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2014

Mweu, MM, Nielsen SS, Halasa T, Toft N.  2014.  Spatiotemporal patterns, annual baseline andmovement-related incidence of Streptococcus agalactiaeinfection in Danish dairy herds: 2000–2009. Preventive Veterinary Medicine. 113:219-230. Abstractspatial_paper.pdf

Several decades after the inception of the five-point plan for the control of contagiousmastitis pathogens, Streptococcus agalactiae (S. agalactiae) persists as a fundamental threatto the dairy industry in many countries. A better understanding of the relative importance ofwithin- and between-herd sources of new herd infections coupled with the spatiotemporaldistribution of the infection, may aid in effective targeting of control efforts. Thus, theobjectives of this study were: (1) to describe the spatiotemporal patterns of infection with S.agalactiae in the population of Danish dairy herds from 2000 to 2009 and (2) to estimate theannual herd-level baseline and movement-related incidence risks of S. agalactiae infectionover the 10-year period.The analysis involved registry data on bacteriological culture of all bulk tank milk samplescollected as part of the mandatory Danish S. agalactiae surveillance scheme as well as livecattle movements into dairy herds during the specified 10-year period. The results indicated that the predicted risk of a herd becoming infected with S. agalactiae varied spatiotempo-rally; the risk being more homogeneous and higher in the period after 2005. Additionally,the annual baseline risks yielded significant yet distinctive patterns before and after 2005 –the risk of infection being higher in the latter phase. On the contrary, the annual movement-related risks revealed a non-significant pattern over the 10-year period. There was neitherevidence for spatial clustering of cases relative to the population of herds at risk nor spatialdependency between herds. Nevertheless, the results signal a need to beef up within-herdbiosecurity in order to reduce the risk of new herd infections.

Mahmmoda, YS, Mweu MM, Nielsen SS, Katholm J, Klaasa IC.  2014.  Effect of carryover and presampling procedures on the results of real-time PCR used for diagnosis of bovine intramammary infections with Streptococcus agalactiae at routine milk recordings. Preventive Veterinary Medicine. 113:512-521. Abstractcarryover_paper.pdf

The use of PCR tests as diagnostics for intramammary infections (IMI) based on compositemilk samples collected in a non-sterile manner at milk recordings is increasing. Carryoverof sample material between cows and non-aseptic PCR sampling may be incriminated formisclassification of IMI with Streptococcus agalactiae (S. agalactiae) in dairy herds with con-ventional milking parlours. Misclassification may result in unnecessary costs for treatmentand culling. The objectives of this study were to (1) determine the effect of carryover onPCR-positivity for S. agalactiae at different PCR cycle threshold (Ct) cut-offs by estimatingthe between-cow correlation while accounting for the milking order, and (2) evaluate theeffect of aseptic presampling procedures (PSP) on PCR-positivity at the different Ct-valuecut-offs.The study was conducted in four herds with conventional milking parlours at routinemilk recordings. Following the farmers’ routine pre-milking preparation, 411 of 794 cowswere randomly selected for the PSP treatment. These procedures included removing thefirst streams of milk and 70% alcohol teat disinfection. Composite milk samples were thencollected from all cows and tested using PCR. Data on milking order were used to estimatethe correlation between consecutively milked cows in each milking unit. Factors associatedwith the PCR-positivity for S. agalactiae were analyzed using generalized estimating equa-tions assuming a binomially-distributed outcome with a logit link function. Presamplingprocedures were only significant using cut-off 37. A first-order autoregressive correlationstructure provided the best correlation between consecutively milked cows. The correla-tion was 13%, 11%, 9% at cut-offs <40, 37, and 34, respectively. PSP did not reduce the oddsof cows being PCR-positive for S. agalactiae. In conclusion, carryover and non-aseptic sampling affected the PCR results and shouldtherefore be considered when samples from routine milk recordings are used. In relativeterms, higher cut-offs resulted in higher between-cow correlation, but the absolute amountof carryover may not be affected although this was not tested.

2013

Mweu, MM, Fournié G, Halasa T, Toft N, Nielsen SS.  2013.  Temporal characterisation of the network of Danish cattle movements and its implication for disease control: 2000–2009. Preventive Veterinary Medicine. 110:379-387. Abstractsna_paper.pdf

Social network analysis provides a valuable framework for understanding the dynamics of diseases on networks as well as a means for defining effective control measures. An understanding of the underlying contact pattern for a susceptible population is advisable before embarking on any strategy for disease control. The objective of this study was to characterise the network of Danish cattle movements over a 10-year period from 2000 to 2009 with a view to understanding: (1) cohesiveness of the network, (2) influential holdings and (3) structural vulnerability of the network.
Network analyses of data involving all cattle movements in Denmark registered during the period of interest were performed. A total of 50,494 premises participated in 4,204,895 individual movements during the 10-year period. The results pointed to a predominantly scale-free structure of the network; though marked by small-world properties in March–April 2001 as well as in 24 other months during the period October 2006 to December 2009. The network was sparsely connected with markets being the key influential holdings. Its vulnerability to removal of markets suggests that targeting highly connected holdings during epidemics should be the focus of control efforts.

2012

Mweu, MM, Nielsen SS, Halasa T, Toft N.  2012.  Annual incidence, prevalence and transmission characteristics of Streptococcus agalactiae in Danish dairy herds. Preventive Veterinary Medicine. 106:244-250. Abstractinc_prev_paper.pdf

Contagious mastitis pathogens continue to pose an economic threat to the dairy industry. An understanding of their frequency and transmission dynamics is central to evaluating the effectiveness of control programmes. The objectives of this study were twofold: (1) to estimate the annual herd-level incidence rates and apparent prevalences of Streptococcus agalactiae (S. agalactiae) in the population of Danish dairy cattle herds over a 10-year period from 2000 to 2009 inclusive and (2) to estimate the herd-level entry and exit rates (demographic parameters), the transmission parameter, ˇ, and recovery rate for S. agalactiae infection.
Data covering the specified period, on bacteriological culture of all bulk tank milk samples collected annually as part of the mandatory Danish S. agalactiae surveillance scheme, were extracted from the Danish Cattle Database and subsequently analysed. There was an increasing trend in both the incidence and prevalence of S. agalactiae over the study period. Per 100 herd-years the value of ˇ was 54.1 (95% confidence interval [CI] 46.0–63.7); entry rate 0.3 (95% CI 0.2–0.4); infection-related exit rate 7.1 (95% CI 5.6–8.9); non-infection related exit rate 9.2 (95% CI 7.4–11.5) and recovery rate 40.0 (95% CI 36.8–43.5). This study demonstrates a need to tighten the current controls against S. agalactiae in order to lower its incidence.

Mweu, MM, Toft N, Katholm J, Nielsen SS.  2012.  Evaluation of two herd-level diagnostic tests for Streptococcus agalactiae using a latent class approach. Veterinary Microbiology. 159:181-186. Abstractdte_paper.pdf

Streptococcus agalactiae mastitis persists as a significant economic problem for the dairy industry in many countries. In Denmark, the annual surveillance programme for this mastitis pathogen initially based only on bacteriological culture of bulk tank milk (BTM) samples, has recently incorporated the use of the real-time PathoProof Mastitis PCR assay with the goal of improving detection of infected herds. The objective of our study was to estimate the herd sensitivity (Se) and specificity (Sp) of both tests of BTM samples using latent class models in a Bayesian analysis while evaluating the effect of herd-level covariates on the Se and Sp of the tests. BTM samples were collected from all 4258 Danish dairy herds in 2009 and screened for the presence of S. agalactiae using both tests. The highest Se of PCR was realized at a cycle threshold (Ct) cut-off value of 40. At this cut-off, the Se of the PCR was significantly higher (95.2; 95% posterior credibility interval [PCI] [88.2; 99.8]) than that of bacteriolog cal culture (68.0; 95% PCI [55.1; 90.0]). However, culture had higher Sp (99.7; 95% PCI [99.3; 100.0]) compared to PCR (98.8; 95% PCI [97.2; 99.9]). The accuracy of the tests was unaffected by the herd-level covariates. We propose that screenings of BTM samples for S. agalactiae be based on the PCR assay with Ct readings of <40 considered as positive. However, for higher Ct values, confirmation of PCR test positive herds by bacteriological culture is advisable especially when the betweenherd prevalence of S. agalactiae is low.

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