About two-thirds of the emerging pathogens come from other animals—and that’s no accident. As our demand for animals for food, skins, and entertainment increases, so do our risks of infectious diseases.
RECIFE, BRAZIL - JANUARY 31: Alice Vitoria Gomes Bezerra,
3-months-old, who has microcephaly, is held by her mother Nadja
Cristina Gomes Bezerra on January 31, 2016 in Recife, Brazil. In the
last four months, authorities have recorded close to 4,000 cases in
Brazil in which the mosquito-borne Zika virus may have led to
microcephaly in infants. The ailment results in an abnormally small
head in newborns and is associated with various disorders including
decreased brain development. According to the World Health
Organization (WHO), the Zika virus outbreak is likely to spread
throughout nearly all the Americas. (Photo by Mario Tama/Getty
Images)
Zika virus, Ebola, Middle East Respiratory Syndrome (MERS) coronavirus,
Severe Acute Respiratory Syndrome (SARS) coronavirus, Nipah virus, Hendra
virus, bird flu, swine flu — these viruses have all grabbed international
attention in recent years. In the past few decades the world has witnessed
an alarming surge in emerging infectious diseases (EIDs). Since 1980, new
pathogens have emerged in the human population at a rate of about three each
year.
Why are we seeing such a surge in new pathogens? One could argue that some
of the pathogens may not be new at all; they could have circulated among
humans for centuries and are just being identified for the first time
because of increased surveillance and reporting. While this is true in a
small number of cases, a study found that even after controlling for
increased surveillance, there has still been a surge in EIDs in recent
times.
In other words, the rise of new pathogens is very real.
So let’s look at the major reasons why we are seeing this rise:
First: human overpopulation. I think we need to change the phrase “breed
like rabbits” to “breed like humans,” as no other species on this planet
even comes close to the human reproduction rate. As our population grows,
available land shrinks and more and more people are forced to live in
crowded, urbanized environments, a situation ripe for the easy spread and
emergence of infectious agents.
Second: increased travel. Our travels significantly increase our chances of
catching a pathogen in one area and unwittingly transporting the infectious
agent to another area, where it was never before seen and where little or no
immunity exists.
Third: climate change. Vector-borne diseases are those that are spread
through insects like mosquitoes, ticks, and spiders. A vector’s life cycle
greatly depends on climatic factors. And climate change is helping certain
vectors, like mosquitoes, to thrive. Warmer temperatures shorten the
incubation time of viruses carried by mosquitoes, accelerate the maturation
of mosquito larvae, and increase the feeding frequency of adult mosquitoes.
All of these factors increase our chances of catching a virus, like Zika,
carried by mosquitoes.
Fourth: deforestation and natural habitat loss. Cleared land collects
rainwater better than rainforests, providing more suitable breeding grounds
for mosquitoes. Lyme disease is on the rise because of our encroachment upon
and fragmentation of woodland habitats in the U.S. The Nipah virus is a
newly discovered pathogen that is causing considerable public health concern
because of its ability to infect a broad range of animals and its high
lethality among humans. It was first detected in Malaysia. Habitat loss
caused a mass exodus of Nipah virus-carrying fruit bats as they searched for
food. This led the bats to cultivated fruit farms that were planted next to
pig farms. Unfortunately, the pigs were highly susceptible to the Nipah
virus. In turn, these pigs passed the virus on to humans.
While these four factors do indeed contribute to the rise in EIDs, a fifth
is rapidly gaining in importance and may be paramount: the global trade in
wildlife and production of animals for food. About two-thirds of the
emerging pathogens come from other animals—and that’s no accident. As our
demand for animals for food, skins, and entertainment increases, so do our
risks of infectious diseases.
This New World
The current capitalist system is broken.
The U.S. is one of the largest importers — and exporters — of animals. These
animals are caught from the wild or bred in captivity and then sold for use
as exotic pets, entertainment (for circuses and zoos), food, fur, skins, and
for experiments. Animals such as foxes, cats, bats, rats, snakes, birds,
bears, monkeys — you name it — are fair game for the wildlife trade.
As we delve deeper into the forests and jungles to seize new animals for the
trade, we risk exposure to rarely encountered animals who may carry viruses
that are entirely new to humans. We likely got HIV and Ebola through the
bushmeat trade. And though we do not know exactly how humans first
contracted Zika, we do know that Zika was first discovered in a rhesus
monkey.
To add insult to injury, the animals in the wildlife trade suffer
tremendously as they are passed from one dealer to another, shipped
overseas, or killed on site in profoundly painful ways. The trade creates
and brings together lots of very distressed and, as a result, very sick
animals — ideal conditions for pathogens to pass on from one animal to
another and ultimately to humans.
This is how humans contracted SARS. It is believed that the SARS virus
originated in fruit bats. At some point in the wildlife trade, fruit bats
were brought into contact with civet cats (both animals captured for the
wildlife trade) in the Guangdong Province of China. The SARS virus likely
passed from fruit bats to civets and then on to humans.
By creating distressed and sick animals, we are also harming humankind.
Nowhere is this more apparent than in the massive production of animals for
meat, eggs, and dairy. If viruses, bacteria and parasites could tell us
about their ideal environments, we would hear them describing animal
agriculture among their top choices. For every human on this planet, there
are about ten land animals raised and killed for food at any one time. As I
have discussed before, the intensive confinement of animals for food is
directly responsible for the explosion of deadly new strains of bird and
swine flus.
Besides directly propelling the formation of new viruses, animal agriculture
also contributes indirectly. Animal agriculture is a major driver of
deforestation and climate change, which exacerbate the problems I described
earlier.
Each time a new pathogen causes an outbreak, we follow a familiar pattern:
we panic, ask ourselves how can this be, scramble to create new drugs, sigh
with relief when the outbreak ends, and then continue the same behaviors
that caused the pathogen to emerge in the first place. We need to stop being
reactive. Medicines and vaccines only provide a temporary fix, at best. Even
worse, vaccines can actually spur the evolution of viruses, creating
resistant strains.
Unless we take a hard look at the choices we make in life, such as eating
animals and reproducing at such a high rate, new pathogens will show
themselves at an ever-increasing rate. As Dr. Dan Bausch from Tulane School
of Public Health and Tropical Medicine once stated:
For every virus that we know about, there are hundreds that we don’t know anything about. There are a lot more pathogens out there. [Calvert S, Kohn D. ‘Out of Africa: A baffling variety of diseases’ The Baltimore Sun May 15, 2005.]
We can try to play catch up each time a new pathogen makes itself known or
we can prevent them from emerging in the first pace. The choice is in our
hands.
Stay tuned for my next post on the wildlife trade: a hug gap in our public
health armor.