Drug-resistant typhoid has become an invisible epidemic in Africa, scientists said on Monday after an unprecedented probe into the disease.

Writing in the journal Nature Genetics, the team sounded the alarm after sequencing more than 1,800 samples of typhoid bacteria from 63 countries.

A U.N.-sponsored independent report by experts on Monday denounced the World Health Organization's slow response to the Ebola crisis.

"It is still unclear to the panel why early warnings approximately from May through to July 2014 did not result in an effective and adequate response," an interim report by the experts said.

A new type of blood test is starting to transform cancer treatment, sparing some patients the surgical and needle biopsies long needed to guide their care.

The tests, called liquid biopsies, capture cancer cells or DNA that tumors shed into the blood, instead of taking tissue from the tumor itself.

San Francisco has become the first city in the nation to outlaw chewing tobacco from its playing fields, including AT&T Park, home to the San Francisco Giants.

Players and the manager of the team expressed support for the ordinance signed into law by Mayor Ed Lee on Friday but also concern about breaking the chewing habit.

Federal health regulators have questions about the benefits of an experimental combination drug for cystic fibrosis, including whether the addition of a second drug ingredient adds to the pill's effectiveness.

The Food and Drug Administration said in an online review that Vertex Pharmaceuticals' drug improved breathing in patients with the deadly inherited disease, but that the effect was small.

French scientists say they have succeeded in creating the world's first lab-grown human sperm cells in what experts said Friday could be a leap forward in tackling male sterility.

The Kallistem laboratory in the eastern French city of Lyon this week announced they had obtained "complete human spermatozoa in vitro", a world first which scientists have labored towards for some 15 years.

The World Health Organization on Saturday declared Liberia to be free of the Ebola virus, which has killed more than 4,700 people in the west African country.

"The outbreak of Ebola virus disease in Liberia is over," the UN health agency said in a statement. "Forty-two days have passed since the last laboratory-confirmed case was buried on 28 March."

China will more than double the tax on tobacco to 11 percent, the government announced Friday, as authorities try to deter smoking in the world's largest producer and consumer of tobacco.

"The cigarette wholesale sector will raise tax from five percent to 11 percent," a statement on the website of China's foreign ministry said.

The World Health Organization is issuing new advice on the best way to name new diseases — guidelines the U.N. health agency itself has previously broken.

In a statement published on Friday, WHO criticized disease names like Middle Eastern Respiratory Syndrome and swine flu, which can be stigmatizing. WHO said officials shouldn't name diseases after geographic locations, animal species, or peoples' names. It said names should include "generic descriptive terms."

Measles can harm the immune system for up to three years, leaving survivors at a higher risk of catching other infectious and potentially deadly diseases, researchers said Thursday.

It was previously known that measles could suppress the body's natural defenses for months, but the findings in the journal Science show that the dangers of the vaccine-preventable disease last much longer, by wiping out essential memory cells that protect the body against infections like pneumonia, meningitis and parasitic diseases.