Transmission Cycle of Tick-Borne Infections and Co-Infections, Animal Models and Diseases

Abstract

Tick-borne pathogens such as species of Borrelia, Babesia, Anaplasma, Rickettsia, and Ehrlichia are widespread in the United States and Europe among wildlife, in passerines as well as in domestic and farm animals. Transmission of these pathogens occurs by infected ticks during their blood meal, carnivorism, and through animal bites in wildlife, whereas humans can become infected either by an infected tick bite, through blood transfusion and in some cases, congenitally. The reservoir hosts play an important role in maintaining pathogens in nature and facilitate transmission of individual pathogens or of multiple pathogens simultaneously to humans through ticks. Tick-borne co-infections were first reported in the 1980s in white-footed mice, the most prominent reservoir host for causative organisms in the United States, and they are becoming a major concern for public health now. Various animal infection models have been used extensively to better understand pathogenesis of tick-borne pathogens and to reveal the interaction among pathogens co-existing in the same host. In this review, we focus on the prevalence of these pathogens in different reservoir hosts, animal models used to investigate their pathogenesis and host responses they trigger to understand diseases in humans. We also documented the prevalence of these pathogens as correlating with the infected ticks’ surveillance studies. The association of tick-borne co-infections with other topics such as pathogens virulence factors, host immune responses as they relate to diseases severity, identification of vaccine candidates, and disease economic impact are also briefly addressed here.

Tick populations and molecular detection of selected tick-borne pathogens in questing ticks from northern and central Tanzania

“…Co-infections of epidemiologically important pathogens in hard ticks have been previously reported and it varies primarily depending on geographic area and the number of pathogens screened (Rocha et al 2022 ). This study has shown that 0.3% of the collected ticks were co-infected by various TBPs.…”

“…In line with the previous reports (Moutailler et al 2016 ; Klitgaard et al 2019 ), which showed a higher percentage of co-infection in adult questing ticks than in questing nymphs, 83% of the co-infected ticks in this study were adult questing ticks. According to Rocha et al ( 2022 ), adult ticks are more likely to be co-infected than nymphs because they may have had additional blood feeding. Ticks co-infected with multiple pathogens greatly increase the risk of co-infections in the vertebrate host, which would result in more complex clinical manifestations and could be misdiagnosed.…”

Global prevalence ofBorrelia burgdorferiandAnaplasma phagocytophilumcoinfection inIxodestick populations: protocol for a systematic review and meta-analysis

“… 33 34 The annual diagnostic expenses for HGA stand at US$1.6 million. 33 34 Infections and coinfections in animals also lead to decreased productivity and mortality, particularly in developing countries, where the estimated economic losses can reach billions of dollars, 35 significantly impacting agriculture and livestock industries.…”

“…Notably, pathogen coinfections within Ixodes ticks are widespread globally, yet there is a marked geographical variability, with coinfection rates as low as 0.5% 24 in some regions and up to 20.2% 35 in others. Additionally, climate change and increasing human activities have expanded tick habitats and extended their active periods, further increasing the chances of human-tick encounters and, consequently, the risk of coinfections.…”

Severe Anaplasmosis With Multiorgan Involvement in a Rheumatoid Arthritis Patient

“…Babesiosis, another tick-borne disease caused by protozoan parasites of the Babesia microti , can be observed as a co-infection with anaplasmosis at 5-20% depending on the prevalence of each infection. The transmission of both pathogens occurs through the bite of infected ticks, and therefore, simultaneous infections can occur in individuals exposed to ticks carrying both pathogens [ 3 ]. In this case report, we comprehensively describe a severe anaplasmosis case with multi-systemic involvement, encompassing neurological, respiratory, and hepatobiliary manifestations.…”