By Dean L. Winslow, MD, FACP, FIDSA
Professor of Medicine, Division of General Medical Disciplines, Division of Infectious Diseases and Geographic Medicine, Stanford University School of Medicine
Dr. Winslow reports no financial relationships relevant to this field of study.
SYNOPSIS: A cross-sectional study of military trainees and instructors who spend significant time in field conditions was performed at Joint Base San Antonio to determine the prevalence of Trypanosoma cruzi infection. None tested positive by polymerase chain reaction nor by enzyme-linked immunosorbent assay or indirect immunofluorescent antibody.
SOURCE: Webber BJ, Pawlak MT, Valtier S, et al. Prevalence and seroprevalence of Trypanosoma cruzi infection in a military population in Texas. Am J Trop Med Hyg 2017. [Epub ahead of print.]
Investigators studied 1,033 military trainees and instructors (most of whom were enrolled in the Security Forces Apprentice course) during a 16-month period (April-November 2015, April-November 2016). Fifteen to thirty percent of students and instructors participated in the study. This population was chosen since they spend more time in field conditions than basic military trainees do. Study participant demographics were consistent with current active duty United States Air Force (USAF) members: 77% male, 55% white/non-Hispanic, with a mean age of 21.6 years. Five subjects reported a triatomine bite and 131 reported a bite from an unidentified insect during the study period. Instructors had more time in field conditions than students did. All polymerase chain reaction (PCR), enzyme-linked immunosorbent assay (EIA), and indirect immunofluorescent antibody (IFA) tests were negative, with the exception of one equivocal EIA result (in a student who was born and lived in Central America before immigrating to the United States and enlisting in the U.S. Armed Forces).
This was an incredibly important study, which was performed in a rigorous manner by the USAF and U.S. Army Military Public Health teams in San Antonio. The findings from this seroprevalence study are reassuring in view of the alarming biosurveillance findings at Joint Base San Antonio (JBSA) and elsewhere in South Texas. These recent biosurveillance findings included: 1) 8% seroprevalence of T. cruzi in military working dogs and a large number of cases of acute Chagasic cardiomyopathy in dogs were observed. 2) Forty-three percent of adult triatomines and 22% of nymphs tested positive for T. cruzi by PCR, and 33% of these triatomines tested positive for human blood in their mid-gut. (Among adult triatomines, Triatoma sanguisuga [66%] and Triatoma gerstaeckeri [30%] were trapped most commonly.) 3) Cases of autochthonous transmission/acquisition of human infection with T. cruzi have been documented in South Texas.
A number of factors may have contributed to the fact that no military trainees or instructors acquired infection with T. cruzi during the relatively short study period. In my opinion, the major reason no new infections were seen may have been because the biosurveillance findings (noted above) were acted upon promptly by the USAF Military Public Health team led by Dr. Leo Cropper (senior author on this paper). This included removal of cotton rat nests from the vicinity of the field tents, application of insecticide inside and outside the tents, and use of DEET as well as permethrin-treated uniforms by all military personnel. Biological reasons for low transmission observed in humans may include the fact that the sylvatic triatomine vectors in the southern United States are less likely to defecate while taking a blood meal. Lastly, it is known that older individuals, those of Hispanic ancestry, and those living in rural or poverty stricken areas are more susceptible to infection with T. cruzi. The subjects in this study population were largely non-Hispanic whites and were young (21.6 years of age), so they may have had high resistance to acquisition of infection.
In the interest of full disclosure, I had the pleasure of working closely with Dr. Cropper and his team (including most of the authors listed on this paper) during one of my last assignments before retiring from the military in late 2015. I was incredibly impressed with the scientific rigor that went into their approach to this and several other health and safety issues they addressed during the time I was assigned to JBSA and the 59th Medical Wing. The excellent but often under-recognized scientific work being conducted by U.S. military scientists and epidemiologists follows in the proud tradition of Walter Reed and other giants of military medicine.