Pure white gold : Subclinical mastitis in dairy camels in Kenya with a special focus on Streptococcus agalactiae

Abstract: In the drylands of the Horn of Africa, camels are fundamental for food and nutritional security due to their ability to produce milk despite limited access to feed and water. Subclinical mastitis (SCM) is common in the region and has a negative impact on food security and household income. In this thesis project, we investigated the prevalence, aetiology and potential biomarkers of SCM. Antibiotic susceptibility was assessed and the molecular epidemiology of Streptococcus agalactiae (SRA) investigated through genomic and phylogenetic analysis. In total, 804 udder quarters in 206 lactating camels were screened using the California Mastitis Test and milk was sampled for bacteriological culture. Whole-genome sequencing was carried out on 122 SRA genomes collected from camel milk and extramammary sources. The prevalence of SCM at quarter, camel and herd level was 26%, 46% and 100% respectively and SCM was associated with a higher age, later stage in lactation and lesions on the udder or teats. The most common udder pathogen was SRA, followed by non-aureus staphylococci and Staphylococcus aureus. Tetracycline resistance was widespread among SRA isolates. Most SRA isolates from milk belonged to sequence type (ST) 616 and showed signs of adaptation to the mammary gland. However, there was a high nasal prevalence in healthy camels and the same STs were found in milk and extramammary isolates, suggesting a more complex epidemiology than previously assumed. Udder health in camels could be improved with the development of informed control strategies adapted to the local context.