The dangers of being too clean
Being exposed to dirt in early childhood - and a healthy sex life - can boost immune system
Usually as winter approaches, there are concerns about ailments like the common cold and influenza, spurring an upsurge of interest in our immune systems. This year, an additional threat looms - the Ebola virus. Though the current outbreak has so far been confined mainly to West Africa, Ebola might occur in Hong Kong or China, as Peter Piot, director of the London School of Hygiene and Tropical Medicine, has warned.
Piot was one of the researchers who discovered Ebola in 1976, when they analysed a sample from a sick patient in Zaire, now the Democratic Republic of Congo. With the largest Ebola outbreak in history now raging, and thousands of Chinese working in Africa, Piot anticipates there's a risk for China, although any outbreaks should be small.
Perhaps surprisingly given advances in medicine, containing any such outbreaks would rely on some basic techniques, like isolating patients, and seeking to care for anyone who does become infected, to give their immune system a chance to combat the virus - while hoping it doesn't kill them in the process.
Though "immune system" is a familiar term, there is still much to be learned about how our bodies defend against diseases. As Stanford Medicine explains, the immune system is, "This dynamic network of biological sensors, cells, secretions and genes … like a sixth sense, able to detect microbial friend from foe in the food we eat, the things we touch and the air we breathe." It adds: "The most intelligent facets of the immune system are still a mystery."
Yet while scientists strive to unravel this mystery - with the Institute for Immunology, Transplantation and Infection of Stanford University in the US even having a "Human Immunome Project" - evolution has produced simple viruses that can impede our defences.
Ebola is one such virus. A study published in August found that a protein created by cells infected with Ebola prevents signalling by interferons, which would normally serve as messengers vital for driving the immune response within cells. This leaves the virus free to multiply unhindered, until by the peak of illness there may be 10 billion viral particles in one-fifth of a teaspoon of blood, which The New York Times compared to the under 20 million particles in someone with untreated hepatitis C.
Many infected cells die, and this awakens the immune system - which responds so strongly that it not only fights the virus, but can also kill the infected person. In what's known as a cytokine storm, an array of immune system messaging proteins are unleashed, triggering immune cells and activating inflammation. Blood vessel walls become more permeable, so blood can ooze out - leading to the disease being known as Ebola haemorrhagic fever. Nitric oxide is released, which also thins the blood. Thomas Geisbert, an immunologist at the University of Texas Medical Branch at Galveston, told US National Public Radio: "You don't die of blood loss, but from something similar to severe septic shock."
Cytokine storms are not unique to Ebola, and have been implicated in diseases such as the 1918 influenza pandemic, H5N1 bird flu, and severe acute respiratory syndrome. Yet with a fatality rate of around 70 per cent this year, Ebola is particularly deadly. Even so, some people do survive its ravages, and there are signs that a small proportion of people in West Africa may be naturally immune - leading to hope that science may improve methods to fight the virus, perhaps in ways as basic as having immune people care for patients.
But overall, our immune systems function superbly. This makes it wise to bolster them as much as possible. Well-known ways of doing so include a healthy diet, exercise and adequate sleep. But research also points to something else that's important, yet runs counter to ways some people might strive to live in Hong Kong: close encounters with dirt during early childhood.
With memories of diseases like cholera, coupled with the shock of the 2003 Sars outbreak along with bird flu fears, Hong Kong has become perhaps a little too obsessed with cleanliness, as if leaving an elevator panel unsterilised for a few hours could threaten us all. Yet there is strong evidence that for children at least, there's a marked downside to living in a sterile environment.
This evidence was boosted by research from Johns Hopkins Medicine in the US. It found that newborns exposed to household germs, pet and rodent dander and cockroach allergens during their first year of life appear to have lower risk of developing asthma and allergies. This is consistent with the "hygiene hypothesis", according to which children who grow up in too-clean environments may develop hypersensitive immune systems that make them prone to allergies.
Of course, no one is recommending that parents deliberately introduce cockroaches and rats to clean homes, but it does show that obsessive cleanliness has its downside. Taking children to experience nature can help too, as indicated by evidence that those growing up on farms with livestock may develop stronger immune systems than urban children.
Then there's a mainly indoor activity that can also help your immune system. A study at the University in Pennsylvania in the US found that students who made love once or twice a week had 30 per cent more immunoglobulin in their saliva than those having less sex - making it less likely they would catch colds. A word of warning, however: the benefit declined with more frequent sex.
Even without lovemaking, having social support helps strengthen immune systems.
But even before diseases reach your immune system, you can ensure a strong line of defence against infection, simply by washing your hands. And for thoroughness, some surgeons advocate washing your hands for as long as it takes to sing "Happy birthday" twice.
Martin Williams is a Hong Kong-based writer and photographer with a PhD in physical chemistry from Cambridge University