If not treated with streptococcal infections can cause damage to kidneys or develop into rheumatic fever.?

That statement is true.

Streptococcal infections, if left untreated, can lead to several complications, including damage to the kidneys and the development of rheumatic fever.

1. Kidney damage: Streptococcal infections can cause a condition called post-streptococcal glomerulonephritis, which is an inflammation of the kidneys filters (glomeruli). This inflammation can lead to leakage of protein and blood into the urine, as well as decreased kidney function. In severe cases, post-streptococcal glomerulonephritis can lead to kidney failure.

2. Rheumatic fever: Streptococcal infections, particularly those caused by certain strains of the bacteria, can also trigger rheumatic fever. Rheumatic fever is an inflammatory condition that affects various parts of the body, including the joints, heart, skin, and brain. It can cause joint pain, swelling, and inflammation of the heart valves (endocarditis). Rheumatic fever can lead to permanent heart damage if not treated promptly and adequately.