Within the last five years, the State of Texas has experienced either transmission or outbreaks of Ebola, chikungunya, West Nile, and Zika virus infections. Autochthonous transmission of neglected parasitic and bacterial diseases has also become increasingly reported. The rise of such emerging and neglected tropical diseases (NTDs) has not occurred by accident but instead reflects rapidly evolving changes and shifts in a “new” Texas beset by modern and globalizing forces that include rapid expansions in population together with urbanization and human migrations, altered transportation patterns, climate change, steeply declining vaccination rates, and a new paradigm of poverty known as “blue marble health.” Summarized here are the major NTDs now affecting Texas. In addition to the vector-borne viral diseases highlighted above, there also is a high level of parasitic infections, including Chagas disease, trichomoniasis, and possibly leishmaniasis and toxocariasis, as well as typhus-group rickettsiosis, a vector-borne bacterial infection. I also highlight some of the key shifts in emerging and neglected disease patterns, partly due to an altered and evolving economic and ecological landscape in the new Texas, and provide some preliminary disease burden estimates for the major prevalent and incident NTDs.

Of particular relevance and concern are the warming effects conductive to insect vector expansion and transmission, which could alter current mosquito, sandfly, flea, and kissing bug distributions [ 15 ]. Finally, it has been noted that a powerful anti-vaxxer movement and lobby is causing 50,000 or more parents to file nonmedical exemptions for childhood and school entry vaccines so that Texas is now at risk for the emergence of vaccine-preventable diseases, especially measles [ 17 ]. The factors of rapid population expansion, human migrations, urbanization, poverty, climate change, declining vaccine rates, transborder traffic, and sea transportation shifts have combined to create a new Texas that is particularly suited for the rise of emerging and neglected diseases ( Box 1 ).

There is also the threat of climate change. Among US states, Texas is disproportionately at risk to global warming and by some estimates, Texas is projected to reach 80–100 days over 95°F by the 2050s, compared to approximately 40 such days over the last 30 years) [ 16 ]. The state will face rising sea levels and other negative effects.

In addition to poverty, trade and human migrations also contribute to the risk of NTDs in the state of Texas. With regards to the former, trade is growing massively due to a doubling in size of the Panama Canal and expansion in size for more than a dozen Texas ports, including Port Arthur, Houston, Corpus Christi, and Brownsville, among others, which generate close to $100 billion in annual revenue [ 14 ] but also expose Texas populations to shipping traffic and potential diseases from Asia, Europe, and Africa [ 8 ]. Similarly, there is massive traffic across the Rio Grande River from Mexico that facilitates human migrations as well as invasions of exotic plant species that promote tick and other vector survival [ 15 ].

Fig 1 shows a map of child poverty in Texas indicating that poverty is not evenly distributed but instead is focused in South Texas and along the border with Mexico, in addition to focal areas of East Texas and the Texas Panhandle. Especially noteworthy are the so-called “colonias”—unincorporated residential communities near the Mexico border that often lack basic services, including access to clean water, sewer systems, and paved roads ( Fig 2 ) [ 12 ]. The major urban areas and cities of Texas also experience high levels of poverty, with child poverty rates exceeding 33% in Dallas and Houston [ 13 ].

Into this mix of rapid growth, urbanization, and immigration are additional and critical factors that could promote the emergence of infectious and neglected diseases [ 5 – 8 ]. First is the rise in poverty in Texas. Despite the state’s enormous wealth and an overall economy that exceeds Canada, Australia, or Russia [ 9 ], Texas also has profound pockets of intense poverty. Poverty has been shown to be an overwhelming social determinant for the promotion of neglected tropical diseases (NTDs), and today, most of the poverty-related NTDs and emerging infections are found in concentrated areas of poverty hidden in wealthy economies—a concept known as “blue marble health” [ 10 ]. Texas ranks in the bottom tier of US states in terms of high poverty levels (37th in terms of overall poverty and child poverty) [ 7 ], but because of its large overall population, with more than 4 million Texans living below the poverty line in 2016, Texas also ranks among the states with the largest number of people living in poverty of any US state and near the bottom (41st) in terms of food insecurity and educational attainment [ 11 ].

Texas has become one of the fastest growing US states, with projections that by 2020, the population will exceed 30 million people [ 1 ]. A majority are expected to live in metropolitan urban areas [ 1 ]. Population growth and urbanization are accelerating at an impressive rate. According to United States Census data released in 2016, Texas now hosts five of the 11 fastest growing small cities and five of the eight fastest growing large cities (Houston, San Antonio, Fort Worth, Dallas, and Austin) [ 2 ]. Growth is due to immigration from both US northern states and abroad, mostly for economic opportunities. In 2014, it was estimated that more than 4.5 million Texans are foreign born, including more than 3 million from Latin America and almost 1 million and 200,000 from Asia and Africa, respectively [ 3 ]. Texas is ranked third among US states in percentage of foreign-born population [ 4 ].

Here I review the current status of NTDs in Texas using a search conducted in December 2016 emphasizing new information published within the previous five years. I used the online database PubMed from 2012 to 2016 with the Medical Subject Headings, the specific diseases listed as NTDs on the PLOS Neglected Tropical Diseases website ( http://www.plosntds.org/static/scope.action , in addition to several selected diseases that have been reviewed regularly at PLOS NTDs, including trichomoniasis, cryptosporidiosis, and borreliosis), and the geographic region of Texas. Reference lists of identified articles and reviews were also hand searched as were databases from the Texas Department of State Health Services (DSHS; https://www.dshs.texas.gov/ ). In a few instances, articles prior to 2012 were also cited when relevant, while some of the findings were also updated when relevant a year later in December 2017.

Findings

Major findings were related to the following three major groups of NTDs: neglected parasitic infections, arthropod-borne virus (arbovirus) infections, and other neglected viral and bacterial infections.

Neglected parasitic infections The major neglected parasitic infections in Texas include Chagas disease, leishmaniasis, trichomoniasis, intestinal protozoan infections, cysticercosis, and toxocariasis. A unique feature about Chagas disease (American trypanosomiasis caused by Trypanosoma cruzi) is that Texas represents one of the few US states in which autochthonous transmission occurs or may be common. Triatomine kissing bug vectors were first described in South Texas during the 1930s, with local human Chagas disease cases associated with triatomines reported in the 1940s and 1950s [18]. In 2015, five patients with autochthonous Chagas disease from southeast Texas were identified through blood screening [19], with counties in South Texas considered especially high-risk areas [15, 20]. A subsequent study looking at risk factors for T. cruzi–positive blood donors included poverty, with older and minority persons at greatest risk [21]. Cardiac manifestations and evidence of Chagasic cardiomyopathy have also been noted among these populations [22]. Sylvatic transmission has also been proposed, including Chagas disease cases among hunters and campers [23, 24]. Human Chagas disease is seldom diagnosed in Texas and is consequently underreported. Between 2013 and 2015, there were only 15 locally acquired cases and 44 imported cases reported to DSHS [25]. The Centers for Disease Control and Prevention (CDC) estimates that there are almost 37,000 people living with Chagas disease in Texas [26], although the percentage of cases transmitted locally versus through immigration across the southern border remains unknown. T. cruzi meningoencephalitis in patients with HIV/AIDS has also been described in Texas [27]. The complete ecology of T. cruzi transmission in Texas and the role of animal reservoirs also need further elucidation. Among triatomine vector species caught locally, Triatoma gerstaeckeri is the most common, followed by Triatoma sanguisuga, with about two-thirds of the bugs caught noted to be PCR positive for T. cruzi [28], but T. gerstaeckeri was the species most commonly found in domestic and human habitats [29]. Dogs are being increasingly recognized as an important reservoir host for T. cruzi infection [30], but their role or importance in zoonotic transmission to humans is unknown. Cutaneous leishmaniasis caused by Leishmania mexicana and transmitted by the New World sandfly vector Lutzomyia anthophora has also been documented in Texas but from the northeastern part of the state and the Dallas–Fort Worth metroplex [31]. A Southern Plains wood rat is a sylvatic animal reservoir in Texas [15]; however, the disease ecology is understudied, and the extent of transmission relative to Mexico (where it remains an important disease) is unclear. Recently, a cluster of cutaneous leishmaniasis caused by Leishmania panamensis was reported among Cuban asylum seekers in Houston who acquired infection during transit through the Panama Darien [32]. Another neglected protozoan infection found in Texas, one of great importance to women’s health and noted to be a health disparity among African American women, is trichomoniasis. In a study of tens of thousands of cervical samples of women aged 12 to 75 years, it was found that the overall detection rate was 4.5 percent [33], indicating that among an adult female population of approximately 10 million adult women [34], there would be approximately 450,000 prevalent cases in Texas. In terms of intestinal protozoan infections, DSHS estimates that there are hundreds of cases of cryptosporidiosis [35] and cyclosporiasis [36] reported each year [36] and approximately 168 cases annually of amebiasis [37]. The two most important parasitic helminth infections in Texas are cysticercosis and toxocariasis. Neurocysticercosis has been estimated to occur at a rate of 1.5–5.8 cases per 100,000 Hispanics in the US [38]. Based on a projection of almost 13 million Hispanics living in Texas by 2020 [1], it can be estimated that there will be 194–752 cases of neurocysticercosis in Texas annually, such that this disease should be considered a possible cause of epilepsy. A systematic review of toxocariasis in North America [39] failed to provide specific information on the prevalence of this disease in Texas. However, CDC surveillance studies finding 21% seroprevalence among non-Hispanic African American populations [40] would indicate that, among 3.466 million African Americans living in Texas by the year 2020 [1], there could be more than 700,000 cases. The role of seroprevalence as an indicator of active disease versus exposure in the case of Toxocara infection is under investigation. These are important data given the finding that toxocariasis has been linked to developmental delays and may have a role in educational achievement gaps [41].

Arbovirus infections Among the arboviral infections, Texas sustains the transmission of West Nile virus (WNV) infection from Culex mosquitoes (C. quinquefasciatus in urban areas and eastern Texas) and the transmission of dengue, chikungunya, and Zika virus infections from Aedes mosquitoes (especially A. aegypti). Among the NTDs affecting Texas, WNV infection ranks at or near the top in terms of severe morbidity and mortality. Autochthonous WNV cases in Texas were first detected in 2002 after the introduction of WNV in the US (New York) in 1999 [42, 43]. During its first decade in Texas, there were over 2,000 reported cases, with a case fatality rate of 6% and an estimated economic cost to the state of $112 million [42]. A national resurgence of WNV cases in the US was observed in 2012 following a gradual decline between the years 2008 and 2011 [44]. The 2012 WNV outbreak in Texas was severe, with almost 1,900 cases (and 89 deaths), of which almost one-half occurred in the Dallas–Fort Worth metroplex [45]. Approximately 2% of the population of northern Texas was infected during the outbreak [46], with the elderly at the highest risk of neuroinvasive disease, as well as males and minority populations [45]. The economic burden of the 2012 WNV epidemic in Texas was estimated to be approximately $50 million [45]. Through genetic sequencing, it was further noted that the WNV isolates from this epidemic were not significantly different from previous strains, suggesting that external factors such as ecological or climate shifts might be responsible factors [47]. For instance, average annual temperatures during the summer of 2012 in Texas were warmer than the previous decade, with temperatures higher in Dallas than Houston [47]. It has been further noted that, during the 2000s, WNV incidence in Texas peaked in three-year cycles, possibly reflecting cyclical patterns in climate or other ecological conditions [45]. According to Texas DSHS, there were substantially fewer cases of WNV infection in 2013 and 2014 [48]. Aerial insecticide spraying was also noted to produce substantial declines in WNV disease incidence in northern Texas [49]. Beyond the acute effects of WNV infection and its association with neuroinvasive disease in Texas are its long-term effects and sequelae, investigated by Murray and her colleagues [50–55]. Patients with WNV encephalitis were found to experience hearing loss, gait and motor disturbances [50], and retinopathy [51]. In addition, WNV neuroinvasive disease was linked to long-term memory loss, fatigue, and depression [52], with fatigue linked to elevation of antiviral and proinflammatory cytokines [53]. WNV in Texas has also been shown to cause persistent infection leading to both chronic neurological and kidney disease [54], the latter associated with proteinuria and hematuria [55]. St. Louis encephalitis previously common in Texas is now associated with fewer than 10 cases annually [48]. Venezuelan equine encephalitis is also transmitted by Culex (as well as Aedes) mosquitoes, and although epizootics have struck Mexico in recent years, there are no recent human cases in Texas [15]. Texas is also at high risk of virus infections transmitted by A. aegypti and possibly A. albopictus dengue, chikungunya, and Zika virus infections. Indeed, Texas and Florida represent the two US states with the widest distribution of A. aegypti [56], while South Texas and South Florida are the only two areas of the continental US with reported year-round A. aegypti activity and disease transmission [57]. In Texas, dengue is endemic in the Rio Grande Valley, associated with limited outbreaks since 1980, including a 2005 outbreak in Brownsville (Cameron County), which represents the most southeast part of Texas on the border with Mexico [58]. But rates of infection are believed to be higher in the colonias due to the lower socioeconomic conditions there [59]. The dengue seroprevalence (immunoglobulin G [IgG]) in Cameron County, Texas, was found to be 38% among 800 randomly selected adults [60]. Outside of Brownsville, outbreaks of dengue fever due to autochthonous transmission were also found to occur in Houston, Texas, between 2003 and 2005 [61]. Overall, Texas DSHS has reported 154 dengue cases between 2003 and 2012 led by 27 cases during this period in Cameron County [62], but the reporting does not distinguish between imported versus autochthonous cases. In 2016, the Texas DSHS reported the first cases of autochthonous transmission of chikungunya and Zika virus infection. The patient with chikungunya became ill in Cameron County in November 2015, and the diagnosis was confirmed in January 2016 [63]. Texas DSHS further reported in November 2016 that Zika transmission was underway in Cameron and Hidalgo Counties, with six mosquito-transmitted cases of locally acquired Zika virus infection reported by the end of December 2016 and a locally transmitted case in December 2017, respectively [64].