Which agent is associated with asymptomatic infections in pregnant women with pets?

Toxoplasma gondii is the correct answer as it is known to cause asymptomatic infections in pregnant women, especially those who have close contact with pets, particularly cats. Toxoplasmosis can be transmitted through contact with cat feces, contaminated soil, or undercooked meat. Most healthy individuals, including pregnant women, often remain asymptomatic when infected with T. gondii. However, if the infection occurs during pregnancy, it can have serious consequences for the fetus, leading to conditions such as congenital toxoplasmosis.

Cytomegalovirus is another virus that can cause asymptomatic infection; however, it is not specifically linked to pet exposure. Rubella virus primarily affects individuals who are not vaccinated, and while it can also pose risks during pregnancy, it is not associated with pets. Herpes simplex virus can lead to symptomatic infections and is more commonly associated with genital or oral lesions, rather than asymptomatic infections related to pet exposure. Therefore, Toxoplasma gondii is the agent most closely associated with asymptomatic infections in pregnant women who have pets.