Containing worm infections as an effective approach to preventing HIV/AIDS

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Scientists from the Munich Tropical Institute, the German Center for Infection Research (DZIF), and the Tanzanian National Institute for Medical Research (NIMR)-Mbeya Medical Research Center (MMRC), together with colleagues from Bonn, have discovered a previously little-noticed risk factor for HIV infection. In an earlier cohort study in Tanzania, they had demonstrated for the first time that infection with the worm Wuchereria bancrofti increases the risk of contracting HIV. This correlation has now been further investigated in the context of a national program in Tanzania to eliminate W. bancrofti, the pathogen that causes lymphatic filariasis. The follow-up study confirms that controlling this worm infection leads to a decline in new HIV infections. The results of the DFG-RHINO study have now been published in the journal The Lancet HIV.

Lymphatic filariasis – a neglected tropical disease

The threadworm W. bancrofti is a parasite that occurs mainly in the tropical regions of Africa and Asia and can cause the disease lymphatic filariasis. This disease damages the lymphatic system and can lead to lymphedema with significant enlargement of the extremities in those affected.

The team led by DZIF researchers Prof. Michael Hoelscher, MD, and Prof. Inge Kroidl, MD, from the Institute for Infectious and Tropical Medicine at LMU Hospital, together with the Tanzanian National Institute for Medical Research – Mbeya Medical Research Center (NIMR-MMRC) from 2007 to 2011. The EMINI (Evaluation and Monitoring of the Impact of New Interventions) study showed that infection with the worm W. bancrofti increases the risk of infection with HI viruses by a factor of 2 to 3 (see The Lancet, 2016).

Cohort study in Tanzania

Between 2009 and 2015, villagers in Tanzania were treated annually with antihelminthic drugs as part of a government program to eliminate lymphatic filariasis. Together with researchers from the UKB and the University of Bonn, the Munich and Tanzanian teams took this as an opportunity to investigate the impact of the quasi-complete elimination of W. bancrofti infection on HIV incidence in a follow-up study (RHINO: Risk of HIV Infections through Nematode Organism).

In 2019, the research team invited individuals at one of the EMINI study sites, Kyela, to participate in the RHINO follow-up study. The subjects—a total of 1,139 study participants aged 14 to 65—were tested for HIV and W. bancrofti (WB) and divided into three groups accordingly : 1. WB-positive, 2. cured of WB (i.e., WB-positive between 2007 and 2011 and WB-negative in 2019), and 3. WB-negative. In a statistical analysis, the research team then compared HIV incidence in these three groups during the study periods 2007-2011 and 2011-2019.

Containing W. bancrofti infections reduces HIV incidence

Analysis of HIV incidence between 2007 and 2011 showed that WB-infected individuals (1.72 cases per 100 person-years/PY) had more than twice the risk of becoming infected with HIV compared to WB-negative individuals (0.69 per 100 PY). In contrast, the HIV incidence among individuals who had been cured of WB (0.73 cases per 100 PI) examined in the period 2011-2019 differed only insignificantly and was not statistically significant from that of individuals who had never been infected with WB (0.68 cases per 100 PI).

In the group of subjects who were cured of W. bancrofti, a comparison of the two study periods showed a decrease in HIV incidence of approximately 60 percent, which was statistically significant even after adjusting for age and gender (measured odds ratio: 0.41, p=0.012). In contrast, the comparison group of individuals who were not infected with W. bancrofti in either period showed no change in HIV incidence.

DZIF researcher Prof. Dr. med. Inge Kroidl from the Tropical Institute at LMU Hospital concludes: "This confirms the earlier hypothesis that it is indeed the W. bancrofti worm that influences the incidence of HIV and that combating W. bancrofti can help reduce the rate of new HIV infections."

"Helminth infections have been shown to increase the risk of HIV infection. We are continuing to investigate which immunological processes could explain this increased susceptibility to HIV transmission through W. bancrofti," says Prof. Michael Hoelscher, MD, Director of the Munich Tropical Institute.

Dr. Mkunde Chachage of NIMR-MMRC emphasizes: "This groundbreaking research shows how important community involvement is in identifying additional measures in our regional HIV control strategies and underscores their crucial role in designing effective health initiatives."

Prof. Said Aboud, Director General of NIMR, commented on the results, saying, "They demonstrate NIMR's commitment to playing a leading role in efforts to eliminate lymphatic filariasis and HIV in Tanzania." He praised the long-standing support of the Tanzanian government through the Neglected Tropical Disease Control Program (NTDCP), which has been fighting these diseases for almost 20 years. This has enabled research that is advancing the fight against HIV.

Co-author of the study Prof. Achim Hörauf, MD, Director of the Institute for Medical Microbiology, Immunology, and Parasitology at the University Hospital Bonn, adds: "Our findings open up new possibilities for HIV prevention in affected regions. The treatment for lymphatic filariasis is not yet optimal. That is why we are continuing to research this topic and hope that in the coming years, at least some of the new drugs developed to combat this infection, including those developed at the DZIF, will be approved."

Original publication:
Inge Kroidl et al.: Impact of quasi-elimination of Wuchereria bancrofti on HIV incidence in southwest Tanzania: a 12-year prospective cohort study. The Lancet HIV 2025, https://doi.org/10.1016/S2352-3018(25)00001-3

Funding and acknowledgements: The study was funded by the European Union under EuropAid (SANTE/2004/078-545/130; SANTE/2006/129-931, funding the EMINI study) and the German Research Foundation (DFG) KR 3615/1-1 and HO 2009/11-1, funding the RHINO study). In addition, IK is funded by the Federal Ministry of Education and Research (BMBF, grant number 01KA2222A). AHoe, CG, MH, BP and IK are funded by the German Centre for Infection Research under TTU 03.815 (to AHoe), 03.816 (to BP) and 03.817 (to MH, CG and IK). The funders had no influence on the study design, data collection and analysis, decision to publish, or preparation of the manuscript. The study team thanks the villagers of the Kyela region for their interest in the research and their support of the activities over many years.