When a song or video goes viral, it’s good news for the artists who created it. When a viral infection causes a human epidemic, it’s the opposite. Viruses are infectious agents that reproduce by injecting their genetic material into living cells. They cannot be killed by antibiotics, which are designed to stop infections spread by much larger bacteria. Viruses cause some of the deadliest known diseases, including Ebola, smallpox, HIV, and influenza.
The newest virus to make headlines is Zika, which is spread by mosquitoes. It was discovered in Uganda in the 1940s, but few human cases were reported until it started appearing in Pacific islands in 2007. Now Zika is spreading in Latin America, where researchers are trying to determine whether it causes birth defects in newborn infants whose mothers have been infected.
Viral epidemics can be frightening, as the world saw in 2014-15 when Ebola killed more than 11,000 people in Guinea, Sierra Leone, and Liberia. Unit 6 of Rediscovering Biology, “HIV and AIDs,” explains how viruses attack our immune systems, and why we need to understand the virus’s life cycle to develop effective treatments. Many medical experts now view HIV/AIDs as a treatable chronic disease, thanks to antiretroviral drugs (although getting these drugs to everyone who needs them is still a major challenge).
Many factors shape the odds that any one of us may be infected by a virus. To assess the risk, we need to know how the virus spreads; where humans may become exposed; and whether they have defenses available, such as vaccines or protective gear. The Habitable Planet’s interactive lab on diseases lets students explore how several simulated diseases spread through populations and the steps that we can take to counter them.
Viruses are an active and fast-moving area of biomedical research. Virologists have identified some 2,000 species of viruses that cause infections in plants, animals, and humans. And some important risk factors for viral infection are increasing today. For example, climate change is expanding the range of vectors that spread viral diseases, such as the Aedes aegypti mosquito, which transmits Zika, chikungunya, and dengue fever. And the expansion of global air travel is bringing more humans into contact with diseases and with each other, increasing the likelihood of spreading infections. Some experts are worried that people who attend the 2016 Summer Olympics in Rio de Janeiro, Brazil could carry Zika virus, which is widespread in Brazil, home with them.
Dr. Pardis Sabeti, a computational geneticist at the Broad institute and Harvard University and host of Annenberg Learner’s Against All Odds: Inside Statistics series, led work by an international team to sequence the Ebola genome during the 2014-15 outbreak. Their research showed that the virus was mutating rapidly during the early phase of the outbreak, which helped public health responders determine which treatments would be more or less effective.
In this 2016 TED talk, Sabeti explains the importance of international cooperation to understand and stop viral epidemics. “This is not the first outbreak of Ebola, it will not be the last, and there are many other microbes out there lying in wait,” she says. “We have the technology and the capacity to have the upper hand over viruses, but we can only [succeed] if we do it together.”
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