The Transmission of Diseases from Livestock: Then and Now
By Josh Loeffler
The signs at the Philadelphia International Airport are bold and make a clear
point. The bright, yellow billboards all but shout: "Keep Foot and Mouth
Disease out of America." Soon after seeing these signs upon entrance to the
airport, travelers are greeted by customs agents who check documentation and bags
to insure that the traveler has not been prone to the disease on his journeys.
Any traveler exhibiting the warning signs of an individual who carries the disease
is quickly swept away- removed from the general populace in order to prevent possible
spreading of the disease.
The above precautions may seem extreme. Then again, the precautions may appear
normal in a world that has quickly strengthened airport security in response to
recent terrorist activities. Neither of these reactions to the security checks
would be fully accurate. The security checks preventing free entrance by individuals
who have come into contact with animals or areas that house animals abroad are
an innovation designed to prevent the most common method for spreading disease.
These precautions have been implemented in order to prevent the spread of diseases
Throughout the course of history, diseases have been the greatest killers of humans.
In fact, the winners of most wars were simply the ones who proved less susceptible
to the germs carried by the enemy (Diamond, p. 197). Diamond correctly points
out, then, that diseases have been the largest shaper of history. For instance,
what would the world look like now if the Native Americans had carried germs that
were far more potent than the Spanish conquistadors? (p. 197)
The diseases that have been the great molders of the human experience are very
often and quite easily traced back to animals, specifically livestock. Food production
was seen relatively early in history of civilization as a better means for providing
for a great number of people than the hunter-gatherer model that was once the
primary model of existence. The success of food production in maintenance of human
life leads to a society which has become dependant on farming, ranching, and other
ways of life that produce foods from animals. The increased number of individuals
able to be supported by a society supported by agriculture serves as an important
factor in the spreading of disease. The most common method for spread of disease
is direct transmittance from the animals to the humans. There are numerous diseases
that afflict humans whose origins scientists now trace back to livestock. The
spreading of the diseases is often due to the proximity to the livestock. Living
close to the blood, excrement, and breath of the livestock allows for high rates
of disease transmittance (Diamond, p. 207).
While it is true that there is a greater probability of disease transmittance
from this lifestyle, the human population has flourished due to food production
and livestock maintenance. Increased numbers of people leads to greater interaction,
and a higher probability of transmitting the disease from person to person. The
feces of the livestock and humans can surround the farmers, as this excrement
is often used to increase fertilization of agrarian fields. The food produced
by such animals can also attract disease-infected rodents (Diamond, p. 205).
Analysis of disease transmittance and evolution of diseases transmitted from animals
to human reveals four stages of disease development in humans from an animal origin.
First are those diseases transferred from pets, which are rare and even more rarely
transmitted between humans. Second are those diseases that are transmitted directly
from animals to humans and create epidemics that eventually disappear. Third are
diseases that are transmitted by animals to humans that still pose a threat to
humanity (ie. AIDS). Fourth are diseases that began with animals and have now
become exclusive to humans. These diseases represent evolution, as microbes that
infected humans and originated from animals transformed to become exclusively
human syndromes (Diamond, pp.207-209).
The last three types of diseases are the type of transmittance and evolution that
have the United States so worried about the spread of Foot and Mouth disease.
All species with cloven feet, or hooves, are susceptible to Foot and Mouth disease.
The disease is transmitted through feces, breath, and proximity to sores or legions
are methods through which the disease is transferred between livestock. The disease
results in lameness or salivation (www.aleffgroup.com/avisfmd/index.html). In
short, the livestock becomes unfit to use in any manner.
While the spread of Foot and Mouth disease to humans is undocumented, and the
origins of no disease in humans has been traced back to Foot and Mouth, there
is still inherent danger. The disease wipes out livestock, (usually slaughtered
to prevent further infection) making it much more difficult to support large civilizations.
Rampant spread of this disease could result in the eventual complete change of
diet. Also, the disease could evolve and later effect humans. As shown above,
history reveals that diseases originating with animals can evolve to infect humans,
or could later reveal effects on humanity. It is very possible, that without prevention
or regulation, Foot and Mouth disease could evolve or reveal effects on humans
over the course of time.
The explosion of travel, especially intercontinental travel has made the transmittance
of Foot and Mouth disease a much greater possibility. This is especially true
regarding Americans, who travel the world more than any other people. As Diamond
points out, with an abundance of international travel, America is becoming a melting
pot for disease (p. 206). As immigration continues, and individuals continue to
travel to countries that contain foot and mouth, the possibility for transmittance
of the disease increases.
It is because of this high level of travel and high chance for transmittance,
that dire measures are taken at the airports. Customs agents must check to see
if travelers visited farmlands, contacted livestock, or are carrying animals.
If so, safety precautions must be taken to insure that the spread of disease is
made nearly impossible. For instance, if an individual visited a farm, the shoes
of that person are inspected and sterilized if found to be carrying manure (www.aleffgroup.com/avisfmd/index.html).
While the safety measures at the airport may seem extreme, they are simply a way
to prevent the spread of disease. In order to allow for travel, and prevent the
spread of epidemics that have proved to be a plague on humanity throughout history,
the precautions must continue. Society changes slightly to prevent the spread
of disease. It does so in order to prevent disease from changing society vastly
in the future.
Diamond, Jared, "Ch. 11: Lethal gift of livestock," in "Guns,
Germs, and Steel" W.W. Norton & Co, 1997, ISBN 0-393-03891-2, pp. 195-214