The specificity of Babesia-tick vector interactions: recent advances and pitfalls in molecular and field studies

Abstract

Background Babesia spp. are protozoan parasites of great medical and veterinary importance, especially in the northern Hemisphere. Ticks are known vectors of Babesia spp., although some Babesia-tick interactions have not been fully elucidated. Methods The present review was performed to investigate the specificity of Babesia-tick species interactions that have been identified using molecular techniques in studies conducted in the last 20 years under field conditions. We aimed to indicate the main vectors of important Babesia species based on published research papers (n = 129) and molecular data derived from the GenBank database. Results Repeated observations of certain Babesia species in specific species and genera of ticks in numerous independent studies, carried out in different areas and years, have been considered epidemiological evidence of established Babesia-tick interactions. The best studied species of ticks are Ixodes ricinus, Dermacentor reticulatus and Ixodes scapularis (103 reports, i.e. 80% of total reports). Eco-epidemiological studies have confirmed a specific relationship between Babesia microti and Ixodes ricinus, Ixodes persulcatus, and Ixodes scapularis and also between Babesia canis and D. reticulatus. Additionally, four Babesia species (and one genotype), which have different deer species as reservoir hosts, displayed specificity to the I. ricinus complex. Eco-epidemiological studies do not support interactions between a high number of Babesia spp. and I. ricinus or D. reticulatus. Interestingly, pioneering studies on other species and genera of ticks have revealed the existence of likely new Babesia species, which need more scientific attention. Finally, we discuss the detection of Babesia spp. in feeding ticks and critically evaluate the data on the role of the latter as vectors. Conclusions Epidemiological data have confirmed the specificity of certain Babesia-tick vector interactions. The massive amount of data that has been thus far collected for the most common tick species needs to be complemented by more intensive studies on Babesia infections in underrepresented tick species. Graphical abstract

Babesiosis in Southeastern, Central and Northeastern Europe: An Emerging and Re-Emerging Tick-Borne Disease of Humans and Animals

“…Feline babesiosis is still very rarely reported globally [ 12 ], including among the reviewed countries. Although there are several species of Babesia that can infect cats [ 12 ], these piroplasms have not been identified in questing I. ricinus or D. reticulatus (reviewed in [ 8 ]). Cats are less frequently infested with D. reticulatus than dogs [ 22 , 326 ], and their susceptibility to B. canis is still to be confirmed.…”

“…The main route of transmission of babesiae to mammalian hosts is through a tick bite, although other routes of transmission (e.g., vertical transmission, transmission through blood transfusion or organ transplantation) have been documented among both humans and animals, including also in wildlife reservoir hosts [ 7 ]. Hard ticks (Ixodidae) act as vectors of babesiae, with evidence of specificity in Babesia -tick vector interactions [ 8 ]. The course of babesiosis can differ considerably, from entirely subclinical infections, through mild non-specific manifestations, to fatal, multisystem disease.…”

“…The ornate dog tick, Dermacentor reticulatus , is one of the fastest-spreading tick species in central and northeastern Europe, with increasing significance as a vector of tick-borne pathogens for domesticated animals [ 22 , 23 , 24 , 25 ]. Dermacentor reticulatus is the main, if not the only, vector of Babesia canis and its spread is accompanied by the expansion of canine babesiosis and the appearance of new foci of the disease [ 8 , 26 ]. Additionally, this tick species may act as a vector of B. caballi and Theileria equi [ 25 , 27 , 28 ].…”

Potential Role of Avian Populations in the Epidemiology of Rickettsia spp. and Babesia spp.

“…Similar studies from North America dealing with I. scapularis, revealed B. microti [98] while B. odocoilei was identified in ticks from Canada, occurring on songbirds [99][100][101]. The occurrence of a pathogen in a tick found on a host does not demonstrate in fact that the tick is the vector of the pathogen, and data would be misleading when the presence of pathogens has not been ascertained in the host [47].…”

“…Babesiosis in wildlife can be fatal, too when associated with stressful management practices [45]. Mammals and birds are involved in life cycles as vertebrate (intermediate) hosts although the specificity of babesia for vector ticks (final hosts) has not been fully elucidated [47].…”