(Reuters) - U.S. stock index futures dipped on Monday after the S&P 500 closed its best week in nearly two years on Friday and ahead of data on U.S. services sector growth and home sales. * Shares of Brazilian companies traded in the United States tumbled after incumbent Dilma Rousseff won reelection in a runoff vote, defeating centrist and market favorite Aecio Neves by a slim margin. Petrobras ADRs (PBR.N) slumped 17.8 percent in premarket trading and Vale (VALE.N) lost 5.5 percent. Itau Unibanco (ITUB.N) and Banco Bradesco (BBD.N) fell about 10 percent each. * Earnings continued to trickle in, with Merck (MRK.N) reporting lower than expected third quarter revenue though it beat earnings forecasts thanks to cost cuts. Its shares were little changed in early trading. * German business sentiment fell in October for a sixth straight month to its lowest level in almost two years, adding to recent concerns the largest European economy may continue to struggle to grow. * Markit's initial gauge of the U.S. services sector in October is due at 9:45 a.m. EDT and will be followed 15 minutes later by a reading on pending home sales for September. * Micron (MU.O) shares rose 2.5 percent premarket after it announced a $1 billion stock buyback authorization. * Sarepta Therapeutics (SRPT.O) shares fell 31.7 percent in premarket trading after it said the U.S. Food and Drug Administration requested additional data regarding a marketing application for its experimental muscle disorder drug. * The S&P 500 closed its best week since January 2013 on Friday, boosted by earnings from Microsoft and Procter & Gamble and as concerns eased over the spread of Ebola in the United States. * A 5-year-old boy who arrived in the United States on Saturday from Guinea is being observed in isolation at Bellevue Hospital in New York City for possible Ebola symptoms, according to media reports on Monday. Futures snapshot at 8:31 a.m.: * S&P 500 e-minis ESc1 fell 4.25 points, or 0.22 percent, with 201,855 contracts changing hands. * Nasdaq 100 e-minis NQc1 lost 2.75 points, or 0.07 percent, in volume of 30,217 contracts. * Dow e-minis 1YMc1 dropped 28 points, or 0.17 percent, with 31,466 contracts changing hands.

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