Findings: 'Harmless' bug may be killer

A seemingly harmless parasite carried by a large percentage of the population could be responsible for up to 1 million road fatalities every year worldwide, according to researchers in the Czech Republic.

A team led by Jaroslav Flegr, in Charles University's department of parasitology in Prague, has discovered that people who are infected by the bug run more than twice the risk of being involved in traffic accidents.

Toxoplasma gondii can be picked up from cat faeces or from undercooked or raw food. Although dangerous to unborn babies and people with immune deficiencies, it can live in healthy adults and children without causing symptoms. At most, it causes a mild fever, headache or muscle ache on initial infection.

The toxoplasma then enters a dormant phase and can remain in the host for life, in a condition known as latent toxoplasmosis. An estimated 30 to 60 per cent of people worldwide are infected.

Research has shown that long-term infection by the parasite leads to longer reaction times and even personality changes.

So the Czech researchers decided to investigate how prevalent the bug was in people involved in traffic accidents. They examined blood samples of 146 people involved in an accident who could have been responsible for it. They discovered that those with latent toxoplasmosis were 2.65 times more likely to have an accident than the general local population. The higher the concentration of anti-toxoplasma antibodies in the subject, the higher the likelihood of them having an accident. But the longer a person had been infected, the lower the relative risk.

The researchers concluded that because of its high prevalence, latent toxoplasmosis represented "a serious and highly underestimated public health problem, as well as an economic health problem".

They estimated that a programme of cat vaccination to eliminate the parasite could prevent almost a third of all deaths annually.

The study was published in the online journal BMC Infectious Diseases .