(Press-News.org) More than three quarters of new, emerging or re-emerging human diseases are caused by pathogens from animals, according to the World Health Organization.
But a widely accepted theory of risk reduction for these pathogens – one of the most important ideas in disease ecology – is likely wrong, according to a new study co-authored by Stanford Woods Institute for the Environment Senior Fellow James Holland Jones and former Woods-affiliated ecologist Dan Salkeld.
The dilution effect theorizes that disease risk for humans decreases as the variety of species in an area increases. For example, it postulates that a tick has a higher chance of infecting a human with Lyme disease if the tick has previously had few animal host options beyond white-footed mice, which are carriers of Lyme disease-causing bacteria.
If many other animal hosts had been available to the tick, the tick's likelihood of being infected and spreading that infection to a human host would go down, according to the theory.
If true, the dilution effect would mean that conservation and public health agendas could be united in a common purpose: to protect biodiversity and guard against disease risk. "However, its importance to the field or the beauty of the idea do not guarantee that it is actually scientifically correct," said Jones, an associate professor of Anthropology.
In the first study to formally assess the dilution effect, Jones, Salkeld and California Department of Public Health researcher Kerry Padgett tested the hypothesis through a meta-analysis of studies that evaluate links between host biodiversity and disease risk for disease agents that infect humans.
The analysis, published in the journal Ecology Letters, allowed the researchers to pool estimates from studies and test for any bias against publishing studies with "negative results" that contradict the dilution effect.
The analysis found "very weak support, at best" for the dilution effect. Instead, the researchers found that the links between biodiversity and disease prevalence are variable and dependent on the disease system, local ecology and probably human social context.
The role of individual host species and their interactions with other hosts, vectors and pathogens are more influential in determining local disease risk, the analysis found.
"Lyme disease biology in the Northeast is obviously going to differ in its ecology from Lyme disease in California," Salkeld said. "In the Northeast, they have longer winters and abundant tick hosts. In California, we have milder weather and lots of Western fence lizards (a favored tick host) that harbor ticks but do not transmit the Lyme disease bacterium."
So, these lizards should be considered unique in any study of disease risk within their habitat. Or, as Salked put it, "All animals are equal, but some animals are more equal than others."
Broadly advocating for the preservation of biodiversity and natural ecosystems to reduce disease risk is "an oversimplification of disease ecology and epidemiology," the study's authors write, adding that more effective control of "zoonotic diseases" (those transmitted from animals to humans) may require more detailed understanding of how pathogens are transmitted.
Specifically, Jones, Salkeld and Padgett recommend that researchers focus more on how disease risk relates to species characteristics and ecological mechanisms. They also urge scientists to report data on both prevalence and density of infection in host animals, and to better establish specific causal links between measures of disease risk (such as infection rates in host animals) and rates of infection in local human populations.
For their meta-analysis, the researchers were able to find only 13 published studies and three unpublished data sets examining relationships between biodiversity and animal-to-human disease risk. This kind of investigation is "still in its infancy," the authors note. "Given the limited data available, conclusions regarding the biodiversity-disease relationship should be regarded with caution."
Still, Jones said, "I am very confident in saying that real progress in this field will come from understanding ecological mechanisms. We need to turn to elucidating these rather than wasting time arguing that simple species richness will always save the day for zoonotic disease risk."
INFORMATION:
Rob Jordan is the communications writer for the Stanford Woods Institute for the Environment.
END
In the wake of last week's meetings at the UN on the definition of the Sustainable Development Goals (SDGs), a group of international scientists have published a call in the journal Nature today, arguing for a set of six SDGs that link poverty eradication to protection of Earth's life support. The researchers argue that in the face of increasing pressure on the planet's ability to support life, adherence to out-dated definitions of sustainable development threaten to reverse progress made in developing countries over past decades.
Ending poverty and safeguarding Earth's ...
In the early 1950's, a 66-year-old woman, sick with colon cancer, received a blood transfusion. Then, unexpectedly, she suffered a severe rejection of the transfused blood. Reporting on her case, the French medical journal Revue D'Hématologie identified her as, simply, "Patient Vel."
After a previous transfusion, it turns out, Mrs. Vel had developed a potent antibody against some unknown molecule found on the red blood cells of most people in the world—but not found on her own red blood cells.
But what was this molecule? Nobody could find it. A blood mystery began, ...
News stories about mass shootings involving a shooter with mental illness heighten readers' negative attitudes toward persons with serious mental illness, according to a new report by the Johns Hopkins Bloomberg School of Public Health. The researchers also examined how such news stories impact support for policies to reduce gun violence. Compared to study respondents who did not read a story about a mass shooting, reading a news article describing a mass shooting raised readers' support for both gun restrictions for persons with serious mental illness, and for a ban on ...
COLUMBUS, Ohio – An obesity intervention taught by teen mentors in Appalachian elementary schools resulted in weight loss, lower blood pressure and healthy lifestyle changes among the younger students learning the curriculum, according to a new study.
In contrast, children taught the same lessons by adults in a traditional classroom saw no changes in their health outcomes.
The results of the eight-week clinical trial conducted by Ohio State University researchers suggest that school systems could consider using teen mentors to instruct younger children in select health-related ...
Visits to the ER are not always for true medical emergencies – and some policymakers have been fighting the problem by denying or limiting payments if the patient's diagnosis upon discharge is for "nonemergency" conditions.
Now a new UC San Francisco study challenges that framework by showing that criteria used as a basis to determine the appropriateness of an emergency room visit and to deny payment is inherently flawed. The study analyzed nearly 35,000 visits to hospital emergency departments around the country.
The research is published online today in JAMA (Journal ...
A group of researchers from 16 institutions around the world has identified a new class of anti-malarial compounds that target multiple stages of the malaria parasite's life cycle (http://www.niaid.nih.gov/topics/malaria/pages/lifecycle.aspx). These compounds could potentially be developed into drugs that treat and prevent malaria infection. Known as 4-(1H)-quinolone-3-diarylethers, the candidate anti-malarials are derived from a compound called endochin that effectively treats malaria in birds. When tested in the laboratory and in mice, the compounds demonstrated strong ...
Scientists at UC San Francisco have discovered how memory recall is linked to decision-making in rats, showing that measurable activity in one part of the brain occurs when rats in a maze are playing out memories that help them decide which way to turn. The more they play out these memories, the more likely they are to find their way correctly to the end of the maze.
In their study, reported this week in the journal Neuron, the UCSF researchers implanted electrodes directly on a region of the rat brain known as the hippocampus, which is already known to play a key role ...
Researchers at the University of California, San Diego School of Medicine have shown that a new imaging dye, designed and developed at UC San Diego Moores Cancer Center, is an effective agent in detecting and mapping cancers that have reached the lymph nodes. The radioactive dye called Technetium Tc-99m tilmanocept, successfully identified cancerous lymph nodes and did a better job of marking cancers than the current standard dye. Results of the Phase III clinical trial published online today in the Annals of Surgical Oncology.
"Tilmanocept is a novel engineered radiopharmaceutical ...
Monsoon rainfall in the Northern Hemisphere impacts about 60% of the World population in Southeast Asia, West Africa and North America. Given the possible impacts of global warming, solid predictions of monsoon rainfall for the next decades are important for infrastructure planning and sustainable economic development. Such predictions, however, are very complex because they require not only pinning down how manmade greenhouse gas emissions will impact the monsoons and monsoon rainfall, but also a knowledge of natural long-term climate swings, about which little is known ...
"Aiden, look!" piped NAO, a two-foot tall humanoid robot, as it pointed to a flat-panel display on a far wall. As the cartoon dog Scooby Doo flashed on the screen, Aiden, a young boy with an unruly thatch of straw-colored hair, looked in the direction the robot was pointing.
Aiden, who is three-and-a-half years old, has been diagnosed with autism spectrum disorder (ASD). NAO (pronounced "now") is the diminutive "front man" for an elaborate system of cameras, sensors and computers designed specifically to help children like Aiden learn how to coordinate their attention ...
