Coccidiosis and Necrotic Enteritis in Broilers: Managing the Eimeria–Clostridium Interaction

A broiler flock may initially appear to have a coccidiosis problem, but the more important clinical question can be what follows the intestinal damage. When Eimeria disrupts the intestinal barrier, could the resulting changes create conditions for necrotic enteritis? The relationship is clinically important because the consequences may extend beyond the primary parasitic infection. 

How Does Coccidiosis Increase the Risk? 

During Eimeria cycling, later asexual stages damage intestinal epithelial cells. This affects the physical barrier of the intestine as well as its physiological functions. Changes have been observed in intestinal morphology, tight-junction protein expression, nutrient absorption and intestinal permeability^[1]. 

Once this barrier is disrupted, the intestinal environment becomes more favourable for pathogenic bacteria to interact with damaged tissue. 

Clostridium perfringens is particularly important in this context. The disruption associated with Eimeria can allow C. perfringens to infect the host and release toxins that contribute to intestinal necrosis and systemic toxemia. 

This means that coccidiosis should not always be considered an isolated intestinal problem. The initial parasitic damage may be one part of a disease sequence that culminates in necrotic enteritis. 

Not Every Coccidial Challenge Carries the Same Risk 

The relationship is not uniform across all Eimeria species. Most coccidia can contribute to necrotic enteritis, but Eimeria maxima has been identified as posing a greater risk than some other species^[2]. 

Other factors can further influence the risk of necrotic enteritis. These include mycotoxins, small-grain diets with higher non-starch polysaccharide content, high-protein diets, management changes and other stressors. 

Therefore, finding Eimeria in a flock should prompt a broader assessment rather than automatically attributing every subsequent intestinal lesion to coccidiosis alone. 

Look Beyond Mortality^[3] 

Severe necrotic enteritis is usually easy to recognise clinically. The quieter effects can be harder to spot but may have greater economic and welfare consequences when they affect a larger proportion of the flock. 

Coccidiosis can damage the intestine, impair nutrient absorption and alter the intestinal environment. So, even when birds survive the episode, the effects may continue to show up as poorer performance. 

The concern also extends to secondary bacterial disease. Internal observations found higher secondary bacterial mortality after an early necrotic enteritis challenge, with an average daily mortality of about 0.086% in challenged groups compared with 0.035% in non-challenged groups. 

This association should be interpreted carefully. Coccidiosis does not mean that secondary bacterial disease will inevitably develop in every affected flock. 

A Practical Clinical Approach 

When investigating suspected necrotic enteritis in a flock with coccidial involvement, consider: 

• The intestinal barrier: Assess the extent of epithelial damage associated with Eimeria. 
• The coccidial profile: Consider which species are involved, particularly when E. maxima is suspected. 
• Concurrent risk factors: Evaluate diet, mycotoxin exposure, management changes and other identified stressors. 
• Performance as well as mortality: Poor growth and feed utilisation may indicate a broader production impact even when mortality is limited. 
• Secondary disease: Consider whether bacterial disease may be contributing to the clinical picture rather than attributing all findings to coccidiosis. 

Clinical Bottom Line 

Coccidiosis and necrotic enteritis should be viewed as interacting intestinal problems rather than completely separate events. Eimeria-associated epithelial damage can compromise intestinal integrity and create an opportunity for C. perfringens to cause further disease. For the practicing veterinarian, recognising this connection can help shift the clinical focus from treating an isolated intestinal lesion to identifying the combination of coccidial damage and accompanying risk factors driving flock-level disease.

References:

1. Liu J, Teng PY, Kim WK, Applegate TJ. Assay considerations for fluorescein isothiocyanate-dextran (FITC-d): an indicator of intestinal permeability in broiler chickens. Poultry science. 2021 Jul 1;100(7):101202. https://www.sciencedirect.com/science/article/pii/S0032579121002364
2. Nicholds JF, McQuain C, Hofacre CL, Mathis GF, Fuller AL, Telg BE, Montoya AF, Williams SM, Berghaus RD, Jones MK. The effect of different species of Eimeria with Clostridium perfringens on performance parameters and induction of clinical necrotic enteritis in broiler chickens. Avian diseases. 2021 Mar 1;65(1):132-7. https://avian-diseases.kglmeridian.com/downloadpdf/view/journals/avdi/65/1/article-p132.pdf
3. Mathis GF, Lumpkins B, Cervantes HM, Fitz-Coy SH, Jenkins MC, Jones MK, Price KR, Dalloul RA. Coccidiosis in poultry: Disease mechanisms, control strategies, and future directions. Poultry Science. 2025 May 1;104(5):104663. https://www.sciencedirect.com/science/article/pii/S0032579124012410