Getting a grip on strangles

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    However, development of such a test requires better under-standing of potential qualitative and quantitative dier-ences in the immune response of carrier horses (i.e. thosethat develop persistent infection) compared to horses that

    diversication through immunological selection pressure.This would oer the potential for diagnostic tests basedon measurement of immune responses to dierent surface

    after its launch in 2004, 24,000 doses of Equilis StrepE weresold in the UK. Suspected adverse reactions have been re-ported for approximately 0.2% of doses administered, themajority being lip swellings as described in the product data-

    multi-component subunit vaccines based on various immu-nogenic S. equi surface proteins as an alternative to liveattenuated vaccines. Laboratory studies have shown such

    73

    Theclear infection completely (i.e. make both a clinical andmicrobiological recovery). The authors propose that persis-tent infection is a major contributor to SeM protein (a ma-jor virulence determinant of S. equi) sequence

    sheet. In a few instances where strangles disease occurredafter vaccination, horses were found to be infected with wildtype bacteria rather than having vaccine-induced disease.

    Waller and Jolley (2007) describe the potential ofGuest

    Getting a gri

    In this issue of The Veterinary Journal, Andrew Wallerand Keith Jolley review the current state of aairs with re-gard to the development of strangles vaccines which inducelong-term immunity and are free from side eects (Wallerand Jolley, 2007). They also describe how improved under-standing of the genetic variation of Streptococcus equi, thecausative agent of strangles, could be useful in epidemio-logical outbreak investigations and carrier detection.

    Subclinical S. equi carriers play a crucial role in the epi-demiology of this disease (Newton et al., 1997; Newtonet al., 2000; Timoney et al., 1998). The site of persistentinfection is usually the guttural pouch and the carrier stateis thought to result from incomplete drainage of infectiveexudate from the guttural pouch and/or sinuses after directinfection or rupture of retropharyngeal lymph node ab-scesses into these structures (Newton et al., 1997). Cur-rently, reliable detection of carriers relies on repeatednasopharyngeal swabbing or, preferably, endoscopy ofthe upper respiratory tract and guttural pouches, to assessthe gross appearance of these tissues and enable gutturalpouch washes to be taken for culture and PCR screeningin the laboratory (Newton et al., 2000; Timoney et al.,1998). The cost and time involved in such procedures makethese diagnostic investigations unsatisfactory for large-scale application after apparent resolution of outbreakson infected premises.

    As suggested by Waller and Jolley (2007), there is a realneed for a highly sensitive and specic diagnostic test foridentication of carriers that is relatively quick and cheapto perform so it can be practically applied in eld settings.

    The Veterinary Journal 11090-0233/$ - see front matter 2006 Elsevier Ltd. All rights reserved.doi:10.1016/j.tvjl.2006.08.012itorial

    on strangles

    proteins or dierent epitopes of particular proteins. The po-tential for dierentiating isolates from acute and persistentstages of infection may also aid in better carrier detection.

    Horse- and management-level risk factors for develop-ment of persistent subclinical infection are currently un-known. Epidemiological studies aimed at identifying whycertain animals become carriers and others do not, as wellas investigations into the circumstances that trigger S. equishedding in subclinically infected animals may help in moreeective management of outbreaks, including the potentialfor targeted investigations of individual horses perceived tobe at heightened risk of becoming carriers in outbreaksituations.

    Waller and Jolley (2007) indicate rightly that the currentlyavailable strangles vaccines are not optimal in terms ofsafety, ecacy and practicality of use. The only stranglesvaccine currently licensed for use in the EU is Equilis StrepE,a live attenuated vaccine that is intended to induce immunityagainst S. equi to reduce clinical signs of the disease andoccurrence of lymph node abscessation. Consultation ofthe European Public Assessment report on this particularvaccine (http://www.emea.eu.int/vetdocs/vets/Epar/equili-sstrepe/equilisstrepeM.htm) reveals a number of adversereactions to vaccine administration in the recommendedway (0.2 mL submucosally in the inside of the upper lip) dur-ing both laboratory and eld safety studies, including localswelling at the site of administration, pyrexia and develop-ment of lymph node abscesses in some cases; however theseresolved over the course of three weeks and the generaldemeanour of the horses was not aected. In the 13 months

    www.elsevier.com/locate/tvjl

    (2007) 475476

    Veterinary Journal

  • vaccines to induce immunity in mice (Flock et al., 2004;Flock et al., 2006), although their ecacy and safety inhorses remains to be tested.

    Current eorts to prevent strangles outbreaks should re-main targeted at eective quarantine procedures andscreening, as well as application of the highest standardsof hygiene on premises where large groups of horses gather.Such measures will remain invaluable even when eectiveand safe S. equi vaccines suitable for routine vaccinationof horses on a large scale enter the equation. Furthermore,better understanding of risk factors for development ofpersistent infection can aid in the prevention or resolutionof the carrier state, which could substantially reduce theincidence of this common disease.

    Kristien VerheyenDepartment of Veterinary Clinical Sciences,

    The Royal Veterinary College, Hawkshead Lane,

    North Mymms, Hateld,

    Hertfordshire AL9 7TA, UK

    E-mail address: kverheyen@rvc.ac.uk

    References

    Flock, M., Jacobsson, K., Frykberg, L., Hirst, T.R., Franklin, A.,Guss, B., Flock, J.I., 2004. Recombinant Streptococcus equiproteins protect mice in challenge experiments and induceimmune response in horses. Infection and Immunity 72, 32283236.

    Flock, M., Karlstrom, A., Lannergard, J., Guss, B., Flock, J.I., 2006.Protective eect of vaccination with recombinant proteins fromStreptococcus equi subspecies equi in a strangles model in the mouse.Vaccine 24, 41444151.

    Newton, J.R., Verheyen, K., Talbot, N.C., Timoney, J.F., Wood,K.H., Lakhani, K.H., Chanter, N., 2000. Control of stranglesoutbreaks by isolation of guttural pouch carriers identied usingPCR and culture of Streptococcus equi. Equine Veterinary Journal32, 515526.

    Newton, J.R., Wood, J.L., Dunn, K.A., DeBrauwere, M.N., Chanter, N.,1997. Naturally occurring persistent and asymptomatic infection of theguttural pouches of horses with Streptococcus equi. Veterinary Record140, 8490.

    Timoney, J.F., Sheoran, A., Artiushin, S., 1998. Detection of stranglescarriers. Veterinary Record 142, 648.

    Waller, A.S., Jolley, K.A., 2007. Getting a grip on strangles: Recentprogress towards improved diagnosis and vaccines. The VeterinaryJournal 173, 492501.

    476 Guest Editorial / The Veterinary Journal 173 (2007) 475476

    Getting a grip on stranglesReferences