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U N I T 4
Infection and Immunity
New and Emerging Infectious
Diseases
In recent years, the terms
emerging
(i.e., newly rec-
ognized) and
reemerging
(i.e., previously recognized)
infectious diseases
have entered the vocabulary of medi-
cal science. These infections also include deliberately
emerging infections that are the result of bioterrorism.
Global Infectious Diseases
Aided by a global market and the ease of interna-
tional travel, the end of the 20th century and the first
years of the 21st century have witnessed the importa-
tion of a host of novel infectious diseases. Unexpected
pathogens in the 1990s, such as the outbreak of the
West Nile virus (WNV) in the New York City area,
have become important reminders of emerging infec-
tions. In fact, WNV has become almost synonymous
with mosquito-borne illness. Because WNV is a
mosquito-borne disease and is transmitted to a num-
ber of susceptible avian (e.g., blue jays, crows, and
hawks) and equine hosts, the potential for rapid and
sustained spread of the disease across the United States
was appreciated early. The disease ranges in intensity
from a nonspecific febrile illness to fulminant menin-
goencephalitis. Efforts to prevent further spread of the
disease are currently centered on surveillance of WNV-
associated illness in birds, humans, and other mam-
mals, as well as mosquito control.
In 2011, one of the largest foodborne outbreaks of
E.
coli
emerged as a global threat. Beginning in May 2011,
German public health authorities reported an outbreak
of hemolytic-uremic syndrome. Within 3 weeks German
authorities announced the source of the outbreak was
cucumbers from Spain, a report later proven incorrect.
As the investigation into the source of the outbreak con-
tinued, patients in surrounding countries also began to
report illness. As the outbreak continued, epidemiolo-
gists focused their investigation on bean sprouts from
a farm in Lower Saxony, Germany. They found that
people who had eaten bean sprouts were 9 times more
likely to develop bloody diarrhea versus those who had
not consumed bean sprouts. Finally, more than one
month following initiation of the outbreak, scientists at
the Robert Koch Care institute isolated a novel strain
of
E. coli
, known as O104:H4, from bean sprouts that
had been contaminated with human feces. Interestingly,
further study has demonstrated the O104:H4 strain of
E. coli
likely circulated in humans for 10 years prior to
the outbreak.
As a result of the outbreak, Germany has imple-
mented a policy to reduce the reporting time for poten-
tial outbreaks from 18 to 3 days. However, there are
many obstacles to improving surveillance from reim-
bursement for medical tests, to communication between
clinicians and public health authorities, to technolo-
gies for identification of relatedness among outbreak-causing diseases.
The worldwide movement of animals for commercial
trade represents a substantial risk for translocation of
zoonotic infections. In 2003, monkeypox, one of the
orthopoxvirus family viruses, was introduced into the
United States when a shipment of African Gambian
giant rats was sold to dealers, one of whom housed the
rats with prairie dogs intended for the pet market. The
prairie dogs subsequently became ill and transmitted
the infection to 71 humans, including prairie dog own-
ers and veterinary staff caring for the animals.
These three scenarios highlight the rapidity with
which novel or exotic diseases can be introduced into
nonindigenous regions of the world and to a susceptible
population. Although great strides in molecular micro-
biology have allowed for the rapid identification of new
or rare microorganisms, the potential devastation in
terms of human life and economic loss is great, under-
scoring the need to maintain resources for public health
surveillance and intervention.
R E V I EW E X E R C I S E S
1.
Newborn infants who have not yet developed
intestinal flora are routinely given an intramuscular
injection of vitamin K to prevent bleeding due to
a deficiency in vitamin K–dependent coagulation
factors.
A.
Use the concept of mutualism to explain why
this is done.
2.
Persons with human granulocytic ehrlichiosis may
be coinfected with Lyme disease.
A.
Explain.
3.
Persons with chronic lung disease are often taught
to contact their health care provider when they
notice a change in the color of their sputum (i.e.,
from white or clear to yellow or green tinged)
because it might be a sign of a bacterial infection.
A.
Explain.
SUMMARY CONCEPTS
■■
The challenges associated with maintaining
health throughout a global community are
becoming increasingly apparent.
■■
Aided by a global market and the ease of
international travel, the past decade has
witnessed the importation and emergence of a
host of novel infectious diseases.There is also
the potential threat of the deliberate use of
microorganisms as weapons of bioterrorism.
