Helminthiasis: a systematic review of the immune interactions present in individuals coinfected with HIV and/or tuberculosis

Abstract

Helminth infections are highly endemic in parts of the world where the two killer epidemics caused by Mycobacterium tuberculosis (M.tb) and the human immunodeficiency virus (HIV) intersect. Sub-Saharan Africa is hardest hit by this epidemiological overlap. Consequently, several studies have investigated the immunological outcomes of helminth co-infection with either HIV or M.tb, to elucidate the central hypothesis that chronic infection with helminths exacerbates the course of HIV and tuberculosis disease. However, there is no conclusive evidence to confirm whether helminth induced immunity modulates HIV- and TB���specific immune responses and their pathogenesis or vice versa. The present chapter summarizes the epidemiology, clinical course, and immune interactions during helminths and HIV/TB coinfections and undertakes a systematic review of the existing literature published from Africa on this subject. The aim was to determine if chronic helminthiasis has a negative impact on HIV and TB infections. A PubMed search was undertaken with no language and time restrictions. Search terms used included a varied combination of ���Helminth co-infection and immunity and TB co-infection or TB immunity and HIV co-infection or HIV immunity and Africa.��� Names of individual species were also permutated in the search terms. Reviews and bibliographies of selected articles were screened to identify additional relevant articles or studies. Of the total 1021 articles retrieved, 47 were relevant with 31 helminth and HIV co-infection and 16 helminths and TB coinfection articles. While many studies failed to find a negative impact of helminth infection on immune responses to HIV and/or TB, a significant number found evidence of deleterious effects of co-infection with helminths such as immune activation, impaired Th1 responses to TB antigens, higher viral loads, lower CD4+ counts, and increased risks of antiretroviral immunologic failure, mother to child HIV transmission or TB disease. Some of the helminth-induced immune dysregulation wasreversed by deworming, while some studies found no benefit of antihelminthic treatment. More studies particularly in Southern Africa are needed to increase the much sought evidence of the impact of deworming among HIV-infected individuals as this seems the most feasible, cost���effective intervention with little or no serious adverse effects. Lastly, with the expansion of ART and increased access to HIV treatment, the effects of helminths on vaccines, TB, and antiretroviral treatments efficacy also need serious consideration, in light of the suggestive evidence of possible immunologic failure due to helminth co-infection.