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

Abstract

Mastitis is an important constraint to milk production in pastoralist camel (Camelus dromedarius) herds in Kenya. The objective of this study was to investigate the prevalence, risk factors, and bacterial panorama of subclinical mastitis (SCM) in pastoralist camel herds in Isiolo County, Kenya. Furthermore, antimicrobial susceptibility in udder pathogens was studied. A cross-sectional sample of 206 camels from 20 milking herds was screened using the California Mastitis Test (CMT), and quarter milk was subjected to bacterial culturing. Isolates were confirmed using MALDI-TOF mass spectrometry analysis, and antimicrobial susceptibility was determined using the broth microdilution method. Interviews focusing on herd management were conducted with camel owners. Subclinical mastitis, defined as a CMT score ≥ 3 (scale 1 to 5) and absence of clinical symptoms in the udder, were present in all visited herds. On the individual level, 46% of the camels had at least 1 quarter affected with SCM, and on the quarter level the prevalence was 26%. Intramammary infections (IMI) were common; out of 798 quarter milk samples, 33% yielded conclusive bacterial growth. The sensitivity and specificity of CMT for correctly identifying quarters with IMI were 82% and 92%, respectively. The most prevalent pathogen was Streptococcus agalactiae (72% of IMI-positive quarters), followed by non-aureus staphylococci (19%) and Staphylococcus aureus (13%). Antimicrobial susceptibility testing revealed that only a low proportion (4.9%) of Strep. agalactiae isolates was sensitive to tetracycline. For Staph. aureus, 59.1% of isolates exhibited sensitivity to penicillin. Skin lesions on the teats or udder were a risk factor for SCM. Increased age, parity, and stage of lactation were associated with increased risk of both SCM and IMI. Older camels with a blind teat or a previous history of mastitis were more likely to be infected with Strep. agalactiae. Hygiene routines for milking were largely absent in the observed herds, and knowledge of adequate milk handling was limited. The poor udder health is likely to depend on multiple factors, most prominently the within-herd maintenance of contagious udder pathogens, in combination with difficult sanitary conditions and lack of awareness among camel keepers. This study showed that in pastoralist camel herds around Isiolo town, SCM and IMI specifically caused by Strep. agalactiae are common udder health problems and are associated with increasing age, parity, and stage of lactation, and skin lesions on the teats and udder. Resistance to tetracycline in Strep. agalactiae was common. Control strategies specifically targeting SCM and adapted to pastorally managed camel herds need to be developed to reduce disease, combat antimicrobial resistance, and improve the livelihoods of pastoralists.