Clostridial dermatitis (CD), caused predominantly by Clostridium septicum, is an economically important disease of turkeys characterized by necrotic dermatitis and sudden death. Disease control strategies such as improved management and feeding probiotics have been only variably successful.
A recent study led by Ravi Kulkarni, PhD, BVSc, MVSc, assistant professor in the Department of Population Health and Pathobiology at North Carolina State College of Veterinary Medicine, reported the potential efficacy of a probiotic-based recombinant, oral, vectored vaccine to protect against CD in turkeys.
“C. septicum alpha toxin (ATX) is a key factor in producing CD, and protection against CD seemingly depends on ATX antibodies,” Kulkarni said.
He noted that the studies reporting these findings used toxoid vaccinations, but a better approach involving a systematic and rational vaccine design and development would provide important value to the poultry industry.
Kulkarni and his research team identified “non-toxic domains of ATX (ntATX)” and developed two types of vaccines to immunize turkeys against CD:
- Recombinant subunit vaccines for parenteral (subcutaneous) immunization
- Oral probiotic bacterial (Lactococcus lactis) vector-based vaccines that may offer protection against CD while improving gut health
Their study had three objectives:
- Identify ntATX domains of septicumand clone/express ntATX gene segments as purified recombinant subunit vaccine antigens, perform subcutaneous immunization of turkeys and assess protection against CD.
- Clone and express ntATX gene domains into an lactisvector to develop the recombinant probiotic vaccine.
- Immunize turkeys via oral administration of the lactisvaccine-expressing ntATX proteins and evaluate protection against CD and immune mechanisms.
Study results
The researchers reported success with objective #1. They identified and cloned two non-toxic C. septicum domains and expressed them in Escherichia coli as recombinant proteins.
Subcutaneous immunization of turkeys with the two recombinant antigens demonstrated significant protection against CD mortality and pathology. Protected birds had increased antibody production and activated adaptive immune T cells, suggesting vaccine-induced immunity enhancement against CD.
For objective #2, the researchers developed two probiotic L. lactis-based vaccines that expressed ntATX antigens.
Objective #3 also proved to be successful. Oral immunization of turkeys with the two L. lactis-based vaccines resulted in a noteworthy reduction in CD mortality. Specifically, one of the L. lactis vaccines carrying the gene sequence for ntATX-Domain 2 demonstrated high efficacy in reducing CD gross and histologic pathology.
The immune evaluation of protection against CD showed that the vaccine could induce higher antibodies and reduce host inflammatory responses.
Practical implications
“Collectively, the studies conducted in this project yielded important findings,” Kulkarni said.
The non-toxic segments of C. septicum ATX possess a protective ability against experimental CD infection of turkeys and, hence, can be suitable vaccine candidates, he explained. Further, employing the subcutaneous and oral routes of vaccination can protect turkeys against CD.
“Considering the importance of CD in turkeys in terms of poultry health and economy, this work is timely in yielding a viable and promising non-antibiotic-based strategy for preventing this devastating disease,” Kulkarni added.
The vaccine discovery reported in this study will open new research-based strategies to control many other economically important poultry diseases, including developing Lactobacillus probiotic-based oral vaccines against Clostridial diseases in turkeys and chickens.
The research was funded by USPOULTRY and the USPOULTRY Foundation, thanks in part to Prestage Farms. Click here to view the industry summary.
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