Yaws is a serious skin disease of children in tropical countries, caused by treponema pertenue, a species closely related to the bacteria that cause syphilis. individual cells of t. pertenue are helical, relatively long, and flexible like the one pictured below. these cells are known as

The correct answer is- spirochetes

Explanation:

Spirochetes are a group of bacteria which are long, flexible and helical shaped. Some of them are associated with some disease in humans like yawns, lime disease, syphilis, etc.  

Yawn is childhood infectious disease caused by a spirochete bacteria called  Treponema pallidum pertenue. These bacterial usually affect the children who live in tropical regions like Africa, Southeast Asia. They can affect skin, bones, and joints. They can spread through direct contact with skin sores.

So the cells of T. pertenue which are helical, relatively long, and flexible known as spirochetes.

answer; ////increased water pollution; ///////////////////////