Long-distance transport of ragweed pollen does not induce new sensitizations in the short term

Pollen can travel long distances and reach areas where the plants producing them are not present. Episodes of the long-distance transport of allergenic pollen of ragweed and birch have been reported in Europe in recent years. We have previously shown that such episodes have occurred over a wide area of Central Italy where ragweed plants are virtually absent or present only in negligible numbers (Cecchi et al. 2006, 2007). At that time we hypothesized that these events could cause new sensitizations among residents who had not previously been exposed to this extremely allergenic pollen. This hypothesis was supported by a report of increases in the incidence of ragweed allergy in Northern Italy, which was attributed to the natural spread of ragweed into the area in the 1980s (Asero 2002). A preliminary observational study revealed an increasing trend of ragweed allergy in Bologna, where ragweed plants are also not present (Zauli et al. 2006).