Chagas Disease in Mammals on Joint Base Lackland Training Annex and Camp Bullis Military Training Reservation, San Antonio, Texas

Chagas disease, also known as American trypanosomiasis, is caused by the etiological flagellate protozoan Trypanosoma cruzi (T. cruzi). It is a significant health concern in South and Central America where millions of people are infected or at risk of infection, and an emerging health concern in the United States. The prevalence of Chagas disease in natural environments is supported by mammal host species but those primary species may vary based on geographic location. In South Texas, the primary host species for the disease is poorly understood requiring a field study to determine the spatial distribution of T. cruzi prevalence in free-ranging mammals.

Chagas disease can reduce force readiness and cause life-long incurable health effects. The persistence and maintenance of the disease parasite in the areas along the southern U.S. threatens essential military weapon detections system (K-9 military working dogs) and personnel as warfighters. Biosurveillance to quantify Chagas disease distribution in DoD environments is important for protecting the health of military communities through an understanding of disease and disease vector presence. Determining the incidence of the parasite and disease on DoD installations, will provide transmission risk assessment to military personnel and allow them to implement management and control initiatives to suppress.

Project objectives were to (1) identify and estimate relative density of triatomine insects in various vegetation types, (2) determine spatial distribution and prevalence of T. cruzi parasites in free-ranging mammalian species, and (3) determine relative mammal abundances by vegetation type and season. Triatomine distribution analyses included light traps and CO2 traps placed throughout Joint Base San Antonio (JBSA) – Lackland Training Annex (2012–2014). This was supplemented by infection data collected from meso-mammal sampling. From 2012–2016, blood and tissue samples from geo- located free-ranging wildlife mammal species were analyzed using antigen strips and polymerase chain reaction (PCR) methods to detect protozoan T. cruzi DNA. Mammal abundance was determined using mark-recapture methodology and recorded capture- site characteristics such as vegetation structure.

Triatomine distribution calculations were hampered by low capture rates using light traps or CO2 traps. This is not unusual in triatomine capture efforts throughout the world. However, mammal infection rates were highest in wooded areas when controlling for relative mammal abundances. This indicated triatomines were primarily feeding on fossorial mammals found in wooded areas. This was supported by both the literature and a concurrent U.S. Army triatomine distribution findings. Chagas disease infection rate in meso-mammals were significantly higher in deciduous forests compared to grasslands or semi-improved woodlands. A disproportionate percentage of infections were also found in lower elevation floodplain and riparian areas (57% positive) compared to upland areas (27% positive). There was high prevalence in small and meso-mammals, but much lower prevalence found in large mammals. This project suggests that common free-ranging fossorial mammal wildlife populations support T. cruzi in natural environments and are a potential public health concern in South Texas. Preventative or mitigation strategies should consider a range of management activities to include, habitat management, selected application of insecticide, and changes in human behavior and personal protection in high-risk areas.