Which of the following is a viral infection?

Hepatitis A is the correct answer because it is a viral infection caused by the hepatitis A virus (HAV). This virus primarily affects the liver and is transmitted through the ingestion of contaminated food or water. Hepatitis A can cause symptoms such as nausea, vomiting, abdominal pain, and fatigue, which can lead to liver inflammation.

The other options represent different types of pathogens. Cryptosporidium is a protozoan parasite that causes gastrointestinal illness, while listeriosis is caused by the bacterium Listeria monocytogenes, leading to severe infections primarily in vulnerable populations such as pregnant women and the elderly. Trichinella is a genus of parasitic roundworms that can cause trichinosis, an infection resulting from consuming undercooked meat containing the larvae of the parasite. These distinctions highlight the distinguishing characteristics of viral infections versus those caused by bacteria or parasites.