In the Dec 24th Issue of Science News, Sonia Shaw reviews increasing concern about infectious disease, against the complacent attitudes of the second half of C20th. She shows how the new era of concern is exemplified by the events of 2016:
• Just as the outbreak of Ebola in West Africa was coming under control in early 2016, WHO declared Zika virus, newly emerging in the Americas, and international public health emergency
• At the same time, what would develop into the largest outbreak of yellow fever in Angola in 30 years had just begun.
• A few months later, scientists reported the just-discovered “superbug” mcr-1 gene in microbes collected from humans and pigs in the US . The gene produces resistance to the last-ditch antibiotic colistin, bringing us another step closer to an era of untreatable infections that would transform the practice of medicine.
• Although in 2015, the WHO had declared Nigeria, one of the three last countries in the world suffering the infection, free of wild polio. By August 2016, it was back. Millions would have to be vaccinated to keep the infection from establishing a foothold.
• 2016 saw the convening of the UN General Assembly to consider the global problem of antibiotic-resistance. It was only the fourth time in its 70-plus-years that the assembly has been compelled to consider a health issue.
This is a far cry from 1962, when Nobel Prize winner Sir Frank Macfarlane Burne wrote “To write about infectious disease is almost to write of something that has passed into history.” Five decades on he would be surprised to know that, since then, over 300 infectious pathogens have either newly emerged or emerged in new places.
Experts suggest that three fundamental, interrelated factors fuel the microbial comeback.
• Across the globe, people are abandoning the countryside for life in the city, leading to rapid, urban expansions. In crowded conditions with limited access to health care and poor sanitation, pathogens like Ebola, Zika and influenza are provided with easy opportunities to spread. With more infections mingling, there are also more opportunities for pathogens to share virulence genes.
• Global demand for meat has quadrupled in the last 5 decades by some estimates, driving spread of industrial livestock farming techniques that can allow benign microbes to become more virulent. Use of colistin in livestock agriculture in China, has been associated with emergence of mcr-1, first discovered during routine surveillance of food animals. Genetic analyses suggest that siting chickens and pig factory farms in proximity to wild waterfowl has played a role in the emergence of highly virulent strains of avian influenza. Crosses of Asian and North American strains of avian influenza caused the biggest outbreak of animal disease in US history in 2014–2015. Containing that virus required the slaughter of nearly 50 million domesticated birds and cost over $950 million. Worryingly, some strains of avian influenza, such as H5N1, can infect humans.
• Globa warming provides further opportunities for pathogens to exploit. Scientists around the world have documented the movement of disease-carrying creatures including mosquitoes and ticks into new regions in association with newly amenable climatic conditions. Climate scientists predict range changes which will encourage bats and other animals. As the organisms spread, they carry pathogens such as Ebola, Zika and Borrelia burgdorferi (a bacterium responsible for Lyme disease) with them.
Since we can rarely develop drugs and vaccines fast enough to staunch the most dangerous waves of disease, early detection will be key. Researchers are now developing models and pilot programs showing how environmental cues such as temperature and precipitation fluctuations. The insights of wildlife and livestock experts can help pinpoint pathogens with pandemic potential before they cause outbreaks in people. Chlorophyll signatures, a proxy for the plankton concentrations associated with cholera bacteria, can be detected from satellite data, potentially providing advance notice of cholera outbreaks.
Shah believes that innovative financing methods, such as the World Bank’s recently launched Pandemic Emergency Financing Facility(a “global pandemic insurance policy” funded by donor countries, the reinsurance market and the World Bank) could help ensure that resources to isolate and contain new pathogens are readily available. The nonprofit organization, EcoHealth Alliance, is one of a handful that aim to detect new pathogens at their source and proactively minimize the risk of their spread – instead of waiting for epidemics to emerge and then spending billions on developing vaccines and drugs.
Shah concludes “The challenge of surviving in a world of pathogens is far from over. In many ways, it’s only just begun”.
Science News, Sonia Shaw Vol. 190, No. 13, December 24, 2016, p. 32
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