much of Southeast Asia, the number of people who could be exposed is enormous. Moreover, it is not necessary to invoke an exotic locale or complex combination of animals for zoonosis to occur; petting zoos, open markets, and state fairs provide sufficient human-animal contact to allow a virus to jump species.
Figure 1.6 Fruit bat geographic range in Southeast Asia, and prevalence of Nipah and Hendra viruses. Outbreaks of Hendra and Nipah virus infections from the late 1990s through 2014 are indicated, as is the geographic range of the Pteropus fruit bat.
The Economic Toll of Viral Epidemics in Livestock
Epidemics affect animals other than humans as well, especially those in dense farming populations. The outbreak of foot-and-mouth disease in the United Kingdom in 2001 caused an agricultural crisis of historical proportions; over 10 million sheep and cattle were killed, an average of 10,000 to 13,000 a day, in an attempt to stop the infection from spreading. As there was no easy way to distinguish infected from uninfected, all of the farm animals in affected areas were destroyed, independent of signs of disease in the livestock. In the 2001 outbreak, the infection could be traced to one pig (the “index case”) on a specific farm in Northumberland. Unfortunately, the farmer did not inform the authorities of the appearance of foot-and-mouth disease, which is relatively easy to identify by characteristic lesions on the snout, mouth, and feet. The epidemic spread rapidly, accelerated by the use of the same trucks to transport animals from both contaminated and uncontaminated farms to slaughter houses. While this outbreak did not affect humans directly, the indirect financial impact on farming and tourism was enormous; it is estimated that this crisis cost the United Kingdom over $16 billion, and created great stress within the government. A vaccine for foot-and-mouth disease virus exists, and was available at the time. However, vaccine use had been rejected because farmers feared that they would then not be able to ship their meat to other countries, as vaccinated animals cannot be distinguished serologically from infected ones. A positive outcome of this epidemic is that all farm animals in the United Kingdom are now vaccinated for foot-and-mouth disease virus. Nevertheless, agricultural threats remain: while one virus of livestock has been eradicated (rinderpest virus, a relative of measles virus), and some are controlled by vaccines, others, including bluetongue virus, continue to pose a significant threat to cattle, sheep, antelopes, and deer.
Population Density and World Travel Are Accelerators of Viral Transmission
While the thought of an ocean cruise may evoke images of endless buffets and poolside piña coladas, to viral epidemiologists, such pleasure ships appear as prime breeding grounds for viral epidemics. Norwalk virus, a member of the norovirus family, is often associated with cruise ship outbreaks of gastroenteritis resulting in vomiting and diarrhea, although other viruses can also cause these nautical nightmares. Moreover, Norwalk virus is not restricted to ships; hot spots include any place in which many people from various locations are in close proximity for an extended period. Other high-density environments include prisons, airplane cabins, day care facilities, dormitories, and elderly care communities. The risk of transmission is enhanced by the fact that noroviruses are quite hardy, and can be transmitted either person to person or via contaminated food or surfaces, resulting in the need to decontaminate all shared surfaces with chlorine-containing solutions following an outbreak. While the gastrointestinal effects of a noroviral infection are unpleasant, the disease is short-lived, and patients usually recover quickly. However, the frequency with which these outbreaks strike is a chilling re minder that, despite improved tools to characterize viral epidemics and reduce their spread, the ease and prevalence of world travel greatly facilitate the encounter between viruses and new hosts.
Focus on Frontline Health Care: Ebolavirus in Africa
In December 2013, a one-year-old boy in Guinea died from complications of Ebola virus: he was the first victim of what would become an epidemic that claimed over 11,000 lives and lasted more than two years. During this period, the virus spread to the neighboring countries of Liberia and Sierra Leone, and it is conservatively estimated that more than 28,000 individuals became infected from December 2013 to late 2016. The epidemic was fueled, in part, by poverty, social unrest, armed conflict, and inadequate or absent health care systems. Furthermore, local burial customs, including ritual washing of the corpse, facilitated person-to-person transmission. Air transportation of infected persons out of these areas caused infections in health care workers, including in hospitals in Spain and the United States. While these latter cases did not spread further, the entry of this highly lethal virus into these countries created widespread public anxiety in these countries. Such anxiety likely contributed to greater awareness of the devastation that was in progress on the west coast of Africa.
Ebola virus is probably transmitted by bats, and, indeed, the index patient’s village was located near a large bat colony. Ebola virus is spread by direct contact with body fluids: mucus, saliva, blood, and, as determined later, semen. Ebola hemorrhagic fever, which typically starts with high fever, headache, and muscle pain, often progresses to vomiting, diarrhea, and rash, and eventually kidney and liver impairment. In some infected individuals, rupture of infected blood vessels leads to internal and external bleeding (hence the name hemorrhagic fever), which can cause death from low blood pressure and fluid loss. The disease carries an extremely high risk of death, killing between 25 and 90% of those infected, although the odds of survival are directly dependent on the efficiency and quality of health care: providing fluids (saline, blood transfusions) greatly increases an infected individual’s chances of survival.
More than any epidemic in recent memory, media attention was particularly focused on the health care workers on site, who provided care for the victims and potential victims (Fig. 1.7). The Médecins Sans Frontières (Doctors Without Borders), which received the 1999 Nobel Peace Prize for its work throughout the developing world, provided much of this frontline care. In late 2014, at the peak of the epidemic, physicians and support personnel were exhausted, hospitals had little room for new patients, and lack of adequate resources forced heartbreaking choices on those doctors: provide optimal care to a few or substandard care to many. To care for the victims, medical personnel put themselves in extreme danger: despite protective gear, approximately 10% of Ebola virus fatalities occurred in health care workers. Lack of running water, oppressive temperatures, and outdated sup plies were all likely contributors.
Eventually, border closings, mandatory quarantines, and public education that led to changes in burial practices slowed the spread of the epidemic. In December 2016, the WHO announced, after a two-year trial, that a recombinant vaccine appeared to offer protection from the Zaire strain of Ebola responsible for the West Africa outbreak (Chapters 7 and 9).
Figure 1.7 Ebola outbreak. Health care workers in areas of the Ebola virus outbreak are completely protected from any contact with body fluids from a potentially infected individual. Standard safety protection includes a suit, apron, boots, gowns, gloves, masks, and goggles. One physician working in Sierra Leone stated: “After about 30 or 40 minutes, your goggles have fogged up; your socks are completely drenched in sweat. You’re just walking in water in your boots. And at that point, you have to exit for your own safety … Here it takes 20–25 minutes to take off a protective suit and must be done with two trained supervisors who watch every step in a military manner to ensure no mistakes are made, because a slip up can easily occur and of course can be fatal.” AP Photo/ Jerome Delay, File 288676002851.
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