Parasitic worm boosts vulnerability to HIV
An international team of researchers has shown that people infected with a worm that causes filariosis, which is widespread in Africa, are significantly more likely to contract AIDS than those who do not carry the parasite.
Wuchereria bancrofti, Wurmlarve. Source: Hörauf, Uniklinikum Bonn
Since the AIDS epidemic began, there has been much speculation as to why the disease, which progressively disables the immune system, is so much more prevalent in Africa than in any other region that the viral pathogen HIV has reached. One possible contributory factor to the massive burden of AIDS in Africa has now been identified by an international team led by LMU’s Professor Michael Hölscher and his colleague Dr. Inge Kroidl. In the course of a population-based cohort study carried out in Tanzania from 2006 until 2011, they have been able to demonstrate that infection with the parasitic worm Wuchereria bancrofti increases susceptibility to HIV by 2- to 3-fold. The results are reported in the leading medical journal The Lancet.
“The finding holds in particular for adolescents and young adults. In this group, infection with W. bancrofti increases the risk of AIDS infection by approximately threefold,” explains Inge Kroidl of the Division of Infectious Diseases and Tropical Medicine at the LMU Medical Center. The study was undertaken in collaboration with researchers at Bonn University, together with Tanzanian partner institutions of the German Center for Infection Research (DZIF).
Entrenched in the lymphatic system
Wuchereria bancrofti infections inevitably lead to what is known as lymphatic filariosis, in which the worm invades the lymphatic vasculature, where it can block the flow of lymph and distend the vessels, which ultimately results in elephantiasis. Encounters with individuals with grotesquely enlarged and deformed limbs are not infrequent in many parts of Africa. Unfortunately, the drugs used to combat the infection are effective only against the transmissible microfilaria produced by the mature worm, which migrate into the bloodstream and are propagated by blood-sucking mosquitos. Mature worms, on the other hand, can survive for years in the lymph vessels.
The new study was designed to identify factors that are associated with increased risk of HIV infection in the general population in southwestern Tanzania. A subgroup consisting of 1055 individuals who were free of HIV in 2006 was subsequently examined for the presence of filarial infection. In this cohort, 32 new cases of HIV infection were recorded. Comparison of the incidence of HIV in uninfected and worm-infected persons revealed that the latter were significantly more likely to carry the virus. Strikingly, the degree of increased risk varied markedly, depending on the age-group considered. Among 14- to 25-year-olds, the risk is 3.2-fold higher, in 25- to 45-year-olds it rises by a factor of 2.4 and in the over 45s by a factor of 1.2.
“With this initial confirmation of a long-standing hypothesis, the real work is just beginning,” says Michael Hölscher, Head of the department of Infectious Diseases & Tropical Medicine at LMU and initiator of these cohort studies. Now further studies are planned, in cooperation with the researchers in Bonn. “We need to find drugs that are capable of rapidly eliminating adult forms of W. bancrofti,” says Professor Achim Hörauf of the Institute of Medical Microbiology, Immunology and Parasitology at the University Hospital in Bonn, who has years of experience in the study of filarial parasites, and is developing a new therapeutic agent directed against the worms.
The project was funded by the European Commission in the context of a program designed to strengthen research activities in the Tanzanian healthcare system, and by the Federal Ministry for Education and Research in Berlin, which has been intensifying its support for health-related research in Africa since 2011. This year, the Ministry is providing funding amounting to approximately 50 million euros for five research networks dedicated to the development of innovations in healthcare in Subsaharan Africa. One of these networks, TAKE-OFF, focuses on filarial parasites and the diseases they cause. Among TAKE-OFF’s members are Achim Hörauf und Inge Kroidl, who plan to continue their quest for effective ways to reduce the incidence of filariosis in three African countries. (Lancet 2016)