Posts or Comments 25 February 2021

Monthly Archive for "January 2020"



Climate &Enteric Pathogens &Floods Bill Brieger | 16 Jan 2020

Viruses and bacteria are spread by floodwater – evidence from the 2011–2012 La Niña floods in Peru

A flooded street in Santa Clara de Nanay, April 2, 2012 (courtesy of Asociación Benéfica Prisma)

Josh Colston of the Division of Infectious Diseases and International Health, University of Virginia School of Medicine, Charlottesville, presented his findings on the connection between floods and enteric pathogens in Peru at the 2019 meeting of the American Society of Tropical Medicine and Hygiene. Below he has shared us with a summary of his work and findings. A link to the recently published work is also provided.

Climate change represents an impending global public health threat since extreme weather events like floods can cause injury and drowning, toxic exposure, and the spread of infectious diseases. Poor people living in unplanned settlements with inadequate infrastructure are most vulnerable to these impacts. Outbreaks of gastroenteritis often occur following floods and can be particularly serious for young children. But there are many different bugs that can cause this illness and it’s not yet known which of them are most prone to contaminating floodwater. However, a newly published paper in the International Journal of Environmental Research and Public Health may shed some light thanks to a small piece of serendipity in an otherwise devastating natural disaster.

Location of the study site

The 2010-2012 La Niña event (the colder counterpart of El Niño) caused huge disruption to weather patterns over several continents. The Amazonian region of Peru around the city of Iquitos was particularly badly hit by heavy rains. It’s a low-lying area particularly prone to flooding since it’s situated at the confluence of several Amazon tributaries. Waterways are the main transport routes in the region, so most of the population lives close to the banks of the rivers. Following months of heavy rainfall in late 2011 and early 2012, three of the rivers – the Ucayali, Marañón, and Nanay – burst their banks, causing widespread flooding and forcing many locals to abandon their homes and evacuate to drier areas. By the end of the disaster, an estimated 50,000 people had been made homeless.

It just so happened that, in a quiet fishing town on the outskirts of Iquitos called Santa Clara de Nanay, an epidemiologic surveillance study was being carried out. Around 300 babies had been recruited and field workers were taking regular measurements and biological samples to see how they were growing and what bugs they were catching. Using a special epidemiologic method known as ‘causal inference’ researchers were able to compare the samples of the infants’ poop before, during and after the flood to see how the rates of infection changed.

Estimated prevalence rates of four viruses and three bacteria before, during and after the flood

Interestingly, two viruses showed substantial upticks during the flood. Rates of rotavirus were 5 times, and sapovirus 2.5 times the normal level for that time of year. What’s more, the rotavirus cases seemed to be caused by unusual virus strains that were not common in the area and which are less preventable by vaccine. Meanwhile, three bacteria – Campylobacter, Shigella and a type of E. coli called ST-ETEC – showed smaller increases. It’s common to catch Campylobacter from poultry and, since a lot of households in Santa Clara keep chickens in their yards, it’s possible that the mini-outbreak was cause by floodwater washing chicken droppings out of the coops and into the wider environment.

What’s clear from this and other recent studies, is that we need to start thinking bigger when it comes to drainage and sanitation solutions. Traditional low-cost, household-level improvements to water sources and sanitation facilities may not be up to the task in the face of climate events that may suddenly and unexpectedly expose entire communities to large amounts of untreated sewage. Investments in more ambitious, municipal-level water, wastewater, and drainage infrastructure – the kind that historically brought about massive, society-wide child health improvements in high income countries – may be the only sure route to climate resilience.

Ebola &Zoonoses Bill Brieger | 09 Jan 2020

Deforestation and Disease

Much attention is focused on the broader environmental and climatic consequences of deforestation, especially as this has seemed to pick up pace in places like the Amazon Basin. More attention is also needed concerning the disease transmission implications of deforestation. Recent studies have shed light on the problem. Basically deforestation as a result of urbanization or expanding commercial agriculture and related human activity brings people closer to areas where diseases can spread.

The connection between bats and the spread of Ebola in humans has been posited for some time. Forest News notes that “Fruit bats (Pteropodidae) are suspected reservoir hosts for the Ebola virus,” and thus, “Deforestation may accelerate the spread of the deadly Ebola disease in the rainforests of West and Central Africa by increasing human-bat interactions.” They are sharing information by Olivero and colleagues recently published in Mammal Review.

These researchers “show that the range of some fruit bat species is linked to human activities within the favourable areas for the Ebola virus. More specifically, the areas where human activities favour the presence of five fruit bat species overlap with the areas where EVD outbreaks in humans were themselves favoured by deforestation.” They have modeled and mapped an area in West and Central Africa based on climate, including annual temperature ranges, the presence of rainforest and mammal distribution to create an area known as “The Ebola Virus Area.”

Concerning malaria, research by Chua and colleagues in Malaysia found that, “contributes to a growing body of evidence implicating environmental changes due to deforestation, expansion of agricultural and farming areas, and development of human settlements near to forest fringes in the emergence of P. knowlesi in Sabah.” Their research is part of more than a dozen studies over the past nine years that links deforestation and greater interaction between humans and macaque monkeys, the normal victim of P. knowlesi. One of the earlier studies reports that, ” ongoing ecological changes resulting from deforestation, with an associated increase in the human population, could enable this pathogenic species of Plasmodium to switch to humans as the preferred host.”

Eliminating the mammal hosts of these diseases is not an option because as Olivero explained about bats, “The entire function and ecology of forests would be put at risk if these vital pollinators and seed dispersers are eliminated.”

Considering another tropical disease, Visser warns that, “Climate change, deforestation, urbanization, and increased population mobility have made the risk of large outbreaks of yellow fever more likely than ever.” The lesson from these experiences is not mainly that we need to increase coverage of proven preventive measures, but that we need broader change in our approaches and policies toward land use.