Salmonella enterica subspecies diarizonae serovar 61:(k):1,5,(7) as cause of caprine abortion

Occurrence of Salmonella spp. in animal patients and the hospital environment at a veterinary academic hospital in South Africa

Background and Aims

Nosocomial infections caused by Salmonella spp. are common in veterinary facilities. The early identification of high-risk patients and sources of infection is important for mitigating the spread of infections to animal patients and humans. This study investigated the occurrence of Salmonella spp. among patients at a veterinary academic hospital in South Africa. In addition, this study describes the environmental factors that contribute to the spread of Salmonella spp. in the veterinary facility.

Materials and Methods

This study used a dataset of Salmonella-positive animals and environmental samples submitted to the bacteriology laboratory between 2012 and 2019. The occurrence of Salmonella isolates at the veterinary hospital was described based on source, month, season, year, and location. Proportions and 95% confidence intervals were calculated for each variable.

Results

A total of 715 Salmonella isolates were recorded, of which 67.6% (483/715) came from animals and the remainder (32.4%, 232/715) came from environmental samples. The highest proportion (29.2%) of Salmonella isolates was recorded in 2016 and most isolates were reported in November (17.4%). The winter season had the lowest (14.6%) proportion of isolates reported compared to spring (31.3%), summer (27.8%), and autumn (26.4%). Salmonella Typhimurium (20.0%) was the most frequently reported serotype among the samples tested, followed by Salmonella Anatum (11.2%). Among the positive animal cases, most (86.3%) came from equine clinics. Most reported isolates differed based on animal species with S. Typhimurium being common in equines and S. Anatum in bovines.

Conclusion

In this study, S. Typhimurium emerged as the predominant strain in animal and environmental samples. Equines were the most affected animals; however, Salmonella serotypes were also detected in the production animals. Environmental contamination was also a major source of Salmonella species in this study. To reduce the risk of transmission, strict infection prevention and control measures (biosecurity) must be implemented.

[Influence of breed and herd size on the intra-herd prevalence of Salmonella enterica subspecies diarizonae serovar 61: k: 1, 5, (7) in sheep]

SUBJECT AND AIM

At present, only little information is available on the within-flock prevalence of Salmonella enterica subspecies diarizonae serovar 61: k: 1, 5, (7) (SASd) in sheep flocks in Germany as well as their possible influencing factors. The aim of the study was to investigate relationships between flock size, breed and within-flock prevalence.

MATERIAL AND METHODS

A total of 1610 clinically healthy ewes from 14 sheep flocks of 9 different breeds aged 2 to 12 years were microbiologically tested for SASd by nasal swab and fecal samples. Linear multivariable models were used to analyse the associations between within-flock prevalence and farm factors (flock size, breed) or detection frequencies in fecal or nasal swabs.

RESULTS

SASd was detected in all sheep flocks examined, with 75% of adults having at least one positive nasal or fecal result. In comparison to the 11 flocks in which commercial breeds were kept, the 3 flocks of landraces had a lower apparent within-flock prevalence (p=0.01). No association with herd size was evident. With respect to the age of the ewes, there was a negative relationship (p=0.05) with the frequency of detection of SASd in the nasal swab but not in the fecal swab. The health status and fertility performance of the flocks were in line with a normal range for commercial sheep flocks, with lambing losses of 5% to 10% and lambing scores of 130% to 158%.

CONCLUSIONS

Despite the high prevalence of SASd infections particularly within commercial breeds, there was no evidence of a relevant risk to sheep health. Compared with commercial breed flocks, a lower spread of SASd within flocks keeping landraces was evident.

CLINICAL RELEVANCE

Despite a high prevalence, infections with SASd are very unlikely to lead to clinical symptoms or disease. Regulation and monitoring of SASd in sheep are of low priority for animal health authorities.

[Longitudinal study on the time of infection of sheep lambs with Salmonella enterica subspecies diarizonae serovar 61: k: 1, 5, (7)]

OBJECTIVE

Infections with Salmonella enterica subspecies diarizonae serovar 61: k: 1, 5, (7) (SASd) are widespread in sheep. SASd is considered as host associated with low virulence. The aim of the study was to determine the time of infection of lambs after birth with consideration of the Salmonella status of the mother.

MATERIAL AND METHODS

Fecal and nasal swabs from 88 ewes of a flock with known SASd status but unknown intraherd prevalence were examined for SASd in the period of 6 weeks before the beginning of the lambing period. Fecal and nasal swabs from one female lamb from each of these ewes were also examined for SASd at 4-6 time points between the 4th and 50th day of life and at 7, 30 and 40 months of age.

RESULTS

In the first two weeks after birth, significantly more lambs were positive in the nasal swab than in the fecal swab. SASd positive nasal swabs were mainly found in lambs originating from ewes also positive in nasal swabs. 43 lambs remained SASd-negative until day 50 of age. There was no correlation between the SASd status of ewes and their off-spring. At 7 months of age, the number of animals with a positive detection of SASd increased significantly. 32% of the nasal swabs and 62% of the fecal samples were positive for SASd.

CONCLUSIONS

There is no rapid and intensive transmission of SASd from ewes to their offspring. Most likely, the infection begins by colonising the nasal mucosa of the lambs and does not cause any clinical symptoms.

CLINICAL RELEVANCE

Even with a high intraherd prevalence, infections with SASd are very unlikely to cause clinical symptoms.

Genetic features of Salmonella enterica subspecies diarizonae serovar 61:k:1,5 isolated from abortion cases in sheep, United States, 2020

Salmonella enterica subspecies diarizonae serovar 61:(k):1, 5, (7) (sheep associated S. diarizonae, SASd) is the most common Salmonella serotype identified in sheep flocks. Despite the involvement with animal and human infections, there is limited information regarding virulence profiles of SASds and their antibiotic resistance gene complement, particularly for those circulating in the U.S. In this study, we genetically characterized three SASds, 20-265, 20-269, and 20-312, isolated from sheep placental tissues during an abortion storm affecting a flock in Connecticut during 2020. SASds were the only bacteria isolated from analyzed sheep tissues. The isolates were sensitive to all the antibiotics tested, but all these SASd isolates carry the aminoglycoside resistance gene, aac(6')-Iaa, and a chromosomal substitution in the parC gene. The proportion of pseudogenes (5.3-5.5%) was similar among the isolates, and these SASds carry IncX1 type plasmids. Comparing with the SASds isolates from Enterobase, the three isolates showed an identical genomic virulence profile carrying virulence genes in the conserved set of other SASd isolates except for steC, iagB, iacP, sseI, and slrP genes. In the SNP-based phylogenetic analysis, SASd sequences were grouped into group A-C, and the group C was further subdivided into subgroup C1-C6. The three isolates clustered with other SASd isolates from the U.S. and Canada in subgroup C6. SASd isolates in the identical phylogenetic groups tended to have similar geographical origin. The results of our study did not provide conclusive evidence about which are the genetic traits that trigger SASds to become virulent in sheep, but our data will provide a point for comparative studies of this Salmonella serovar.

Complete Genome Sequence of Salmonella enterica subsp. diarizonae Serovar 61:k:1,5,(7) Strain 14-SA00836-0, Isolated from Human Urine

Salmonella enterica subsp. diarizonae serovar 61:k:1,5,(7) is commonly associated with sheep. Occasionally, the serovar has been found to also infect humans. Here, we report the complete genome sequence of strain 14-SA00836-0, isolated from human urine. To our knowledge, this is the first reported complete genome sequence of this serovar isolated from a human clinical sample.

Salmonella enterica subsp. diarizonae serovar 61:k:1,5,(7) is commonly associated with sheep. Occasionally, the serovar has been found to also infect humans. Here, we report the complete genome sequence of strain 14-SA00836-0, isolated from human urine. To our knowledge, this is the first reported complete genome sequence of this serovar isolated from a human clinical sample.