Dogs as Reservoirs for Leishmania donovani, Bihar, India, 2018-2022

Abstract

Visceral leishmaniasis derived from Leishmania donovani is transmitted by sand flies (Phlebotomus argentipes) throughout the Indian subcontinent. Although considered anthroponotic, L. donovani infects other mammals susceptible to sand fly bites, including dogs. Aggressive strategies to reduce sand fly populations in India have led to flies seeking nonhuman hosts, so understanding the role of dogs in L. donovani transmission has become critical. Our study investigated L. donovani infection in dogs and the potential for such infections to be transmitted back to sand flies. We performed xenodiagnosis by using P. argentipes on dogs (n = 73) with quantitative PCR-detectible parasitemia in both endemic and outbreak villages. We found that 12% (9/73) of dogs were infectious to sand flies during winter and rainy seasons. Patients with visceral leishmaniasis remain primary sources of L. donovani transmission, but our findings suggest a possible link between canine infection and human exposure.

Keywords: India; Leishmania donovani; One Health; Phlebotomus; Xenodiagnosis; dogs; global health; leishmaniasis; parasites; seasonal; transmission; vector-borne infections; zoonoses.

Figure 1

Locations of study villages and 5-year incidence of VL in a study of dogs as reservoirs for Leishmania donovani, Bihar, India, 2018–2022. A) Map of India showing Bihar; B) Bihar detail showing Muzaffarpur district study area; C) detail of sampling locations and VL cases, Muzaffarpur district. Geographic information system locations of study sampling sites calculated from a latitude-longitude application. Map produced using QGIS software version 3.30.3 (https://qgis.org) with open-access shapefile (https://onlinemaps.surveyofindia.gov.in). KAMRC, Kala-Azar Medical Research Center.

Figure 2

Seropositivity among endemic dogs with clinical signs consistent with CanL from the Muzaffarpur district in a study of dogs as reservoirs for Leishmania donovani, Bihar, India, 2018–2022. A,C,E) Results from subclinical (healthy) dogs; B,D,F) results from dogs with >2 clinical signs of CanL. Percentage of positive (black) versus negative (white) results by kinetoplastid-targeted qPCR or by rK39 ELISA are shown. E,F) Percentage of dogs with single-positive or double-positive diagnostic status among subclinical dogs (E) and clinical dogs (F). Statistical significance between subclinical and clinical groups measured by Fisher exact test. CanL, canine leishmaniosis; qPCR, quantitative PCR; +, positive; −, negative.

Figure 3

Plot of dogs with detectable parasitemia during the rainy season from villages in the Muzaffarpur district in a study of dogs as reservoirs for Leishmania donovani, Bihar, India, 2018–2022. Lower level of whiskers indicate mean, upper level indicates standard deviation. A) Parasitemia measured by quantitative PCR of whole blood DNA. Statistical significance between different seasons (shown above diamond bars) measured by Fisher exact test. B) Leishmania rK39 ELISA absorbance ratio detected from canine serum. Dotted line indicates OD cutoff. Kruskal-Wallis with Dunn’s posttest was performed, but no statistically significant differences were found for B. OD, optical density.

Figure 4

Plot of parasite load in sand flies in a study of dogs as reservoirs for Leishmania donovani, Bihar, India, 2018–2022. Plots show higher transmission and parasite load in sand flies fed on dogs with signs consistent with CanL in the Muzaffarpur district. A) Number of parasite DNA–positive sand flies obtained from each dog undergoing xenodiagnosis by qPCR. B) Parasite load calculated within individual L. donovani qPCR-positive sand flies. C) Percent positive sand flies out of total number of sand flies fed per dog. D) Average parasite burden of blood-fed sand flies per canine subject. Data for healthy, subclinical dogs depicted with white dots. Data for dogs with CanL clinical signs depicted with black dots. Lower lever of whiskers indicate mean, upper level indicates standard deviation. Statistical results by Mann-Whitney test shown above diamond bars. CanL, canine leishmaniosis; CL, CanL clinical signs; SC, subclinical (i.e., healthy) dogs; SF, sand fly.

Figure 5

Results of xenodiagnoses in a study of dogs as reservoirs for Leishmania donovani, Bihar, India, 2018–2022. Plots show dogs infect more sand flies in winter and transmit more parasites per sand fly during the rainy season. A) Number of positive sand flies; B) parasite load in xenodiagnosis-positive sand flies; C) percent positive sand flies fed on dogs; D) average parasite burden of fed sand flies; E) evaluation of infectiousness of dogs to sand flies by clinical classification and seasonal variation. Lower lever of whiskers indicate mean, upper level indicates standard deviation. Kruskal-Wallis test with Dunn’s post-test used to calculate statistical significance between groups (shown above diamond bars). CanL, canine leishmaniosis; CL, CanL clinical signs; SC, subclinical (i.e., healthy) dogs; SF, sand fly.