3. Insect Bite Hypersensitivity (IBH)
• ETIOLOGY
• Causative insect varies from region to region and includes
mosquitoes, bugs, fleas, etc.
• When an insect bites, the skin reaction could be due to:
• Pharmacologically active substances: chemicals like
histamine and proteases injected by arthropods cause
immediate reaction.
• Microorganisms: introduced into the skin during the bite
or due to scratching may result in:
• Pyoderma.
• Vector-borne diseases.
4. • Clinical Features
• Onset
• Lesions appear in recurrent crops, most frequently
• in summer and rainy season.
• Morphology
• Prototype lesion: Is called papular urticaria
• which has two components:
• Immediate reaction:
• Is due to direct action of pharmacologically
• active substances injected.
• A wheal (Fig. 16.1A) which appears within
• a few minutes of insect bite.
• Lasts few minutes—couple of hours. May
• evolve into a papule.
Variants:
• Bullous papular urticaria:
• Seen in children.
• Frank vesicles and bullae, which frequently
• get secondarily infected.
• Most frequently occur on legs.
