Efficient infection of hamster with Leishmania donovani by retro-orbital inoculation

Visceral leishmaniasis caused by the anthroponotic Leishmania donovani (VL) and the zoonotic L.infantum (ZVL) are among the most lethal Neglected Tropical Diseases (NTD). They are transmitted by Phlebotominae sand flies (Phlebotomus sp and Lutzomyia sp) and are widely distributed in tropical and subtropical areas [1]. Human vaccination has been elusive [2] and the marketed vaccines for canine infections caused by L.infantum have several shortcomings [3]. Environmental control of this vector-borne disease is unpractical [4]. Moreover, indiscriminate culling of canine population has not yielded the expected benefits to limit the human infections in areas where ZVL is prevalent [5] and it is not acceptable by ethical reasons. Main control system is chemotherapy in both humans and dogs although available treatments have important drawbacks including toxicity and less toxic presentations are highly priced [6]. Emergence of resistant isolates and treatment failures are frequent [7,8] and the drug discovery pipeline is slim [9]. Thus, it is clear that there are research areas where a substantial effort has to be made, namely immune response and chemotherapy. While in vitro and ex vivo models (e.g. macrophage lines; bone-marrow-derived or peritoneal macrophages) are useful for some experimental purposes they have important limitations in all aspects related to immunology, pathology or chemotherapy; thus animal models of the disease are needed. BALB/c mice have been extensively used in drug screening and immunological studies. However, despite the obvious advantages of this species (price, size and housing, genetic homogeneity, availability of reagents) and their receptivity to L.donovani and L.infantum infections by different routes, murine infections do not reproduce the human or canine visceral infections and minor or none clinical signs are observed in infected mice [10–12]. Hamster (Mesocricetus auratus) is probably the best rodent model for VL since they develop chronic leishmanial infections with clinical and lesions comparable to those found in humans and dogs [12–14]. Besides using infected sand flies [15] to initiate infections several routes of infection have been used in hamster including intraperitoneal (IP), intracardiac (IC), intradermal (ID) and intravenous (IV). IV inoculations, in absence of developed tail, are quite limited (e.g. lingual vein) [16]. IP injection is a frequently used via because it is easily performed and does not require anesthesia [17,18] although on occasion it can yield suboptimal and nonconsistent infections [19]. ID injection, although more closely related to the natural inoculation by sand flies, does not guarantee visceral infection of inoculated hamsters [19]. By its part, IC route allows accurate infective dosage [13,17,20–22] but it demands highly skilled personnel and the risk of early death of animals after inoculation cannot be ruled out. Retro-orbital (RO) inoculation is a well-described technique in mice for drug administration, bone marrow transplantation or gene therapy [23]. Recently this route has been used in mice to inoculate L.infantum [24] but as far as we know this route of infection has not been tested or reported in hamster. This manuscript presents a comparative study of IP, IC, and RO inoculation routes of L.donovani by determining clinical course and lesions, biochemical and immunological profile of infected hamsters, and parasite burdens in target organs.