Porth's Essentials of Pathophysiology, 4e

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Infection and Immunity

U N I T 4

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.

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.

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.