Antigenic variation in vector-borne pathogens

Several pathogens of humans and domestic animals depend on hematophagous ar thropods to transmit them from one vertebrate reservoir host to another and maintain them in an environment. These pathogens use antigenic variation t o prolong their circulation in the blood and thus increase the likelihood o f transmission. By convergent evolution, bacterial and protozoal vector-bor ne pathogens have acquired similar genetic mechanisms for successful antige nic variation. Borrelia spp. and Anaplasma marginale (among bacteria) and A frican trypanosomes, Plasmodium falciparum, and Babesia bovis (among parasi tes) are examples of pathogens using these mechanisms. Antigenic variation poses a challenge in the development of vaccines against vector-borne patho gens.