high incidence of haemonchus infestation. Vaccinated animals showed a lower rate of infection, with fewer worm eggs than non-vaccinated sheep. On-going trials suggested the vaccine should be commercially feasible and Prof Smith hoped one may be available in the next five years.

Drench resistance

Unless anthelmintics were used sensibly they could soon be exhausted, Frank Jackson warned delegates. “And with rising temperatures extending the parasite season, control is needed now,” he said.

“In Scotland, 80% of lowland farms have benzimidazole (white drench) resistance and 30% ivermectin (yellow drench) resistance. But, even when you stop using a wormer family, resistance will still persist on individual farms for many years.

“We need to slow the process of resistance and this can be done by not exposing worms to anthelmintics and treating all animals of a class in a flock. However, when we have a means of identifying animals requiring treatment then we could use a targeted selected treatment approach,” he said.

Targeted treatments currently being used included faecal egg counting, however, this required lab analysis, said Dr Jackson. Current research had been looking at liveweight gain as an indication of worm infestation.

The thinking behind this was because early on in infection, appetite decreased, thus having an impact on liveweight gain. Nematodes alone could reduce feed intake between 10% and 40% and reduce food use by up to 40%.

“Electronic ear tags and automated shedding systems would mean large numbers of sheep could be handled with minimal labour input,” said Dr Jackson.

“Moredun is currently developing a model which predicts what weight lambs should be at a certain point in time and, using this system, could also calculate the efficiency of production. Preliminary tests show weight is an important indictor of worm infection, however, an issue requiring further research is how often animals needs weighing.”

Scrapie

Detecting sheep with scrapie was set to become much easier following the development of a new test for use on live sheep, explained vet research pathologist, Mark Dagleish.

A test developed at Moredun could now be used to screen large numbers of live sheep at farm level, detecting infection up to one year before animals show any clinical signs.

This allowed for large-scale sampling quickly and accurately, said Dr Dagleish. “The abnormal form of the prion protein (PrP) causing scrapie is detected in nervous and lymph glands. The protein also accumulates in the recto-anal-mucosal-associated-lymphoid-tissue (RAMALT), which is more easily accessed using a rectum speculum.

“The rectum speculum inserted up the anus exposes crypts where the abnormal prion protein is found. Forceps are then used to cut the crypt off. This part of the procedure is quick the hardest part is catching the sheep and holding them in place on the bale,” he said.

A local anaesthetic was used around the anus, although Dr Dagleish said there were no health or welfare problems resulting from the procedure. Currently the procedure was being used purely for research, but Dr Dagleish said in future if there was to a move over to scrapie resistant genotypes, this test would become more widely available, particularly since it was 98.7% positive in detecting clinically infected animals.

Ovine pulmonary adenocarcinoma

A disease still proving difficult to combat is the contagious viral disease, ovine pulmonary adenocarcinoma (OPA). The disease, also known as Jaagsiekte, has non-specific clinical symptoms including loss of condition, increasing breathing difficulties and in some cases, discharge of fluid from nostrils.

The true numbers of affected flocks were unknown as people didn’t want to admit they’d got it, but it was thought to be quite widespread, said research scientist Chris Cousens.

Out of 125 tested farms in Scotland 61% of flocks had some clinical cases of OPA. And although several sheep in a flock may be affected, often only a single sheep was noticed at any one time, added Dr Cousens.

“Many more animals are infected with Jaagsiekte sheep retrovirus (JSRV) than will develop the disease and some of the carriers will never get sick. It is thought the disease is transmitted by lung fluid, which contains 50m particles of JSRV a teaspoonful of lung fluid. Respiratory route and also milk could be important transmissions routes,” said Dr Cousens.

“There is no treatment for affected animals, nor a vaccine to prevent infection,” she added. “The current control strategy is regular inspection of adult sheep and testing of animals showing clinical symptoms. OPA can cause losses of 25% in a flock, so it is important to buy animals from reputable sources.”