Walmart has pulled infant formula from the shelves of its 3,000 stores after two babies in Missouri got sick and one of them died, the retailer said Thursday.

Health officials have not yet determined whether the bacterial infection which sickened the newborns was linked to the powdered formula, but Walmart said it was pulling the product "out of an abundance of caution."

France's health ministry has said there is no cancer risk from breast implants made by local firm Poly Implant Prothese (PIP) but has recommended that women with the implants have them removed after eight cases of cancer.

Women with PIP implants "do not have a higher risk of cancer than women who have implants manufactured by other firms", a statement said but added there were "well-established risks of ruptures."

A two-headed baby born in Brazil this week is actually a set of conjoined twins sharing one body because of a rare birth defect, doctors said Thursday.

The twins, born on Monday and named Jesus and Emanuel in honor of the upcoming Christmas holiday, have distinct brains and spinal cords but share internal organs, appearing as a single baby with two heads.

A landmark clinical trial that showed HIV drugs can be as effective as condoms in preventing transmission of the virus that causes AIDS was declared Science magazine's breakthrough of the year on Thursday.

Other top achievements of 2011 included a Japanese spacecraft's return to Earth with dust from an asteroid, progress toward a malaria vaccine and discoveries about modern humans' gene links to cavemen.

The journal Science is retracting a research paper suggesting that chronic fatigue syndrome may be caused by a particular virus.

The paper was published in 2009. The authors reported finding a virus called XMRV in blood cells from patients with the syndrome. But follow-up studies found no such connection.

Taiwanese authorities said Thursday they had slaughtered nearly 1,000 pigs following the island's worst outbreak of foot-and-mouth disease in more than 14 years.

The pigs were culled earlier this week at a farm in the southern city of Tainan after showing symptoms of the disease.

Philip Morris International's decision to slash the price of its best-selling Marlboro brand by 40 percent in Senegal has left health officials and activists fuming and sparked calls to toughen tobacco laws.

PMI, when contacted by AFP, refused to explain the shock decision to cut the prices of Marlboro -- the world's top-selling cigarette sold in some 180 countries -- to 400 CFA francs (61 euro cents, 79 US cents) from 650 CFA francs.

Health authorities sought Wednesday to reassure 50,000 British women who have breast implants made by a French company at the heart of a cancer scare, saying there was no evidence of a link to the disease.

France has said up to 30,000 women there may need to remove defective implants produced by the Poly Implant Prothese (PIP) company amid cancer fears, even though no "causal link" to the disease had yet been established.

The U.S. government asked scientists Tuesday not to reveal all the details of how to make a version of the deadly bird flu that they created in labs in the U.S. and Europe.

The lab-bred virus, being kept under high security, appears to spread more easily among mammals. That's fueled worry that publishing a blueprint could aid terrorists in creating a biological weapon, the National Institutes of Health said.

People who took blood pressure medicine during a 1980s clinical trial showed longer life expectancy two decades later than people who took a placebo, a U.S. study said on Tuesday.

The randomized trial included 4,736 patients aged 60 and over who had high blood pressure. Some were given a drug called chlorthalidone and others were given a sugar pill for a 4.5 year period beginning in 1985.