Some burglars walk through the front door.
Others make a forced entry. They include Plasmodium, the protozoan that causes malaria, and Cryptosporidium, the water-borne microbe that can trigger deadly outbreaks of diarrhea. Sibley and graduate student Janice M. Dobrowolski discovered that Toxoplasma forces its way into host cells with a motor made of actin. This rod-shaped protein also is involved in muscle contraction. It just eats and eats' Humans can acquire Toxoplasma from cat litter boxes or by eating undercooked meat, though healthy people do not develop disease.