Исследование: Риск ВИЧ-инфицирования повышается при заражении паразитическими червями W bancrofti

People infected with a parasitic worm called Wuchereria bancrofti in areas where HIV is endemic may be more likely to acquire HIV than people who are not infected with the worm, according to a new study in southwest Tanzania, published in The Lancet. W bancrofti causes most cases of lymphatic filariasis (elephantiasis) in sub-Saharan Africa, and the authors say that the findings add a strong argument for tackling this neglected disease, which not only causes morbidity, but may also increase the risk of HIV infection.

Lymphatic filariasis affect one in four people in Tanzania, and has long been suspected to be one of the factors driving the HIV epidemic in sub-Saharan Africa, but previous studies have focused on individuals who are already co-infected with both HIV and parasitic worms. This paper is the first study focusing on HIV susceptibility in individuals with lymphatic filariasis.

W bancrofti is a mosquito borne parasitic worm (or helminth). Worldwide, it causes 90% of lymphatic filariasis cases, a disease commonly known as elephantiasis, which is a neglected tropical disease as defined by the World Health Organisation. Lymphatic filariasis currently affects 120 million people (mostly in Asia, Africa, the western Pacific, and parts of the Caribbean and South America) and causes abnormal enlargement of limbs, causing pain, severe disability and social stigma.

In this study, conducted between 2006 and 2011, the researchers analysed 2699 people in the Kyela district of Mbeya, southwest Tanzania. Participants were visited once annually for 5 years and interviews were conducted to measure behavioural factors involved in HIV acquisition such as sexual activity. Samples of blood, urine, stool, and sputum were collected to test for HIV and for W bancrofti infection, as well as for Schistosoma haematobium, intestinal helminths, tuberculosis, and malaria.

Participants with lymphatic filariasis were twice as likely to become infected with HIV as those without lymphatic filariasis. Overall, there were 1.91 new HIV infections per 100 person-years in patients with lymphatic filariasis, versus 0.80 new HIV infections per 100 person-years in patients without lymphatic filariasis. Of 1055 HIV-negative patients with lymphatic filariasis, 32 contracted HIV within 3 years, and the effect of lymphatic filariasis was highest among adolescents and young adults, appearing to more than triple the relative risk of HIV acquisition in 14-25-year-olds.

The authors say that although they controlled for HIV risk factors such as sexual behaviour and socioeconomic status, the observational nature of the study means that it does not definitively prove cause and effect, but does add to evidence of an association between lymphatic filariasis and HIV infection. The study controlled for malaria, tuberculosis, and other parasitic infections, but did not find any impact of these factors on the increased risk of HIV acquisition. The authors say this highlights the dominant association with filariasis.