Infections in Egypt raise scientists' fears that the virus will be spread by humans. This paradox, emerging from Egypt, the most recent epicenter of the disease, threatens to increase the disease's ability to spread from person to person.
The World Health Organization is to back an investigation into a change in the pattern of the disease in Egypt, the most seriously affected country outside Asia. Although infections have been on the rise this year, they have almost all been in children under the age of 3, while 12 months ago, it was mainly adults and older children who were affected.
And the infections have been much milder than usual; the disease normally kills more than half of those affected; all of the 11 Egyptians so far infected this year are still alive.
Experts say that these developments make it more likely that the virus will spread. Ironically, its very virulence has provided an important safeguard. It did not get much chance to infect other people when it killed its victims swiftly, but now it has much more of a chance to mutate and be passed on.
The WHO fears that this year's rise in infections among small children, without similar cases being seen in older people, raises questions about whether adults are being infected but not falling ill, so acting as symptomless carriers of the disease.
Its investigation, due to start this summer, will see whether this is happening by testing the blood of people who may have been in contact with infected birds but who have not themselves become sick, according to ProMed.