Mutations in the bird flu virus have been found in two infected people in Egypt, in a form that might be resistant to the medication most commonly used to treat the deadly disease, the World Health Organization said Thursday.
The mutations in the H5N1 virus strain were not drastic enough to make the virus infectious enough to spark a pandemic, WHO officials said. But more such mutations could prompt scientists to rethink current treatment strategies.
Samples taken from two bird flu patients in Egypt — a 16-year-old girl and her 26-year-old uncle — were not as responsive as regular H5N1 viruses to Tamiflu, a drug also know as oseltamivir that is used to treat the disease, the officials said.
The girl and her uncle died in late December, as did the man's 35-year-old sister, although she has not yet been confirmed as having had H5N1. The three — who lived together in Gharbiyah province, 50 miles northwest of Cairo — fell ill within days of one another after being exposed to sick ducks.
"Based on the information we have, we can't yet rule out human-to-human transmission," said Dr. Fred Hayden, a WHO bird flu and antivirals expert. "We need to better understand the dynamics of this outbreak."
Although people have passed the virus on to other people, such infections are rare, and most patients have been infected by direct contact with sick birds.
Scientists fear, however, that the virus could mutate into a form more easily passed between people, which could spark a flu pandemic.
The drug-resistant strains found in Egypt likely developed after the patients were hospitalized and treated with Tamiflu, with the virus responding directly to the drug, Hayden said. It was not proven, however, that that was the case, and a more worrying scenario would be if drug-resistant strains were already circulating among birds.
Although Tamiflu remains the drug of choice to treat H5N1, experts may have to consider other options if they find more resistant viruses.
Because flu viruses evolve constantly, mutations are only worrisome if they make the virus more infectious, lethal or drug-resistant.
"What the resistance tests look for are markers associated with antiviral resistance," though finding the markers did not necessarily mean Tamiflu would not work, said Dr. Angus Nicoll, flu director at the European Centre for Disease Prevention and Control.
Hayden said the mutations found in Egypt were different from Tamiflu-resistant H5N1 viruses found in patients two years ago in Vietnam. The Vietnamese strains were definitely resistant to Tamiflu, whereas the Egyptian viruses have only proven they are not as susceptible to the drug, he said.
Tamiflu-resistant viruses such as those found in Vietnam are often treatable with an older, less expensive class of antivirals, known as amantadanes. Some bird flu virus strains from Indonesia and China have also proven susceptible to amantadanes.
H5N1 first hit Egypt last year, and has since infected 18 people, 10 of whom have died.
Since the H5N1 outbreak first began in late 2003, it has decimated the Asian poultry industry and infected at least 265 people worldwide, 159 of whom have died, according to WHO.