COCCI R&D - Irrefutable Evidence

New study validates theory that vaccinating with Coccivac-B restores Eimeria sensitivity to diclazuril

Dr. David Chapman
Dr. Harry Danforth

Along-held theory that vaccinating with Coccivac-B for just two cycles restores Eimeria sensitivity to the new-generation in-feed anticoccidial diclazuril (Clinacox) was validated recently in a large-scale field trial with a major US poultry company.

The results, according to poultry disease specialists involved in the study, could change the broiler industry's strategy for managing coccidiosis, a costly parasitic disease in poultry.

Previous investigations into the relationship between coccidiosis vaccination and in-feed anticoccidials - including studies by wellknown researchers Dr. David Chapman of the University of Arkansas, Dr. Harry Danforth, USDA, and Dr. Greg Mathis of Southern Poultry Research in Athens, Georgia. "have demonstrated that vaccinating with Coccivac-B restores anticoccidial sensitivity in a poultry house by replacing resistant Eimeria organisms with ones still sensitive to in-feed anticoccidials used today.

"In addition, pen trials over the years have indicated that Coccivac-B used in a rotational program can effectively displace wild field strains of coccidia and restore sensitivity to the current infeed anticoccidials," says Dr. Rick Phillips, director of worldwide poultry technical services, Schering-Plough Animal Health.

"Those studies, however, focused on ionophore anticoccidials, not on diclazuril, now a widely-used, chemical anticoccidial.

Despite the research and all the field reports in hand, we felt it was important to test our hypothesis in the field where the proverbial 'rubber meets the road'," Phillips says. "These latest trials with diclazuril without a doubt prove our hypothesis."

Study background and design

The study, sponsored by Schering- Plough Animal Health, was conducted at the site of a large US integrator. Independent investigators involved in the trial were the poultry company's veterinarian and Dr. Mathis of Southern Poultry Research, who conducted sensitivity testing.

The integrator, which asked not to be identified in this report, added Coccivac-B to its anticoccidial rotation to see if using the live-oocyst vaccine improved the effectiveness of diclazuril "or changed the coccidial population to one more sensitive to diclazuril "as well as conventional ionophores. The move was part of a concerted effort by the company to develop new tools and long-term strategies for managing coccidiosis.

The poultry company first collected litter samples from eight farms involved with its seven complexes to obtain baseline diclazuril sensitivity information. Prior to this, the complexes had been on a variety of in-feed anticoccidial rotation programs, all of which included diclazuril for one to two cycles the previous year, he says.

Dr. Charlie Broussard, worldwide poultry technical services manager for Schering-Plough Animal Health,explains that after collecting initial litter samples, four of the seven complexes continued their annual rotation using ionophores or chemical-ionophore shuttle programs. The remaining three complexes incorporated two cycles of Coccivac-B vaccine into the annual rotation. Identical houses were re-sampled after two cycles of Coccivac-B or anticoccidial rotation.

To determine diclazuril sensitivity, Mathis looked at weight reduction and coccidial lesion scores in test birds and compared them to unchallenged controls. He then summarized diclazuril's efficacy as "good," "moderate" or "poor."

"Even though diclazuril was given a rest, diclazuril sensitivity did not improve or improved very little in the complexes that rotated diclazuril with other in-feed anticoccidials, rather than with the vaccine," Broussard says. "On the other hand, diclazuril sensitivity improved significantly in the complexes that used two cycles of Coccivac-B in the rotation. Not one of the samples tested scored 'poor' for sensitivity following Coccivac-B use." (See Figure 1.)

A few highlights from the trial follow, according to Broussard: "� In one complex, diclazuril sensitivity before vaccination was rated "good" in only 30% of samples. After vaccination, however, 100% of samples were rated "good."

"� In another complex, only 33% of samples were rated good before vaccine use, compared to 83% after vaccination. (See Table 1.)

"� In contrast, one complex where the vaccine was not used, investigators rated only 25% of samples as "good" for diclazuril sensitivity at the start of the study. After continuing on a traditional rotation program and "resting" diclazuril, 0% of the samples were rated "good" for diclazuril sensitivity.

Considering its 2-to 3-years' experience with coccidiosis vaccination and the results of this trial, the poultry company plans to continue using Coccivac and will carefully monitor results as well as assess the vaccine's role in long-term methodology. "Many other factors are involved with the selection process so we cannot say that the process is sensitivity driven, though that's a major factor," says a veterinarian for the company.

Take-home message

Pointing to the good performance of the vaccinated flocks and the reduction in lesion scores, investigator Mathis notes that two cycles of Coccivac-B prompted a dramatic shift toward increased diclazuril sensitivity.

"We followed exactly the same houses before and after diclazuril was used, then used Coccivac so we could pinpoint for sure whether we were replacing resistance," he says. "The results demonstrate that we can replace or at the very least dilute the amount of Eimeria resistance that's out there by using Coccivac for several cycles and making it part of a long-term control program."

Mathis, who calls the landmark trial "one of the most coccidiosis-significant studies" he's worked on in more than 20 years, thinks the results will go a long way toward directing coccidiosis management in the future.

"The take-home message is that to get the performance you got when you originally had diclazuril or other in-feed anticoccidials, you're going to have to use a vaccine. Coccivac is the only coccidiosis vaccine that has clearly demonstrated that it can replace resistance."

Phillips agrees and says the results are almost an exact duplication of past pen study trial results. "These are powerful findings that could revolutionize the way the industry controls coccidiosis for years to come," he adds.

"For the first time in decades, vaccination is being viewed as a foundation to successful coccidiosis management "one that can be used either yearround or in a carefully planned, longterm rotation with in-feed anticoccidials to maximize their impact."

Source: CocciForum Issue No.7, Schering-Plough Animal Health.

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