Leishmaniosis is a disease caused by the infection of protozoan parasite Leishmania spp. and transmitted by sandflies of the family Psychodidae (genus Phlebotomus in the Mediterranean region) [1,2,3,4]. The World Health Organization (WHO) estimates between 700,000 and 1,000,000 new cases in humans annually. This parasitosis is the third most important vector-born disease in humans, only preceded by malaria and lymphatic filariases, and it is considered endemic in tropical and subtropical areas, where the higher temperatures favor the development of sandflies [5]. Humans, together with domestic dogs (Canis lupus familiaris), are the main hosts, in which the diseases, caused by Leishmania infantum, represent an important problem for public health [6]. Infection in other animals, such as cats (Felis catus), wild canids, and horses, has been reported [7,8,9]. Although dogs used to be considered uniquely and mainly responsible for the spread of the disease to human, the increase in the number of cases diagnosed in domestic cats [10,11], and L. infantum parasites detected in cats sharing the same genetic characteristics with L. infantum strains isolated from humans and dogs [12,13,14], indicate that this species may play an important role currently in the epidemiology of infection in humans and dogs.

The first case of feline leishmaniosis (FL) was detected by Sergent et al. (1912) in Argelia [15]. FL cases have been described later in Europe, Latin America, and Asia, and their prevalence has increased considerably in recent years, with results of prevalence from 1.3% in Portugal or Qatar, to 22.5% and 25% in Brazil and Iran, respectively [10,16,17,18,19,20,21]. Although the highest prevalence of feline leishmaniosis has been found in countries where the disease is endemic, there are cases reported in other areas as well, such as the United States [22]. This FL rise could be connected with a host change due to the use of sandfly repellents in dogs, making them look for other hosts in which feed on [23,24]. In fact, the number of human leishmaniosis is also increasing, probably because the human companion animal bond is becoming higher with dogs and cats, rising the probability of infection [25]. Furthermore, some studies indicate that the use of secondary hosts by the parasite could be related to an increase in the virulence of L. infantum in humans. Concretely, human leishmaniosis outbreak in Spain with high virulence seems to be related to wild hares and wild rabbit’s infection. Both species were found to be asymptomatic reservoirs for the parasite in an area with a low dog population density [26,27]. Early detection of infection in dogs and cats, together with its surveillance and treatments, are strategies to control and avoid human infection, following the “One Health” concept. In addition, and considering cats as emergent hosts with a possible role in the spread of the disease, a new evaluation for the epidemiology and control in this species is necessary [6,28]. However, detection in cats is often confused with other infections, as the clinical signs of leishmaniasis in cats are nonspecific. Furthermore, in some cases, disease appears without clinical signs, making its detection and control more difficult. Moreover, immunosuppression provoked by viruses such as those causing leukemia or feline immunodeficiency can increase parasite multiplication [7]. Due to the scarce information about the role of cats in the distribution of the disease or as reservoir, it is necessary to carry out studies focused on FL, as it could also constitute a point of infection for humans.

2. Epidemiology of Feline Leishmaniosis