Inaugural Conference - June 2002

EVALUATION OF PHOCINE HERPESVIRUS TYPE 1 (PHHV-1) SUBUNIT VACCINES IN CATS AND SEALS

Martina B.E.E¹., Airikkala M.I¹, Harder T.C², Amerongen G van¹ , Kuiken T¹, Osterhaus A.D.M.E¹

1. Institute of Virology, Erasmus MC, Rotterdam, The Netherlands.
2. Institute of Medical Microbiology and Virology, Christian-Albrechts University Clinics, Brunswiker Str. 4, D-24105 Kiel, Germany

Phocid herpesvirus type 1 (PhHV-1) infection causes significant morbidity and mortality among young and immunocompromised harbour seals (Phoca vitulina). Therefore, a safe and effective vaccine against PhHV-1 is needed for use in rehabilitation centres. Since possibilities to test PhHV-1 candidate vaccines in the target species are limited, a feline herpesvirus (FHV) cat system was used to evaluate safety and efficacy of a candidate PhHV-1 vaccine. The FHV cat system was based on the close genetic and antigenic relationships that exist between PhHV-1 and FHV. The proof of principle was demonstrated by vaccinating cats with an iscom adjuvanted vaccine based on complete virus (PhHV-1, FHV, or mock). Cats were vaccinated thrice and one month after the last vaccination all cats were challenged with a virulent strain of FHV. All PhHV-1 and FHV vaccinated cats were protected from developing severe disease (P = 0.03 and P = 0.01 respectively) and excreted significantly less FHV than the mock vaccinated cats (throat: P = 0.02 and P = 0.006 respectively; nose: P = 0.001 and P < 0.001 respectively). Subsequently, recombinant PhHV-1 glycoproteins B and D vaccines were evaluated in the FHV cat model. Both vaccines (gB or a combination of gB + gD) prevented the development of severe disease (P=0.01 and P=0.02 respectively) and significantly reduced FHV excretion in cats (P = 0.03 and P = 0.05 respectively). The addition of gD to the gB iscom vaccine did not result in a significant improvement of the protective efficacy of the vaccine. Consequently, the gB based iscom vaccine was tested for safety and immunogenicity in harbour seals rehabilitated at the Seal Rehabilitation and Research Centre in Pieterburen, the Netherlands. All seals that received the vaccine developed neutralising antibody titres (range 80-160) and T cell proliferative responses to PhHV-1. Considering the protective efficacy of the gB iscom vaccine in the FHV-cat system as well as the immunogenicity of the vaccine in harbour seals, the gB iscom vaccine is a potential candidate to induce protection of seals against severe PhHV-1 induced disease.

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