Over the past five years, an average of about 14 cruise ships a year have had outbreaks of diarrheal illness, and the culprit is almost always norovirus

The best way to avoid it is prevention, and the best prevention is hand washing.

The problem, he said, is passengers. “If Grandma is sick when she gets on, she’s going on the cruise anyway,” Dr. Vinjé said. “And that’s how the virus gets onboard. Then it lands on handrails and doorknobs, and the transmission continues.”

The industrial-size servings of food on a cruise ship with hundreds of passengers can be particularly worrisome, since once the virus enters the food it can spread rapidly. Food can also get more easily contaminated with the virus if it sits out for several hours, as is often the case with buffet-style meals.

And so many people being in one place eases the virus's spread. "In close quarters it doesn't get away, everything's concentrated," Zimring says.

The best defense against gastrointestinal disease, Zimring says, is to wash and sanitize your hands constantly

On Tuesday night, administration officials said the Pentagon would ask Congress to redirect $500 million from existing Defense Department funds to fight Ebola. The money is in addition to $500 million the Pentagon requested last week in redirected funds for both Iraq and Ebola.

Previous reports have also highlighted a potential association of the norovirus VPg protein with components of the eIF3 complex (28) and eIF4E, PABP, and eIF4G as well as the ribosomal protein S6 (29), although the functional relevance of these interactions has yet to be demonstrated. Here we describe the proteomic characterization of the murine norovirus translation initiation factor complex, demonstrating that VPg associates directly with the core components of the eIF4F complex and PABP. We further demonstrate that the interaction between eIF4G and VPg is essential for norovirus translation. Furthermore, we demonstrate that eIF4G is required for efficient virus replication in cell culture.

The first possibility is that the Ebola virus spreads from West Africa to megacities in other regions of the developing world.

The second possibility is one that virologists are loath to discuss openly but are definitely considering in private: that an Ebola virus could mutate to become transmissible through the air.

The current Ebola virus’s hyper-evolution is unprecedented; there has been more human-to-human transmission in the past four months than most likely occurred in the last 500 to 1,000 years. Each new infection represents trillions of throws of the genetic dice.