Establishment of co-infection models in ticks and mice with two bacteria and one virus
Résumé
Nowadays, ticks and tick-borne pathogens (TBPs) are an increasing One Health problem. The main tick-borne diseases in Europe are Lyme borreliosis, granulocytic anaplasmosis and tick-borne encephalitis. Their vector is Ixodes ricinus, which has a wide geographical distribution and can feed on many different vertebrate hosts. It can acquire and/or transmit more than one pathogen to animals including humans at each blood-feeding stage. Tick co-infections and co-transmissions of pathogens by ticks have been demonstrated in diverse studies. For example, co-infections in ticks are common in the wild. In humans, a study of patients with chronic Lyme disease (confirmed by medical diagnosis) has demonstrated that among them 23.5 % of the patients show at least one co-infection with other tick borne pathogens like Babesia, Bartonella, Ehrlichia, and Anaplasma and 30% report two or more co-infections with those pathogens by laboratory diagnosis. The outcome of these co-infections and co-transmissions deserves to be considered with great interest because they are likely to lead to synergy and/or competition between pathogens. Those interactions could have ,consequences for individual pathogen fitness in mammalian hosts. In particular, individual infection ,rates can be reduced if pathogens directly compete for resources or via toxin production. Conversely, the down-regulation of the host immune response can result in an increased pathogen burden and facilitate transmission from host to vector. Thus, these interactions can potentially have a major impact on public health, both clinically and in terms of therapeutic applications. The small number of co-infection or multiple infection models to study the complex interactions between TBPs in co-infected ticks, and co-infected vertebrate hosts prompted us to establish co-infection models using two bacteria (Borrelia afzelii and Anaplasma phagocytophilum) and a virus (Tick-Borne Encephalitis ,Virus (TBEV)) in ticks (I. ricinus) and mammals (mice). Ticks were co-infected using different techniques (artificial feeding system, capillary feeding and micro-injection), whereas the mice were co-infected by inoculation of the different pathogens (intraperitoneal/subcutaneous/intradermal). Our preliminary results obtained: (i) in mice, single and co-infection with TBEV and B. afzelii were established using different concentrations/amounts of each pathogen; (ii) in ticks, single infections and co-infection were set up using an artificial feeding system with B. afzelii and TBEV; (iii) in ticks, single infections and co-infections were set up by capillary feeding and microinjection by B. afzelii, TBEV and A. phagocytophilum. These preliminary results are the first steps to studying the transmission success of these pathogens from co-infected ticks to non-infected mice and from co-infected mice to non-infected ticks.