Final answer:
The congenital problem that affects the nares of South American camelids is choanal atresia, a condition where nasal passageways are sealed off, leading to breathing difficulties.
Step-by-step explanation:
The congenital problem that affects the nares of South American camelids is choanal atresia. This condition occurs when the choanae, the passageways that connect the nasal cavity to the throat, are abnormally sealed off by tissue. Affecting species such as llamas, alpacas, vicuñas, and guanacos, choanal atresia can lead to breathing difficulties and requires surgical intervention for correction. It is a significant health issue in these animals and often requires the expertise of a veterinarian experienced in camelid medicine.