**Core Concept**
Cataracts and patent ductus arteriosus (PDA) in a newborn can be a manifestation of congenital rubella syndrome, which is caused by the rubella virus. This condition occurs when the rubella virus infects the fetus in utero, leading to various congenital abnormalities.

**Why the Correct Answer is Right**
Rubella virus infection in the first trimester can cause a range of congenital abnormalities, including cataracts and PDA. This is due to the virus's ability to cross the placenta and infect the developing fetus. The virus can cause damage to the developing eyes, leading to cataracts, and also affect the development of the cardiovascular system, resulting in PDA.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because congenital varicella syndrome, caused by the varicella-zoster virus, typically presents with skin lesions, limb abnormalities, and other congenital defects, but not typically cataracts and PDA.

**Option B:** This option is incorrect because toxoplasmosis, caused by the Toxoplasma gondii parasite, can cause congenital infections, but the classic triad of symptoms includes hydrocephalus, intracranial calcifications, and chorioretinitis, not cataracts and PDA.

**Option C:** This option is incorrect because congenital CMV (cytomegalovirus) infection can cause a range of congenital abnormalities, including hearing loss, developmental delay, and vision impairment, but not typically cataracts and PDA.

**Option D:** This option is incorrect because congenital syphilis can cause a range of congenital abnormalities, including skin lesions, joint pain, and vision impairment, but not typically cataracts and PDA.

**Clinical Pearl / High-Yield Fact**
The rubella virus can cause congenital abnormalities if infection occurs during the first trimester, emphasizing the importance of rubella vaccination in pregnant women and avoiding exposure to the virus during this critical period.

**Correct Answer: A. Rubella.**