Emerging infections and the parasite’s dilemma

January 12th, 2015

Emerging infectious diseases continue to pose a threat to the global village, with a novel coronavirus and the first reported human infections with avian H7N9 influenza A being but the latest examples. I remember covering a meeting on this subject years ago in Atlanta when the late Nobel laureate Joshua Lederberg waxed philosophical at the podium.

"In a global village, bugs emerging anywhere are going to be a matter of very common concern very quickly," he said, adding the rhetorical and somewhat paradoxical question about whether humans owe our existence to a “shared interest’ with the very microbes we endlessly battle.

“In pondering this - and I have spent all of my life looking at microbial variability and diversity; I know all of the marvelous things they are able to do - I'm sort of left with, why are we still here?" he said. "It's perfectly easy to imagine the microbe that could wipe us out. We could conceptually design it, and we have had some close calls with something like the 1918 [Spanish] flu."

The answer may be that pathogenic microorganisms have a "shared interest" in our ultimate survival that is as much factored into their genetic makeup as the ability to mutate and thwart eradication, he noted.

"With very rare exceptions, our microbial adversaries have a certain degree of shared interest in our survival," he said. "The bug that lets its host live another day, itself survives another day. . . . There is the parasite's dilemma. If it proliferates rapidly, it may kill the host as a byproduct."

Hong Kong health authorities on Tuesday stepped up checks on travelers and hospital patients after it was reported that the new H7N9 bird flu virus had infected four people in eastern China, according to published reports. Two patients in Shanghai have died and a third in Anhui has fallen seriously ill since their infection last month. And a fourth case involving a poultry butcher was reported on Tuesday afternoon in Nanjing – the capital city of Jiangsu province, which neighbors Anhui, the South China Morning Post reported.

Officials advised Hong Kong travelers – especially those from Shanghai, Anhui and Jiangsu – to wear face masks and seek medical attention if respiratory symptoms developed. The cases have not been epidemiologically linked and appear to be due to poultry exposures rather than human transmission. Still, the flu virus is infamously mutable and the situation could change at any time.

Hong Kong is also casting a wary eye at an emerging coronavirus, presumably because the rapid emergence of SARS there a decade ago continues to resonate. “Without a single confirmed human case of the new virus in East Asia so far, the government of the autonomous Chinese territory has already begun alerting and training employees at hospitals, clinics and the airport to identify possible cases,” the New York Times reported.

According to the World Health Organization, coronavirus has killed 11 of the 17 people infected so far, including a man in Britain who fell ill after traveling to Saudi Arabia and Pakistan. “WHO does not advise special screening at points of entry with regard to this event, nor does it recommend that any travel or trade restrictions be applied,” the agency said.