Most countries in Asia and Africa already hit by bird flu continue to have weak surveillance programs for detecting the deadly virus in both humans and flocks, the World Health Organization (WHO) warned on Tuesday.The United Nations agency also said that the virus' spread to 32 countries since February marked "the fastest and most extensive geographical spread" of any avian influenza virus since the disease was first reported in 1878.Migratory birds are partly responsible for the dramatic recent spread to new areas, bringing to 48 the number of countries with H5N1 virus in domestic or wild birds, according to the WHO. This had complicated control measures in animals as eliminating it in wild birds was "considered impossible"."...surveillance of both human cases and poultry outbreaks remains weak in most affected countries in Africa and Asia," said a WHO report, prepared for its annual assembly of 192 member states being held in Geneva from May 22-27.Shigeru Omi, WHO director for the Western Pacific, told Reuters earlier in Jakarta that Indonesia -- the nation with the most bird flu deaths this year -- had the will to combat the disease but far-flung provinces of the huge archipelago had fallen short at putting plans into action.In humans, detection was complicated as early symptoms of influenza are sometimes hard to identify as being caused by the H5N1 virus, there is high incidence of other respiratory diseases in affected countries, as well as technical difficulties in confirming the diagnosis, according to the WHO.The H5N1 virus remains essentially an animal disease, but has infected 205 people and killed 113 since late 2003, it says.Some mutations have occurred and if the virus acquires the ability to spread easily from human to human it could spark a deadly pandemic and could kill millions of people, the WHO says.While instances of limited human-to-human transmission have occurred, "in no case has the virus spread beyond a first generation of close contacts", it added.The WHO has drawn up a game plan, including "fire blanket" use of Swiss drugmaker Roche's antiviral drug Tamiflu, to try to stamp out an outbreak if it starts spreading easily among humans."To increase the likelihood that early intervention using an international stockpile of antiviral agents will be successful, surveillance in affected countries needs to improve, particularly the capacity to detect clusters of cases closely related in time and place," the agency said.The WHO said it was maintaining the level of its pandemic alert at phase 3 out of six, meaning a new virus subtype is causing human infections but does not spread easily.The agency noted that there had several cases in mammals including domestic cats, but reiterated that the species barrier was substantial. However, greater vigilance for any signs that cats are becoming more widely infected was "essential".