No virus directly “causes” autism. However, certain maternal infections during pregnancy have been associated with modestly increased autism risk, likely through their effects on fetal brain development.

Rubella

Rubella (German measles) infection during pregnancy is the best-documented infectious risk factor. The 1964 rubella epidemic produced elevated autism rates in affected children. Congenital rubella syndrome can cause brain damage that results in autism-like features. Modern vaccination has made this extremely rare in developed countries.

Cytomegalovirus (CMV)

CMV is a common virus that usually causes no symptoms in adults but can affect fetal development. Some research has found associations between congenital CMV infection and developmental outcomes including autism, though the evidence is limited and the absolute risk increase is small.

General Maternal Infection and Fever

Several studies have found that maternal fever during pregnancy, regardless of the specific infection, is associated with a slight increase in autism risk. This may be related to the inflammatory immune response rather than any particular pathogen. The risk is modest and does not mean that getting sick during pregnancy will cause autism.

Putting Risk in Perspective

Even the strongest infectious risk factors produce only modest increases in autism probability. The vast majority of children born to mothers who had infections during pregnancy do not develop autism. Genetics remain the primary driver of autism risk. Good prenatal care, vaccination, and prompt treatment of infections during pregnancy are the practical takeaways.