Donald Mcneil

Officials in Dallas reported that a patient with Zika virus was infected after having sex with an ill individual who had returned from a country where Zika was circulating.

Tropical diseases are marching northward as climate change lets mosquitoes and ticks expand their ranges. The list of scary bug-borne illnesses seems to get longer every year: Lyme, West Nile. Chagas, dengue, chikunguyna — and now Zika.