Comparative vector competence of North American Lyme disease vectors

Abstract

Background: Understanding the drivers of Lyme disease incidence at broad spatial scales is critical for predicting and mitigating human disease risk. Previous studies have identified vector phenology and behavior, host community composition, and landscape features as drivers of variable Lyme disease risk. However, while the Lyme disease transmission cycles in the eastern and western USA involve different vector species (Ixodes scapularis and Ixodes pacificus, respectively), the role of vector-specific differences in transmission efficiency has not been directly examined. By comparing the performance of traits involved in vector competence between these two species, this study aims to identify how vector competence contributes to variable Lyme disease risk. Methods:We used a suite of laboratory experiments to compare the performance of traits related to vector competence for the two USA Lyme disease vectors. For each species, we measured the rate of attachment to a common rodent host, the engorgement weight, and the efficiency of pathogen acquisition (host to tick) and pathogen transmission (tick to host) from laboratory mice. In measuring pathogen acquisition and transmission, we used two different pathogen strains, one sympatric with I. scapularis and one sympatric with I. pacificus, to assess the importance of vector-pathogen coevolutionary history in transmission dynamics. Results:We found I. pacificus had significantly higher host attachment success and engorgement weights, but significantly lower pathogen transmission efficiency relative to I. scapularis. Molting success and pathogen acquisition did not differ between these two species. However, pathogen acquisition efficiency was significantly higher for both sympatric vector and pathogen strains than the allopatric pairings. Conclusions:This study identified species-specific vector traits as a potential driver of broad scale variation in Lyme disease risk in the USA. In particular, the exceedingly low rates of pathogen transmission from tick to host observed for I. pacificus may limit Lyme disease transmission efficiency in the western USA. Further, observed variation in pathogen acquisition between sympatric and allopatric vector-pathogen strains indicate that vector-pathogen coevolutionary history may play a key role in transmission dynamics. These findings underscore the need to consider vector traits and vector-pathogen coevolution as important factors governing regional Lyme disease risk.

Tick populations from endemic and non-endemic areas in Germany show differential susceptibility to TBEV

“…Furthermore, genetic adaptation of pathogen and vector has been shown for I. pacificus and I. scapularis ticks infected with B. burgdorferi s.l. The sympatric vector/pathogen pairing showed significantly higher infection rates as compared to the allopatric vector/pathogen pairings 35 . In addition, first evidence of the genetic stability of TBEV strains of particular TBE natural foci over decades demonstrates the optimal adaptation of a TBEV strain to its vector and host in the respective natural focus (Dobler, unpubl.…”

“…species has been analysed. Those studies have shown remarkable differences in vector competence for Ixodes and Borrelia depending on population and species 33 , 35 . Although similar associations of particular tick species, i.e.…”

“…observ and 40 ). Interestingly, feeding and transmission rates also differed between the two Ixodes species with I. pacificus showing higher feeding but lower Borrelia transmission rates 35 . For I. ricinus , neither the genetic diversity of populations in Germany nor the relationship of genetically distinct populations and vector competence for TBEV has been described so far.…”

Ticks Resist Skin Commensals with Immune Factor of Bacterial Origin

“…We previously found that dae2 Is modestly limits B. burgdorferi levels in I. scapularis 2 . Paradoxically, B. burgdorferi is a stablyassociated tick microbe that is not cleared by I. scapularis immunity and does not appear to negatively impact tick fitness 13,14 . These observations suggest that Dae2 may promote tick tolerance of B. burgdorferi by preventing excessive proliferation in the vector, similar to what has been observed for host-commensal interactions in other systems 15 .…”

Immune factor of bacterial origin protects ticks against host skin microbes

“…We previously found that dae2 Is modestly limits B. burgdorferi levels in I. scapularis 2 . Paradoxically, B. burgdorferi is a stablyassociated tick microbe that is not cleared by I. scapularis immunity and does not appear to negatively impact tick fitness 13,14 . These observations suggest that Dae2 may promote tick tolerance of B. burgdorferi by preventing excessive proliferation in the vector, similar to what has been observed for host-commensal interactions in other systems 15 .…”