Question

The top two layers of the epithelia, the layer of skin on the outside of the body, are the stratum corneum and the stratum lucidum. Both of these layers are metabolically inactive, in other words they are dead cells that do not manufacture anything. Since viruses rely on the manufacturing apparatus of their host cell to proliferate, how do viruses infect and penetrate these two layers?

This question pertains only to viruses that infect the body of the host through the epidermis. So, that would include viruses that cause warts, herpes viruses and viruses that infect the respiratory epithelia like cold viruses. If these different kinds of viruses penetrate epidermal defenses in different ways then that would be relevant to the answer.

Answer 1

Viruses infect the epidermis by penetrating the stratum corneum and stratum lucidum through minor breaches. They target metabolically active cells in deeper layers to proliferate. The infection strategies differ among viruses, depending on their structure and life cycle specificities.

Step-by-step explanation:

How Viruses Infect the Epidermis

The epidermis is the outermost layer of skin, incorporating several layers including the stratum corneum and, in areas of thick skin, the stratum lucidum. These upper layers consist of dead keratinocytes that present a barrier to pathogens, including viruses. Despite this, certain viruses have mechanisms to penetrate these layers. Viruses infect the epidermal layer primarily by exploiting microabrasions or other minor breaches in the stratum corneum to reach the metabolically active, living cells in deeper layers.

The stratum corneum and stratum lucidum serve as the primary defense against physical damage and pathogens. They are composed largely of keratinocytes filled with keratin, a tough protein that renders them waterproof and protects against microbial penetration. However, viruses that cause warts, herpes, and some respiratory infections, for instance, manage to surpass these defenses in different manners.

Warts are caused by human papillomavirus (HPV), which can enter through minute damages in the skin surface. Herpes simplex virus (HSV) can infect through similar breaches, establishing latency in nerve cells. Respiratory viruses may adhere to and penetrate mucosal epithelia, which does not have the same keratinized protection. While detailed mechanisms vary among viruses, their success involves either local disruption of the stratum corneum or accessing less protected areas.