Effects of temperature on Renibacterium salmoninarum infection and transmission potential in Chinook salmon, Oncorhynchus tshawytscha (Walbaum).

Renibacterium salmoninarum is a significant pathogen of salmonids and the causative agent of bacterial kidney disease (BKD). Water temperature affects the replication rate of pathogens and the function of the fish immune system to influence the progression of disease. In addition, rapid shifts in temperature may serve as stressors that reduce host resistance. This study evaluated the effect of shifts in water temperature on established R. salmoninarum infections. We challenged Chinook salmon with R. salmoninarum at 12 °C for 2 weeks and then divided the fish into three temperature groups (8, 12 and 15 °C). Fish in the 8 °C group had significantly higher R. salmoninarum-specific mortality, kidney R. salmoninarum loads and bacterial shedding rates relative to the fish held at 12 or 15 °C. There was a trend towards suppressed bacterial load and shedding in the 15 °C group, but the results were not significant. Bacterial load was a significant predictor of shedding for the 8 and 12 °C groups but not for the 15 °C group. Overall, our results showed little effect of temperature stress on the progress of infection, but do support the conclusion that cooler water temperatures contribute to infection progression and increased transmission potential in Chinook salmon infected with R. salmoninarum.

[Rhodococcus equi infections in animals and humans]. / Zakazenia Rhodococcus equi u zwierzat i ludzi.

Little is known about the occurrence of R. equi infection in humans at the present time. However, an increasing number of R. equi infections mainly in immunocompromised patients has been reported recently and R. equi is now considered an emerging zoonotic pathogen. Nevertheless sources and routes of human infection are not fully understood. Recently R. equi was detected in tissues of animals intended for human consumption. Clinical course of infection is often diversified and atypical. The physicians are frequently unaware of R. equi pathogenic potential due to little epidemiological and risk factors data.

Rhodococcus equi infection in foals: the science of 'rattles'.

Infection with Rhodococcus (Corynebacterium) equi is a well-recognised condition in foals that represents a consistent and serious risk worldwide. The condition manifests itself primarily as one of pulmonary abscessation and bronchitis, hence the terminology of 'rattles' derived from its most obvious clinical sign, frequently terminal when first identified. This review addresses the clinical manifestation, bacteriology and pathogenesis of the condition together with recent developments providing knowledge of the organism in terms of virulence, epidemiology, transmission and immune responses. Enhanced understanding of R. equi virulence mechanisms and biology derived from the recently available genome sequence may facilitate the rational development of a vaccine and the improvement of farm management practices used to control R. equi on stud farms in the future. Reliance on vaccines alone, in the absence of management strategies to control the on-farm challenge is likely to be disappointing.

Evaluation of fecal samples from mares as a source of Rhodococcus equi for their foals by use of quantitative bacteriologic culture and colony immunoblot analyses.

OBJECTIVE: To determine whether mares are a clinically important source of Rhodococcus equi for their foals. SAMPLE POPULATION: 171 mares and 171 foals from a farm in Kentucky (evaluated during 2004 and 2005). PROCEDURES: At 4 time points (2 before and 2 after parturition), the total concentration of R equi and concentration of virulent R equi were determined in fecal specimens from mares by use of quantitative bacteriologic culture and a colony immunoblot technique, respectively. These concentrations for mares of foals that developed R equi-associated pneumonia and for mares with unaffected foals were compared. Data for each year were analyzed separately. RESULTS: R equi-associated pneumonia developed in 53 of 171 (31%) foals. Fecal shedding of virulent R equi was detected in at least 1 time point for every mare; bacteriologic culture results were positive for 62 of 171 (36%) mares at all time points. However, compared with dams of unaffected foals, fecal concentrations of total or virulent R equi in dams of foals with R equi-associated pneumonia were not significantly different. CONCLUSIONS AND CLINICAL RELEVANCE: Results indicate that dams of foals with R equi-associated pneumonia did not shed more R equi in feces than dams of unaffected foals; therefore, R equi infection in foals was not associated with comparatively greater fecal shedding by their dams. However, detection of virulent R equi in the feces of all mares during at least 1 time point suggests that mares can be an important source of R equi for the surrounding environment.

A virulent clone of Devriesea agamarum affects endangered Lesser Antillean iguanas (Iguana delicatissima).

Infectious diseases affecting wildlife are drivers of global biodiversity loss. Here we report a bacterial threat to endangered wild reptiles. Since April 2011, a severe skin disease has affected free-ranging, endangered Lesser Antillean iguanas (Iguana delicatissima) on the French Caribbean island of Saint Barthélemy and we identified Devriesea agamarum as the causative agent. The presence of this bacterium was also demonstrated in healthy lizards (anoles) co-inhabiting the island. All isolates from the iguanas corresponded to a single AFLP genotype that until now has exclusively been associated with infections in lizard species in captivity. The clonal relatedness of the isolates and recent emergence of the disease suggest recent arrival of a virulent D. agamarum clone on the island. The presence of healthy but infected lizards suggests the presence of asymptomatic reservoir hosts. This is the first description of a bacterial disease that poses a conservation threat towards free-ranging squamates.

Immunosuppression in progeny of chinook salmon infected with Renibacterium salmoninarum: re-analysis of a brood stock segregation experiment.

Female spawner infection level and temperature variation through rearing are sufficient to explain in-hatchery mortality rates and infection levels and smolt to adult return ratios (SARs) of progeny of Renibacterium salmoninarum infected spring chinook salmon. Data from published reports and manuscripts regarding a 1988 brood stock segregation experiment that held progeny of highly infected female spring chinook salmon spawners separate from progeny of other spawners during 16 mo of hatchery rearing are analyzed to test the hypothesis that immunosuppression could account for differences in survival and infection levels between the 2 segregates. Immunosuppression, caused by the presence of the p57 antigen of R. salmoninarum in sufficient concentration within the salmon egg before spawning, can account for differences in infection levels, mortality rates, and SARs for each hatchery raceway in that study. This immunosuppression may be characterized by immunotolerance, or might only affect cell mediated immunity, which appears the most effective defense mechanism against R. salmoninarum infection, as antibody production can result in tissue damaging antibody-antigen complexes. Low-temperature mediated immunosuppression can account for the nearly identical trajectories of infection and mortality between the 2 segregates during the first 8 mo of hatchery rearing. There is no evidence of widespread vertical infection from spawner to progeny, nor is there evidence that brood stock segregation reduces overall mortality. Rather, the suppression of cell-mediated immune mechanisms may condemn progeny of highly infected female spawners to an almost certain eventual premature demise.

Application of Sartwell's model (lognormal distribution of incubation periods) to age at onset and age at death of foals with Rhodococcus equi pneumonia as evidence of perinatal infection.

The distributions of the incubation periods for infectious and neoplastic diseases originating from point-source exposures, and for genetic diseases, follow a lognormal distribution (Sartwell's model). Conversely, incubation periods in propagated outbreaks and diseases with strong environmental components do not follow a lognormal distribution. In this study Sartwell's model was applied to the age at onset and age at death of foals with Rhodococcus equi pneumonia. The age at onset of clinical signs and age at death were compiled for 107 foals that had been diagnosed with R. equi pneumonia at breeding farms in Argentina and Japan. For each outcome (disease and death), these data followed a lognormal distribution. A group of 115 foals with colic from the University of California were used as a comparison group. The age at onset of clinical signs for these foals did not follow a lognormal distribution. These results were consistent with the hypothesis that foals are infected with R. equi during the 1st several days of life, similar to a point-source exposure.

Dermatophilosis in camels (Camelus dromedarius Linnaeus, 1758) in Kenya.

Natural dermatophilosis (caused by Dermatophilus congolensis Van Saceghem, 1915) has only recently been described in camels (Camelus dromedarius). Further work has shown that the disease is actually widespread. At the Ol Maisor farm where it was first diagnosed (in the Laikipia district of northern Kenya), detailed investigations have revealed that thirty camels (ten calves and twenty adult animals) were infected. The signs varied from mild to more than 50% skin involvement. Patches of wool on the rump were easily detachable with many hard, white crusts. Similarly, another twenty camels from a totally different area of northern Kenya (Samburu district) were found to be infected with D. congolensis. Bacterial isolation was used to confirm the diagnosis. At Ol Maisor farm, twenty sheep were also found to have severe dermatophilosis. There were scabs and many areas of wool shedding. The shed wool had crusts similar to those observed on camels. Experimental infection with D. congolensis isolated from camels was conducted, by means of scarification, on the skin of two goats. The same experimental infection was possible in two calves, taking two weeks to become established. After thirty days there were disseminated foci of infection on the heads of the calves, especially around the eyes. Although these findings cannot show the actual source of D. congolensis, it is possible that the same organism causes dermatophilosis in the different animals.

Characterization of Rhodococcus equi isolates from submaxillary lymph nodes of wild boars (Sus scrofa), red deer (Cervus elaphus) and roe deer (Capreolus capreolus).

Rhodococcus equi is a soil saprophyte and an opportunistic pathogen causing infections in animals, and rarely in humans. The presence of R. equi in tissues and faeces of some wild animal species was demonstrated previously. In this study we characterized R. equi isolates from submaxillary lymph nodes of free-living wild boars (n=23), red deer (n=2) and roe deer (n=2). This is the first description of R. equi strains isolated from tissues of the Cervidae. All isolates were initially recognized as R. equi based on the phenotypic properties. Their identification was confirmed by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry, detection of the choE gene and by sequence analysis of the 16S rRNA and rpoB genes. The presence of three plasmidic genes (traA, vapA and vapB) associated with R. equi virulence was investigated by PCR. In 16 wild boar isolates the traA and vapB genes were detected and they were located on virulence plasmids type 5, 7 or 11. The isolates from cervids and the remaining wild boar isolates were classified as avirulent based on a genotype traA(-)/vapA(-)B(-). In summary, these results confirm that wild boars can be a source of intermediately virulent R. equi strains, and indicate that red deer and roe deer can be a reservoir of avirulent R. equi strains.

Transfer of the virulence-associated protein a-bearing plasmid between field strains of virulent and avirulent Rhodococcus equi.

BACKGROUND: Virulent and avirulent isolates of Rhodococcus equi coexist in equine feces and the environment and are a source of infection for foals. The extent to which plasmid transfer occurs among field strains is ill-defined and this information is important for understanding the epidemiology of R. equi infections of foals. OBJECTIVES: To estimate the frequency of transfer of the virulence plasmid between virulent and avirulent strains of R. equi derived from foals and their environment. ANIMALS: None. METHODS: In vitro study; 5 rifampin-susceptible, virulent R. equi isolates obtained from clinically affected foals or air samples from a farm with a history of recurrent R. equi foal pneumonia were each mixed with 5 rifampin-resistant, avirulent isolates derived from soil samples, using solid medium, at a ratio of 10 donor cells (virulent) per recipient cell. Presumed transconjugates were detected by plating on media with rifampin and colony immunoblotting to detect the presence of the virulence-associated protein A. RESULTS: Three presumed transconjugates were detected among 2,037 recipient colonies, indicating an overall estimated transfer frequency of 0.15% (95% CI, 0.03­0.43%). All 3 transconjugates were associated with a single donor and 2 recipient strains. Genotyping and multiplex PCR of presumed transconjugates demonstrated transfer of the virulence-associated protein A-bearing plasmid between virulent and avirulent R. equi. CONCLUSIONS AND CLINICAL IMPORTANCE: Transfer of the virulence plasmid occurs with relatively high frequency. These findings could impact strategies to control or prevent R. equi through environmental management.

Rhodococcus equi: the many facets of a pathogenic actinomycete.

Rhodococcus equi is a soil-dwelling pathogenic actinomycete that causes pulmonary and extrapulmonary pyogranulomatous infections in a variety of animal species and people. Young foals are particularly susceptible and develop a life-threatening pneumonic disease that is endemic at many horse-breeding farms worldwide. R. equi is a facultative intracellular parasite of macrophages that replicates within a modified phagocytic vacuole. Its pathogenicity depends on a virulence plasmid that promotes intracellular survival by preventing phagosome-lysosome fusion. Species-specific tropism of R. equi for horses, pigs and cattle appears to be determined by host-adapted virulence plasmid types. Molecular epidemiological studies of these plasmids suggest that human R. equi infection is zoonotic. Analysis of the recently determined R. equi genome sequence has identified additional virulence determinants on the bacterial chromosome. This review summarizes our current understanding of the clinical aspects, biology, pathogenesis and immunity of this fascinating microbe with plasmid-governed infectivity.

Gordonia bronchialis sternal wound infection in 3 patients following open heart surgery: intraoperative transmission from a healthcare worker.

We describe an investigation of 3 postoperative Gordonia bronchialis sternal infections. A nurse anesthetist was identified as the source of the outbreak, her scrubs likely becoming contaminated by her home washing machine. The outbreak ended after disposal of the implicated washing machine. Domestic laundering of surgical scrubs may need reevaluation.

Rhodococcus equi pneumonia in the foal--part 1: pathogenesis and epidemiology.

Rhodococcus equi pneumonia is a worldwide infectious disease of major concern to the equine breeding industry. The disease typically manifests in foals as pyogranulomatous bronchopneumonia, resulting in significant morbidity and mortality. Inhalation of aerosolised virulent R. equi from the environment and intracellular replication within alveolar macrophages are essential components of the pathogenesis of R. equi pneumonia in the foal. Recently documented evidence of airborne transmission between foals indicates the potential for an alternative contagious route of disease transmission. In the first of this two-part review, the complexity of the host, pathogen and environmental interactions that underpin R. equi pneumonia will be discussed through an exploration of current understanding of the epidemiology and pathogenesis of R. equi pneumonia in the foal.

Incidence and severity of Arcanobacterium pyogenes injection site abscesses with needle or needle-free injection.

Nursery-age pigs (n=198) were used to evaluate the difference in abscess formation at needle-free jet and conventional needle-and-syringe injection sites. Needle-free jet injection was used to administer injections in the neck and ham on one side of the animal whereas needle-and-syringe was used for neck and ham injections on the opposite side. Immediately prior to injection, the injection site surfaces were contaminated with an inoculum of Arcanobacterium pyogenes. Each pig was humanely euthanized 27 or 28 days after injections. Histopathological results showed that needle-free jet injection was associated with more abscesses than needle-and-syringe injection at both neck (P=0.0625) and ham (P=0.0313) injection sites. Out of 792 injection sites, only 13 abscesses were observed, with 12 of those present at needle-free jet injection sites. Needle-free jet injection may increase the occurrence of injection site abscesses that necessitate carcass trimming at pork processing plants.

Bearded dragons (Pogona vitticeps) asymptomatically infected with Devriesea agamarum are a source of persistent clinical infection in captive colonies of dab lizards (Uromastyx sp.).

Devriesea agamarum causes dermatitis and septicaemia in a variety of lizards, notably those belonging to the genus Uromastyx, whereas other species such as bearded dragons (Pogona vitticeps) seem to be asymptomatic carriers. Using amplified fragment length polymorphism (AFLP), the relatedness between 69 D. agamarum isolates was examined. The isolates derived from 44 diseased lizards, of which 31 belonged to the genus Uromastyx, and from 25 healthy lizards, of which 21 were bearded dragons. Eight AFLP genotypes were obtained, four of which comprised 93% of the isolates. These four genotypes were each present in 2, 2, 8 and 13 different captive colonies. Up to three genotypes were isolated from a single infected colony simultaneously. On two occasions, the same genotype was found in healthy bearded dragons and diseased Uromastyx lizards from the same colony, confirming the role of the former as an asymptomatic source of infection for the latter. Two genotypes, comprising 12 isolates, were exclusively associated with diseased Uromastyx lizards, suggesting strain dependent host adaptation. Finally, D. agamarum was shown to be able to persist for at least seven years in a lizard colony, persistently causing severe disease in several lizard species.

Amblyomma variegatum ticks and the occurrence of bovine streptothricosis in Antigua.

The association between the occurrence of Amblyomma variegatum ticks and streptothricosis was studied on the Caribbean island of Antigua. The prevalence of streptothricosis was higher on animals having A. variegatum ticks compared to that of animals not infested with A. variegatum ticks. There was a steady increase in the prevalence of severe lesions as the level of infestation with adult A. variegatum ticks increased. However the distribution of skin lesions could not be related to the predilection feeding sites of adult A. variegatum ticks.