The Next Species: The Future of Evolution in the Aftermath of Man (14 page)

Ostfeld, a senior scientist at the institute—a calm, meticulous man whose broad shoulders attest to his weight lifting—has been studying Lyme disease here for twenty-four years. Dutchess County and four other mid–Hudson Valley counties have the nation’s highest rates of Lyme disease.

Ostfeld and others at the Cary Institute are investigating the ecosystem surrounding Lyme disease, the West Nile virus, and similar diseases recently proliferating in the US that are transmitted by ticks and insects through their animal hosts. Recently they discovered that the black-legged ticks that spread Lyme disease could also infect people with
Powassan virus encephalitis, which can cause central nervous system disruption, meningitis, and even death in 10 to 15 percent of reported cases. Adding to the problem is the fact that unlike Lyme disease and other ailments carried by black-legged ticks that take hours to transmit once a tick is attached to its victim, Powassan virus encephalitis and its variants can be transmitted in just fifteen minutes.
This leaves very little “grace period” for removing ticks, and underscores the importance of vigilance when in tick habitats.

Tick removal has become a critical activity of late for Northeastern outdoorsmen. Lyme disease was first reported in the United States in the town of Lyme, Connecticut, in 1975. “It reached a high of 30,841 reported cases in 2012,” says Ostfeld. “But the CDC [Centers for Disease Control] has recently estimated that reported cases represent only 10 percent of the actual number of cases, so it is likely that Lyme disease exceeds 300,000 cases per year.” Such statistics keep some hikers at home on the couch on weekends, a not-too-healthy alternative.

Most cases occur in the Northeast and upper Midwest, but there have been many reported along the Pacific Coast and elsewhere. If diagnosed in the early stages, Lyme disease can be cured with antibiotics. It may start out feeling just like the flu, which is sometimes ignored by patients, but the results can be severe. Without treatment, the CDC claims it can affect joints, the heart, and the nervous system—causing pain, paralyzed facial muscles, and nerve damage in the arms and legs.

In his laboratory at the Cary Institute, Ostfeld showed me a slide of the slender spiral-shaped bodies of
Borrelia burgdorferi
, the bacterium that causes Lyme disease and all its symptoms. Certain ticks carry the bacterium, though they aren’t born with it. They acquire it when they bite an infected mouse or chipmunk. Man acquires the disease when bitten by an infected tick.

The black-legged tick (
Ixodes scapularis
) carries Lyme disease bacteria in these woods. It goes through three stages in its short two-year life span—as larvae, nymph, and then adult—with each period requiring at least one good blood meal before moving on to the next. It is during these blood meals that the ticks acquire the disease and pass it on.

Ostfeld came to the Cary Institute in 1990 with a background in the behavior and evolutionary ecology of small mammals like voles, which undergo periodic, dramatic population swings. The biologist studied the disease, black-legged ticks,
the ticks’ animal hosts, and the forest that surrounded them to see how all the players in this disease drama functioned together. Ostfeld and his colleagues soon realized that the booms and busts he witnessed in small mammals and in forests themselves could play an important role in the spread of infectious disease.

The cycle may begin with an abundant crop of oak acorns in any year. Because acorns are a highly nutritious and long-lasting food source, they create an explosion of white-footed mice and eastern chipmunks in the following year. These small mammals are the preferred hosts of black-legged ticks. Still, the ticks must go through several phases before they start transmitting the disease to man, meaning the risk of Lyme disease is highest two years after plentiful acorns. It’s a complex system.

It is understandable that people in New England, the Middle Atlantic states, and the upper Midwest live in fear of contracting Lyme disease, but many use it as an excuse to stay out of the woods. Press reports of the disease have people believing that ticks are much more abundant than they once were, and that Lyme disease is spread by ticks carried by deer. This belief has resulted in calls to dramatically reduce deer populations in different areas of the Northeast. Black-legged ticks are sometimes called deer ticks, though Ostfeld claims that deer are not such important carriers as rodents are.

Ostfeld found that when deer are reduced by hunting or excluded by fencing, disease rates actually increase over the next few years. That’s because deer are highly unlikely to transmit a spirochete infection to feeding ticks; they are good hosts for ticks but not for the disease.
Small mammals are much better at handing off infections to ticks. Thus deer protect people from Lyme disease by being lousy hosts for Lyme-bearing ticks, “so taking away deer, at least initially, removes the protective role they play in reducing tick infections,” said Ostfeld.

He told me that ecologists tend to be excluded from the pool of rapid emergency funding, and are often left out of the first-response teams when new diseases appear. Also, it seems that money is more
available for what Ostfeld explained as “the disease of the month.” Funding for SARS and West Nile peaked in the year or two after the worst disease outbreaks. “Ironically it is the study of those well-established diseases that give us a good grip on how disease systems work. We shouldn’t abandon these intensive studies. They are the gold mine from which we get an understanding of basic disease processes,” said Ostfeld.

In the course of Ostfeld’s studies, he has learned a number of things about Lyme disease. He knows that taking a walk in a fragmented forest, one split up by roads and development, is more dangerous than taking a walk in extensive virgin forest. And he knows that the more opossums, squirrels, and foxes there are in a forest, the less chance there is of catching Lyme—and he suspects that the same is true for the presence of hawks, owls, and weasels. He is focusing now on determining the reasons for these observations, a major part of his studies.

As we’ve said, forest fragmentation enhances the spread of disease. Fragmentation occurs when large, continuous forests are divided into smaller pieces, either by roads, agriculture, urbanization, or other human development—shrinking the area available to animals and plants that rely on the habitat. Some critters, like predators and large-bodied animals, need large areas to maintain viable populations. Some are poor dispersers for whom the strip mall or suburban development is a severe barrier. The results are species losses. The species that are most resilient to fragmentation—mice, chipmunks, etc.—are often the only ones that remain. And these are the bad guys when it comes to disease transmission.

Ostfeld told me that if the tick we found on the mouse earlier that day had bit me, my chances of catching Lyme disease would have been at least 40 percent, but if we’d found the tick in a vacant woodlot in the nearby town of Poughkeepsie, my chances would be closer to 70 or 80 percent. A woodlot is an example of fragmentation, and the town of Poughkeepsie has lots of that.

To test Ostfeld’s theory that
fragmented forests increase disease,
he and a number of biologists selected fourteen forest fragments that were similar in types of vegetation but were isolated from other suitable habitat for Lyme hosts. What they found was that the larger the forest patch, the smaller the proportion of black-legged ticks infected by the disease it contained.

In the Midwest, tracts of trees in the middle of corn and soybean act like islands in the middle of the ocean. Corn and soybeans play the part of the ocean, since they are sufficiently inhospitable to native animals and create a barrier to dispersal much like the ocean would to an island animal. Thus corn and soybean crops deter many larger forest animals, but small mammals like mice and chipmunks do just fine there. Wooded lots have fewer species altogether, but the animals they do have are the disease amplifiers. Ostfeld found that the larger the size of the wooded tract, the smaller the proportion of diseased black-legged ticks there. But in smaller lots the numbers of infected ticks are astronomical.

The idea that peaceful patches of forest amid cornfields could be harbingers of disease is ominous, but so is the fact that the antibiotics we’ve been counting on to treat those diseases may not be able to help us for much longer.

Antibiotic resistance is growing so fast that we may soon have nothing left to tackle the new diseases we are fostering. The failure of our medicines is due to farmers who use antibiotics in animal feed to fight off diseases promoted by overcrowded conditions in confined-animal feeding operations for pigs, chickens, and cattle. These practices are creating superbugs that are immune to the antibiotics they’ve already adapted to.

Resistance to antibiotics normally occurs if your doctor prescribes a dosage that is not sufficient to eliminate the disease, or if you don’t take the full number of doses prescribed. In the process, the disease
gets stronger and is less affected by the medication on subsequent usage. Bacteria that survive the first treatment multiply and are resistant to the next treatment.

But antibiotic resistance can also come from eating meat from animals once treated by antibiotics. Disease is a particular problem in confined feeding operations where animals are kept in close quarters and fattened up for market. Putting antibiotics into animal feed is meant to lessen the threat of disease and to promote animal growth, but some scientists are finding that part of our increased resistance to antibiotics comes from eating animal products tainted by antibiotics.

Feeding our cattle, chickens, and pigs low doses of antibiotics is a setup for our own resistance to the medicine. In reality, low-dose medication that is not monitored selects for resistant strains of bacteria even in the food we eat. They are the ones that survive, reproduce, and grow stronger.

Antibiotic-resistant bacteria can spread into the air from confined-animal feeding operations that use antibiotics to compensate for the overcrowded conditions in their pens, affecting nearby residents. The resistant bacteria in animals’ manure can wash downstream and enter waterways where people swim and play. Scientists have even found in the sand on Florida beaches resistant bacteria brought there by seagulls.

The FDA recently announced new regulations to urge drug companies and agribusinesses to phase out the use of certain antibiotics in livestock and poultry, but the regulations are voluntary. And according to Ostfeld, this will definitely not end antibiotic resistance. There are large numbers of antibiotics used for livestock that will not be regulated, and so microbes will continue to evolve antibiotic resistance.

But the resistance issues generated by farm animals are not our only worry. The Cary Institute aquatic ecologist Emma J. Rosi-Marshall has studied how
antimicrobial chemicals used in personal-care products leak into the environment. Rosi-Marshall claims that putting antibiotics into toothpaste and hand cleaners serves no health purpose—they’re no better than antibiotic-free toothpaste or soap and water—yet they increase antibiotic resistance in the
environment.

Common afflictions like gonorrhea have developed resistance to many common antibiotics, including penicillin and tetracycline. Gonorrhea is transmitted sexually between humans. The World Health Organization reports that the disease is becoming a major health challenge in Australia, France, Japan, Norway, Sweden, and the UK due to antibiotic resistance that developed in the late 1990s and early 2000s. Left untreated, gonorrhea can cause painful infections of the reproductive organs, infertility, an increased risk of catching HIV, stillbirths, spontaneous abortions, and blindness in newborns.

Another ailment
currently resurging is tuberculosis (TB), a potentially fatal lung disease that has also grown resistant to antibiotics. The bacteria that cause tuberculosis are spread from person to person through tiny droplets released into the air via coughs and sneezes, though you are most likely to get the disease from someone you live with. It was once rare in developed countries, but the number of TB cases has increased worldwide since the 1980s. Part of the problem was caused by the emergence of HIV, the virus that causes AIDS. HIV weakens a person’s immune system so it can’t fight TB germs.

People who have tuberculosis often must take a variety of medications for long periods to get rid of the infection and deal with drug resistance. Various strains of tuberculosis have been found resistant to medications generally used to treat the disease. Multidrug-resistant tuberculosis rampages through the Russian prison system, where prisoners easily catch the disease and spread it to other inmates. The TB bacterium has developed immunity to many drugs, and has begun to proliferate among homeless people and AIDS patients.

The effects of drug resistance are serious and global. An estimated 630,000 people are presently ill with multidrug-resistant tuberculosis. Some 88 million people are infected with gonorrhea, which is also multidrug-resistant. There are 448 million new cases of curable sexually transmitted diseases (STDs)—including syphilis, chlamydia, and trichomoniasis—every year, and health authorities are watching those diseases for the development of resistant strains.

Should drug resistance and a host of new diseases brought on by the elimination of species concern us? How might a major pandemic occur? The influenza epidemic of 1918–19 killed 50 million. The Hong Kong flu of 1968–69 took about one million. The AIDS epidemic has taken some 30 million people so far. It is still a virulent killer in Africa, where the chief victims are now heterosexuals. WHO reports that malaria caused 627,000 deaths in 2012. Right now tuberculosis is making a big comeback.

Michael Greger looks at bird flu as earth’s next big catastrophe. Over the better part of the last two decades a killer strain of avian influenza has devastated birds in Asia, Europe, the Middle East, and Africa. It kills more than half of all its avian victims, and some strains kill even more. And it’s a virus. It can spread through coughing or sneezing, through the air, just as H1N1 or any of our common viruses can.