Status of Argasid (Soft) Ticks (Acari: Parasitiformes: Argasidae) In Relation to Transmission of Human Pathogens

Ticks are distributed worldwide and have an enormous medical and veterinary importance owing to the direct damage they cause to their hosts, and especially because these are vectors of a large variety of human and animal pathogens. In fact, ticks are second to mosquitoes as vectors of human pathogens and the most important vectors of pathogens affecting cattle worldwide [1-3]. Tick species can be grouped in two main families, the Argasidae (soft ticks), and the Ixodidae (hard ticks). A third tick family, Nuttalliellidae, only has one species, Nuttalliella namaqua (represented by a monotypic species restricted to South Africa). These three families share common basic properties that are modified distinctively inside each family according to their particular behavior patterns and life-style [4]. They transmit a variety of pathogens of medical and veterinary interest, including viruses, bacteria, rickettsiae, helminthes, and protozoans, all of which are able to cause damage to livestock production and human health. The global threat of tick-borne diseases is increasing, with new pathogens identified continuously. In humans, tick infestations typically involve few specimens and the greatest risk for people bitten by a tick lies in infection due to tick-borne pathogens. Such pathogens are diverse and mainly include viruses, bacteria, and protozoa [5]. The most commonly observed human tick-borne diseases are reportedly Lyme disease, tick-borne encephalitis, Crimean-Congo hemorrhagic fever, Q fever, tularemia, and North-Asia tick-borne spotted fever. Epidemiologically important tick-borne diseases, such as human granulocytic anaplasmosis and severe fever with thrombocytopenia syndrome, have also emerged in recent years. The characterization of a new bunyavirus (associated with fever, thrombocytopenia and leukopenia syndrome) has prompted greater attention to ticks and tick-borne diseases [6].