Leishmania infantum in Tigers and Sand Flies from a Leishmaniasis-Endemic Area, Southern Italy

We detected Leishmania infantum infection in 45% of tigers and 5.3% of sand flies tested at a zoo in southern Italy in 2019. These infections in tigers and the abundance of Phlebotomus perniciosus sand flies represent a potential risk to other animals and humans living in or visiting the zoo.

Consensus sequences of the vertebrate host mitochondrial cytochrome b from all female sand flies (positive specimens) displayed 100% identity to the nucleotide sequences of Panthera tigris available in the GenBank database (accession nos. MH124112 and KC879295).

Conclusions
The high prevalence (45%) of L. infantum infection recorded indicates that tigers living in the zoologic park are highly exposed to sand flies and thus have a high risk for acquiring the parasite. The finding of engorged sand flies that fed on tigers and were also positive for L. infantum suggest that tigers could be an alternative host of this parasite; however, the possibility that L. infantum-positive sand flies had acquired the infection from another host, before feeding on tigers, cannot be ruled out.
Although Leishmania spp. infection has been scantly described in wild felids (3)(4)(5), the diagnosis of this parasitic infection should also be considered while screening these animals for pathogens potentially impairing their health and welfare. No information is available on the immune response against L. infantum infection in tigers, and serologic tests have not been validated for this host, but one could reasonably suspect that their antibody production would follow a pattern similar to that occurring in cats. Nonetheless, the absence of L. infantum DNA in tigers that were positive for L. infantum antibodies (4/9 tigers [44.4%]) could be expected, given that this lack of correlation between molecular and serologic positivity has also been observed in cats (2), indicating that the diagnosis of the infection in these animals might   be a difficult task, as it is in cats. The detection of L. infantum DNA in the lymph node aspirate and skin biopsy suggests that these tissues are more suitable than blood for the diagnosis of this infection, as previously reported in dogs and cats (8,9). Otherwise, the conjunctival swab seems to be not as good a sample for this purpose in tigers. Unlike some studies with cats (2), no correlation between L. infantum infection and FIV, FELV, or both FIV and FELV infection has been observed in the tigers in our study.
The predominance of P. perniciosus sand flies, along with their positivity for L. infantum DNA already recorded in southern Italy (10,11), is somewhat expected, given that this sand fly species is recognized as the main vector for L. infantum in different foci of visceral leishmaniasis in Italy (12). The high proportion of L. infantum-infected sand flies suggests that the risk for parasite transmission in this environment should be considered. Furthermore, the detection of L. infantum DNA in S. minuta sand flies has already been reported in southern Italy (4.2%) and Portugal (4%) (11,13). In addition, although consideration of the role played by S. minuta (the proven vector of L. tarentolae) in the circulation of Leishmania spp. of zoonotic concern has been raised (11,14), further studies are necessary to fully assess its vector role.
P. perniciosus sand flies frequently feed on tigers, because dogs are not allowed to roam in the zoo, the role of tigers as local reservoir hosts needs to be ascertained. Because P. perniciosus sand flies feed on a wide range of domestic and wild animals, and because L. infantum might infect the sand flies after taking a blood meal from infected felids (15), the role of tigers in the transmission cycle of L. infantum is probable.
In summary, L. infantum infection should be included in the differential diagnosis of infectious diseases in tigers in areas where visceral leishmaniasis is endemic. The role of tigers as sentinels for L. infantum, the occurrence of P. perniciosus sand flies infected by the protozoan, and its abundance in the study area might represent an eminent risk for animals and humans living in or visiting the zoo. Therefore, prevention measures are needed for providing protection against L. infantum infection in these animals and for controlling sand flies.

About the Author
Dr. Iatta is an associate professor at the Department of Veterinary Medicine, University of Bari "Aldo Moro" in Italy. Her research interests include the diagnosis, epidemiology, and prevention of parasitic infectious diseases.