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Pathogenic plant virus jumps to honeybees, may explain bee population decline

Jan. 21, 2014 — A viral pathogen that typically infects plants has been found in honeybees and could help explain their decline. Researchers working in the U.S. and Beijing, China report their findings in mBio, the online open-access journal of the American Society for Microbiology.

The routine screening of bees for frequent and rare viruses “resulted in the serendipitous detection of Tobacco Ringspot Virus, or TRSV, and prompted an investigation into whether this plant-infecting virus could also cause systemic infection in the bees,” says Yan Ping Chen from the U.S. Department of Agriculture’s Agricultural Research Service (ARS) laboratory in Beltsville, Maryland, an author on the study.

“The results of our study provide the first evidence that honeybees exposed to virus-contaminated pollen can also be infected and that the infection becomes widespread in their bodies,” says lead author Ji Lian Li, at the Chinese Academy of Agricultural Science in Beijing.

“We already know that honeybees, Apis melllifera, can transmit TRSV when they move from flower to flower, likely spreading the virus from one plant to another,” Chen adds.

Notably, about 5% of known plant viruses are pollen-transmitted and thus potential sources of host-jumping viruses. RNA viruses tend to be particularly dangerous because they lack the 3′-5′ proofreading function which edits out errors in replicated genomes. As a result, viruses such as TRSV generate a flood of variant copies with differing infective properties.

One consequence of such high replication rates are populations of RNA viruses thought to exist as “quasispecies,” clouds of genetically related variants that appear to work together to determine the pathology of their hosts. These sources of genetic diversity, coupled with large population sizes, further facilitate the adaption of RNA viruses to new selective conditions such as those imposed by novel hosts. “Thus, RNA viruses are a likely source of emerging and reemerging infectious diseases,” explain these researchers.

Toxic viral cocktails appear to have a strong link with honey bee Colony Collapse Disorder (CCD), a mysterious malady that abruptly wiped out entire hives across the United States and was first reported in 2006. Israel Acute Paralysis Virus (IAPV), Acute Bee Paralysis Virus (ABPV), Chronic Paralysis Virus (CPV), Kashmir Bee Virus (KBV), Deformed Wing Bee Virus (DWV), Black Queen Cell Virus (BQCV) and Sacbrood Virus (SBV) are other known causes of honeybee viral disease.

When these researchers investigated bee colonies classified as “strong” or “weak,” TRSV and other viruses were more common in the weak colonies than they were in the strong ones. Bee populations with high levels of multiple viral infections began failing in late fall and perished before February, these researchers report. In contrast, those in colonies with fewer viral assaults survived the entire cold winter months.

TRSV was also detected inside the bodies of Varroa mites, a “vampire” parasite that transmits viruses between bees while feeding on their blood. However, unlike honeybees, the mite-associated TRSV was restricted to their gastric cecum indicating that the mites likely facilitate the horizontal spread of TRSV within the hive without becoming diseased themselves. The fact that infected queens lay infected eggs convinced these scientists that TRSV could also be transmitted vertically from the queen mother to her offspring.

“The increasing prevalence of TRSV in conjunction with other bee viruses is associated with a gradual decline of host populations and supports the view that viral infections have a significant negative impact on colony survival,” these researchers conclude. Thus, they call for increased surveillance of potential host-jumping events as an integrated part of insect pollinator management programs.

Agriculture and Food News — ScienceDaily

Emerging Pathogens: Listeria Threatens a Growing Senior Population

From August through October 2011, 147 people in 28 states were infected with Listeria monocytogenes after eating cantaloupe from Jensen Farms in Colorado. There were 33 deaths, and one pregnant women had a miscarriage as a result, making it one of the deadliest outbreak of foodborne illness in the U.S. in recent years.

Apart from some diarrhea or minor gastrointestinal problems, most people don’t get sick when they’re exposed to Listeria. But, if the pathogen gets into their bloodstream, it can cause listeriosis, a disease that kills one out of every five victims. Because of these odds, Listeria has the highest mortality rate of foodborne pathogens.

Groups most at risk for Listeria infections are older adults, pregnant women and people with an underlying medical conditions such as cancer liver or kidney disease, diabetes or HIV/AIDS.

People 65 and older are four times more likely to get sick from Listeria poisoning than the general population, and pregnant women – who may not develop listeriosis themselves but whose babies could be threatened – are 10 times more likely.

While it’s important to remember that there are only about 800 laboratory-confirmed cases of Listeria in the U.S. each year, more than half of them occur among older adults. In the 2011 cantaloupe-related outbreak, most of the cases involved people older than 60, and those who died were between the ages of 48 and 96.

“Typically, when the highly susceptible populations are infected, they’re the ones that experience the most severe symptoms and often the high mortality rates,” said Michael Doyle, director of the Center for Food Safety. “As we age, we need to be more careful about the types of foods we eat. That means making sure that foods that are likely to be contaminated with harmful microbes should be cooked or somehow processed or treated to ensure safety. We should not be taking the risks that maybe younger people would take – eating less well-cooked meat, for example.”

Foods that typically cause Listeria outbreaks are Mexican-style soft cheeses made with unpasteurized milk, deli meats, and hot dogs. Produce was not often identified as a source in the past, but sprouts caused an outbreak in 2009, and pre-cut celery caused an outbreak in 2010.

“There have been a lot of successes on the ready-to-eat meat front,” said Alicia Cronquist, an epidemiologist with the Colorado Department of Public Health and Environment who investigated the 2011 outbreak. “Manufacturers have put in enormous efforts, and we’ve seen a real decline in outbreaks due to those deli meats and poultry products.”

Doyle agrees and says this is why he’s not as concerned about lunch meats now as he is about fresh produce.

“I am very concerned about fruits and vegetables – not just because of Listeria, but because we’ve had hiccups with a lot of other pathogens with fresh fruits and vegetables,” he said.

“We frequently identify new vehicles when we do outbreak investigations, whether it’s Listeria, E. coli or Salmonella,” Cronquist said. “This outbreak was very unusual in that it was huge and had a terrible number of fatalities, but it was also notable in that [cantaloupe] was a novel Listeria vehicle.”

In addition to its high mortality rate, Listeria is an unusual foodborne pathogen because it can survive and multiply at refrigerator temperatures. In order to avoid Listeria, CDC recommends that high-risk consumers heat hot dogs, lunch meats and cold cuts to an internal temperature of 165 degrees F and avoid products with unpasteurized milk, refrigerated paté or meal spreads, and uncooked smoked seafood.

When it comes to melon safety, consumers and food preparers should wash their hands before and after handling a whole melon, scrub the outside of melons under running water and dry them with a clean cloth or paper towel before cutting, and then promptly consume or refrigerate cut melon and keep it for no more than a week.

FDA has also released “Food Safety for Older Adults” to address threats from all major pathogens and offer prevention tips for seniors. Because, as Doyle says, “It’s the elderly that are going to be more susceptible to all these different pathogens, not just Listeria. They’re the ones that are going to suffer the most severe consequences.”

Food Safety News

Genetic study pushes back timeline for first significant human population expansion

Sep. 24, 2013 — About 10,000 years ago, the Neolithic age ushered in one of the most dramatic periods of human cultural and technological transition, where independently, different world populations developed the domestication of plants and animals. The hunter-gatherers gave rise to herders and farmers. Changes to a more sedentary lifestyle and larger settlements are widely thought to have contributed to a worldwide human population explosion, from an estimated 4-6 million people to 60-70 million by 4,000 B.C.

Now, researchers Aiméa, et al., have challenged this assumption using a large set of populations from diverse geographical regions (20 different genomic regions and mitochondrial DNA of individuals from 66 African and Eurasian populations), and compared their genetic results with archaeological findings. The dispersal and expansion of Neolithic culture from the Middle East has recently been associated with the distribution of human genetic markers.

They conclude that the first significant expansion of human populations appears to be much older than the emergence of farming and herding, dating back to the Paleolithic (60,000-80,000 years ago) rather than Neolithic age. Therefore, hunter-gatherer populations were able to thrive with cultural and social advances that allowed for the expansion. The authors also speculate that this Paleolithic human population expansion may be linked to the emergence of newer, more advanced hunting technologies or a rapid environmental change to dryer climates.

Finally, they also suggest that strong Paleolithic expansions may have favored the emergence of sedentary farming in some populations during the Neolithic. Indeed, the authors also demonstrate that the populations who adopted a sedentary farming lifestyle during the Neolithic had previously experienced the strongest Paleolithic expansions. Conversely, contemporary nomadic herder populations in Eurasia experienced moderate Paleolithic expansions, and no expansions were detected for nomadic hunter-gatherers in Africa. “Human populations could have started to increase in Paleolithic times, and strong Paleolithic expansions in some populations may have ultimately favored their shift toward agriculture during the Neolithic,” said Aiméa.

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The above story is based on materials provided by Molecular Biology and Evolution (Oxford University Press), via EurekAlert!, a service of AAAS.

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