Necrotic Enteritis

Because necrotic enteritis (NE) is the most common disease among broilers, researchers are hard at work getting to know it better. In the past, NE received little research attention because the disease has long been controlled with the use of prophylactic antibiotics. However, following Europe’s lead, the use of these drugs may eventually be phased out in North America, and it’s therefore critical that other methods of effective control (such as vaccines) are developed. 

NE is caused by a bacterium called Clostridium perfringens, which produces toxins that damage gut tissues. This can affect nutrient absorption and, in some cases, lead to other gut infections. Affected flocks may see increased numbers of deaths and/or reduced performance.

It was believed that NE was caused by a toxin called alpha-toxin, produced by essentially all strains of C. perfringens. Recently, however, another toxin called NetB has been implicated by scientists in Australia. Very recently, three research groups from University of Guelph (UG), Guelph Food Research Centre of Agriculture and Agri-Food Canada (AAFC), and University of Arizona (UA), reported their breakthrough discovery regarding the bacterium that causes NE. They’ve identified three major NE gene clusters – about 30 genes in total – the largest of which includes the gene that produces NetB.

The research is funded by Agriculture and Agri-Food Canada, the Ontario Ministry of Food and Rural Affairs, the Poultry Industry Council, the U.S. Department of Agriculture, and Pfizer Animal Health. Principal investigators of the three groups are Dr. John F. Prescott (UG), Dr. Joshua Gong (AAFC), and Dr. J. Glenn Songer (formerly with UA, now with Iowa State University) who is an internationally recognized expert in clostridial research. Mr. Dion Lepp (AAFC), Dr. Bryan Roxas (UA), and Dr. Valeria R. Parreira (UG) were key players and each contributed significantly to the research. Both Dr. Prescott and Dr. Gong emphasize the importance of their international collaboration that has led to the discovery.

Two of the gene clusters are located on plasmids, which are small bits of DNA found inside bacteria that can be easily transferred from one bacterium to another. “These findings suggest that NE is caused by multiple virulence factors,” says Lepp, “and that these genes may be passed on from one C. perfringens isolate to another.”

This genetic discovery will have a significant impact on the direction of future research by influencing the thinking of researchers towards the disease and its control. “Before, people have looked for one gene or one toxin,” says Gong. “Now we all have the awareness that clusters are involved and more than one toxin.”

“It’s a major discovery,” says Prescott. “It makes us realize that the disease is far more complex than we thought it was, which is somewhat daunting, but it also means we have lots of options open to explore in terms of approaches to better control. There are lots of areas to address, lots of antigens to use, lots of genes to manipulate.”

The researchers will now embark on a journey to understand how the plasmids and their genes work together to cause the disease. They will remove the plasmids and inactivate genes one by one and see what disease effects each mutant produces when introduced into chickens. Further understanding of the function of the plasmids and genes and their roles in the disease process may lead to novel innovations for controlling NE, such as a vaccine and other control strategies to block adhesion or signalling of the pathogen. 

Control of NE strategies to replace prophylactic antibiotics is one of the research funding priorities of the Chicken Farmers of Canada, one of the founding members of the Canadian Poultry Research Council (CPRC). The CPRC, with more than a dozen other organizations, has received funding application from the Canadian Agri-Science Cluster Initiative for projects under three main themes. One of these is “enteric diseases of poultry, as impacted by reduced emphasis on the use of feed-borne antibiotics and their potential for impacting human health.” Expected outputs from this research include development of a novel vaccine and natural antimicrobials to protect birds against pathogenic Clostridia bacteria.