Doctors used a rapid DNA test to identify a Wisconsin teen's unusual infection with Leptospira bacteria (yellow), which are common in the tropics. CDC/Rob Weyant hide caption

itoggle caption CDC/Rob Weyant

Red blood cells infected with the Plasmodium falciparum parasite. Plasmodium is the parasite that triggers malaria in people. Gary D. Gaugler/Science Source hide caption

itoggle caption Gary D. Gaugler/Science Source

False-color transmission electron micrograph of a field of whooping cough bacteria, Bordetella pertussis. A. Barry Dowsett/Science Source hide caption

itoggle caption A. Barry Dowsett/Science Source

This mouse egg (top) is being injected with genetic material from an adult cell to ultimately create an embryo — and, eventually, embryonic stem cells. The process has been difficult to do with human cells. James King-Holmes/Science Source hide caption

itoggle caption James King-Holmes/Science Source

In this colored transmission electron micrograph, an infected cell (reddish brown) releases a single Ebola virus (the blue hook). As it exits, the virus takes along part of the host cell's membrane (pink, center), too. That deters the host's immune defenses from recognizing the virus as foreign. London School of Hygiene & Tropical Medicine/Science Source hide caption

itoggle caption London School of Hygiene & Tropical Medicine/Science Source

I'm not trying to lead you astray. It's just that scientists are not skeptical enough about their mouse studies. iStockphoto hide caption

itoggle caption iStockphoto

The research team used yeast chromosome No. 3 as the model for their biochemical stitchery. Pins and white diamonds in the illustration represent "designer changes" not found in the usual No. 3; yellow stretches represent deletions. Lucy Reading-Ikkanda hide caption

itoggle caption Lucy Reading-Ikkanda