Final answer:
Pregnant women should avoid cleaning cat litter boxes to prevent the risk of infection by Toxoplasma gondii, which causes toxoplasmosis, a disease that can severely affect the unborn child.
Step-by-step explanation:
Pregnant women are advised to avoid contact with a cat's litter box or feces to prevent the risk of contracting toxoplasmosis. This infection is caused by the protozoan Toxoplasma gondii, which can be transferred from contaminated cat feces to humans, primarily when cleaning a litter box without adequate protection. Toxoplasmosis during pregnancy is particularly dangerous as it can cross the placenta and infect the developing fetus, possibly leading to stillbirth, miscarriage, or severe health issues such as mental deafness, or blindness in the infant. The CDC recommends that pregnant women take particular care to avoid this risk through proper food handling, gardening practices, and especially avoiding contact with cat feces. For pregnant cat owners, the recommendation is usually to have someone else handle the litter box duties or to do so with protective gloves and meticulous hand washing.
Therefore, the nurse's best response to why a pregnant woman should not be cleaning the litter box would be option a: "Your cats could be carrying toxoplasmosis. This is a zoonotic parasite that can infect you and have severe effects on your unborn child." This response accurately represents the health risks associated with toxoplasmosis in pregnancy.