There’s something romantic about riding on a train…
Trains can whisk us to another city in an hour or two, or across the country in a matter of days
But we aren’t the only ones riding the rails
Traveling with us are untold millions of microbes, hitching a ride on our technological coat tails
Microbes quickly evolve to take advantage of new environmental opportunities
Our modern transportation networks can deliver the next plague as efficiently as an overnight package
In this lecture, and the one that follows, we’ll look at some of the ways that we’ve changed the world, and how microbes have responded to those changes
Along the way, we’ll consider new dispersal routes, like highways, transcontinental railroads, and hypodermic needles, and new habitats, like kitty litter and air conditioners
We’ll look at changes caused by agriculture, warfare, and global climate change
And finally, we’ll examine the emergence of new diseases, like Ebola and Lassa Fever
All of these changes present new challenges, and new opportunities, for the microbes that surround us
The trade routes and roads of antiquity were interstate highways for microbes
We’ve already discussed several ancient plagues that arose in the Orient and Africa and were carried throughout the Mediterranean
The Plague of Antonine, which ran from 165 to 180 AD, for example, was carried to Rome from the orient by returning legions, killing up to 5 million
The Plague of Cyprian in 250 AD was also an oriental plague, reaching Europe from Egypt
One reason we were so vulnerable to these oriental plagues, is that the western world had been isolated from the eastern world for a very long time
They fell on us like a hammer blow - we had no herd immunity, we were a naïve population
They were “virgin soil” epidemics, comparable to the effects of the 1918 flu on naïve native populations like the Inuit
The casualties were so high in both of these ancient plagues that the historian William McNeill believes they were caused by two different diseases, smallpox and measles
And witness the plagues introduced by early Pacific explorers, like Captain Cook
When Captain Cook arrived in Hawaii in 1778, he carried more than trade goods
His cargo may have included syphilis or gonorrhea
He admits that his crew had an unknown venereal disease, but claims he did not spread it to the natives
The optimistic Cook writes:
“As there were some venereal complaints on board both the ships in order to prevent its being communicated to the people, I gave orders that no women on any account whatever were to be admitted on board the ships, I also forbid all manner of connection with them, and ordered that none who had the venereal upon them should go out of the ships. But whether these regulations had the desired effect or no time can only discover.”
And the disease broke out as soon as he left - a tribute to the ingenuity of sailors
Later traders and settlers brought a horrible plague to Hawaii in 1804, probably cholera
Hawaiians called it the “Great Sickness”, or the “squatting sickness” - half the population died
These and other epidemics reduced the native Hawaiian population from between 250,000 and a million in 1778, to about 84,00 by 1850, and to 37,500 by 1900
Spanish explorers carried smallpox to the New World, along with measles, flu, bubonic plague, diphtheria, typhus, cholera, scarlet fever, chickenpox, yellow fever and whooping cough
The Pre-Columbian New World native population of 18-20 million was down to about 530,000 by the late 1800’s!
We’ll talk more about the role of microbes in the Columbian Exchange in lecture 22, and consider why it seems to have been a one-way street
The transatlantic slave trade brought many Old World diseases to the New World, like yellow fever and hookworms
The filthy, crowded slave ships were breeding grounds for microbes
The slave trade spread infected slaves all along the Atlantic seaboard
The most infamous hitchhikers of them all were the diminutive creatures that rode to Europe in the furs and fabrics of traders following the great Silk Road to the Far East
I’m talking, of course, about fleas, and their even tinier riders, Yersinia pestis, the bacterium that causes bubonic plague
Bubonic plague struck the Mediterranean world in the plague of Justinian, around 541 AD, although the second major wave didn’t hit until much later, about 1346 AD
The new overland trade routes to China probably carried flea-infested furs into Europe from somewhere in Central Asia, perhaps the Gobi Desert
But we have done our ancestors one better…
Our modern network of international trade and travel unites the entire planet into one vast microbial breeding farm, and distribution network
The building of the great Canadian-Pacific railroad was a triumph of engineering
But it brought more than trainloads of settlers – it also carried tuberculosis to Saskatchewan in the 1880’s
At the peak of the epidemic, the Qu’Appelle Indians were losing 9,000 per 100,000 of their tribe per year
Fort San, near Fort Qu’Appelle, was built in the early 1900’s as a TB sanitarium
Now slated for the wrecking ball, it treated thousands of patients
It acquired a reputation for being haunted by the victims of the “white plague” who had died within its walls
Among other ghostly apparitions was said to be the sound of wheelchairs rolling up and down the halls…
Modern airplanes can deliver microbes much faster and more efficiently than steam locomotives…
Cholera nearly escaped into the US in 1992, when infected shrimp were served to a planeload of Peruvians, aboard Aerolineas Argentina Flight 386
The shrimp were tainted from a cholera epidemic that was then killing thousands of people in Peru
75 passengers were infected, and one of them died
The disease nearly escaped into Los Angeles - once the first cases were reported, health officials had to spend several weeks tracking down and testing all the passengers
But fortunately, given the current odds of being served shrimp on an airplane, this type of accident is pretty unlikely to happen again…
Transportation isn’t the only area where new technology has created new ways for microbes to disperse
Hypodermic needles, first used in 1844, have provided new evolutionary pathways for diseases to spread
Their use in blood transfusions, allergy injections, and illegal narcotics, have given microbes a new express route into our bloodstream
Hepatitis B and Hepatitis C are often spread by sharing needles among drug addicts
Hepatitis affects millions of Americans, and can cause severe liver damage
AIDS is also spread by sharing hypodermic needles, as well as by sexual contact
And, ironically, injections of antibiotics can also put us at risk of infection!
This is a really bad problem in Less Developed Countries, where needles are relatively rare and expensive, and are often reused by doctors and nurses
New technology has not only created new microbial highways, it has also created new microbial habitats
Kitty litter, for example, has created a new way for Toxoplasmosis to spread from cats to humans
Toxoplasma gondii occurs in most warm-blooded animals
As many as one-third of us carry it in our bodies, and it’s most dangerous to those with weakened immune systems, like pregnant women
You usually catch it from handling or eating undercooked meat that contains the cysts
Or, because it lasts for up to a year outside its host, it can be picked up from gardening, or any other contact with soil contaminated with feces, like the dirt in a child’s sandbox, or your cat’s litter box
So don’t blame it all on poor Fluffy - but because it can be transmitted to the fetus through the mother’s bloodstream, pregnant women are well advised to avoid cleaning the litter box
My wife informs me that this is one of the few advantages of being pregnant -other than the end result, of course…
New technology can be a blessing or a curse – it all depends on your point of view
Members of the American Legion discovered this the hard way…
In July of 1976, members of the American Legion were holding their annual convention in Philadelphia
This being the American Bicentennial, it seemed like they were in the right place at the right time
The conventioneers stayed at the Bellevue-Stratford Hotel
Upon returning home, many of them fell ill, with a disease similar to pneumonia, with fever, coughing, and in some cases, respiratory failure
Of the 221 victims, 34 of them died
Enter the CDC…
The Centers for Disease Control (CDC) in Atlanta is our first and strongest line of national defense against epidemic diseases
The CDC sent a team of 23 agents to Philadelphia to track down the killer
It helps a disease to have a memorable name, and the press obliged by dubbing this one “Legionnaire’s Disease”
But research at the site had ruled out contaminated food, water, rodents or other vectors
That left only the air itself…
CDC agent Joseph McDade was part of the small army marshaled to attack Legionnaire’s Disease
McDade later became Deputy Director of the CDC’s National Center for Infectious Diseases
McDade had been investigating Q fever rickettsiae, a form of bacterial pneumonia which is carried by cattle, and sometimes spread to farmers
But this seemed like a dead end, because the records were very clear - no farm animals had been registered at the hotel…
He discovered a mysterious bacterium in samples from dead victims
But it was a stubborn strain, and he couldn’t culture it at first
He almost gave up, but he kept coming back to it, and he finally got it to grow on a culture made from hen’s eggs
The survivors’ blood serum was tested against the bacterium
Over 90% of the patients had antibodies to this mystery virus
Named Legionella pneumophila, it was tracked to the hotel’s air-conditioning system
Legionella could survive for a year or more in fresh water
It had found a new ecological habitat in the air conditioning system’s coolant water, and the fine aerosol drops of moisture in the cool air spread the disease all over the hotel
Many outbreaks of Legionnaire’s disease have occurred since then
Between 8,000 and 18,000 people are treated for it every year in the U.S alone
It’s turned up in showers, fountains, hot-water towers, whirlpool baths, hospital respiratory therapy equipment, even in those artificial rain-storm misters in up-scale supermarket aisles!
So where did it come from?
Turns out, the disease had been there all along…
It’s fairly common in fresh water habitats, and not all of the many different species are harmful
This one only required a new aerosol route to reach a new host
New diseases often emerge in response to changes in the environment
Microbes quickly evolve to take advantage of both man-made changes and natural changes
Take global climate change for example
One of the most significant ways in which we’re changing our global environment is by slowly raising the Earth’s average temperature
Global climate change is mostly due to the release of millions of tons of CO2 from the combustion of fossil fuels
It ‘s a complicated business, and we could easily spend several lectures discussing how it works
But beneath the complexities of climate change, lies one simple fact…
Atmospheric gases absorb infrared radiation, heat energy, trapping it in the atmosphere
This is analogous to the way a greenhouse warms up…
The glass keeps some of the incoming infrared radiation from escaping – hence the “greenhouse effect”
Any and all atmospheric gasses have this property
Even Oxygen and water vapor can act as greenhouse gases – most of the natural greenhouse effect, about 35-70% of it, is actually due to water vapor
We focus on carbon dioxide and methane when we talk about global climate change because these gasses, methane in particular, retain the most heat
There is a very strong correlation between atmospheric levels of carbon dioxide and global temperature, with good data going back 160,000 years
We can be very grateful for the greenhouse effect – without it, we would be shivering under our blankets in the summertime
Without the greenhouse effect, surface temperatures would drop about 70 degrees
The real problem is too much of a good thing…
Carbon dioxide is actually a trace gas, making up only about 0.03% of our atmosphere
But we are adding billions of tons of carbon dioxide every year, which means more infrared gets trapped in the atmosphere, and the planet gets gradually warmer
How hot will it get?
The answer varies from model to model…
By the end of the 21st Century, predictions range from 2.5o F - 10.4o F degrees
More than hot enough to trigger many environmental changes that will benefit harmful microbes
In fact, those changes are already underway…
Global climate change will create some new health problems, and worsen some old ones, like allergies
It’s already changing the natural range or distribution of a wide variety of species, including many microbes and their vectors
Mosquitoes, ticks, and other vectors that need tropical or subtropical temperatures to survive, are being found farther north, at higher altitudes, and in greater numbers
The Asian tiger mosquito, for example, Aedes albopictus, has taken advantage of the warmer temperatures, and is already firmly established in the southern US, reaching as far north as Maine
What makes this aggressive biter especially dangerous is that it feeds in the daytime, not just at dawn and dusk, which greatly increases the chances of finding a victim
Tropical vector-borne diseases like West Nile virus are becoming more and more common in the United States
West Nile virus is carried by mosquitoes, and is generally benign
Birds are its intermediate hosts, and viral populations build up in their bodies until the virus reaches infective levels
Mosquitoes then carry it from infected birds to humans
Most people who are infected are asymptomatic (about 90% of them)
But about one in ten develop West Nile fever, suffering from flu-like symptoms, with drowsiness and heavy sweating
One in every 150 victims, however, has a severe and potentially fatal reaction, either:
West Nile encephalitis – (encephalitis is an inflammation of the brain)
or West Nile meningitis – (meningitis is an infection of the membranes that protect the spinal cord and brain)
Because most people don’t even know they’ve been infected, we can only judge the extent of the disease by the more serious infections that require medical intervention
The CDC reports that there were 663 cases reported in 2009, and 335 of them were serious, with 30 deaths
More frequent bites from uninfected mosquitoes, incidentally, actually seem to increase the chances of acquiring the virus
Some components of mosquito saliva seem to compromise the immune system in a way that makes us more vulnerable to viral infections from other mosquitoes!
Warmer temperatures allow mosquitoes to build up larger seasonal populations
Higher temperatures also allow the young insects to reach biting age more rapidly
All of which results in more effective transmission of the microbe
Malarial and dengue mosquitoes will also benefit from global climate change
Dengue fever, and the more severe form called dengue hemorrhagic fever, or DHF, evolved as a tropical forest species in Asia, spread by mosquitoes to monkeys
It relies for dispersal on the mosquito Aedesegypti
As the mosquito’s range increases, so does the range of dengue fever
Also known as breakbone fever, dengue is nasty stuff!
The viral disease starts with a sudden fever, chills, and headaches, severe pain behind the eyes, and agonizing joint pains
A characteristic rash spreads over the body, and in extreme cases internal bleeding can lead to shock and death
There is no cure, nor any vaccine
WHO estimates that over 2.5 billion people in over 100 countries are at risk for dengue
50 to 100 million people get dengue fever every year, and 22,000 of them will die from it
It’s a rare disease in the United States, but with the mosquito expanding its range in response to global climate change, it may soon become a major problem in Southern states
We are rapidly changing the global environment
And many of these environmental changes will provide new opportunities for the evolution or dispersal of pathogens…
We’ve already talked about some of the effects of agriculture on our relationship to microbes
One of the most profound effects of agriculture is how it changes habitats, primarily through deforestation, clearing land for pastures and crops
Deforestation often brings us into contact with new species of pathogens
Over time, ecosystems evolve a fragile balance between species
And disrupting that balance can give some species the opportunity for rapid population growth
Which brings us to the subject of …
Sadly, money doesn’t grow on trees
But fortunately for us, chocolate does!
And like citrus, it has to be harvested by hand
Chocolate is a dry fruit, whose flowers are pollinated by tiny midges
The fruit has a fleshy pulp, the part that’s designed to bribe animals to disperse it
When we pick it, however, we throw the pulp away, and only keep the seeds
We leave the seeds to ferment and dry in the sun, and then we roast them
Now it helps to appreciate that seeds in general are often bitter or even mildly toxic, which is a neat adaptive mechanism to keep animals like us from feeding on them (apple seeds contain cyanide!)
We carefully extract the bitter alkaloid-laden seeds and throw away the tasty fleshy pulp
A nice example of evolutionary irony!
Chocolate comes from Theobroma cacao, and was first used by the Mayans and Aztecs
Theobroma is an apt scientific name for chocolate, it means “food of the gods”
A recent discovery dates the first use of chocolate to around 1100 BC
People then used the fermented pulp, rather than the seeds, to make chocolate beer!
We later discovered that the fermented and roasted seeds made a much tastier drink
The Aztecs invented hot chocolate!
Montezuma was said to drink 50 cups a day (from golden goblets, of course)
It was given to Cortez and his men, in return for smallpox and syphilis (gee, thanks…)
The bitter and spicy Aztec version, however, wasn’t popular in Europe, but the sweetened version was an instant hit!
Milk chocolate was invented by Daniel Peter in 1867, using a process that his neighbor, Henri Nestlé, had developed to make baby food
Chocolate, incidentally, qualifies as a recreational drug, a stimulant
The chemical formula of theobromine is nearly identical to that of caffeine
Chocolate has been cultivated for over 3,000 years, and it is still one of the planet’s most valuable cash crops
Although most chocolate comes from West Africa, a large portion comes from the Caribbean and from South America…
In Belém, Brazil, in the early 1960’s, over 11,000 residents came down with an unknown flu-like illness
The disease turned out to be Oropouche Fever, a nasty but rarely fatal disease
Okay, I admit it…I pulled you in with a lurid lecture title
The only way you can really die from chocolate is by eating way too much of it
Which, for a few of us, unfortunately, may be a distinct possibility...
While trying to determine the correct pronunciation of Oropouche Fever, I ran across a letter in a health forum that said “If you can’t pronounce it, and it ends in fever, WORRY!”
And Oropouche Fever can be serious stuff…
The symptoms are similar to dengue fever, with severe bone and joint pains, chills and headaches – a few victims develop meningitis
This viral disease is named after the Oropouche River in Trinidad and Tobago, where it was first described, and is carried by midges or mosquitoes from sloths to humans
But why the sudden outbreak at Belém?
It took 19 years to solve the mystery
The Belém-Brasilia road, one of the first major state highways into the rain forest, was constructed in the 1960’s
Settlers followed the highway, clearing large areas for chocolate plantations – and in the process, disturbing the habitat of a forest midge
The midge, Culicoides paraensis, turned out to be the vector for Oropouche Fever
It had found a new habitat in the discarded fruit shells, building up huge populations near farms and villages
The cultivation of chocolate reminds us that ecosystem disruption often represents an evolutionary opportunity for many species
It’s what ecologists call a disturbance
A disturbance is any force or factor that disrupts an ecosystem
Remember that microbes are r-selected organisms, poised to take quick advantage of an environmental disturbance
Disturbances can be natural – like fires and floods - or man-made, like land conversion and deforestation
The historic pattern in diseases like Oropouche Fever is:
The ecosystem is disturbed
The disturbance leads to first contact between humans and formerly separated species of microbes, or microbe vectors
Then, finally, the microbe enters and adapts to its new human host
Man-made changes in global trade and travel have opened up new pathways and habitats for microbes
And changes in technology, like hypodermic needles and air conditioning, have also provided new routes of dispersal, and new microbial habitats
We are rapidly changing the global environment
And many of these environmental changes will provide new opportunities for the evolution or dispersal of pathogens
In our next lecture we’ll look at further examples of how ecological disturbances, both natural and man-made, can benefit harmful microbes
