Abstract
Leishmaniasis is caused by vector-borne protozoan parasite. Visceral leishmaniasis (VL) in man and animals is caused by L. donovani and L. infantum and is prevalent throughout the tropical and sub-tropical regions of Africa, Asia, the Mediterranean, Southern Europe (old world) and South and Central America (new world). The disease in human is endemic in 61 countries including Bangladesh and is responsible for the annual disability of 1.3 million people and 20000 to 30000 deaths. In the Indian subcontinent, visceral leishmaniasis (VL) is considered to be an anthropozonotic and transmitted biologically by the infected sand flies. In Bangladesh, literature is scanty. describing the role of domestic animals as carrier of infection. To determine animals whether they act as carrier of VL, animals from the endemic zone of Mymensingh district were investigated. Samples from a total of 50 cattle, 50 goats and 50 dogs were collected during the period between 2011 and 2014. Five cattle, five goats and five dogs were sampled from the known infected premises of Fulbaria Upazilla, Mymensingh District. Samples from the 45 cattle and 45 goats were collected from slaughter houses and 45 dogs from the street. Leishmanial infections due to L. donovani and L. infantum were determined by using necropsy, histopathology, impression smear staining, PCR and phylogenetic analysis. Impression smear staining, gross and histopathological examination failed to identify existence of leishmanial infection in cattle and goats. However impression smear staining and histopathological examination identified amastigote stages of protozoa and microgranulomas in three and two dogs, respectively. Polymerase chain reaction (PCR) technique was adapted using the published primers targeting kinitoplast minicircle DNA (KDNA). Genomic DNA extracted from the liver of cattle (N=50), goats (N=50) and dogs (N=50) were used in PCR; 145bp amplicon was generated from one cattle, seven goats and seven dogs. Cattle and goats of PCR positive cases did not reveal any amastigote stages of protozoa and microgranulomas in the hosts and the results of this study was further validated by using PCR and targeting Cysteine proteases gene. Two more PCR techniques targeting Cysteine proteases and 18S rRNA genes were standerdized with the known positive human samples and used in this study. DNA from the liver of two dogs found to generate 741bp and 311bp amplicons in PCR specific for infectivity due to L. Donovani. Phylogenetic analysis of the 741bp fragment of Cysteine proteases gene of Leishmanial protozoa derived from human and dog's samples showed clustering of Dog BAU/TL/MD1/2014 and Human BAU/TL/MH1/2014 leishmania belonging to L. donovani. Street dogs of Mymensingh district started contacting L. Donovani and this is for the first time in Bangladesh documented that dogs constitute a carrier of VL. PCR protocols adapted targeting Cysteine proteases and 18S rRNA genes of Leishmania are accurate, rapid and can be used to identify causes of VL in man and animals. This observations warrant further investigation and a close monitoring of goats, rodents and birds as carrier of leishmaniasis. The possible role of dog in the transmission cycle of VL in human and animals in Bangladesh requires further observation.