The present invention provides heavy chain immunoglobulins of the VHH type or fragment thereof having affinity for a target antigen of interest, including glycoprotein D2 (gD2) of HSV-2 or antigen thereof, and for envelope proteins of HIV-1 or an antigen thereof linked to Pseudomonas exotoxin A or functional fragments thereof. Also included are multimeric forms of the immunoglobulins and their use in the prevention and/or treatment of HSV2 and/or HIV-1.
