Rhodococcus equi is a bacterial pathogen that primarily affects foals, leading to pneumonia and other systemic infections. It is a significant concern in equine health due to its impact on the respiratory system of young horses. The bacterium is found in soil and can be inhaled by foals, leading to infection. Clinical signs of Rhodococcus equi infection in foals include coughing, fever, and respiratory distress. Diagnosis is typically confirmed through bacterial culture or polymerase chain reaction (PCR) testing. Management of the disease involves antimicrobial therapy and supportive care. This page compiles peer-reviewed research studies and scholarly articles that explore the pathogenesis, diagnosis, treatment, and prevention of Rhodococcus equi infections in horses.
Ganbaatar O, Batbaatar V, Kimura T, Ganzorig S, Tseren-Ochir EO, Suzuki Y, Takai S.ELISA antibody titers against Rhodococcus equi strain ATCC 6939 were measured in serum samples collected from 644 horses aged 1-21 years at 13 provinces and the capital of Mongolia, of which 631 (98%) samples showed values of approximately zero. The mean antibody titers in the 14 areas ranged from -0.08 to -0.01. Nine samples (1.4%) exhibited titers of 0.1-0.2, and surprisingly, four horses (0.6%) each aged 2, 5, 8, and 9 years demonstrated positive values in the range of 0.3-0.8. Considering the age resistance characteristic of this disease, the positive horses were hypothesized to exhibit no...
Ganbaatar O, Ganzorig S, Tseren-Ochir EO, Suzuki Y, Takai S.In 2024, 90 soil samples and 11 fecal samples were collected from nine Mongolian provinces. Using NANAT selective agar, R. equi was successfully isolated from 23 soil samples (25.6%) across five provinces and from three fecal samples (27.3%) collected in two provinces. A total of 122 isolates were identified as R. equi via choE-targeted polymerase chain reaction (PCR) and subsequently screened for virulence-associated genes (vapA, vapB, and vapN) by PCR. Of these, 17 isolates tested positive for the vapA gene, while the remaining 105 isolates were negative for both vapB and vapN. Plasmid prof...
Żychska M, Rzewuska M, Kizerwetter-Świda M, Chrobak-Chmiel D, Stefańska I, Kwiecień E, Witkowski L.The rise of antibiotic resistance is a global health crisis affecting human and veterinary medicine, highlighted within the One Health framework. Horses, classified as both meat and companion animals, play a crucial role in facilitating resistant bacteria spread to humans. Despite increased awareness and reduced antibiotic use in livestock, data on equine antibiotic use and resistance remain limited. This retrospective study examines antimicrobial resistance in 978 bacterial isolates from horses in Poland over 12 years (2010-2022), utilizing data from the Microbiological Diagnostic Laboratory ...
Baptiste KE, Kyvsgaard NC, Ahmed MO, Damborg P, Dowling PM.Rifampin is an enigma among antimicrobials. Blood and tissue compartment concentrations are a "moving target" along the treatment course due to the complex pharmacodynamic interactions within the body. Rifampin concomitant therapies are for the prevention and treatment of Rhodococcus equi infection in foals, for nearly 40 years. The necessity of rifampin concomitant therapies is based on beliefs that both antimicrobials (e.g., rifampin plus macrolide) penetrate into pulmonary abscesses and intracellular compartments above R. equi minimum inhibitory concentrations (MICs), as well as better ef...
Legere RM, Ott JA, Poveda C, Vanover D, Borba KER, Yeon Joo J, Martin CL, da Silveira BP, Bray JM, Landrock K, Wright GA, Blazier JC, Hillhouse AE....Inhalation of Rhodococcus equi causes severe pneumonia in humans and animals worldwide, most commonly affecting horse foals. The standard for preventing R. equi pneumonia in foals is transfusion of hyperimmune plasma, which is expensive and carries the risk of adverse effects. Our goal was to passively immunize foals against R. equi by nebulizing mRNA encoding an equine monoclonal antibody (mAb) against the virulence-associated protein A (VapA) directly into the lungs. VapA-specific memory B cells from an immunized horse were used to identify and select the sequence for an equine immunoglobuli...
da Silveira BP, Kahn SK, Legere RM, Bray JM, Cole-Pfeiffer HM, Golding MC, Cohen ND, Bordin AI.Using a horse foal model, we show that enteral immunization of newborn foals with Rhodococcus equi overcomes neonatal vaccination challenges by reprogramming innate immune responses, inducing R. equi-specific adaptive humoral and cell-mediated immune responses and protecting foals against experimental pneumonia challenge. Foals were immunized twice via gavage of R. equi (immunized group) or saline (control group) at ages 1 and 3 days. At age 28 days, all foals were challenged intrabronchially with R. equi. Post-challenge, all 5 immunized foals remained healthy, whereas 67% (4/6) of control foa...
Ekinci G, Deniz O, Tüfekci E, Timur MC, Onmaz AC, Günes V, Citil M, Keles I, Hoven RVD.Rhodococcus equi (R. equi) is a primary cause of pyogranulomatous pneumonia of foals between three weeks and five months of age. Early diagnosis of rhodococcal pneumonia has always been considered a preferable approach as it can lead to more successful treatment and better outcomes. Horse stud farms where the disease is common, neonatal foals are subjected to tests such as complete blood count and fibrinogen analysis at certain intervals. However, new biomarkers are needed in addition to blood count and fibrinogen measurement in this field for early diagnosis of diseases. Based on this need, i...
da Silveira BP, Cohen ND, Lawhon SD, Watson RO, Bordin AI.Rhodococcus equi causes pyogranulomatous pneumonia in foals and immunocompromised people. Despite decades of research efforts, no vaccine is available against this common cause of disease and death in foals. The purpose of this narrative review is to summarise the current understanding of interactions between R. equi and the host innate immune system, to describe features of the immune response that are associated with resistance or susceptibility to R. equi infection, and help guide strategies for developing novel approaches for preventing R. equi infections. Virulence of R. equi in foals has...
Deniz Ö, Ekinci G, Onmaz AC, Derelli FM, Fazio F, Aragona F, Hoven RVD.Rhodococcus equi (R. equi), a gram-positive facultative intracellular pathogen, is a common cause of pneumonia in foals and represents a major cause of disease and death. The aim of the present study was to investigate the time-depended changes in White Blood Cells (WBC), basophils (Baso), neutrophils (Neu), lymphocytes (Lymf), monocytes (Mon), eosinophils (Eos), platelet (PLT) counts, fibrinogen (Fbg) concentration, interferon (IFN-α, IFN-γ) and interleukins (IL-2 and IL-10) in foals with clinical R. equi pneumonia. The main treatment was with azithromycin-rifampicin for 14 days. Blood was ...
Berghaus LJ, Cathcart J, Berghaus RD, Ryan C, Toribio RE, Hart KA.Rhodococcus equi (R. equi), a pneumonia-causing intracellular bacterium, results in significant morbidity and mortality in young foals, while healthy adult horses rarely develop disease. Survival and replication within alveolar macrophages (AMφ) are the hallmarks of R. equi's pathogenicity. The vitamin D receptor (VDR) and its ligand, the active vitamin D metabolite 1,25(OH)2D, are important in immune responses to intracellular bacteria. The vitamin D/VDR pathway regulates the downstream production of cytokines in infected human AMφ. The immunomodulatory role of the vitamin D/VDR pathway in ...
Legere RM, Poveda C, Ott JA, Bray JM, Villafone EG, Silveira BPD, Kahn SK, Martin CL, Mancino C, Taraballi F, Criscitiello MF, Berghman L, Bordin AI....Design and evaluate immune responses of neonatal foals to a mRNA vaccine expressing the virulence-associated protein A (VapA) of Rhodococcus equi. Methods: Cultured primary equine respiratory tract cells; Serum, bronchoalveolar lavage fluid (BALF), and peripheral blood mononuclear cells (PBMCs) from 30 healthy Quarter Horse foals. Methods: VapA expression was evaluated by western immunoblot in cultured equine bronchial cells transfected with 4 mRNA constructs encoding VapA. The mRNA construct with greatest expression was used to immunize foals at ages 2 and 21 days in 5 groups: (1) 300 μg neb...
Rakowska A, Czopowicz M, Bereznowski A, Witkowski L.Rhodococcus equi is a widely recognized bacterium responsible for pneumonia in preweaned foals. On endemic farms, foals with a subclinical course of the disease usually outnumber those presenting clinical signs. The disease is typically chronic and mainly manifests as fever and dyspnoea. Currently, field diagnosis is often based on lung ultrasound (LUS); however, both diagnostic and therapeutic approaches vary among practitioners and considerably change over time. This longitudinal, prospective study was designed to describe the appearance and progression of rhodococcal pulmonary lesions durin...
Tsuzuki N, Maruko T, Takeyama A, Ikeda H, Mizuguchi Y.Forty-five foals with Rhodococcus equi infection and pneumonia symptoms were classified into a surviving group and a dead group. Using serum samples, the oxidative stress index (OSI) was determined at the first visit and the follow-up visit. The OSI of the surviving group was significantly lower at the follow-up than that at the first visit. No significant difference was observed between the OSI of the dead group at the first and follow-up visits. In the surviving group, treatment at the first visit mitigated inflammation and reduced OSI. However, in the dead group, poor response to the treatm...
Liu L, Yu W, Cai K, Ma S, Wang Y, Ma Y, Zhao H. () is a zoonotic opportunistic pathogen that can cause life-threatening infections. The rapid evolution of multidrug-resistant and the fact that there is no currently licensed effective vaccine against warrant the need for vaccine development. Reverse vaccinology (RV), which involves screening a pathogen's entire genome and proteome using various web-based prediction tools, is considered one of the most effective approaches for identifying vaccine candidates. Here, we performed a pangenome analysis to determine the core proteins of . We then used the RV approach to examine the subcellular l...
Zúñiga MP, Badillo E, Abalos P, Valencia ED, Marín P, Escudero E, Galecio JS.Rhodococcus equi is responsible for foal pneumonia worldwide, with a significant economic impact on the production and breeding of horses. In Chile, the first case was reported in 2000, and since then, its incidence has been increasing. Distinctive characteristics of R. equi as an intracellular pathogen in macrophages, emergence of virulence plasmids encoding surface lipoprotein antigens, and appearance of antibiotic resistance against macrolides and rifampicin have significantly complicated the treatment of R. equi pneumonia in foals. Therefore, in vitro susceptibility studies of first-line a...
Higgins C, Huber L.Rhodococcus equi, a gram-positive facultative intracellular pathogen and a soil saprophyte, is one of the most common causes of pneumonia in young foals. It poses a threat to the economy in endemic horse-breeding farms and to animal welfare annually. Many farms use thoracic ultrasonographic screening and antimicrobial treatment of subclinically affected foals as a preventive measure against severe R. equi infections. The wide use antimicrobials to treat subclinically affected foals has contributed to the emergence of multidrug resistant (MDR)-R. equi in both clinical isolates from sick foals a...
Sanz MG.Foals become infected shortly after birth; most develop subclinical pneumonia and 20% to 30% develop clinical pneumonia that requires treatment. It is now well established that the combination of screening programs based on thoracic ultrasonography and treatment of subclinical foals with antimicrobials has led to the development of resistant Rhodococcus equi strains. Thus, targeted treatment programs are needed. Administration of R equi-specific hyperimmune plasma shortly after birth is beneficial as foals develop less severe pneumonia but does not seem to prevent infection. This article provi...
Hassanpour A, Moghaddam S.Early detection of Rhodococcus equi pneumonia in foals is essential for horse health and for veterinarians. Objective: This study aimed to demonstrate the usefulness of assessing the serum concentration of acute-phase proteins (APPs) in the early diagnosis of pneumonia. Methods: The study evaluated APPs in 19 Arabian foals with R. equi pneumonia and compared them with 18 normal Arabian foals in equestrian clubs in Tabriz, Iran. Affected foals were identified through history, clinical findings and bacterial culture of tracheal washing. Biochemical methods and polymerase chain reaction tests wer...
Sanclemente JL, Rivera-Velez SM, Horohov DW, Dasgupta N, Sanz MG.Foals that develop pulmonary ultrasonographic lesions on Rhodococcus equi (R. equi) endemic farms are treated with antibiotics because those at risk of developing clinical pneumonia (~20%) cannot be recognised early. Candidate biomarkers identified using metabolomics may aid targeted treatment strategies against R. equi. Objective: (1) To describe how foal ageing affects their plasma metabolome (birth to 8 weeks) and (2) to establish the effects that experimental infection with Rhodococcus equi (R. equi) has on foal metabolome. Methods: Experimental study. Methods: Nine healthy newborn foals...
Lord J, Carter C, Smith J, Locke S, Phillips E, Odoi A.Surveillance of antimicrobial resistance (AMR) among veterinary pathogens is necessary to identify clinically relevant patterns of AMR and to inform antimicrobial use practices. Streptococcus equi subsp. zooepidemicus and Rhodococcus equi are bacterial pathogens of major clinical importance in horses and are frequently implicated in respiratory tract infections. The objectives of this study were to describe antimicrobial resistance patterns and identify predictors of AMR and multidrug resistance (MDR) (resistance to three or more antimicrobial classes) among equine S. zooepidemicus and R. equi...
Sangal V, Goodfellow M, Jones AL, Sutcliffe IC.Opinion 106 of the Judicial Commission has clarified the nomenclature of the taxon variously named , ' and . As a consequence, we present here the genus name and that of its nomenclatural type species, comb. nov., for valid publication and propose the reclassification of four rhodococcal species as novel combinations in the genus, namely Guo et al. 2015 comb. nov., Kämpfer . 2014 comb. nov., Li . 2015 comb. nov. and Lee . 2019 comb. nov. In addition, we note that a clinical isolate, strain 86-07 (=W8901), likely represents an additional species within the genus . Nearly a century after ...
Xu Z, Hao X, Li M, Luo H.Rhodococcus equi (R. equi) is a Gram-positive coccobacillus that causes pneumonia in foals of less than 3 months, which have the ability of replication in macrophages. The ability of R. equi persist in macrophages is dependent on the virulence plasmid pVAPA. Gram-positive extracellular vesicles (EVs) carry a variety of virulence factors and play an important role in pathogenic infection. There are few studies on R. equi-derived EVs (R. equi-EVs), and little knowledge regarding the mechanisms of how R. equi-EVs communicate with the host cell. In this study, we examine the properties of EVs prod...
Val-Calvo J, Darcy J, Gibbons J, Creighton A, Egan C, Buckley T, Schmalenberger A, Fogarty U, Scortti M, Vázquez-Boland JA.A multidrug-resistant clone of the animal and human pathogen Rhodococcus equi, MDR-RE 2287, has been circulating among equine farms in the United States since the 2000s. We report the detection of MDR-RE 2287 outside the United States. Our finding highlights the risk for MDR-RE spreading internationally with horse movements.
Rivera-Velez A, Huber L, Sinha S, Cohen ND.Rhodococcus equi is a common cause of severe pneumonia in foals. Emergence of macrolide-resistant R. equi isolated from foals and their environment has been reported in the United States. A novel erm(51) gene was recently identified in R. equi in soil from horse farms in Kentucky. Our objective was to determine the effect of the erm(51) gene and associated rpoB mutation on the fitness of multidrug resistant-R. equi (MDR-R. equi) under different nutrient conditions. Bacterial growth curves were generated for 3 MDR-R. equi isolates and 3 wild-type (WTN) R. equi isolates recovered from environmen...
Kahn SK, Cohen ND, Bordin AI, Coleman MC, Heird JC, Welsh TH.The bacterium Rhodococcus equi causes pneumonia in foals that is prevalent at breeding farms worldwide. In the absence of an effective vaccine, transfusion of commercial plasma from donor horses hyperimmunised against R. equi is used by many farms to reduce the incidence of pneumonia among foals at farms where the disease is endemic. The effectiveness of hyperimmune plasma for controlling R. equi pneumonia in foals has varied considerably among reports. The purposes of this narrative review are: (1) to review early studies that provided a foundational basis for the practice of transfusion of h...
Salek Ardestani S, Zandi MB, Vahedi SM, Janssens S.The genetic structure and characteristics of Iranian native breeds are yet to be comprehensibly investigated and studied. Therefore, we employed genomic information of 364 Iranian native horses representing the Asil (n = 109), Caspian (n = 40), Dareshuri (n = 44), Kurdish (n = 95), and Turkoman (n = 76) breeds to reveal the genetic structure and characteristics. For these and 19 other horse breeds, principal component analysis, Bayesian model-based, Neighbor-Net, and bootstrap-based TreeMix approaches were applied to investigate and compare their genetic structure. Additionally, thre...
Takai S, Ohashi M, Suzuki Y, Sasaki Y, Kakuda T, Broens EM, Wagenaar JA, van Duijkeren E.Clinical samples from 123 foals with suspected rhodococcosis submitted to the Veterinary Microbiological Diagnostic Centre of the Faculty of Veterinary Medicine between 1993 and 2006 were tested for the presence of the virulence gene vapA. Of the 123 samples, 120 were vapA-positive and 3 vapA-negative Rhodococcus equi were isolated. The 120 vapA-positive R. equi were isolated from 70 tracheal wash, 19 lung tissues, 7 lymph nodes, 6 synovial fluids, 13 abscesses or pus and single isolates from the uterus, gut, cerebrospinal fluid, abdomen fluid and faeces. Of the 120 isolates, 46 were from Dutc...
Narváez SÁ, Fernández I, Patel NV, Sánchez S. is an important veterinary pathogen that takes the lives of many foals every year. With the emergence and spread of MDR to current antimicrobial treatment, new tools that can provide a fast and accurate diagnosis of the disease and antimicrobial resistance profile are needed. Here, we have developed and analytically validated a multiplex qPCR for the simultaneous detection of and related macrolide resistance genes in equine respiratory samples. The three sets of oligos designed in this study to identify housekeeping gene and macrolide resistance genes (46) and (51) showed high analytic se...
Cohen ND, Flores-Ahlschewde P, Gonzales GM, Kahn SK, da Silveira BP, Bray JM, King EE, Blair CC, Bordin AI.Diagnostic accuracy of real-time, quantitative PCR (qPCR) assays to quantify virulent Rhodococcus equi using rectal swab samples has not been systematically evaluated. Objective: To evaluate the accuracy of qPCR of rectal swab samples to differentiate foals with pneumonia from healthy foals of similar age from the same environment. Methods: One hundred privately owned foals born in 2021 from 2 farms in New York. Methods: An incident case-control study design was used. Rectal swabs were collected from all foals diagnosed with R. equi pneumonia at 2 horse-breeding farms (n = 47). Eligible pneu...
Suzuki Y, Takai S, Kubota H, Hasegawa N, Ito S, Yabuuchi Y, Sasaki Y, van Duijkeren E, Kakuda T.Rhodococcus equiis the causative agent of pyogenic pneumonia in foals, and a virulence-associated protein A (VapA) encoded on the pVAPA virulence plasmid is important for its pathogenicity. In this study, we analyzed the virulence of R. equi strain U19, originally isolated in the Netherlands in 1997 and the genetic characteristics of the pVAPA_U19 plasmid. U19 expressed VapA that was regulated by temperature and pH and underwent significant intracellular proliferation in macrophages. The restriction fragment length polymorphism of pVAPA_U19 digested with EcoRI was similar to that of pREAT701 (...
Prescott JF.Recent isolations of Rhodococcus equi from cavitatory pulmonary disease in patients with AIDS have aroused interest among medical microbiologists in this unusual organism. Earlier isolations from humans had also been in immunosuppressed patients following hemolymphatic tumors or renal transplantation. This organism has been recognized for many years as a cause of a serious pyogranulomatous pneumonia of young foals and is occasionally isolated from granulomatous lesions in several other species, in some cases following immunosuppression. The last decade has seen many advances in understanding o...
Hondalus MK, Mosser DM.Rhodococcus equi is a facultative intracellular bacterium of macrophages that can cause serious pneumonia in both young horses and immunocompromised people. Essential to understanding rhodococcus pathogenesis is a quantitative documentation of the intracellular events that follow macrophage phagocytosis of the organism. By using a bacterial immunofluorescence staining assay, we verified the intracellular survival and replicative potential of R. equi in both murine peritoneal macrophages and equine alveolar macrophages in vitro. Following an initial lag period of 6 to 12 h, the intracellular nu...
Takai S.An overview of epidemiology of R. equi infection in foals is presented, emphasizing the importance of the virulence-associated antigens and plasmids as epidemiological markers. The monoclonal antibody-based colony blot test has been developed to identify rapidly and accurately virulent R. equi. Epidemiological studies conducted during the recent 5 years have revealed that: (1) avirulent R. equi are widespread in the feces of horses and their environment on every farm; (2) the feces of horses and the environment of the horse farms having endemic R. equi infections demonstrated heavy contaminati...
von Bargen K, Haas A.The soil actinomycete Rhodococcus equi is a pulmonary pathogen of young horses and AIDS patients. As a facultative intracellular bacterium, R. equi survives and multiplies in macrophages and establishes its specific niche inside the host cell. Recent research into chromosomal virulence factors and into the role of virulence plasmids in infection and host tropism has presented novel aspects of R. equi infection biology and pathogenicity. This review will focus on new findings in R. equi biology, the trafficking of R. equi-containing vacuoles inside host cells, factors involved in virulence and ...
Takai S, Koike K, Ohbushi S, Izumi C, Tsubaki S.Antigens of Rhodococcus equi were analyzed by immunoblotting with naturally infected foal sera. Immunoblots of whole-cell antigen preparations of clinical isolates of R. equi revealed that major protein bands with molecular masses of 15 to 17 kDa were present in all clinical isolates tested and all isolates virulent for mice. In contrast, the 15- to 17-kDa antigens were not identified by immunoblotting in ATCC 6939, a type strain of R. equi that was avirulent for mice. Whole-cell antigens of 102 environmental isolates were investigated by immunoblotting and the mouse pathogenicity test. Twenty...
Meijer WG, Prescott JF.Rhodococcus equi is an important cause of subacute or chronic abscessating bronchopneumonia of foals up to 3-5 months of age. It shares the lipid-rich cell wall envelope characteristic of the mycolata, including Mycobacterium tuberculosis, as well as the ability of pathogenic members of this group to survive within macrophages. The possession of a large virulence plasmid in isolates recovered from pneumonic foals is crucial for virulence. The plasmid contains an 27 kb pathogenicity island (PI) that encodes seven related virulence-associated proteins (Vaps), including the immunodominant surface...
Vázquez-Boland JA, Giguère S, Hapeshi A, MacArthur I, Anastasi E, Valero-Rello A.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 fo...
Giguère S, Cohen ND, Chaffin MK, Hines SA, Hondalus MK, Prescott JF, Slovis NM.Pneumonia is a major cause of disease and death in foals. Rhodococcus equi, a gram-positive facultative intracellular pathogen, is a common cause of pneumonia in foals. This article reviews the clinical manifestations of infection caused by R. equi in foals and summarizes current knowledge regarding mechanisms of virulence of, and immunity to, R. equi. A complementary consensus statement providing recommendations for the diagnosis, treatment, control, and prevention of infections caused by R. equi in foals can be found in the same issue of the Journal.
Slovis NM, Elam J, Estrada M, Leutenegger CM.Diarrhoea caused by infectious agents is common in foals but there is no comprehensive molecular work-up of the relative prevalence of common agents and appearance of coinfections. Objective: To determine the prevalence of 9 infectious agents in gastrointestinal (GI)-diseased and healthy foals with ages ranging from 1 to 20 weeks of age and to what degree coinfections are associated with clinical signs of GI disease. Methods: Retrospective controlled observational study. Methods: The population consisted of 88 Thoroughbred foals aged 2 days to 17 weeks born on 32 different studfarms in Kentuck...
Hondalus MK.Inhalation of the soil-borne organism, Rhodococcus equi, can lead to a chronic and severe pyogranulomatous pneumonia in young horses and immunocompromised people. In addition, ulcerative colitis is a common sequela to infection in foals, and dissemination from the lung to other body sites is not uncommon in either the horse or man. Although the facultative intracellular bacterium is susceptible to neutrophil-mediated killing, it is able to resist innate macrophage defenses and establish residence within the intracellular environment of that phagocyte. Definitive virulence factors of R. equi ha...
Burton AJ, Giguère S, Sturgill TL, Berghaus LJ, Slovis NM, Whitman JL, Levering C, Kuskie KR, Cohen ND.Macrolide and rifampin resistance developed on a horse breeding farm after widespread use was instituted for treatment of subclinical pulmonary lesions in foals. Resistance occurred in 6 (24%) of 25 pretreatment and 8 (62%) of 13 (62%) posttreatment isolates from affected foals. Drug-resistant isolates formed 2 distinct genotypic clusters.
Giguère S, Cohen ND, Chaffin MK, Slovis NM, Hondalus MK, Hines SA, Prescott JF.Rhodococcus equi, a gram-positive facultative intracellular pathogen, is one of the most common causes of pneumonia in foals. Although R. equi can be cultured from the environment of virtually all horse farms, the clinical disease in foals is endemic at some farms, sporadic at others, and unrecognized at many. On farms where the disease is endemic, costs associated with morbidity and mortality attributable to R. equi may be very high. The purpose of this consensus statement is to provide recommendations regarding the diagnosis, treatment, control, and prevention of infections caused by R. equi...
Tkachuk-Saad O, Prescott J.Fifty-four strains of Rhodococcus equi from different clinical sources (mainly horses and pigs) were examined for their plasmid content by two screening methods. Plasmids were detected in 49 of 54 strains. A plasmid of approximately 80 kb was isolated from 21 of 22 isolates from horses and 20 of 28 isolates from pigs, and a 105-kb plasmid was isolated from 7 of 28 isolates from pigs. The 80-kb plasmid was significantly associated with strains of equine rather than porcine origin, and the 105-kb plasmid was significantly associated with strains of porcine origin. The type strain, ATCC 6939, con...
Giguère S, Prescott JF.Since the 1986 Rhodococcus equi workshop, there have been major breakthroughs in understanding the epidemiology of, the virulence of, and the immune response to, this intriguing pathogen. However, with the exception of the use of hyperimmune plasma for the prevention of the disease (Martens et al., 1989; Madigan et al., 1991) the clinical aspects of R. equi infections have essentially remained unchanged. This article reviews the various clinical manifestations and summarizes recent advances in diagnosis, treatment and prevention of R. equi infections in foals.
Giguère S, Lee E, Williams E, Cohen ND, Chaffin MK, Halbert N, Martens RJ, Franklin RP, Clark CC, Slovis NM.To determine the prevalence of antimicrobial resistance to macrolide antimicrobials or rifampin in Rhodococcus equi isolates and to describe treatment outcome in foals infected with antimicrobial-resistant isolates of R equi. Methods: Cross-sectional study. Methods: 38 isolates classified as resistant to macrolide antimicrobials or rifampin received from 9 veterinary diagnostic laboratories between January 1997 and December 2008. Methods: For each isolate, the minimum inhibitory concentration of macrolide antimicrobials (ie, azithromycin, erythromycin, and clarithromycin) and rifampin was dete...
Breathnach CC, Sturgill-Wright T, Stiltner JL, Adams AA, Lunn DP, Horohov DW.The increased vulnerability of foals to specific pathogens such as Rhodococcus equi is believed to reflect an innate immunodeficiency, the nature of which remains poorly understood. Previous studies have demonstrated that neonates of many species fail to mount potent Th1 responses. The current research investigates the ability of circulating and pulmonary lymphocytes of developing foals to produce interferon gamma (IFNgamma). Peripheral blood mononuclear cells (PBMC) were prepared from up to 10 horse foals at regular intervals throughout the first 6 months of life. Bronchoalveolar lavage (BAL)...
van der Geize R, Grommen AW, Hessels GI, Jacobs AA, Dijkhuizen L.Rhodococcus equi causes fatal pyogranulomatous pneumonia in foals and immunocompromised animals and humans. Despite its importance, there is currently no effective vaccine against the disease. The actinobacteria R. equi and the human pathogen Mycobacterium tuberculosis are related, and both cause pulmonary diseases. Recently, we have shown that essential steps in the cholesterol catabolic pathway are involved in the pathogenicity of M. tuberculosis. Bioinformatic analysis revealed the presence of a similar cholesterol catabolic gene cluster in R. equi. Orthologs of predicted M. tuberculosis vi...
Zink MC, Yager JA, Prescott JF, Fernando MA.It has been suggested that R. equi causes pulmonary disease in foals by persisting within the lung as a facultative intracellular parasite of alveolar macrophages. This paper describes an ultrastructural study of the intracellular events after ingestion of R. equi by foal alveolar macrophages, in an attempt to determine the mechanism of intracellular survival of R. equi. Secondary lysosomes of alveolar macrophages recovered from foals by bronchoalveolar lavage were labelled with electron-dense ferritin, and the cells were challenged with either viable or formalin-killed R. equi. After 0-, 3-, ...
Hillidge CJ.The selection of lipid-soluble antibiotics capable of intracellular penetration is considered critical for the successful treatment of Rhodococcus equi pneumonia and lung abscesses in foals. Two such antibiotics: erythromycin (25 mg kg-1, three times daily) and rifampin (5 mg kg-1 twice daily) have been used in combination for this purpose at the University of Florida since 1981. Positive evidence of R. equi was present on culture of tracheal aspirates in 57 foals, most of which exhibited radiographic evidence of extensive lung abscessation. The duration of therapy ranged from 4 to 9 weeks. Mi...
Perkins GA, Wagner B.The development of equine immunity from the fetus to adulthood is complex. The foal's immune response and the immune mechanisms that they are equipped with, along with changes over the first months of life until the immune system becomes adult-like, are only partially understood. While several innate immune responses seem to be fully functional from birth, the onset of adaptive immune response is delayed. For some adaptive immune parameters, such as immunoglobin (Ig)G1, IgG3, IgG5 and IgA antibodies, the immune response starts before or at birth and matures within 3 months of life. Other antib...
Byrne BA, Prescott JF, Palmer GH, Takai S, Nicholson VM, Alperin DC, Hines SA.Rhodococcus equi causes severe pyogranulomatous pneumonia in foals. This facultative intracellular pathogen produces similar lesions in immunocompromised humans, particularly in AIDS patients. Virulent strains of R. equi bear a large plasmid that is required for intracellular survival within macrophages and for virulence in foals and mice. Only two plasmid-encoded proteins have been described previously; a 15- to 17-kDa surface protein designated virulence-associated protein A (VapA) and an antigenically related 20-kDa protein (herein designated VapB). These two proteins are not expressed by t...
Hietala SK, Ardans AA.The interaction of Rhodococcus equi with alveolar macrophages from adult horses, foals experimentally exposed to R. equi (sensitized foals) and non-exposed foals was studied using in vitro bactericidal assays, cytochemical staining and transmission electron microscopy. It was demonstrated that R. equi is a facultative intracellular parasite, able to survive and multiply within the alveolar macrophages of the host by interfering with phagosome-lysosome fusion. Opsonization of R. equi with antibody against capsular components was associated with increased phagosome-lysosome fusion and significan...
Takai S, Ohbushi S, Koike K, Tsubaki S, Oishi H, Kamada M.The prevalence of virulent Rhodococcus equi in isolates from soil and feces of foals on a farm with endemic R. equi infections was significantly higher than that of a farm with no history of the disease. Foals bred on a farm with the endemic disease might be constantly exposed to virulent R. equi in their environment.
Hultén C, Demmers S.Differentiation between infectious and noninfectious disease and rapid initiation of accurate treatment are essential in managing diseases in the neonatal and young foal. Identification of useful inflammatory markers for these purposes is, therefore, of great importance. The aim of this study was to compare the responses of the acute phase protein serum amyloid A (SAA) with the responses of fibrinogen and total leucocyte and neutrophil counts in infectious diseases encountered in the young foal, and to assess whether SAA measurements give additional information useful in the management of thes...
Ashour J, Hondalus MK.Rhodococcus equi is a facultative intracellular opportunistic pathogen of immunocompromised people and a major cause of pneumonia in young horses. An effective live attenuated vaccine would be extremely useful in the prevention of R. equi disease in horses. Toward that end, we have developed an efficient transposon mutagenesis system that makes use of a Himar1 minitransposon delivered by a conditionally replicating plasmid for construction of R. equi mutants. We show that Himar1 transposition in R. equi is random and needs no apparent consensus sequence beyond the required TA dinucleotide. The...
Cywes-Bentley C, Rocha JN, Bordin AI, Vinacur M, Rehman S, Zaidi TS, Meyer M, Anthony S, Lambert M, Vlock DR, Giguère S, Cohen ND, Pier GB.Immune correlates of protection against intracellular bacterial pathogens are largely thought to be cell-mediated, although a reasonable amount of data supports a role for antibody-mediated protection. To define a role for antibody-mediated immunity against an intracellular pathogen, Rhodococcus equi, that causes granulomatous pneumonia in horse foals, we devised and tested an experimental system relying solely on antibody-mediated protection against this host-specific etiologic agent. Immunity was induced by vaccinating pregnant mares 6 and 3 weeks prior to predicted parturition with a conjug...
Martens RJ, Martens JG, Fiske RA, Hietala SK.The immunoprophylactic capacity of specific immune plasma was evaluated in pony foals infected experimentally with Rhodococcus equi. Immune plasma, produced by repeated parenteral administration of viable R. equi to adult horses, was harvested and frozen. Group I (six control foals) and Group II (six principal foals) received lactated Ringers solution and immune plasma respectively at three and five days of age. R. equi were aerosolised into a caudal lung lobe of all foals at seven days of age. Clinical signs, haematological alterations, immune responses, thoracic radiographs and technetium99m...
Huber L, Giguère S, Slovis NM, Carter CN, Barr BS, Cohen ND, Elam J, Erol E, Locke SJ, Phillips ED, Smith JL.The objective of this study was to determine the prevalence of strains resistant to macrolides and rifampin over time in clinical samples from foals submitted to diagnostic laboratories in central Kentucky. We performed a retrospective observational study of all clinical samples from foals that were submitted to veterinary diagnostic laboratories in Kentucky between January 1995 and December 2017. Samples were included if the bacterium was cultured and tested for susceptibility to erythromycin or rifampin. susceptibility testing to erythromycin was available for 2,169 isolates of , while s...
Yager JA.The pathogenesis of Rhodococcus equi pneumonia in foals is reviewed. The main routes of infection are respiratory and alimentary. The latter is probably the chief route of exposure in all foals and probably leads to development of specific immunity. Susceptible foals, those whose maternal immunity wanes before generation of their own immune response, readily develop disease if exposed aerogenously to sufficient numbers of R. equi. Management and environmental circumstances have a major role to play in determining the magnitude of this challenge and, therefore, in the prevalence of the disease....
Barton MD, Hughes KL.A selective broth enrichment technique was used to study the distribution of Rhodococcus equi in soil and grazing animals. Rhodococcus equi was isolated from 54% of soils examined and from the gut contents, rectal faeces and dung of all grazing herbivorous species examined. Rhodococcus equi was not isolated from the faeces or dung of penned animals which did not have access to grazing. The isolation rate from dung was much higher than from other samples and this was found to be due to the ability of R. equi to multiply more readily in dung. Delayed hypersensitivity tests were carried out on ho...
