The Tree Structures consist of 15 subject categories used to classify all the MeSH headings. Each category is divided into many subcategories. The subcategories show the hierarchical relationships between related headings. The Trees are not intended to be an authoritative subject classification system.
Some categories provide only a sketchy outline of their topics while others are comprehensive.
The level of detail included in any category reflects the amount of literature published on the topic and its importance to health care and biomedical research. For example, although there are many more species of insects than mammals, MeSH include only about 60 headings for different kinds of insects but over 150 headings for mammals. All Dengue headings begin with C2.81 . Click on the category letter to view subcategories.