published epidemiological studies begin to provide a reasonable estimate of the frequency and characteristics of MS in Latin America. In Mexico, hospital-based and population-based studies indicate an increase in the incidence and prevalence of MS. In 1970, Alter and Olivares [8] reported a relatively low prevalence of 1.6/100,000. This study was not confi rmed by community-based data. More recent studies based on referrals to a tertiary neurological center demonstrate an important increase in

more »

... S incidence [9] [10] [11] . A study in northern Mexico (25° north) found a prevalence of 13/100,000 inhabitants [9] . However, this study included only patients with social security benefi ts, representing 51% of the population. Other studies performed in central areas of the country have registered lower prevalences of about 5/100,000 at latitudes 16-20° north [10] . Clearly, MS has become one of the main causes of neurological consultation in Mexico. For instance, optic neuritis represents 12% of the patients referred to a specialized neuro-ophthalmology clinic [12] ; about 40% of them are eventually diagnosed as having MS [12, 13] . Potential risk factors responsible for the increase in MS in Mexico include a decrease in breastfeeding for large segments of the society and an increased incidence of varicella and childhood eczema [14] . Research conducted at the National Institute of Neurology and Neurosurgery of Mexico has demonstrated activation of varicella-zoster virus during MS relapses [15] , suggesting that this herpes virus could be an etiological agent of MS. In 1999, the Latin American Committee for Treatment and Research in MS (LACTRIMS) was formally organized generating renewed interest in numerous coun-