Still on the topic of HSV-2 … A clinically effective vaccine has yet to be achieved, though efforts are being made to develop one. A replication-defective HSV-2 mutant virus – the US strain HSV-2 dl5-29 – has been shown to induce immunity against the US strains HSV-2 G and 333 in mice and guinea pigs. The potential benefits of an effective vaccine could be enormous in sub-Saharan Africa, where epidemiological studies have shown that genital herpes leads to a multi-fold increase in the risk of HIV transmission.
In line with these ambitions, a recent study has sought to improve our knowledge of the genetic and epitope diversity of HSV-2, and its effect on vaccine efficacy, by testing HSV-2 vaccine candidates against HSV-2 strains derived from African, as well as, US isolates. A first stage involved the testing of HSV-2 dl5-29 against both a panel of three US strains (G, 89-390, 186) and a panel of African strains (SD15, SD66, SD90). HSV-2 dl5-29 proved effective against both US and African strains, though in the latter case equivalent protection required higher doses. A second stage involved assessment of the ability of two replication-defective mutant viruses to protect against the same panels of US and African derived viruses – 5BlacZ, deriving from a US strain, and SD90-8LacZ, deriving from an African one. The US derived 5BlacZ tended to be more protective against US strains, and the African derived SD90-LacZ against African strains; at the same time, neither vaccine was as protective against the African strains as 5BlacZ was against the US ones, despite levels of humoral and cellular immune response that were equivalent in the US and African case.
The authors draw two conclusions: first, that immune protection appears to be partially specific for the viruses from the US versus Africa; second, that the African HSV-2 viruses seem more virulent. They call for further research in this area on account of its potential impact on the reduction of HIV transmission risk.
Timothy E. Dudek, “Evidence for Differences in Immunologic and Pathogenesis Properties of Herpes Simplex Virus 2 Strains From the United States and South Africa”, Journal of Infectious Diseases 2011:203 (15th May)