USA Biology Olympiad (USABO) Practice Exam

An elevated eosinophil count in a patient may indicate an infection caused by which organism?

1. Parasites

2. Schistoma

3. Bacteria

4. Virus

The correct answer is: Schistoma

An elevated eosinophil count, or eosinophilia, is commonly associated with various conditions, including allergic reactions, autoimmune diseases, and notably, infections caused by parasitic organisms. Eosinophils are a type of white blood cell that play a crucial role in the body's immune response, particularly against parasites. Infection with Schistosoma, a genus of parasitic flatworms commonly referred to as blood flukes, is known to lead to elevated eosinophil levels. This is due to the immune system's response to the presence of these parasites, which can cause tissue inflammation and an increase in eosinophil production. While other organisms such as certain bacteria or viruses can cause elevation in some white blood cells, they typically do not result in a significant increase in eosinophils. Instead, conditions involving bacterial infections may elevate neutrophils, while viral infections often lead to an increase in lymphocytes. Thus, the specific association between elevated eosinophils and parasitic infections, especially schistosomiasis, is what makes this option most relevant in the context of the question.