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Sentinel animals

Underground coal mines are dangerous places to work, in part because toxic, even fatal, levels of carbon monoxide can build up in caves with poor ventilation. Because carbon monoxide is odorless, miners would often keep a bright yellow canary in the mines with them; if the canary remained alive, no carbon monoxide was present, but if the canary died, the miners were forewarned. The “canary in a coal mine” is perhaps the best-known case of using animals as sentinels or harbingers, though this approach has been used to identify viral infections in the wild as well. For ex ample, sentinel species, such as monkeys, are placed inside cages near the entrance to caves where bats reside. Epidemiologists periodically check on the health of the monkey; if the animal became sick, not only would this indicate a health concern, but virus could be isolated from the affected host to determine the nature of the pathogen, and perhaps to learn something about how it was spread. Methods that do not require the incarceration of the sentinel organism are also in use, including collection of feces and urine in the wild for subsequent laboratory analysis. In fact, in 1947, scientists conducting routine surveillance for yellow fever virus in the Zika forest of Uganda recovered a novel virus, later named Zika virus.

Publications and websites help to distribute consistent and timely information to health care workers across the globe. The Morbidity and Mortality Weekly Report, published by the CDC, provides a central clearinghouse for health care providers in the United States to communicate individual cases of infectious diseases or to report unusual observations. ProMED (Program for Monitoring Emerging Diseases), sponsored by the International Society for Infectious Diseases, is a world-wide effort to promote communication among members of the international infectious disease community. Reporting of individual cases, when considered by epidemiologists in the aggregate, may catch an epidemic in its earliest days, when intervention is most effective.

More-informal “crowdsourced” approaches have recently gained attention for their power to share data, educate the public, and rapidly identify a potential outbreak. Real-time data-gathering tools, such as Google Flu Trends and Google Dengue Trends, are Web-based applications that survey search queries from more than 25 countries to predict epidemics. The predictions made from these applications have been generally consistent with more traditional surveillance data-gathering approaches. The innovative use of keyword collection to monitor viral outbreaks underscores how collaboration between distinct fields (e.g., epidemiology and search engine design) can lead to creative ways to detect incipient epidemics. Social media monitoring also is an excellent way to gauge the impact of public education efforts in understanding viral infections (Fig. 1.9).

Figure 1.9 Twitter as a tool in viral epidemiology. Between May 1 and December 31, 2009, the relative proportion of tweets using “H1N1” increased in an almost linear fashion, indicating a gradual adoption of the WHO-recommended H1N1 terminology as opposed to “swine flu.” Blue = use of the term “swine flu”; red = use of the term “H1N1”; green = combined use of “swine flu” and “H1N1.” Adapted from Chew C, Eysenbach G. 2010. PLoS One 5:e14118, under license CC BY 4.0. © 2010 Chew et al.