Invited review: A critical appraisal of mastitis vaccines for dairy cows

Abstract

Infections of the mammary gland remain a frequent disease of dairy ruminants that negatively impact animal welfare, milk quality, farmer serenity, farming profitability, and increases use of antimicrobials. There is a need for efficacious vaccines to alleviate the burden of mastitis in dairy farming, but despite decades of research this need has not been satisfactorily fulfilled. A careful appraisal of past and current research on mastitis vaccines reveals the peculiarities but also the commonalities among mammary gland infections associated with the major mastitis pathogens, Escherichia coli, Staphylococcus aureus, Streptococcus uberis, S. agalactiae or S. dysgalactiae. A major pitfall is that the immune mechanisms of effective protection have not been fully identified. Until now, vaccine development has been directed towards the generation of antibodies. In this review, we drew up an inventory of the main approaches used to design vaccines aiming at the major pathogens for the mammary gland, and critically appraised the current and tentative vaccines. In particular, we sought to relate efficacy to vaccine-induced defense mechanisms, in order to shed light on some possible reasons for current vaccine shortcomings. Based on the lessons learned from past attempts and the recent results of current research, the design of effective vaccines may take a new turn in the years to come.

Comparative secretome analysis of Staphylococcus aureus strains with different within-herd intramammary infection prevalence

“…Conversely, in the case of GTB/ST8 strains, evasion of the immune response through inflammation-dampening mechanisms including moonlighting and molecular mimicry, Ig binding, complement inhibition and antimicrobial peptide neutralization, might represent a better “escape strategy” in the specific context of the mammary gland, enabling these strains to establish chronic, subclinical infections, and infect a higher number of animals in the herd. As type 3 immunity is probably the most relevant defense mechanism in the mammary gland [ 55 ], a higher ability to avoid inflammation might translate into better chances for maintaining and spreading infection.…”

“…Nevertheless, the redundancy and multiplicity of immune evasion strategies, as clearly emerged also in this study, remains a challenge [ 26 ]. We will also need to understand in better detail the roles of humoral immunity, innate immunity, tolerance, type 3 immunity, and the microbiota in the mammary gland response to infection, as well as the complex kinetics and interactions of immune evasion factors with host factors [ 55 , 63 , 64 , 65–66 ]. Still, understanding the complexities in the S. aureus secretome will be a crucial step toward this goal.…”

Progress towards the Elusive Mastitis Vaccines

“…It is the most common reason for antimicrobial use in dairy farms [1]. Efficacious vaccines would be very helpful, but unfortunately, currently they are not available, despite decades of research [2]. The question that arises is: can we design new approaches to achieve protection against MG infection through vaccination?…”

“…In the mastitis field, a similar position was stated in the late 1970s: "Currently the attitude is of exasperated optimism" [4], and the possibility of developing a vaccine against Staphylococcus aureus mastitis has been doubted. Indeed, if we confront the glut of vaccine trials to the results in terms of efficacious mastitis vaccines presently in use, the expression "trial and error" takes on its full meaning [2]. It must be admitted that none of the mastitis vaccines currently on the market are satisfactory [2].…”

“…Indeed, if we confront the glut of vaccine trials to the results in terms of efficacious mastitis vaccines presently in use, the expression "trial and error" takes on its full meaning [2]. It must be admitted that none of the mastitis vaccines currently on the market are satisfactory [2]. Of course, it depends on the height where the bar is set: most mammary infections are persistent infections, we cannot be satisfied with limiting the number and severity of clinical episodes.…”