No immediate threat

August 13, 2013 12:06 am | Updated November 16, 2021 08:15 pm IST

The influenza A(H7N9) virus may not have the characteristics required to quickly and easily spread among humans but the first confirmed case of human-to-human transmission recently reported in the British Medical Journal (BMJ) indicates that it is not completely devoid of such ability either. The novel bird flu strain that emerged in China in late March caused infections in about 134 people and killed 43; WHO declared it to be “one of the most lethal influenza viruses seen so far.” As per an April 24 study, only two family clusters showed any possibility of spread among humans. The BMJ study has now confirmed a person-to-person transmission in one of the two suspected clusters — a 60-year-old father passing the virus to his 32-year-old daughter; the index patient and daughter both died. The father had definite exposure to poultry like a majority of infected people, while she only came in contact with his oral secretions. The route of transmission from the index patient has been confirmed by genome sequencing — the strains from both the patients are “almost genetically identical.”

The number of new infections in humans has dropped significantly in recent weeks. The closing down of poultry markets, and not the virus’s waning infectivity, could be the likely reason for this. In fact, the last infection was as recent as August 3. A recent study has detailed the H7N9’s potential to spread through air. While the avian strains failed, a strain isolated from humans was found to be “highly transmissible in ferrets” through respiratory droplets. Ferrets are the best animal models to study virus transmission among humans. The virus’s ability to efficiently replicate in human airway cells has also been demonstrated. Hence, there is no reason to drop our guard, considering the number of undetected cases in humans and H7N9’s ability to silently spread in poultry without causing disease. People with undetected infection may provide the virus an ideal opportunity to “adapt to humans.” The virus may also re-emerge in winter. Transmissibility among humans has so far been “non-sustainable” but it is important to know what changes are required to make the virus spread easily and become more virulent. Though controversial, there is a case for allowing scientists to engineer H7N9 strains to “assess the pandemic potential” of the circulating strains. This is a test case for the U.S. Department of Health and Human Services after the huge controversy triggered last year over the H5N1 strain. Its decision would go a long way in dictating the kind of research that can be undertaken using U.S. federal funds.

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