Pathogenic Landscape of Transboundary Zoonotic Diseases in the Mexico-US Border Along the Rio Grande

Abstract

Transboundary zoonotic diseases, several of which are vector borne, can maintain a dynamic focus and have pathogens circulating in geographic regions encircling multiple geopolitical boundaries. Global change is intensifying transboundary problems, including the spatial variation of the risk and incidence of zoonotic diseases. The complexity of these challenges can be greater in areas where rivers delineate international boundaries and encompass transitions between ecozones. The Rio Grande serves as a natural border between the US State of Texas and the Mexican States of Chihuahua, Coahuila, Nuevo León, and Tamaulipas. Not only do millions of people live in this transboundary region, but also a substantial amount of goods and people pass through it everyday. Moreover, it occurs over a region that functions as a corridor for animal migrations, and thus links the Neotropic and Nearctic biogeographic zones, with the latter being a known foci of zoonotic diseases. However, the pathogenic landscape of important zoonotic diseases in the south Texas-Mexico transboundary region remains to be fully understood. An international perspective on the interplay between disease systems, ecosystem processes, land use, and human behaviors is applied here to analyze landscape and spatial features of Venezuelan equine encephalitis, Hantavirus disease, Lyme Borreliosis, Leptospirosis, Bartonellosis, Chagas disease, human Babesiosis, and Leishmaniasis. Surveillance systems following the One Health approach with a regional perspective will help identifying opportunities to mitigate the health burden of those diseases on human and animal populations. It is proposed that the Mexico-US border along the Rio Grande region be viewed as a continuum landscape where zoonotic pathogens circulate regardless of national borders.

Keywords: Babesia; Chagas; Hantavirus; Leishmania; Lyme borreliosis; VEE; global change; pathogenic landscapes.

Figure 1

Invasion of exotic Arundo donax, giant reed, is facilitating the invasion of Cattle Fever Ticks in the transboundary region by creating a microclimate that is favorable for its survival. (A) Arundo donax on Rio Grande near Eagle Pass, TX, USA. (B) Arundo donax on Rio Grande near Del Rio, TX, USA.

Figure 2

Integrated VEE area-severity index. Integrated VEE area-severity index (dark solid line, left axis) based on historical reconstruction of areal extent and severity in equine and human populations over the 1920 through 2013 period. Three major VEE outbreaks (I, II, III) and three gap-intervals (a, b, c) of low VEE are shown. (A) Eleven-year running means of accumulated cyclonic energy index (ACE, red font) and (B) the Southern Oscillation Index (SOI, green font) given on right axis.

Figure 3

Observed integrated area-severity index for Venezuelan equine encephalitis (VEE) in the Americas, 1920–2010. Integrated Area-Severity (IAS) index (dark solid line, left axis, log10 scale, 5-year point-centered moving average) for Venezuelan Equine Encephalitis (VEE) in the Americas, based on reconstruction of actual disease incidence reported in literature, 1920–2010. Hypothetical reconstruction of expected levels of VEE, 1920–2010, achieved by sequential repeat of the average IAS index levels over Outbreak Two (1950–1979) and Outbreak Three (1980–2009) (dashed line, right axis, log10 scale), with standard error of mean added (light vertical lines). Outbreak One (1920–1949) values excluded from average due to lack of solid data. Subdued levels of VEE over Outbreak Three could be the result of assertive mosquito control programs related to dengue fever epidemics, and/or improved VEE management approaches and infrastructure (see text for details).