TUCKER, Ga. — Histomoniasis outbreaks in turkeys and broiler breeders can lead to major economic losses for the poultry industry. Histomonas meleagridis is the causative agent of blackhead disease, resulting in low mortality in chickens and up to 100 percent mortality in turkeys.
Reports of histomoniasis outbreaks dramatically increased after the last approved treatment was taken off the market in 2016. There is an urgent need to understand and develop an intervention strategy to alleviate histomoniasis in turkeys and broiler breeders. Thus, USPOULTRY and its Foundation funded a board research initiative in 2020 at North Carolina State University to provide methods for preventing blackhead disease in poultry.
The objectives of the completed project were to 1) understand the immune response in turkeys elicited by H. meleagridis, 2) understand the factors and pathways of H. meleagridis lateral transmission in turkeys, and 3) investigate the role of production practices on histomoniasis in broiler breeders.
There is a lack of understanding of immune responses in turkeys during a H. meleagridis infection. Using the broiler breeder chicken as a model of successful immune responsiveness to H. meleagridis infection, it was demonstrated through RNA-sequence analysis that the turkey exhibits a prolonged, dysregulated immune response suggesting a cytokine storm-like syndrome compared to chickens.
The cause of this dysregulation may lie in the early innate activation of defenses against the pathogen. This information contributes to understanding why chickens have lower mortality than turkeys during infection. T-cell activities during the infection were closely observed, and important information about early immune response activation during an H. meleagridis infection were recorded.
Understanding the intricate details of the turkey and the chicken immune responses to H. meleagridis provides vital information for producing an efficacious H. meleagridis vaccine in the future.
Three experiments were performed to assess lateral transmission but were unsuccessful. However, the lack of lateral transmission among turkeys under various environmental and dietary regimes known to exacerbate histomoniasis development and progression does not abrogate the concept of lateral transmission of histomoniasis in turkeys.
Although lateral transmission was not observed in this research effort, the effects of feed withdrawal and reduced crude protein feed formulation increased the overall infection rate and cecal lesion scores of birds directly challenged via trans-cloacal infusion. Coccidiosis and feed withdrawal, along with reduced crude protein feed formulation, had an overall increase in mortality rate. These findings clarify the effects of common stressors on turkey histomoniasis.
Since no significant lateral transmission was observed, researchers evaluated the potential of an oral-fecal alternative infection/transmission pathway. The oral-fecal infection model was successfully created and challenged the ideas that have been established for many years that H. meleagridis could only be infected cloacally via reverse peristalsis.
Utilization of cecal content as a medium of infection was studied. Inoculation of turkeys with H. meleagridis in cecal content produced increased infection rates compared to unprotected H. meleagridis. The capacity of fresh cecal content to protect H. meleagridis has not been previously studied nor has it been compared to frozen cecal content as a medium for oral inoculation.
The mechanism that facilitated oral transmission is not completely understood at this time. Nevertheless, the current study provided evidence that cecal contents affords different levels of protection for H. meleagridis, allowing it to survive passage through the acid upper gastrointestinal tract of the turkey.
Many turkey farms were visited during the project, and researchers discovered new potential vectors for bringing H. meleagridis onto a farm. Grasshoppers, crickets, slugs, grub, harvestmen, garden spiders, multiple beetle species, tree bugs, darkling beetles and earthworms were identified as vectors for H. meleagridis using the polymerase chain reaction (PCR) assay.
One hundred and thirty-two feed additives were also screened on histomoniasis in turkeys. Several categories of additives were shown to have a higher potential to reduce histomoniasis mortality during a mild outbreak.
The data presented in the current report provides valuable information for understanding immune responses to histomoniasis. The project also emphasizes that management practices and nutrition could play an important role in histomoniasis in turkeys and broiler breeders, which may help the industry develop a better management/nutrition program to reduce the loss from a histomoniasis outbreak.
The groundbreaking finding in the new infection model of histomoniasis opens many opportunities for controlling histomoniasis during an outbreak. And, the extension related works, and product screening move forward the process of looking for biosecurity control and the potential treatments for histomoniasis.
Upon completion of the project, principal investigator Dr. Chongxiao Chen, commented, “Even though we see several measures that could reduce the mortality and disease symptoms at different levels during the infection, we still need to find a therapeutic treatment for histomoniasis.”
Dr. Denise Heard is director of research programs with the U.S. Poultry & Egg Association based in Tucker, Ga. She can be reached by e-mail at dheard@uspoultry.org.
