Strangvac is an intramuscular vaccine against strangles and is indicated to reduce the clinical signs and the number of abscesses within submandibular and retropharyngeal lymph nodes in horses during the acute stage of strangles.

Clinical signs include: body temperature increase, coughing, difficulty swallowing, and signs of depression (inappetence, changes in demeanour).

Which technology is used in strangvac?

Strangvac uses innovative recombinant fusion protein technology. DNA fragments encoding 8 important Strep. equi proteins are joined together to make 3 synthetic ‘genes’ and each is placed into Escherichia coli bacteria. The Escherichia coli is grown in fermenter cultures and uses the synthetic genes as a blueprint to make each protein. The fermented Escherichia coli is then lysed and each protein is extracted and purified ready for use in Strangvac. It is key to note that Strangvac contains no Strep. equi bacteria nor DNA and therefore has DIVA capability.

Which strep. Equi antigens are included in strangvac?

Strangvac contains the following proteins:

  • Recombinant protein CCE, comprised of Strep. equi antigens CNE, SclF, SclI, SclC, EAG
  • Recombinant protein Eq85, comprised of Strep. equi antigens: Eq5, Eq8
  • Recombinant protein IdeE, comprised of Strep. equi antigen IdeE

These antigens, with the exception of IdeE, are localised on the bacterial surface and antibodies against them are assumed to be opsonic and block bacterial adherence to tissue surfaces and the ability of these important proteins to help Strep. equi to cause disease. The seven cell wall proteins are surface-anchored to the peptidoglycan bacterial cell wall. CNE binds collagen1 and Strangvac responses blocked the attachment of Strep. equi to collagen (Flock et al., unpublished data). EAG binds alpha 2-macroglobulin, serum albumin and IgG2, 3. The function of SclF, SclI, SclC, Eq5 and Eq8 are currently unknown, but likely to not only be involved in adhesion as many of these classes of proteins have multiple functions in mis-directing host immune responses. Interestingly, SclF, SclI, SclC and Eq8 are each individually essential to Strep. equi in order for it to cause strangles in horses (Charbonneau et al., unpublished data). Therefore, the immune responses generated by Strangvac target Strep. equi for killing, but also block key virulence functions, making it easier for the immune response to kill Strep. equi.

Does strangvac protect against all field strains of strep. Equi?

The antigens in Strangvac are extremely well conserved and Strangvac is expected to protect against all variants of Strep. equi that currently circulate worldwide (Frosth et al., new paper). All 759 strains examined in this survey had at least 6 identical antigens to the 8 in Strangvac. 98% of strains had none or only one amino acid variation relative to the 1580 amino acids that make up the 8 antigens in Strangvac. Strangvac is based on BAPS2 strain (the most prevalent cause of strangles in Europe) and the studies that determined the effectiveness of Strangvac used a heterologous BAPS5 strain, which is the second most prevalent type of Strep. equi in Europe.

– Will a Strangvac-vaccinated horse test positive for strangles?

No, Strangvac does not contain live Strep. equi, nor Strep. equi DNA.

Therefore horses that have been vaccinated with Strangvac will not test positive in culture tests or PCR tests, unless they have been recently infected with Strep. equi.

In addition, Strangvac does not contain the proteins used in the strangles blood test. Therefore, vaccinated horses will not test seropositive unless they have been exposed to Strep. equi.

This means that Strangvac, unlike other strangles vaccines, possesses DIVA capability (DIVA = Differentiating Infected from Vaccinated Animals).