What portal of entry should a field sanitarian protect to avoid contracting Lyme disease?

The correct answer is the skin because Lyme disease is primarily transmitted through the bite of infected black-legged ticks, also known as deer ticks. These ticks attach themselves to the skin of their hosts, often in hidden areas where they are not easily noticed, such as the groin, armpits, and scalp. When a tick bites, it can introduce the Lyme bacteria into the bloodstream through the skin.

Protecting the skin from tick bites is essential in preventing Lyme disease. This can be achieved by wearing protective clothing, applying insect repellent, and checking for ticks regularly after being outdoors in areas where ticks are prevalent.

The other portals of entry, such as the respiratory tract, reproductive organs, and digestive tract, are not relevant for Lyme disease transmission. Lyme disease does not spread through air, sexual contact, or ingestion of food or water, thereby making skin protection the primary concern for field sanitation professionals dealing with this specific disease.