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“STAPH” Meeting: A Different Approach To Combating Mastitis?

The numbers don’t lie: Mastitis infections in dairy herds are one of the most financially detrimental occurrences a producer can face. With an estimated $2 billion in losses each year in the U.S. and $400 million in Canada, more preventative and sustainable measures to alleviate mastitis infections are sorely needed. Staphylococcus aureus remains one of the most prevalent causes of contagious mastitis as it proliferates quickly, is prone to resurgence, and due to its ability to often evade immune responses and develop resistance to antimicrobials, is difficult to eliminate from herds. A study of Finnish dairy cattle found that cows infected with aureus mastitis experienced a loss of roughly 5 lbs. of milk/day. Management strategies such as segregation and culling of infected animals, cleanliness and efficient treatment upon identification have helped dairies to better combat staphylococcal mastitis infections, but control and eradication in herds remains a struggle.

The use of purified surface protein vaccines isn’t a novel area of research, but new applications are being explored as a means to improve mastitis treatments. Surface proteins are located in the bacterial cell wall and determine how  the cell interacts with its environment, especially with regard to immune response. By removing virulence factors (the disease-inducing mechanisms) from foreign antigens, the  surface  proteins can be used to mimic a natural infection and spur an immune response in the host. Antigenic similarities between two different strains of bacteria can result in one exhibiting cross-protective effects against another; this has captured the attention of researchers in the quest to find vaccine development strategies that are cost-effective and sustainable. Research from the University of Tennessee in a recent volume of Veterinary Immunology and Immunopathology evaluated the protective effects of Staphylococcus chromogenes (a common causative agent of subclinical mastitis) against S. aureus infection. Results from the study showed that not only did inoculating cows with  a S. chromogenes surface protein result in a protective immune  response,  but the presence of S. chromogenes also prevented intramammary  colonization  of S. aureus. Current mastitis  vaccines on the market create antibodies against staphylococcal infections, but don’t prevent new infection. Wouldn’t it be great if staphylococcal bacteria  could use their powers for good, rather than for evil? While this study was not without its limitations and the exact mechanism of immune response and antibody production is not yet known, opportunities exist to conduct further study and broaden this avenue of research.

With the push to reduce antimicrobial use on farms (such as in the practice of the prophylactic treatments administered at dry-off), development of more treatments of this nature shows promise as a potential method of eliminating resurgent infections in herds. While currently the most effective means of treatment, intramammary therapy for clinical and subclinical mastitis accounts for the greatest amount of drug use on dairy farms. Many antimicrobials on the market are targeted to treat gram-negative bacteria (S. aureus is gram-positive), so may not be as clinically effective without the use of additional, off-label drug use. While veterinarians are permitted to use off-label drugs for treatment if clinically appropriate, there are many criteria which must be met as many of these drugs are also used in human medicine and may create a public health risk. Residues from use of these additional drugs also has an effect on withholding times. Development of a vaccine that reduces the need to turn to blanket prophylaxis  or antimicrobial therapies would invoke a realm of possibilities of improving herd health. It would be interesting  to see the application of such a vaccine in youngstock or transition cows to evaluate protective effect in stages of sensitive immunity. This is one “staph” meeting we should be looking forward to hearing more about.

— Cari Reynolds

Source: WH Miner Institute

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