Case 203. Mosquito bite hypersensitivity (5 y-o F)
         
    A 1.5 cm deep ulcer of the forearm skin formed several days after mosquito bite, subsequently with nodal and tonsillar swelling and atypical lymphocytosis    
         
   
Key words : Mosquito bite hypersensitivity, EB virus
   
     
 
     
Skin test to Aedes sp. was positive in this case (gross findings). Elevation of IgE level, positive antibody titers to EB virus and 17% appearance of atypical lymphocytes were also recorded.   Biopsied skin tissue reveals dense infiltration of small lymphocytes and a good number of eosinophils. Mitoses are occasionally seen in the lymphoid cells (HE).
     
 
     
Luna stain discloses marked infiltration of eosinophils, suggesting an allergic nature of the ulcerative lesion.   EBER-1 reactivity is observed in the nuclei of some of the small lymphocytes (in situ hybridization). EBER-1 positivity was also confirmed in the lymph node. Activation of EBV plays a pathogenetic role in the mosquito bite hypersensitivity.