VN July 2023

Vetnuus | July 2023 6 Introduction Mastitis, a multifactorial disease, is one of the main culprits causing significant economic losses for dairy producers worldwide. Mastitis is inflammation of the mammary gland, most often caused by bacterial infection, leading to a decrease in milk production and quality, negatively impacting animal welfare, increased antibiotic usage and increased culling. During the last decades, a changing trend in the predominant pathogens causing mastitis has been seen globally. A similar phenomenon is happening in SouthAfrica: a decrease in contagious mastitis and an increase in environmental mastitis. More specifically, we see a significant rise in mastitis caused by Streptococcus uberis in both pasture-based and TMR (total mixed ration) dairy systems. Characteristics and pathogenesis of Streptococcus uberis S. uberis is a gram-positive, catalase-negative and non-motile coccus that grows well in blood agar in aerobiosis. This bacterium is found predominantly in organic material such as soil, bedding material and faeces. S. uberis can also be found in the respiratory tract, alimentary tract, urogenital tract, infected wounds, teat skin, teat orifice, teat canal, and infected mammary glands of cattle. Even though this bacterium is classified as one of the main environmental mastitis-causing pathogens, some S. uberis strains that are specifically host-adapted might be capable of cow-to- cow transmission. S.uberis is particularly prevalent in herds with poor hygiene, overcrowding and inadequate milking procedures, where it causes subclinical and clinical mastitis leading to increased somatic cell counts. The pathogenesis of S.uberis is complex, and after entering the teat canal, S.uberis can produce various virulence factors, facilitating the bacteria’s survival in the mammary gland. One of the main mechanisms of colonization and persistence in the mammary gland is the production of biofilm. Dairy cows are most commonly infected during the dry period, leading tomastitis in the subsequent lactation. When infection occurs during lactation, the first 90 days of lactation are generally the highest risk period. Symptoms and treatment of Streptococcus uberis As with any intramammary infection, the symptoms can vary. Milk from infected quarters can show no visible changes in subclinical cases to denaturation of milk with clots, swollen udder or even a sick cow in clinical cases. The most typical clinical mastitis caused by S.uberis is classified as Grade 1 (only milk affected) and Grade 2 (milk and udder affected), with only a few cases progressing to Grade 3 (milk, udder and cow affected). Mastitis can be successfully treated with antimicrobials when the host’s efficient immune response is combined with the antimicrobials’ ability to kill bacteria or prevent their growth. If the host successfully recovers from the infection and the microorganism is eliminated, infectionswill be cured. Unfortunately, some intramammary infections with S.uberis have a low probability of curing, with the treatment at drying off being more successful than treatment during lactation. S. uberis commonly causes recurrent clinical mastitis, making it one of the most frustrating bacteria to deal with. Non-steroidal anti- inflammatory agents also provide treatment benefits. Extended therapy is frequently necessary to achieve acceptable cure rates and reduce the risk of latent and recurring infections. Extended therapy increases the usage of antibiotics, which is unfavourable at a time when there should be a more prudent and global reduction in antibiotic use. The accurate detection of mastitis remains a challenge amongst South African dairy producers. Regular monitoring, recording, and testing of clinical mastitis cases should all play a part in a management strategy. In the current push towards “One Health” and the responsibility related to antibiotic usage, relying solely on treatment for the control of mastitis, and specifically, Streptococcus uberis mastitis, will not be the most sustainable long-term control strategy. Streptococcus uberis By Dr Donavin Reynolds Technical and Marketing Manager, HIPRA Southern Africa donavin.reynolds@hipra.com