Scientists need to take into account that worm infestation could compromise the success of a potential AIDS vaccine as is the case with established vaccines against viral diseases such as cholera and tuberculosis, local researchers have warned.
Professor Miles Markus (University of the Witwatersrand) and Dr John Fincham (Medical Research Council), both experts in the field of worm infestation, have warned that helminthiasis (worm infestation) diminishes post-vaccination immune responses to diptheria, tetanus, oral cholera vaccine and BCG for tuberculosis.
Writing in The Lancet, Markus and Fincham said that there was no obvious reason why helminthic and perhaps some other pre-existing infections would not similarly compromise the efficacy of certain types of HIV vaccines.
“AIDS vaccine researchers need to take this possibility into account. De-worming of individuals before vaccination might improve the post-vaccination immune response,” they said.
Taking it further, Markus and Fincham said there were also research results which suggested that treatment of worm infestations in AIDS patients might slow down the progression of the disease and increase efficacy of anti-retroviral treatment.
“There are other results which suggest that prevention of worm infection in mothers, could reduce the risk of perinatal HIV infection,” they said.
Worm infestations of one sort or another are widespread in regions such as sub-Saharan Africa.
In 1995 when Fincham and his team started surveying worms in Khayelitsha schools, they found that between 91% and 100% of school children tested had worms.
Intervention, which involved de-worming the school children, has since seen a significant drop (between 80% and 98%) in the prevalence of worm eggs in the stools.
Dr Lynn Morris, head of the HIV/AIDS Division at the National Institute for Virology, said a number of local factors might impact on vaccine efficacy, such as environmental, nutritional and genetic factors.
Morris has been tasked with testing the immunology of AIDS vaccines developed by scientists at the universities of Cape Town and Stellenbosch.
“The presence of endemic diseases such as worms and tuberculosis woulddefinitely be included in this,” Morris said.
“Since vaccines aim to stimulate immunity, the presence of such factors may impact on how immunogenic some vaccines are.
“It is precisely because of these reasons that three phases of clinical trials are done in each country.
“Each phase aims to do a different thing – safety, immunogenicity and efficacy,” Morris said.
She pointed out that even if a vaccine was shown to work in the United States it would be important to still conduct these three trial phases because of these different factors in different settings.
“Until this is done it won’t be possible to know what impact these factors might have.”