Potential effects of mixed infections in ticks on transmission dynamics of pathogens: comparative analysis of published records

Abstract

Ticks are often infected with more than one pathogen, and several field surveys have documented nonrandom levels of coinfection. Levels of coinfection by pathogens in four tick species were analyzed using published infection data. Coinfection patterns of pathogens in field-collected ticks include numerous cases of higher or lower levels of coinfection than would be expected due to chance alone, but the vast majority of these cases can be explained on the basis of vertebrate host associations of the pathogens, without invoking interactions between pathogens within ticks. Nevertheless, some studies have demonstrated antagonistic interactions, and some have suggested potential mutualisms, between pathogens in ticks. Negative or positive interactions between pathogens within ticks can affect pathogen prevalence, and thus transmission patterns. Probabilistic projections suggest that the effect on transmission depends on initial conditions. When the number of tick bites is relatively low (e.g., for ticks biting humans) changes in prevalence in ticks are predicted to have a commensurate effects on pathogen transmission. In contrast, when the number of tick bites is high (e.g., for wild animal hosts) changes in pathogen prevalence in ticks have relatively little effect on levels of transmission to reservoir hosts, and thus on natural transmission cycles.

Anaplasmataceae and Borrelia burgdorferi sensu lato in the sand lizard Lacerta agilis and co-infection of these bacteria in hosted Ixodes ricinus ticks

“…Such correlations suggest that the more ticks feed on a lizard, the greater chance of contact with infected ticks, and hence more chance of acquiring tick-borne infection. The results confirmed previous studies [38,39] which show that the probability of host exposure to a tick-borne pathogen is correlated with tick abundance. Therefore, the best way to avoid infection with tick-borne disease is to avoid areas with a high density of its vectors [18].…”

Diverse tick-borne microorganisms identified in free-living ungulates in Slovakia

“…In general, infections of ticks with multiple pathogens can result in co-transmission of various combinations of tick-borne microorganisms to vertebrate hosts, which may have severe implications for human and animal health [154–156]. We assume that co-transmission of the detected microorganisms to ungulates by ticks does not occur in the study area, or it may occur to a very low extent (e.g.…”

Imbalanced presence of Borrelia burgdorferi s.l. multilocus sequence types in clinical manifestations of Lyme borreliosis

“…It has been previously shown that B. burgdorferi s.l. coexists in ticks with some other tick-borne pathogens (Belongia, 2002;Burri et al, 2011;Coipan et al, 2013b;Ginsberg, 2008;Koetsveld et al, 2015;Lommano et al, 2012;Nieto and Foley, 2009;Reye et al, 2010). Likewise, it is known that the severity of LB may be affected by simultaneous infections with other bacteria, such as Anaplasma phagocytophilum (Belongia, 2002;Holden et al, 2005;Swanson et al, 2006;Thomas et al, 2001), that are capable to modulate host immunity and, therefore, increase susceptibility to various second pathogens.…”