Which organism is associated with serious congenital infections?

• A. Borrelia burgdorferi
• B. Borrelia recurrentis
• C. Treponema pallidum subsp. pallidum
• D. Treponema pallidum subsp. pertenue

Answer: (C)

Transplacental transmission of Treponema pallidum from an infected pregnant person leads to congenital syphilis, causing serious fetal and neonatal disease. Treponema pallidum subsp. pallidum is the organism responsible for the venereal form of syphilis and is well documented to cross the placenta and infect the fetus, with potential outcomes ranging from miscarriage or stillbirth to severe neonatal symptoms and later developmental problems. The other spirochetes listed cause diseases primarily acquired after birth or in different contexts (Lyme disease from Borrelia burgdorferi, relapsing fever from Borrelia recurrentis, yaws from Treponema pallidum subsp. pertenue) and are not classically associated with serious congenital infections. Hence, this organism is the one most linked to congenital infection.