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Xanthomonas 
Invasion: Type III Secretion System

Gram-negative bacteria of the genus Xanthomonas infect more than 300 different species worldwide. Xanthomonas campestris pv. vesicatoria causes bacterial spot disease on pepper and tomato plants.

  • The bacteria enter the plant intercellular spaces via natural openings.
  • Bacterial surface structures allow the attachment to host cells.
  • Xanthomonas produces the extracellular polysaccharide xanthan  that protects the bacteria from environmental factors.
  • An essential pathogenicity factor is the type III protein secretion system which spans the bacterial membranes…
  • … And is associated with an extracellular pilus.
  • The pilus is connected to a channel-like translocon that is inserted into the plant plasma membrane.
  • The type III secretion system transports approximately 30 different bacterial effector proteins into the plant cell.
  • Bacterial effector proteins are transported to different cellular compartments and manipulate host cellular pathways. Some effector proteins reach the plant cell nucleus and modify plant gene expression.
  • Effector proteins suppress plant defense responses and promote bacterial multiplication at the infection site.

Video by Bernd Montag, Duc Phan Tran, Felix Herbst, Frank Montag.

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Are We At The Dawn Of The Age of Epidemics?

Over the past several weeks and months, we’ve seen a startling number of disease outbreaks pop up around the globe. It’s a trend that’s not completely surprising — one that could characterize the coming decades as the Age of Epidemics. Here are some of the scariest new diseases you need to know about.

The First Case of MERS in the U.S.

On May 2, 2014, the first confirmed case of MERS-CoV was reported in a traveler to the United States. This virus, more formally known as Middle East Respiratory Syndrome Coronavirus, causes people to develop severe respiratory illness with symptoms of fever, cough, and shortness of breath. To date, about 30% of people who contract the virus have died, most of them with a pre-existing medical condition.

At this point, the U.S. Center for Disease Control is not recommending that anyone change their travel plans because of MERS.

MERS is different from the coronavirus that causes SARS. Coronaviruses are unusually large RNA viruses that primarily infect the upper respiratory and gastrointestinal tracts of mammals and birds. They feature a series of surface projections that make them look like a solar corona, hence the name. These viruses are typically spread in the air, but the World Health Organization (WHO) is considering the possibility that MERS may have been transmitted directly by animals. And in fact, UAE scientists are currently investigating the possibility of transmission between camels and humans.

Countries with lab-confirmed MERS cases currently include Saudi Arabia, United Arab Emirates, Qatar, Oman, Jordan, Kuwait, UK, France, Tunisia, Italy, Malaysia, and the USA.

WHO Declares Polio a Public Health Emergency

Polio outbreaks are now a public health emergencyand civil strife is primarily to blame. Earlier this week, the World Health Organization described the recent resurgence of the disease as “an extraordinary event" and a public health risk to certain nations for which "a coordinated international response is essential." Bruce Aylward, a Canadian physician and WHO’s assistant director-general of polio, told CBC News that

It’s really attributed to two things. One is the spread out of Pakistan through the intense transmission there because of the suspension of the vaccine in one area. And then combined with an increase in vulnerability of some highly unstable areas like Syria where it’s been able to get another foothold.

By the end of last year, some 60% of all polio cases were the result of international spread, with increasing evidence that travelers were the primary contributors. One of the biggest concerns is Pakistan and its volatile area of North Waziristan (which borders Afghanistan), where polio vaccinations have been banned by the Taliban.

Polio mainly affects young children and is usually spread through contaminated water. It’s a crippling and potentially deadly infectious disease that invades the brain and spinal cord, causing paralysis. 

Measles On the Rise

Last week, Calgary and Edmonton had to declare a measles outbreak. At the same time, the U.S. is in the midst of its largest outbreak in decades. The Examiner reports:

In 2000, the U.S. considered measles to be eliminated because of vaccines, but the disease is currently making a big comeback because of a trend of parents not to vaccinating their children and frequent international travel. One to two percent of the population is at risk for developing measles, even in a vaccinated community.

"I’ve seen a lot of measles outbreaks in developing countries where vaccines aren’t available. I’ve stood by children’s bedsides and cared for them as they suffered. It is heartbreaking to see these children suffer from a disease that is preventable," said Nadia Qureshi, MD, pediatric infectious disease specialist at Loyola University Health System.

"We are seeing a rise in children in the U.S. with measles because international travel has become so common. People bring it back from endemic areas and because it’s highly contagious. If your child is not vaccinated, they are at risk.”

The Chikungunya Virus is Proliferating Rapidly in the Caribbean

The Chikungunya virus is galloping across the Caribbean and will almost certainly hit the United States. The mosquito-borne virus, which was documented in the region for the first time in December 2013, is now resident in Haiti. In the neighboring Dominican Republic, there have been anywhere from 150 to 200 cases confirmed since March. The virus is not currently found in the United States, but given climate change, the proximity of the U.S. to the Caribbean, and high rates of travel, it’ll only be a matter of time.

The disease, which can cause a fever and joint pain for months to years, is rarely fatal. Most people recover within a week. There is no vaccine and it’s spread by Aedes aegypti mosquito, which also transmits dengue fever in the region.

Dengue Fever Continues to Spread

Speaking of which, dengue fever, which only started to become a problem in the 1950s, is an emerging disease that’s still extending its geographical range; incidence has increased 30-fold over the last 50 years. This upward trend is attributed to long-distance travel, population growth and urbanization, lack of sanitation, ineffective mosquito control, and increases in the surveillance and official reporting of dengue cases. Approximately 40% of the world’s population live in regions where it can be transmitted. Dengue spreads via tropical and subtropical mosquitoes in the genus Aedes.

Ebola Ravages West Africa

As of May 3, 2014, the current outbreak of Ebola in West Africa has resulted in at least 244 infections and around 166 deaths (155 deaths in Guinea and 11 deaths in Liberia). Spread of the disease may be slowing down, as witnessed by the re-opening of the border between Guinea and Senegal. The ongoing epidemic began in January, spreading throughout Guinea and beyond the nation’s borders in West Africa.

The H5N1 Avian Flu Is Mutating in Bangladesh

Back in 2012, scientists discovered that the H5N1 virus requires only two mutations to become transmissible to humans. It’s considered one of the deadliest potential pandemics currently facing the world. Now, a team of scientists from Bangladesh have published a paper reporting that newer strains have replaced the older ones. According to the study, the H5N1 virus acquired a crucial gene from a low disease-causing bird flu virus ‘H9N2,’ and “accumulated single-point genetic changes that have the potential to modify the way the virus gets hinged to the host.”

And on the topic of influenza, there’s also H7N9 to consider.

A New Kind of Bird Flu Has Been Found in Antarctic Penguins

A new kind of influenza virus has been detected in Adelie penguins in Antarctica, though it doesn’t appear to make them sick. The recently discovered virus is unlike other avian flu strains, thus warranting further study. The finding also shows that avian influenza viruses can get down to Antarctica and be maintained in penguin populations.

Bovine Leukemia Is Transmissible to Humans

The CDC is reporting that bovine leukemia (BLV) has been found in human breast tissue. This is a strong indication that BLV can be contracted by and spread among humans. This is particularly frightening when considering that BLV-infected cattle are found worldwide. In the United States alone, about 38% of beef herds, 84% of dairy herds, and 100% of large-scale dairy operation herds are infected.

Studies done back in the 1970s indicated that transmission to humans wasn’t possible. But the advent of immunoblotting, which is 100 times more sensitive than previous techniques, revealed BLV DNA in human breast tissue. The new report concludes:

In view of the potential public health implications of BLV in humans, future research should address how humans acquire BLV infection, how frequently BLV infection occurs in different populations, and whether the virus is associated with human disease.

A Mysterious Kidney Disease Is Afflicting Male Farmworkers in Central America

An unknown form of kidney disease is afflicting male agricultural works, particularly sugar cane cutters, along the Pacific coast. Though researchers have known about it for at least 20 years, they’re struggling to explain it. NPR reports:

"We don’t know. That’s the unfortunate part, and we do desperately need to find some answers," says Reina Turcios-Ruiz, a medical epidemiologist with the U.S. Centers for Disease Control and Prevention’s office in Guatemala City.

This form of kidney failure, known as insuficiencia renal cronica in Spanish (or chronic kidney disease of unknown origin in English), is now found from southern Mexico to Panama, Turcios-Ruiz says. But it occurs only along the Pacific coast.

The disease is killing relatively young men, sometimes while they’re still in their early 20s. Researchers at Boston University have attributed about 20,000 deaths to this form of kidney failure over the past two decades in Central America.

As the disease progresses, agricultural laborers, who may earn a couple of thousand dollars a year, if they’re lucky, end up in need of dialysis that costs tens of thousands of dollars annually.

MRSA and the Pending Antibiotic Apocalypse

Methicillin-resistant Staphylococcus aureus is a strain of bacteria that has evolved resistance to a wide range of antibiotics, making it deadly and extremely difficult to treat. Indeed, it’s expected that within a few decades we'll enter into the “post-antibiotic era,” a time when even the most routine infections could threaten our lives.

Others

This is just a partial list — there are many other diseases currently afflicting human populations. To stay up to date, you can always check the CDC Current Outbreak List and Traveler’s Health Advisory.

Image1: MRSA bacteria 

Image2: Coronavirus (MERS)

Image3: Chikungunya virus

Human brain specimen with glioblastoma multiforme.

Brain Cancer Cells Hide While Drugs Seek
Tumor cells temporarily lose mutation to evade drugs targeting mutation

A team of scientists, led by principal investigator Paul S. Mischel, MD, a member of the Ludwig Institute for Cancer Research and professor in the Department of Pathology at the University of California, San Diego School of Medicine, has found that brain cancer cells resist therapy by dialing down the gene mutation targeted by drugs, then re-amplify that growth-promoting mutation after therapy has stopped.

The findings are published in the December 5, 2013 online issue of Science.

“This discovery has considerable clinical implications because if cancer cells can evade therapy by a ‘hide-and-seek’ mechanism, then the current focus (of drug therapies) is unlikely to translate into better outcomes for patients,” said Mischel.

In recent years, new cancer therapies have emerged that target tell-tale gene mutations to identify specific cancer cells for destruction. Unfortunately, a variety of “resistance mechanisms” have also emerged, among them incomplete target suppression, second-site mutations and activation of alternative kinases or enzymes that maintain growth-promoting signals to the cancer itself. 

“Most research is aimed at developing better drugs or better drug combinations to suppress these downstream signals,” Mischel said. “However, one thing that has not been carefully considered is whether cancer cells can modulate the levels of – and thus their dependence on – the target of the drug, evade therapy, and then re-acquire the oncogene to promote tumor growth when the drug is withdrawn.”

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