Within-Flock Population Dynamics of Dichelobacter nodosus.

Footrot causes 70-90% of lameness in sheep in Great Britain. With approximately 5% of 18 million adult sheep lame at any one time, it costs the UK sheep industry £24-84 million per year. The Gram-negative anaerobe Dichelobacter nodosus is the causative agent, with disease severity influenced by bacterial load, virulence, and climate. The aim of the current study was to characterize strains of D. nodosus isolated by culture of swabs from healthy and diseased feet of 99 ewes kept as a closed flock over a 10-month period and investigate persistence and transmission of strains within feet, sheep, and the flock. Overall 268 isolates were characterized into strains by serogroup, proline-glycine repeat (pgr) status, and multi-locus variable number tandem repeat analysis (MLVA). The culture collection contained 87 unique MLVA profiles and two major MLVA complexes that persisted over time. A subset of 189 isolates tested for the virulence marker aprV2 were all positive. The two MLVA complexes (76 and 114) comprised 62 and 22 MLVA types and 237 and 28 isolates, respectively. Serogroups B, and I, and pgrB were associated with MLVA complex 76, whereas serogroups D and H were associated with MLVA complex 114. We conclude that within-flock D. nodosus evolution appeared to be driven by clonal diversification. There was no association (P > 0.05) between serogroup, pgr, or MLVA type and disease state of feet. Strains of D. nodosus clustered within sheep and were transmitted between ewes over time. D. nodosus was isolated at more than one time point from 21 feet, including 5 feet where the same strain was isolated on two occasions at an interval of 1-33 weeks. Collectively, our results indicate that D. nodosus strains persisted in the flock, spread between sheep, and possibly persisted on feet over time.

Survival of the ovine footrot pathogen Dichelobacter nodosus in different soils.

Dichelobacter nodosus (D. nodosus) is the causative agent of footrot in sheep; one of the most important health and welfare issues of sheep worldwide. For control programmes to be effective, it is essential that the transmission cycle of D. nodosus is understood and bacterial reservoirs in the environment are better defined. This study evaluated the survival of D. nodosus in different soils using soil microcosms. Cultivation independent and dependent methods were used to detect D. nodosus over 40 days from seeding in soil. A D. nodosus specific probe was used for quantification by qPCR and viability was assessed by cell permeability to an intercalating dye, PMA, and by culture. Survival varied dramatically depending on soil type, matric potential (MP) and temperature. Our findings indicate that D. nodosus survival was higher at 5 °C compared with 25 °C in all soils and significantly longer at both temperatures in clay soil (>44% clay) compared with other soil types. Survival under all conditions was longer than 30 days for both culture independent and dependent methods, this is substantially longer than previous studies and, if this is an infectious dose, longer than the current recommendation of resting a field for 14 days to prevent onward infection.

Risk and protective factors for recreational and hard drug use among Malaysian adolescents and young adults.

INTRODUCTION: This study investigated risk and protective factors for recreational and hard drug use in Malaysian adolescents and young adults. METHODS: Participants (n = 859; M age = 17.24 years, SD = 2.75 years, range = 13-25 years; 59% male) were recruited from secondary schools, technical colleges, a juvenile detention center and a national training center in Malaysia. A version of the Communities That Care survey validated for use in Malaysia (Razali & Kliewer, 2015) was used to assess study constructs. RESULTS: One in 6 adolescents and 1 in 3 young adults reported lifetime recreational and hard drug use, with greater use reported by males across all drug categories. Structural equation modeling was used to determine the strongest risk and protective factors for recreational and hard drug use. The overall pattern of findings was similar for recreational and hard drug use. Shared risk factors for lifetime recreational and hard drug use included early initiation of antisocial behavior, peer antisocial behavior, and peer reinforcement for engaging in antisocial behavior; shared protective factors included religious practices and opportunities for prosocial school involvement. Multiple group analyses comparing adolescents and young adults indicated that patterns of risk and protective factors predicting drug use differed across these age groups. There were fewer significant predictors of either recreational or hard drug use for young adults relative to adolescents. CONCLUSIONS: Results suggest that interventions should target multiple microsystems (e.g., peer groups, family systems, school environments) and be tailored to the developmental stage of the individual.

The role of the environment in transmission of Dichelobacter nodosus between ewes and their lambs.

Dichelobacter nodosus (D. nodosus) is the essential causative agent of footrot in sheep. The current study investigated when D. nodosus was detectable on newborn lambs and possible routes of transmission. Specific qPCR was used to detect and quantify the load of D. nodosus in foot swabs of lambs at birth and 5-13 h post-partum, and their mothers 5-13 h post-partum; and in samples of bedding, pasture, soil and faeces. D. nodosus was not detected on the feet of newborn lambs swabbed at birth, but was detected 5-13 h after birth, once they had stood on bedding containing naturally occurring D. nodosus. Multiple genotypes identified by cloning and sequencing a marker gene, pgrA, and by multi locus variable number tandem repeat analysis (MLVA) of community DNA from swabs on individual feet indicated a mixed population of D. nodosus was present on the feet of both ewes and lambs. There was high variation in pgrA tandem repeat number (between 3 and 21 repeats), and multiple MLVA types. The overall similarity index between the populations on ewes and lambs was 0.45, indicating moderate overlap. Mother offspring pairs shared some alleles but not all, suggesting lambs were infected from sources(s) other than just their mother's feet. We hypothesise that D. nodosus is transferred to the feet of lambs via bedding containing naturally occurring populations of D. nodosus, probably as a result of transfer from the feet of the group of housed ewes. The results support the hypothesis that the environment plays a key role in the transmission of D. nodosus between ewes and lambs.