Blood-feeding ectoparasites constitute a growing burden for human and animal health, and animal production worldwide. In particular, mites (Acari: Gamasida) of the genera Dermanyssus (Dermanyssidae) and Ornithonyssus (Macronyssidae) infest birds and cause gamasoidosis in humans. The tropical fowl mite, Ornithonyssus bursa, is commonly found in tropical and subtropical countries but rarely reported in Europe. In this research we characterized the first two cases in Spain of clinical gamasoidosis diagnosed in patients infested with O. bursa, and investigated the IgE, IgM and IgG antibody response to mite proteins and the carbohydrate Galα1-3Galβ1-(3)4GlcNAc-R (α-Gal) involved in the tick-bite associated alpha-Gal syndrome (AGS). The results suggested that O. bursa is establishing across Mediterranean countries, and may increase the risk for gamasoidosis. The immune antibody response to mite proteins was higher for IgM and similar for IgE and IgG antibodies between patients and non-allergic control individuals exposed to mite or tick bites. The anti-α-Gal antibody levels were similar between patients and controls, a result supported by the absence of this carbohydrate in mites. These results suggested that mite bites do not correlate with antibody response to acarine proteins or α-Gal, and are not associated with the AGS.