Detecting enzootic leishmaniasis and American trypanosomiasis in stray dogs in El Paso County, Texas and the potential for autochthonous transmission to humans
Cutaneous leishmaniasis and Chagas disease (American trypanosomiasis) are two vector-borne, protozoal zoonoses whose emergence into the southern United States is a public health problem of increasing significance. Cutaneous leishmaniasis is caused by several species of intracellular protozoa in the genus Leishmania and is most often characterized by the formation of large, ulcerative skin lesions that can result in considerable scarring and permanent disfigurement. Infection with Leishmania is prevalent throughout the world in tropical and sub-tropical regions and in areas where people are regularly exposed to the hematophagous sand fly vectors that transmit the disease. Chronic infection with Trypanosoma cruzi, the causative agent of Chagas disease, is a well-known cause of heart failure, arrhythmia, and enlargement of the esophagus and colon. Between 6 and 8 million people currently living in Latin America and the United States are believed to be chronically infected with Trypanosoma cruzi with complications from these infections resulting in approximately 45,000 deaths annually. In the southern United States, enzootic transmission of both Leishmania mexicana and Trypanosoma cruzi has been documented in addition to sporadic reports of autochthonous human cases of cutaneous leishmaniasis and Chagas disease. Future climate change may lead to the emergence of these pathogens into new foci across the southern United States and could possibly result in an increase in the incidence of human infections. Domestic dogs (Canis familiaris) have been implicated as potential reservoirs or incidental hosts of both Leishmania and Trypanosoma cruzi in endemic foci throughout the Americas. This study among a sample of stray canines provides evidence that transmission of these pathogens is occurring in El Paso County, Texas. From July 2014 to May 2015, skin, spleen, and heart biopsies from 159 stray canines were collected. Genomic DNA of sufficient quality for use in PCR analyses was successfully extracted from these biopsies in 156 of the stray canines surveyed. PCR-amplification of Leishmania spp. or Trypanosoma cruzi DNA was attempted using extracted genomic DNA from these biopsies to screen for evidence of infection. Using agarose gel electrophoresis, Leishmania spp. DNA was detected in 41 stray dogs and Trypanosoma cruzi DNA was detected in 21 stray dogs, representing 26.3% and 13.5% of the total sample, respectively. From the group of animals identified as PCR-positive for Leishmania spp., 18 biopsy PCR products were randomly chosen for bidirectional sequencing. Analysis of sequenced PCR products showed that all infections were caused by Leishmania mexicana. A multiple sequence alignment was created to show homology between sequenced PCR products and known reference strains of Leishmania mexicana and a distantly related species, Leishmania major. Collectively, these results suggest that enzootic transmission of Leishmania mexicana and Trypanosoma cruzi is occurring over a wide portion of El Paso County and nearby densely populated areas in the city of El Paso. The majority of stray dogs infected with Leishmania mexicana were found during the late summer and early fall, and the majority of those infected with Trypanosoma cruzi were found during the late fall and winter, suggesting that these may be periods during which increased transmission is occurring. The behaviors of many stray canines and their relatively close associations with humans could potentially put people in El Paso County at greater risk for infection. Whether the finding of Leishmania mexicana and Trypanosoma cruzi in these stray canines is evidence of a relatively new emergence of these pathogens warrants additional investigation. Further research is also needed to better understand the epidemiology and transmission of these pathogens in order to better assess any potential for autochthonous transmission to people living in the region.
Kipp, Evan James, "Detecting enzootic leishmaniasis and American trypanosomiasis in stray dogs in El Paso County, Texas and the potential for autochthonous transmission to humans" (2015). ETD Collection for University of Texas, El Paso. AAI10000792.