A long-term study in southwest Tanzania has linked mass treatment for Wuchereria bancrofti, the parasite that causes lymphatic filariasis (elephantiasis), with a fall in new HIV infections. The 12-year RHINO study, published in The Lancet HIV in May 2025, involved researchers from LMU University Hospital in Munich and the National Institute for Medical Research in Mbeya and followed residents of Kyela district from 2007 to 2019 as anti-parasitic drugs were rolled out.
The study monitored 1,139 HIV-negative people in four groups and found differing HIV incidence rates:
- 848 people who never had the parasite: 0.68 HIV cases per 100 people per year;
- 272 people infected but later cured: 0.73 cases per 100 people per year;
- 15 people who remained chronically infected: 1.5 cases per 100 people per year.
Researchers concluded that clearing the parasite reduced susceptibility to HIV and noted that their findings build on a 2016 Lancet paper that reported a two- to threefold higher HIV vulnerability with Wuchereria bancrofti infection. The team, led by Inge Kroidl, suspects that adult worms cause chronic immune activation in the lymphatic system, creating conditions that allow HIV to establish and replicate more easily. The effect appears particularly strong in adolescents, who often have fewer other HIV risk exposures.
Despite the potential public-health benefit, neither Tanzanian health authorities nor the World Health Organization have yet integrated lymphatic filariasis elimination into routine HIV prevention policies. Public health scientist Ibrahim Simiyu said the results challenge the long-standing separation of neglected tropical disease and HIV programmes. Because mass drug administration with medicines such as ivermectin and albendazole already exists in many countries, researchers describe the HIV benefit as an add-on with little extra cost. The team is testing whether similar trends appear in other endemic countries, including Mozambique, and warns that gains could reverse if treatment coverage falls.
Difficult words
- lymphatic filariasis — tropical infection causing swollen limbs and lymph damage
- incidence — number of new cases in a time period
- susceptibility — likelihood of becoming infected or affected
- chronic — lasting for a long time or recurring
- immune activation — immune system becoming more active than normal
- mass drug administration — delivering medicines to many people at once
- endemic — commonly present in a particular region
- coverage — proportion of people who receive a treatment
Tip: hover, focus or tap highlighted words in the article to see quick definitions while you read or listen.
Discussion questions
- What are the advantages and possible challenges of combining neglected tropical disease programmes with HIV prevention?
- How could public health officials keep treatment coverage high to avoid reversing the study's gains?
- If mass drug administration can reduce HIV incidence, how should countries prioritise and fund these programmes?
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