WADN Tropical

Mosquito-borne virus has infected millions of people in Asia, Africa and Europe

GALVESTON, Texas — Imagine a mosquito-borne virus that has already infected millions of people in recent outbreaks in South and Southeast Asia, the islands of the Indian Ocean, Africa and northern Italy. Although seldom fatal, it causes highly painful arthritis-like symptoms that can linger for months or even years. It's capable of adapting to spread through a mosquito species common in much of North America. And no vaccine or treatment exists to protect humans from its effects.

The scenario may sound like something dreamed up as a training exercise by public health authorities, but the virus is all too real. Called chikungunya, from an East African tribal word describing the contorted postures of its pain-wracked victims, the pathogen has been the focus of intense scientific interest ever since a 2006 outbreak on the island of La Reunion in the Indian Ocean infected about 266,000 people, killing 260 of them.

A clinical trial of a vaccine against a major cause of pneumonia and meningitis has shown that it can prevent three out of four cases of re-infection in HIV-infected adults in Africa.

The trials, conducted in Malawi and funded by the Wellcome Trust, studied the efficacy of a vaccine against infection with the Streptococcus pneumoniaebacteria. These bacteria are a primary cause of pneumonia and when they invade the blood stream and brain – so called invasive pneumococcal disease (IPD) – they cause the serious and often fatal illnesses of septicaemia and meningitis. In HIV-infected adults, particularly in sub-Saharan Africa, the risk of developing IPD increases between thirty and a hundred-fold.

The pneumococcal polysaccharide vaccine (PPV), which is currently used to protect adults in the UK and US, has been shown to have limited efficacy in HIV-infected adults and is not recommended in Africa.

A study into why some people are more resistant than others to diseases such as tuberculosis (TB) and leprosy has identified a new genetic variant which affects susceptibility to these diseases. The findings, published today in the journal Cell, may have implications for future treatments for the two conditions.

TB and leprosy, whilst seemingly very different diseases, are both caused by rod-shaped, aerobic bacteria known as mycobacteria; TB is caused by M. tuberculosis; leprosy by M. leprae. Exposure to the bacteria causes very varied outcomes amongst patients: for example, in the case of M. tuberculosis, some people will resist infection, others will carry the bacteria asymptomatically, and yet others may develop life-threatening symptoms.

Our immune system uses two broad strategies to defend us from infection: innate immunity and adaptive immunity. Innate immunity is the immune response that we are born with; it is the first line of defence, swift, but more generalised than adaptive immunity. The latter strategy enables the immune system to adapt its response to infection in order to better target itself towards specific invading pathogens.

University of Washington (UW) researchers have identified a gene involved in susceptibility and resistance to tuberculosis. This same gene, they have found, has a role in the severity of leprosy, which is caused by a related pathogen. The researchers also have learned why this gene is important for susceptibility.

The gene, lta4h, appears to orchestrate pro-inflammatory and anti-inflammatory responses. When these responses are balanced, the body destroys invaders without unduly hurting itself. But an imbalance results in problems. Either the infection takes hold or damage occurs from an overly aggressive defense.

The findings will be published tomorrow, Friday, March 5, as the cover story forCell.