What diseases a peripheral blood smear shows? can it show that there is an infectious disease or viral?

Many many Blood: and other disorders including Infectious disease/viral and bacterial! Hope this helps! Dr Z

See below: A peripheral blood smear shows white blood cells(leukocytes), lymphocytes, red blood cells and platelets . Bacterial diseases will often cause an elevated number of leukocytes and viral diseases often cause an elevation of lymphocytes. But there are many conditions other than infectious that can cause an increase in these cells. And infection can be present even if the peripheral smear is normal.

Many different thing: can be seen on a peripheral smear. It can demonstrate signs of some viral, bacterial and parasite infections. It can demonstrate changes associated with cancer or other immune related problems. It can even demonstrate genetic problems like sickle cell disease or nutritional deficiencies. It's a very powerful tool in the right hands.