Update on Streptococcus equi subsp equi Infections

Streptococcus hepaticus sp. nov. isolated from the liver of domestic pigs (Sus scrofa domesticus)

A Gram-positive coccus-shaped bacterium, which could not be identified by classical determinative bacteriology approaches, was isolated from the liver of two pigs in the United Kingdom. Initial testing based on cellular morphology and biochemical characteristics tentatively assigned the isolates to the genus Streptococcus but did not match any previously described species. The analysis of the 16S rRNA sequence determined that the isolates were most closely related to Streptococcus gallinaceus (98.6% identity). Analysis of three further housekeeping genes frequently applied in streptococcal taxonomy, groEL, sodA and rpoB, and a comparison against available type strain sequences confirmed that the isolates were most similar to S. gallinaceus in all cases (84.3%, 86.9% and 90.2% identity, respectively). The comparison of the average nucleotide identity (ANI) and in silico DNA-DNA hybridization values demonstrated that the novel species was distinct from other streptococcal species. Pairwise ANI values revealed that the two studied strains shared a pairwise ANI of 99.25% but were clearly distinct from previously described Streptococcus species (ANI ≤81.1% - best match S. gallinaceus). The taxonomic analysis described confirmed that the two strains represent a novel Streptococcus species for which the name Streptococcus hepaticus sp. nov. is suggested, with strain 20-1249T (=NCTC 15092T=LMG 33498T) as the type strain.

Variation in SeM genotype is associated with virulence of Streptococcus equi subspecies equi in mice

Strangles is a common infectious disease caused by Streptococcus equi subspecies equi (S. equi) that primarily affects the upper respiratory system. To date, 271 alleles of the M protein (seM) have been identified that may be related to antigenic differences of isolates. This study evaluated the virulence of S. equi isolates from different alleles of the M protein in an experimental mouse model. Thirty-six Swiss mice were allocated into 12 groups (G1-G12) and each infected group received a different isolate of S. equi recovered from horses with strangles: G1: seM-117; G2: seM-61; G3: seM-123; G4: seM-115; G5: seM-271; G6: seM-124; G7: seM-158, and G8: seM-39, G9: no allele, G10: seM-28, G11: control (no infection - Brazil), G12: control (no infection - Texas). Mice were infected intranasally with 2 × 106 CFU/mL and monitored for clinical signs, weight, and nasal culture over 10 days. Clinical signs varied among mice inoculated with different isolates of S. equi, ranging from lethargy, serous ocular discharge, and rhinitis to tachypnea and neurological alterations. Isolates from alleles seM-158 (G7), seM-39 (G8), and seM-271 (G5) were classified as highly virulent, frequently resulting in death or euthanasia, along with consistent bacterial excretion and enlargement of lymph nodes. Mice in G4 (seM-115), G6 (seM-124), G9 (no allele), and G10 (seM-28) showed moderately severe clinical signs of disease, whereas clinical signs for mice in G1 (seM-117), G2 (seM-61), and G3 (seM-123) were mild or absent. Results demonstrate that isolates of S. equi with different M protein alleles exhibit varying levels of virulence in mice, ranging from asymptomatic infection to severe illness and mortality. Additional investigations should be conducted to assess whether virulence in horses is associated with S. equi M protein variability and whether the association of M protein genotype with virulence is causal.

Myosin Heavy Chain Myopathy and Immune-Mediated Muscle Disorders

Several inflammatory myopathies have an infectious or immune-mediated basis in the horse. Myosin heavy chain myopathy is caused by a codominant missense variant in MYH1 and has 3 clinical presentations: immune-mediated myositis, calciphylaxis, and nonexertional rhabdomyolysis in Quarter Horse-related breeds. An infarctive form of purpura hemorrhagica affects numerous breeds, presenting with focal firm, painful muscle swelling, and subsequent infarction of multiple tissues. While Streptococcus equi equi is often the inciting cause, anaplasmosis, sarcocystis, piroplasmosis, viruses, and vaccines can also be inciting agents. This article describes the diagnosis, pathophysiology, and treatment of these inflammatory myopathies.

Streptococcus equi subspecies equi from strangles suspected equines: molecular detection, antibiogram profiles and risk factors

Strangles, caused by Streptococcus equi subspecies equi, is a highly infectious disease of equines causing major health issues and financial losses. The aim of the study was to detect the presence of the SeM gene in Streptococcus equi isolated from equine suspected of having strangles. A cross-sectional study design was conducted from July to December 2022 in five districts of the central Gondar zone, Ethiopia. One-hundred sixty swab samples were taken from animals that had been clinically suspected. The SeM gene was detected using polymerase chain reaction, and the antimicrobial susceptibility test was performed using the Kirby-Bauer disc diffusion method. The binary logistic regression model was employed to test for statistical significance. In 31.87% (51/160) of the samples, Streptococcus equi species were isolated, and 31.37% (16/51) of these species carried the SeM gene. There was a significant amount of tetracycline (81.5%), erythromycin (81.5%), and vancomycin (75.5%) resistance among the 16 isolates. Strangles were more likely to be present in animals who shared feed containers (AOR = 7.59; 95% CI = 1.44-39.93), drank from the same water troughs (AOR = 7.74; 95% CI = 1.44-41.01), and spent the night together (AOR = 5.97; 95% CI 1.41-25.37). The findings of this study showed that the research areas harboured Streptococcus equi subspecies equi. Sharing feed containers and water troughs were potential sources of strangles infection; thus, these containers need to be cleaned regularly.

Development of a Real-Time Recombinase-Aided Amplification Method for the Rapid Detection of Streptococcus equi subsp. equi

Streptococcus equi subspecies equi (S. equi) is the causative pathogen of strangles in horses, donkeys, and other equine animals. Strangles has spread globally and causes significant losses to the horse industry. In response to the urgent need for effective disease control, this study introduces a novel nucleic acid diagnostic method known as a real-time recombinase-assisted amplification (RAA) assay, developed based on the eqbE gene, for the rapid detection of S. equi nucleic acid. The real-time RAA method employs specifically designed probes and primers targeting the eqbE gene, enhancing the overall specificity and sensitivity of the detection. After efficiency optimization, this real-time RAA method can detect 10 or more copies of nucleic acid within 20 min. The method demonstrates high specificity for S. equi and does not cross-react with other clinically relevant pathogens. Real-time RAA diagnostic performance was evaluated using 98 nasal swab samples collected from horses and compared with the real-time PCR detection method. Results revealed that 64 and 65 samples tested positive for S. equi using real-time RAA and real-time PCR, respectively. The overall agreement between the two assays was 96.94% (95/98), with a kappa value of 0.931 (p < 0.001). Further linear regression analysis indicated a significant correlation in the detection results between the two methods (R2 = 0.9012, p < 0.0001), suggesting that the real-time RAA assay exhibits a detection performance comparable to that of real-time PCR. In conclusion, the real-time RAA assay developed here serves as a highly specific and reliable diagnostic tool for the detection of S. equi in equine samples, offering a potential alternative to real-time PCR methods. In conclusion, the real-time RAA nucleic acid diagnostic method, based on the eqbE gene, offers rapid and accurate diagnosis of S. equi, with the added advantage of minimal equipment requirements, thus contributing to the efficient detection of strangles in horses.

Strangles in equines: An overview

Strangles, caused by Streptococcus equi subspecies equi, is a highly infectious respiratory disease affecting horses and other equines. The disease is economically important and compromises the productivity of equine farm significantly. The disease is characterized by pyrexia, mucopurulent nasal discharge, and abscess formation in the lymph nodes of the head and neck of horses. The disease transmission occurs either directly by coming in contact with infectious exudates or indirectly via fomite transmission. Besides this, carrier animals are the primary and most problematic source of disease infection. The organism not only initiates outbreaks but also makes the control and prevention of the disease difficult. The diagnosis of strangles is best done by isolating and characterizing the bacteria from nasal discharge, pus from abscesses, and lymphoid tissues or by using PCR. ELISA can also be used to detect serum protein M (SeM) antibodies for diagnosis. The most popular treatment for strangles is with penicillin; however, the treatment is affected by the stage, feature and severity of the disease. Prevention and control of strangles can be achieved through vaccination and good hygiene practices. Basically, this review describes the global prevalence of S. equi, as well as general aspects of the disease, like pathogenesis, diagnosis, treatment, prevention, control and management of the disease.

Vancomycin resistant Streptococcus equi subsp. equi isolated from equines suffering from respiratory manifestation in Egypt

Background and Aim:

Upper respiratory tract infections are common in horses and can be caused by a variety of pathogens, mainly Streptococcus equi subsp. equi, which are a significant equine pathogen causing major health issues as well as financial losses to the equine industry. This study aimed to determine the prevalence of Streptococcal bacteria in equines in Egypt, and characterize vancomycin-resistant S. equi subsp. equi phenotypically and genotypically.

Materials and Methods:

S. equi subsp. equi was isolated from internal nares of horses. All strains were confirmed by polymerase chain reaction-based detection of Streptococcus genus-specific 16S rRNA, sodA and seeI genes. Antibiotic susceptibility was determined phenotypically using the disk diffusion method. Genotypic detection of antibiotic resistance genes was performed by analyzing as b-lactamase resistance (blaZ), tetracycline resistance (tetK), vancomycin resistance (vanA), and chloramphenicol resistance (fexA).

Results:

Eight streptococcal isolates were confirmed as S. equi subsp. equi. The genotypic characterization of antibiotic resistance showed resistance to vanA and tetK, with a frequency of 87.5% and 12.5%, respectively, while the frequency of sensitivity was 100% for blaz gene and fexA gene.

Conclusion:

In this study, we assessed vancomycin-resistant S. equi subsp. equi from equines suffering from respiratory manifestation in Egypt.

Pathogenicity and drug resistance of animal streptococci responsible for human infections

Bacteria of the genus Streptococcus, earlier considered typically animal, currently have also been causing infections in humans. It is necessary to make clinicians aware of the emergence of new species that may cause the development of human diseases. There is an increasing frequency of isolation of streptococci such as S. suis, S. dysgalactiae, S. iniae and S. equi from people. Isolation of Streptococcus bovis/Streptococcus equinus complex bacteria has also been reported. The streptococcal species described in this review are gaining new properties and virulence factors by which they can thrive in new environments. It shows the potential of these bacteria to changes in the genome and the settlement of new hosts. Information is presented on clinical cases that concern streptococcus species belonging to the groups Bovis, Pyogenic and Suis. We also present the antibiotic resistance profiles of these bacteria. The emerging resistance to β-lactams has been reported. In this review, the classification, clinical characteristics and antibiotic resistance of groups and species of streptococci considered as animal pathogens are summarized.

Immunogenicity of Streptococcus equi subsp. equi recombinant SeM protein and bacterin in mice

ABSTRACT: The infection caused by Streptococcus equi, known as strangles, affects the respiratory system of horses, causing high morbidity and rapid spread among the herd. Bacterin vaccines, composed of inactivated whole cells of S. equi, have variable efficacy and duration. Infected animals produce specific antibodies against SeM, the immunodominant antigen of S. equi. This makes it a promising target for vaccine development. In this context, the objective of this work was to evaluate a vaccine combining S. equi bacterin and recombinant SeM protein. Mice were vaccinated with bacterin (S. equi ~1.2 × 108CFU/ml); rSeM protein (20μg); bacterin-rSeM combination; or PBS (Control Group) and challenged with a suspension of S. equi, containing 10 × LD50. All vaccinated mice survived the challenge and produced anti-rSeM and anti-S. equi antibodies, which were assessed by indirect ELISA. The Control Group reached endpoint criteria 96 h after infection. These results demonstrate that a vaccine combining the S. equi bacterin with rSeM protein protects mice against strangles. This combination vaccine could potentially protect horses and overcome the limitations of currently available strangle vaccines.

Streptococcus caledonicus sp. nov., isolated from sheep

Five strains of an unidentified Gram-positive, catalase-negative, chain-forming coccus-shaped organism recovered from sheep in Scotland were characterized using phenotypic and molecular taxonomic methods. Based on morphological and biochemical criteria, the strains were tentatively identified as streptococci but they did not appear to correspond to any recognised species of the genus. Comparative 16S rRNA gene sequencing showed the strains were highly related to each other and confirmed their placement in the genus Streptococcus, with a maximum nucleotide identity of around 97 % to extant species. Best matches were with Streptococcus hillyeri followed by Streptococcus porci. Average nucleotide identity and in silico DNA-DNA hybridization values determined from whole-genome sequence were also consistent with the group representing a novel species. Best matches, again seen to S. hillyeri, followed by S. porci and S. plurextorum, were below accepted cut-off values for species delineation. Based on biochemical criteria and molecular genetic evidence, it is proposed that the unknown isolates from sheep be assigned to a new species of the genus Streptococcus as Streptococcus caledonicus sp. nov. The type strain of Streptococcus caledonicus is S784/96/1^T=CCUG 73951^T=NCTC 14363^T.

Prevalence of upper respiratory diseases and associated factors in Colombian Creole horses

ABSTRACT To determine the prevalence of diseases of the upper respiratory tract and associated factors in the Colombian Creole Horse Valley Aburrá in 2015, a random sampling of 15 farms in southern Aburrá Valley under different management conditions was performed. A total of 105 CCC underwent general clinical examination, respiratory endoscopic evaluation and a detailed inspection of housing conditions and management. A low prevalence of upper respiratory tract diseases was observed, including Pharyngeal Lymphoid Hyperplasia 38.1%, Recurrent Laryngeal Neurophaty 12.38%, Dorsal Displacement of the Soft Palate 7.62%, and presence of tracheal secretions not associated with a specific pathology. A bivariate analysis showed association between tracheal secretions and frequency of training per week (OR = 9.86), duration of the training sessions (OR = 5.55) and inadequate ventilation of the stable (OR = 10.52). Association between HLR and inadequately ventilated barns was also observed (OR = 14.9). Logistic regression showed association between tracheal secretions and inadequate ventilation (OR = 7.18). We conclude that inadequate ventilation was the most important factor for the incidence of upper respiratory tract diseases in horses at the southern area of the Aburrá Valley.

Discrimination of Streptococcus equi subsp. equi and Streptococcus equi subsp. zooepidemicus using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

Accurate and timely identification of infectious etiologies is of great significance in veterinary microbiology, especially for critical diseases such as strangles, a highly contagious disease of horses caused by Streptococcus equi subsp. equi. We evaluated a matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) platform for use in species- and subspecies-level identification of S. equi isolates from horses and compared it with an automated biochemical system. We used 25 clinical isolates each of S. equi subsp. equi and S. equi subsp. zooepidemicus. Using the MALDI-TOF MS platform, it was possible to correctly identify all 50 isolates to the species level. Unique mass peaks were identified in the bacterial peptide mass spectra generated by MALDI-TOF MS, which can be used for accurate subspecies-level identification of S. equi. Mass peaks (mass/charge, m/ z) 6,751.9 ± 1.4 (mean ± standard deviation) and 5,958.1 ± 1.3 were found to be unique to S. equi subsp. equi and S. equi subsp. zooepidemicus, respectively. The automated biochemical system correctly identified 47 of 50 of the isolates to the species level as S. equi, whereas at the subspecies level, 24 of 25 S. equi subsp. equi isolates and 22 of 25 S. equi subsp. zooepidemicus isolates were correctly identified. Our results indicate that MALDI-TOF MS can be used for accurate species- and subspecies-level identification of S. equi.

Immune-Mediated Muscle Diseases of the Horse

In horses, immune-mediated muscle disorders can arise from an overzealous immune response to concurrent infections or potentially from an inherent immune response to host muscle antigens. Streptococcus equi ss. equi infection or vaccination can result in infarctive purpura hemorrhagica (IPH) in which vascular deposition of IgA-streptococcal M protein complexes produces ischemia and complete focal infarction of skeletal muscle and internal organs. In Quarter Horse–related breeds with immune-mediated myositis, an apparent abnormal immune response to muscle antigens results in upregulation of major histocompatibility complex class (MHC) I and II on muscle cell membranes, lymphocytic infiltration of lumbar and gluteal myofibers, and subsequent gross muscle atrophy. Rarely, an inflammatory event results in myositis with subsequent systemic calcinosis characterized by a pathognomonic hyperphosphatemia and high fatality rate. This review presents an overview of these immune-mediated myopathies and highlights clinical and pathological features as well as the suspected pathophysiology.

Strangles in Arabian horses in Egypt: Clinical, epidemiological, hematological, and biochemical aspects

Aim:

Respiratory tract infections are considered the major problem of equine worldwide. Strangles is an infectious and highly contagious respiratory bacterial disease of equine caused by Streptococcus equi. This study is aimed to evaluate some clinical and epidemiological investigation associated with strangles and to study the hematological and biochemical changes in 20 Arabian horse naturally infected with S. equi during the disease and after 10 days from treatment by procaine penicillin with benzathine penicillin.

Materials and Methods:

A total of 490 Arabian horses have been examined, 120 (24.5%) have been clinically diagnosed as strangles. Under complete aseptic conditions, nasal swabs and pus samples from those were collected for bacterial culture. 20 horses from the positive infected with S. equi have been treated by 6 mg/kg b.wt procaine penicillin with 4.5 mg/kg b.wt benzathine penicillin deep intramuscular injection/twice dose/4 days interval.

Results:

102 horses (20.8%) were found positive for S. equi. Horses with age group under 1 year were the most prone to strangles (32.25%) followed by horses of the age group from 1 to 2 years (20%) and finally of the age group over 2-4 years (11.89%). Hematological parameters revealed anemia in the infected horses, while leucogram revealed a significant increase in the total leucocytic, granulocytic and monocytic counts without a significant change in the lymphocytic count. Biochemical parameters revealed a significant increase in serum aspartate aminotransferase, total proteins, globulins, cardiac troponin I (cTnI), and potassium. In other side, hypoalbuminemia and hyponatremia have been reported, whereas alanine aminotransferase activity and creatinine level showed non-significant changes. Respiratory acidosis has been exhibited in the infected horses. Treatment of horses by procaine penicillin with benzathine penicillin revealed improvement of these parameters toward the healthy horses.

Conclusion:

S. equi easily spreads from infected to susceptible horses through contaminated water and other fomites. Therefore, good biosecurity is very important if the welfare and economic costs of an outbreak are to be reduced. The presence of respiratory acidosis with increased of cTnI could indicate pneumonia secondary to strangles with risk of heart involvement.