Bats harbor many types of coronaviruses and were probably the original source of the new coronavirus that appeared in the Middle East. iStockphoto.com hide caption

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Cheryl Gleasner, a research technologist at the Los Alamos National Laboratory, works with a genome sequencing machine designed for disease surveillance. Since the SARS epidemic in 2003, advances in sequencing technologies have greatly speed up the ability to detect and track a new virus. Ross D. Franklin/AP hide caption

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The genetic factors responsible for a cat's stripes might help researchers understand disease resistance in humans. kennymatic via Flickr hide caption

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A medical worker from the U.S. Centers for Disease Control and Prevention works at the laboratory where Ebola specimens from the Congo were tested at the start of the latest outbreak. Stephen Wandera/AP hide caption

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A medical worker from the U.S. Centers for Disease Control and Prevention works at the laboratory in Uganda where Ebola specimens were tested at the start of the latest outbreak in the Democratic Republic of Congo. Stephen Wandera/Associated Press hide caption

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Technicians with the Contra Costa County Mosquito and Vector Control District spray insecticide in Brentwood, Calif., last month. Workers fogged areas of the county that had an increase in the numbers of mosquitoes carrying the West Nile virus. Justin Sullivan/Getty Images hide caption

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A hog gets a closeup at the Illinois State Fair in August. Officials took special precautions to make sure no livestock sick with a new strain of swine were part of the fair. Seth Perlman/AP hide caption

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A health worker in the Domincan Republic sprays insecticide between houses to stop dengue fever outbreaks this month. Erika Santelices/AFP/Getty Images hide caption

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Nurse Irena Majola tests Justice Mlambo's blood for HIV at a roadside AIDS testing table in a suburb near Cape Town. Under the "test and treat" strategy, about 45 million South Africans would need to be screened for HIV each year. Rodger Bosch/AFP/Getty Images hide caption

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A doctor examines chest X-rays at a tuberculosis clinic in Gugulethu, Cape Town, South Africa in late 2007. The number of TB cases that don't respond to both first- and second-line medications is rising worldwide. Karin Schermbrucker /AP hide caption

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Two men from northwestern Missouri became ill after tick bites infected them with a previously unknown virus. iStockphoto.com hide caption

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A Beechcraft airplane sprays insecticide over Dallas early Monday morning to curb the spread of West Nile virus. LM Otero/AP hide caption

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