Monday, May 29, 2023
| Isolate (Patient, Source) | APIStrep† | STR Rapid ID32† | Agglutination with Group Serum Specimens | VITEK2 GP-ID† | AccuProbe |
|---|---|---|---|---|---|
| Hum1 (patient 1, CSF) | 0063607 (99.9% S. zooepidemicus) |
15412061151 (99.9% S. zooepidemicus) |
Group C | Not done | Not done |
| Hum2 (patient 2, blood) | Not done | 15412061151 (99.9% S. zooepidemicus) |
Group C | 053450364317451 (99% S. zooepidemicus) |
Streptococcus agalactiae‡ |
| Hum3 (patient 3, abdominal aortic wall) |
Not done | 15512061111 (99.9% S. zooepidemicus) |
Group C | Not done | Not done |
*ISLAB, Eastern Finland Laboratory Centre Joint authority Enterprise; CSF, cerebral spinal fluid.
†bioMérieux, Marcy l’Etoile, France.
‡S. agalactiae (315,588 reflective light units, the reference range below 50,000 reflective light units). S. agalactiae and S. zooepidemicus are known to cross-react in the AccuProbe Group B Streptococcus Culture ID Test (Gen-Probe, San Diego, CA, USA).
| Isolate ID no. | Origin | Year | Stable | MLST sequence type | SzP type | SzP GenBank accession no. |
|---|---|---|---|---|---|---|
| Hum1 | Patient 1, blood | 2011 | A | ST-10 | I | AF519489 |
| Hum2 | Patient 2, blood | 2011 | H | ST-10 | I | AF519489 |
| Hum3 | Patient 3, aortic wall | 2011 | Not done | ST-209 | VII | AF519488 |
| 642/11 | Horse, nasal swab, nonclinical | 2011 | A | ST-147 | IV | AF519482 |
| 645/11 | Horse, nasal swab, nonclinical | 2011 | A | ST-175 | II | AFKC287220† |
| 646/11 | Horse, nasal swab, nonclinical | 2011 | A | ST-66 | V | AFKC287221† |
| 647/11 | Horse, nasal swab, nonclinical | 2011 | A | ST-175 | II | AFKC287220† |
| 648/11 | Horse, nasal swab, nonclinical | 2011 | A | ST-10 | I | AF519489 |
| 744/11 | Horse, nasal swab, nonclinical‡ | 2011 | C | ST-80 | VIII | U04620 |
| 1128/11 | Horse, foal, sepsis | 2011 | B | ST-5 | VI | AFKC287222† |
| 627/11 | Horse, nasal swab, nonclinical‡ | 2011 | C | ST-115 | III | AF519478 |
| 6939/10 | Horse, nasal swab, nonclinical‡ | 2010 | D | ST-201 | VII | AF519488 |
| 8110/09 | Horse, synovial fluid (arthritis) | 2009 | E | ST-299† | III | AF519478 |
| 7723/09 | Horse, foal, tracheal fluid, respiratory infection§ | 2009 | F | ST-XX†¶ | III | AF519478 |
*ID, identification; MLST, multilocus sequence typing.
†Not previously described.
‡The samples were collected for screening of S. equi subsp. equi, but S. equi subsp. zooepidemicus was identified.
§Co-infection with Pasteurella sp. and S. suis.
¶Recorded in the PubMLST database: 8 (arcC)–52 (nrdE)–2 (proS)–14 (spi)–1 (tdk)–22 (tpi)–n/a (yqiL).
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Associate Professor and Residency Director, Department of Family Medicine, University of California, Irvine
This activity is intended for infectious disease specialists and other physicians who care for patients with possible Sez infection.
The goal of this activity is to analyze the clinical and molecular characteristics of Streptococcus equi zooepidemicus.
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Associate Professor and Residency Director, Department of Family Medicine, University of California, Irvine
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Streptococcus equi subspecies zooepidemicus (S. zooepidemicus) is a zoonotic pathogen for persons in contact with horses. In horses, S. zooepidemicus is an opportunistic pathogen, but human infections associated with S. zooepidemicus are often severe. Within 6 months in 2011, 3 unrelated cases of severe, disseminated S. zooepidemicus infection occurred in men working with horses in eastern Finland. To clarify the pathogen’s epidemiology, we describe the clinical features of the infection in 3 patients and compare the S. zooepidemicus isolates from the human cases with S. zooepidemicus isolates from horses. The isolates were analyzed by using pulsed-field gel electrophoresis, multilocus sequence typing, and sequencing of the szP gene. Molecular typing methods showed that human and equine isolates were identical or closely related. These results emphasize that S. zooepidemicus transmitted from horses can lead to severe infections in humans. As leisure and professional equine sports continue to grow, this infection should be recognized as an emerging zoonosis.
Streptococcus equi subspecies zooepidemicus (S. zooepidemicus) is a β-hemolytic, Lancefield group C streptococcal bacterium. S. zooepidemicus is considered an opportunistic commensal in horses,[1–3] but it may also cause infections in other domestic animals such as cattle, sheep, goats, pigs, dogs, and cats.[4–10] Another subspecies of the same genus, Streptococcus equi subsp. equi (S. equi), causes strangles, the highly contagious and serious disease in horses.[1,11,12]
S. zooepidemicus shares >98% DNA sequence homology with S. equi[1] and >80% DNA sequence homology with Streptococcus pyogenes,[13] a Lancefield group A streptococcus and major human pathogen. Although considered an opportunistic pathogen, S. zooepidemicus shares important virulence factors with both S. equi and S. pyogenes such as the M-like proteins, superantigens (sAgs), and the presence of a hyaluronic acid capsule in certain strains. The variable M-protein, located on the surface of S. pyogenes, can be used to differentiate S. pyogenes strains serologically where the M1 serotype is associated with invasive disease in humans.[14] The M-like, cell-wall–anchored surface protein SzP, found in all strains of S. zooepidemicus, is essential for the pathogenesis of the disease, at least in horses, where it binds fibrinogen and exhibits antiphagocytic activity that impairs with host protection. The sAgs SeeH, SeeI, SeeL, and SeeM found in S. equi share 96%–99% amino acid sequence homology with S. pyogenes sAgs SpeH, SpeI, SpeL, and SpeM.[15] However, few investigated strains of S. zooepidemicus contain homologs to these sAgs. Instead, novel sAgs (SzeF, SzeN, and SzeP) have been identified in certain strains, sharing 34%–59% homology with SpeH, SpeM, and SpeL of S. pyogenes.[16]
S. zooepidemicus has seldom been isolated from humans. Surprisingly, most published data on humans go back to the latter part of the 1980s.[17] Occasional human infection was reported as a result of the consumption of homemade cheese or unpasteurized milk from cows with mastitis.[17] In humans, S. zooepidemicus may cause glomerulonephritis and rheumatic fever, which are known sequelae of S. pyogenes (group A) infections.[18] Meningitis and purulent arthritis have also been reported.[19,20]
S. zooepidemicus displays a wide genetic variation between different isolates.[13,21–23] The sequence of the SzP protein gene (szP) has been shown to vary greatly between different strains of S. zooepidemicus,[24–26] and the variable regions of szP can be used to genetically differentiate strains within the subspecies.[27–29] Pulsed-field gel electrophoresis (PFGE) is a DNA-based typing technique that is highly discriminatory and has been used in epidemiologic investigations of S. zooepidemicus outbreaks.[30,31]
Multilocus sequence typing (MLST) is a method for characterization of bacterial isolates by comparing sequences of several gene fragments. Webb et al.[22] developed a MLST protocol for S. zooepidemicus consisting of 7 housekeeping genes. Obtained sequences are compared to previously deposited sequences, and a sequence type (ST) is assigned from the online PubMLST S. zooepidemicus database (http://pubmlst.org/szooepidemicus) developed by Jolley et al.[32]
Within a 6-month period, through our routine practice, we found 3 cases of severe disseminated disease in humans caused by S. zooepidemicus. The purpose of this study was to 1) characterize the clinical presentation of the disease caused by S. zooepidemicus, 2) microbiologically characterize the isolated strains, and 3) identify clonality of human isolates for comparison to equine isolates from contact horse stables and other horse farms of the surrounding area.
