Drinking water contaminated with low doses of arsenic reduces immunity to influenza, new research suggests.

In a US-based study, mice were given drinking water containing 100 parts per billion of arsenic for five weeks before being exposed to the influenza A (H1N1) virus — the influenza subtype that includes swine flu. When researchers then measured the animals' immune response to infection, it was found to be significantly weakened when compared with that of mice in a control group.

The findings were published online last month (May) in Environment Health Perspectives.

Arsenic is widely distributed throughout the earth's crust and hundreds of millions of people are exposed to levels in drinking water that exceed guideline values (set at ten parts per billion by the US Environmental Protection Agency). Countries affected include numerous developing countries, Australia and the United States.

Joshua Hamilton, co-author of the study and chief academic and scientific officer at the Marine Biology Laboratory in Massachusetts, United States, explains in a press release that under normal conditions a human or mouse exposed to the flu would develop an immediate immune response.

But the mice in his study showed a response that was initially feeble and then, a few days later, when a response finally kicked in, too robust and too late.

Writing in EHP, the study's researchers say the impact of arsenic exposure on the potential for a pandemic flu outbreak is of particular concern, given that many of the areas with confirmed human cases of avian and swine flu are known to include populations that are exposed to significant levels of arsenic — such as Mexico and parts of South-East Asia.

But Hamilton believes the negative effects of arsenic exposure are not limited to people exposed to the flu, or even viruses.

"We believe there is a general suppression of innate immunity," he told SciDev.Net. "…our results on the effects of arsenic on the immune system argue this would lead to problems with virtually any immune challenge."

Scientists from the International Centre for Diarrhoeal Disease Research (ICDDR) based in Bangladesh, a country with high levels of arsenic contamination of ground water, say that at this stage the direct link between arsenic and H1N1 susceptibility is "speculative".

But according to Stephen Luby, head of ICDDR's programme on infectious diseases and vaccine sciences, the US study has generated important ideas and draws attention to the health effects of being exposed to arsenic.

Source: SciDev.Net
Date: 3 June, 2009