BioEd Online

A team of experts from the World Heath Organization (WHO) is making its way north in Pakistan to investigate a cluster of at least eight cases of avian flu in people living near the Afghan border. They will be seeking to establish whether the disease is spreading, and whether the cases were caused by human-to-human transmission.

Cases of bird flu continue to occur worldwide, mostly in Indonesia, and this is the colder time of year when flu is expected to hit hardest in the northern hemisphere. But this latest outbreak is worrying in that it involves the biggest batch of closely related cases since a cluster of eight infected people was reported in Indonesia in May 2006.

"So far, we are not seeing anything different than in previous instances of H5N1 outbreaks," says Gregory Hartl, a spokesman for WHO, whose current information comes from Pakistani authorities.

The Pakistan cases started in mid-November, or possibly earlier, when five family members fell ill in Abbottabad, north of Islamabad. Two of the brothers have died, one of whom was buried before he could be tested for H5N1.

In December, a man and his niece in the same town were found to have H5N1. They are thought to have worked on the same farm as the first family affected. Another man was found to have H5N1 in a nearby town some distance from there. Another case is suspected but not yet confirmed, which would bring the cluster to nine.

Pakistan has had repeated outbreaks of avian flu in poultry over the past two years.

On the track

The WHO team will be tracking down, treating and testing people who came into contact with the infected cases. Monitoring for cases in the area will be key to establishing whether the virus has become more virulent or shows signs of spreading.

Meanwhile, Pakistani health authorities are poring over hospital records from the past few months to see, retrospectively, whether there has been any upsurge in the incidence of respiratory illnesses.

Human-to-human transmission cannot be ruled out, says Hartl, as it has occurred on a limited basis on several occasions in the past. Tests of 40 people who have had contact with the patients have so far all turned up negative. Genetic sequencing will help to pin down the mode of transmission and whether any important genetic changes have occurred in the virus.

Early warning

The Pakistan cluster highlights the obstacles faced by the WHO in containing the spread should a pandemic strain of H5N1 appear. The strategy calls for early diagnosis of cases, in the hope that blanket treatment with antivirals will stamp out an emerging pandemic before it spirals out of control. Computer models suggest that for this to have any chance of succeeding, WHO would have a window of three weeks for this diagnosis at most.

But although the first cases occurred in mid-November at the latest, Pakistan only officially informed WHO on 12 December, a day after the first media reports. WHO made the cases public on 15 December.

Last Friday, the WHO also confirmed the first case in Myanmar: a 7-year old girl from Kyaing Tone Township, Shan State, who was hospitalized in late November, and has since recovered. A WHO team has so far found no evidence of infections in any of the case's contacts or in the area.