 SCP-149 is a breed of mosquito, which carries a strain of retrovirus that mutates regenerating human cells into fertilized mosquito eggs. SCP-149-A is injected directly into the bloodstream when SCP-149 feeds. The SCP-149-A quickly works on the nucleus of the cells, warping the DNA. The first set of cells bred from these changed instructions closely resemble cysts, and are concentrated in the lining of the esophagus and the sinuses. Upon dissection, however, these cysts are revealed to be filled with SCP-149's larvae, the cysts acting as a protective casing against external forces. SCP-149 appears to go through its maturation cycle in a matter of hours. By the time the subject is able to feel any effects, the first generation of SCP-149 has already grown inside the subject's body.