Young farm animals given antibiotics gain weight quickly. Now a study suggests that the same thing may happen to human infants treated with antibiotics.

Researchers writing in the International Journal of Obesity studied 11,532 English children born at normal weight in 1991 and 1992. They found that infants given antibiotics within six months of birth were 22 percent more likely than those given none to be overweight at age 3. Among those given antibiotics between 6 and 14 months, there was no link to body mass in childhood, but exposure from 15 to 23 months was linked to higher body mass index at age 7.

Antibiotics change the composition of the microbiome, the trillions of microbes that inhabit the body, and this, researchers say, may help explain the result. The exact mechanism is unknown.

"This study does not suggest that antibiotics are bad for you," said the lead author, Dr. Leonardo Trasande of New York University. "But our findings add to concerns about the inappropriate use of antibiotics."


Tick-borne virus new to hemisphere

Federal scientists have isolated a virus in ticks that has never before appeared in the Western Hemisphere and are calling on scientists to look for evidence of the disease-causing pathogen.

Virus hunters from the Centers for Disease Control and Prevention said the virus causes an illness nearly identical to ehrlichiosis, a tick-borne disease that is caused by a bacterium.

The newfound pathogen, known as a phlebovirus, was isolated in 2009 in two Missouri men who doctors knew had been bitten by ticks but whose disease didn't respond to antibiotics, which are useless against viral pathogens.

Dr. William Nicholson, chief of pathogen biology and disease ecology at the CDC, said the unexpected appearance of a phlebovirus in the United States stunned his research team. "This is the first time a phlebovirus has infected humans in the Western Hemisphere," he said.

Both men developed a fever and a drop in blood platelets, which are critical in the formation of blood clots. One suffered fatigue and recurrent headaches and the other reported fatigue, short-term memory loss and anorexia. Those symptoms have abated, doctors said.

To date, nearly 40 other viruses are known to be transmitted through tick bites. Nicholson's research was published in the New England Journal of Medicine.



A substance in human breast milk seems to reduce the risk of mother-to-child transmission of HIV, scientists reported.

Researchers collected breast milk samples from 81 HIV-positive Zambian women who transmitted the virus to their infants during breast-feeding, 86 HIV-positive women who did not transmit, and 36 uninfected women. The scientists analyzed the samples for concentrations of a carbohydrate called human milk oligosaccharides. There is growing evidence that the substance contains immunologically active components that may minimize the risk of viral transmission.

The study, led by Lars Bode of the University of California, San Diego, and published in the American Journal of Clinical Nutrition, found that women whose breast milk held concentrations of human milk oligosaccharides above the median were less than half as likely to have transmitted the infection to their babies as those with concentrations below the median. In resource-poor countries, the risk of HIV transmission from breast milk is outweighed by its benefits, so infected women are encouraged to breast-feed while taking antiretroviral drugs.