What is a defining symptom of anthrax?

The defining symptom of anthrax is the development of dark scabs on the skin, known as eschars, specifically associated with its cutaneous form. When anthrax spores enter through a cut or abrasion on the skin, they can cause a localized infection that initially appears as a small raised bump resembling an insect bite. This can then progress to a blister and subsequently form a distinctive ulcer with a characteristic black necrotic area in the center, leading to dark scabs. This symptom is unique to the cutaneous form of anthrax and is an important indicator of the disease.

In contrast, other symptoms listed are associated with different health conditions. For example, a persistent cough and wheezing are typically linked to respiratory illnesses rather than anthrax. High blood pressure and headaches could be indicators of numerous other non-specific health issues, but they are not defining symptoms of anthrax. Severe diarrhea and dehydration are more commonly associated with gastrointestinal infections, not anthrax. Therefore, the presence of dark scabs on the skin effectively distinguishes anthrax as a unique and identifiable condition.