Agriculture Reference
In-Depth Information
human health, whereas livestock producers are seen to over-
use antibiotics in search of higher profits.
Although it is clear that these low, regular doses of antibi-
otics given to animals can lead to human health problems, it
is easy to overstate the problem. Around 80 percent of all the
antibiotics sold in the United States are given to livestock, but
most of these are not used by humans. The livestock category
of antibiotics even includes ionophores, which have no human
equivalent. In fact, ionophores are so different from other anti-
biotics that in 2007 Tyson Foods was able to raise chickens
using only ionophores, and label their meat “raised without
antibiotics” (something producers are no longer allowed to
do). Although 80 percent of antibiotics sold are given to live-
stock, if we look only at the antibiotics used by both animals
and
humans, that percentages falls to 45 percent.
To what extent is human health threatened by antibiotic use
in livestock? People disagree. One view suggests the probabil-
ity is low. For regular, low doses of antibiotics to harm human
health the following chain of events must take place: (1) a bacte-
ria infecting livestock must develop resistance to an antibiotic,
(2) that antibiotic must also be used for humans, (3) the resis-
tant bacteria must also be able to infect humans, and (4) they
must make people so sick that they need antibiotics. To some
observers, the probability of all four events occurring seems
incredibly low. A researcher in the animal health industry (an
admittedly biased source) calculates this probability to be as
low as 0.00034 percent, and some scientific articles suggest a
similarly low probability.
This probability makes a number of assumptions that
might not be true, and when those assumptions are relaxed,
the probability of a human health threat rises. One assump-
tion regards the horizontal transfer of genes. However odd it
may sound, bacteria can share genes for antibiotic resistance.
This means that if one bacterium develops resistance, even if
that bacterium cannot harm humans, it can share its immunity
with bacteria that can. Though the rate of horizontal transfer is
