Subclinical mastitis in pastoralist dairy camel herds in Isiolo, Kenya: Prevalence, risk factors, and antimicrobial susceptibility

摘要

Mastitis is an important constraint to milk productionin pastoralist camel (Camelus dromedarius) herdsin Kenya. The objective of this study was to investigatethe prevalence, risk factors, and bacterial panorama ofsubclinical mastitis (SCM) in pastoralist camel herdsin Isiolo County, Kenya. Furthermore, antimicrobialsusceptibility in udder pathogens was studied. A crosssectionalsample of 206 camels from 20 milking herdswas screened using the California Mastitis Test (CMT),and quarter milk was subjected to bacterial culturing.Isolates were confirmed using MALDI-TOF mass spectrometryanalysis, and antimicrobial susceptibility wasdetermined using the broth microdilution method. Interviewsfocusing on herd management were conductedwith camel owners. Subclinical mastitis, defined as aCMT score ≥ 3 (scale 1 to 5) and absence of clinicalsymptoms in the udder, were present in all visitedherds. On the individual level, 46% of the camels had atleast 1 quarter affected with SCM, and on the quarterlevel the prevalence was 26%. Intramammary infections(IMI) were common; out of 798 quarter milk samples,33% yielded conclusive bacterial growth. The sensitivityand specificity of CMT for correctly identifyingquarters with IMI were 82% and 92%, respectively. Themost prevalent pathogen was Streptococcus agalactiae(72% of IMI-positive quarters), followed by non-aureusstaphylococci (19%) and Staphylococcus aureus (13%).Antimicrobial susceptibility testing revealed that onlya low proportion (4.9%) of Strep. agalactiae isolates wassensitive to tetracycline. For Staph. aureus, 59.1% of isolatesexhibited sensitivity to penicillin. Skin lesions onthe teats or udder were a risk factor for SCM. Increasedage, parity, and stage of lactation were associated withincreased risk of both SCM and IMI. Older camels witha blind teat or a previous history of mastitis were morelikely to be infected with Strep. agalactiae. Hygieneroutines for milking were largely absent in the observedherds, and knowledge of adequate milk handling waslimited. The poor udder health is likely to depend onmultiple factors, most prominently the within-herdmaintenance of contagious udder pathogens, in combinationwith difficult sanitary conditions and lack ofawareness among camel keepers. This study showedthat in pastoralist camel herds around Isiolo town,SCM and IMI specifically caused by Strep. agalactiaeare common udder health problems and are associatedwith increasing age, parity, and stage of lactation,and skin lesions on the teats and udder. Resistance totetracycline in Strep. agalactiae was common. Controlstrategies specifically targeting SCM and adapted topastorally managed camel herds need to be developedto reduce disease, combat antimicrobial resistance, andimprove the livelihoods of pastoralists.