Persistent Prions: Soilbound Agents are More Potent!

Science News, July 21, 2007; Vol. 172, No. 3 , p. 36

Carolyn Barry

Deformed proteins called prions cause fatal brain-destroying disorders, such as chronic wasting disease in deer and elk and mad cow disease, which can infect people. Evidence suggests that prions make their way into animals’ nervous systems through ingestion, but scientists aren’t sure.

A new study shows that prions become more infectious when they latch on to soil particles that animals eat, suggesting that ingestion is a primary route of disease transmission. “Our study points us in one direction that explains how these animals are getting infected,” says study author Judd Aiken of the University of Wisconsin–Madison.

Prions enter the environment from the remains of infected animals, and, to some degree, from body fluids such as urine and saliva. Prions linger in soil for at least 3 years (see related SN article below) by binding tightly to clay and other minerals. Aiken had hypothesized that soil would hinder the action of the clingy prions, making them less infectious. He was surprised to find the opposite.

“The binding of infectious agents in soil actually greatly enhances the infection,” Aiken says. “It makes the disease more transmissible.”

Wild and farm animals often swallow up to several hundred grams of soil per day when eating plants, drinking muddied water, and licking the ground to get minerals. In doing so, they may consume prions. The relationship between ingestion and infectivity is unclear, though, because previous experiments showed that prions are inefficient at infecting animals that eat diseased tissue.

Aiken and his team fed each of three groups of hamsters a different soil type containing prions. Other hamsters were given an equivalent dose of a prion mixture derived from the brains of infected animals. All soil-eating hamsters were at least as likely to contract the prion disease as those that had ingested the prion-brain mixture, which has been considered an efficient transmitter of prions.

Two of the three soils had an even more dramatic effect. Hamsters that ate either of those soils had a higher rate of prion disease than did animals that ate the prion-brain mix. Animals that ate the third soil, which contained more organic matter than the other two did, had the same infection rate as hamsters that ate the prion-brain mix.

Researchers hypothesize that soil might protect prions from the destructive environment of the digestive system. Alternatively, Aiken says, soil particles might break up clumps of prions into smaller, more numerous clusters. Or, the particles could change the way in which prions enter nervous system tissues.

The study, in the July PLoS Pathogens, yielded “very fascinating findings,” says Michael Miller, a wildlife veterinarian at the Colorado Division of Wildlife in Fort Collins. “It ties together observations that people have made throughout the years.” He suggests that the different infectivity rates of prions in the three soils may also explain why the disease afflicts animals in some areas more than in others.

Prions’ Dirty Little Secret

Science News, Feb. 11, 2006; Vol. 169, No. 6 , p. 93

Janet Raloff

Fifteen years ago, scientists at the National Institutes of Health reported that malformed prions—proteins that can trigger lethal illnesses including mad cow disease—remain on soil surfaces for at least 3 years. Now, scientists report why rain doesn’t flush away the prions: The proteins bind almost irreversibly to clay.

In fact, clay can “retain up to its own mass of … prion proteins,” says Peggy Rigou of the National Institute of Agronomic Research (INRA) in Jouy-en-Josas, France.

Her team added sheep prions to pure clay, sandy soil, and loam. Positively charged parts of the protein molecules bound to the negatively charged surface of the clay that was present in all the soil samples. Extensive washing failed to dislodge the prions. However, when the chemists treated the mixtures to make the proteins negatively charged and then ran an electric current through each mixture, the prions migrated off the clay particles.

Freeing the prions was a major achievement, Rigou notes, because it enables scientists for the first time to measure prion concentrations in soil. Until now, no technique could confirm that intact prions were present in soil. In an upcoming Environmental Science & Technology, her team reports that the new procedure permits detection of concentrations as low as 0.2 part per billion.

Soils might acquire prions from animal wastes or carcasses. Scientists’ concern is that livestock might ingest infected clay particles while eating grass or drinking from mud puddles, Rigou says.

PRION is an acronym for a unique infectious agent called a prion (proteinaceous infectious particle), composed of abnormal proteinaceous material devoid of detectable amounts of nucleic acid. These are abnormal versions of prion protein, or “PrP” which is ubiquitous to cell membranes, but is highly species specific. These infective agents can infect cows in the form of Bovine Spongiform Encephalopathy (BSE) and is also known as “Mad Cows Disease”. Feline Spongiform Encephalopathy (FSE) occurs in cats. In sheep and goats, the disease is called Scrapie, In mink, the disease is Transmissible Mink encephalopathy (TME). In mule deer and elk, the disease is called Chronic Wasting disease. Human disease can be classified as Creutzfeldt-Jakob Disease (CJD), variant CJD (vCJD), Gerstmann-Staussler-Scheinker Disease (GSS), Kuru, Fatal Familial Insomnia (FFI), or in infants, Alpers Syndrome.

Virulence Factors: Prions are proteins. The body encodes a gene for a normal protein, PrP, usually found in lymphocytes and CNS neurons. PrP has a normal conformation known as PrPc, which is genetically encoded. It becomes misfolded into a form known as PrPsc, and causes other proteins to become misfolded as well.

The protein goes from a 40% alpha helix with almost no beta sheet to 30% alpha helix and 45% beta sheet but retains same amino acid sequence. It had previously been thought that the amino acid sequence could have mainly one active structure, but this shows that’s not true. Unlike PrPc, the misfolded PrPsc is not easily digested by proteases. It does not cause an immune response. The abnormal protein can’t be broken down in the body and so it aggregates in the brain.

These particles do not infect cells or tissues and propagate, but rather are able to convert normal prion proteins into the abnormal form. The conversion rate is logarithmic but slow.

Trouble for forests of the Northern U.S. Rockies?

published Science News, June 16, 2007; Vol. 171, No. 24 , p. 382

Climate change expected to occur in the coming decades may cause forests in northern stretches of the U.S. Rockies to stop absorbing carbon dioxide and even to release some to the atmosphere, exacerbating the planet’s warming.

Trees pull carbon dioxide from the air as they grow. Much of the carbon from that gas is stored in wood and foliage, but some ends up in material littering the forest floor and in the underlying soil. From there, it can make its way back into general circulation, says Céline Boisvenue, an ecologist at the University of Montana in Missoula.

She and her colleague Steven W. Running used computer models to estimate how three climate-change scenarios might affect carbon storage at forest sites in Idaho, western Montana, and northwestern Wyoming.

The good news: By 2089, the growing season in the forests will be at least 3 weeks longer than it was in 1950. The bad news: Over that same period, higher temperatures will cause the trees to suffer water stress—slowing or stopping their growth—for an additional 8 weeks each year. Even under a climate scenario with higher precipitation than at present, trees will have insufficient water for 54 more days each year in 2089 than they did in 1950.

By the year 2020, under a scenario with reduced precipitation, dieback of trees and decomposition of leaf litter at three of the six studied sites will cause the forests to emit more carbon dioxide than they absorb. By the year 2070, the forests at five of those sites will be net producers of carbon, says Boisvenue.

reported by Sid Perkins from the American Geophysical Union meeting in Acapulco, Mexico.

Global-Warming Myths

It’s time to move forward on regulating greenhouse gases and here’s a regulatory plan that makes sense.

By Hoff Stauffer

The debate on global warming is burdened with unfortunate misconceptions that inhibit progress in moving forward.

One misconception is that “draconian measures” would be required to mitigate global warming. This is simply not so, if we implement a prudent program right away. Such a program would include four major strategies: increased energy efficiency (in buildings, autos, and appliances), coal mitigation (which includes increased use of solar, wind, geothermal, and perhaps nuclear power, as well as carbon capture and sequestration for coal-fired power plants), the development of new biofuels (such as cellulosic ethanol), and reversal of deforestation. These strategies can stabilize atmospheric concentrations of greenhouse gases at acceptable levels and for acceptable economic costs.

Another misconception is that it would be better to wait to take action until technology provides new options. In fact, we need to start reducing emissions right away. If we delay, the world will face a dreadful dilemma: the choice between adopting draconian measures and passing the “tipping point beyond which it will be impossible to avoid climate change with far-ranging undesirable consequences,” as the NASA climate scientist James Hansen puts it.

Another misconception is that a cap-and-trade system is the best approach to controlling the various greenhouse gases. Such a system sets a cap on total emissions and distributes emission allowances (or permits to emit) to market participants. These participants must buy allowances if they don’t have enough, and they may sell them if they have an excess. Such a system has helped reduce sulfur and nitrogen emissions from power plants in the United States.

But there are major problems with relying too heavily on this approach. The biggest is that it is too hard to figure out the economic and environmental effects. Prudent people do not want to risk unacceptable economic consequences. Other prudent people do not want to risk accomplishing too little. A politically acceptable compromise might take a long time and would probably tilt too far toward economic prudence, failing to achieve the necessary reductions.

Performance standards are a simpler approach. They would directly regulate the pollutants from new sources of emissions, such as power plants and autos, and mandate greater efficiency for new appliances and buildings. Performance standards can be implemented right away, without fear of unforeseen adverse economic consequences. They alone would result in major emission reductions over time. Such reductions could then be complemented by whatever additional help a cap-and-trade system provides.

Hoff Stauffer is the managing director of the Wingaersheek Research Group, which focuses primarily on global climate change. He previously worked at the U.S. Environmental Protection Agency.