West Nile Virus Outbreak in Houston and Harris County, Texas, USA, 2014

Spatial and seasonal dynamics of mosquito species in Harris County, Texas, highlight risk of arbovirus introduction and transmission

Mosquito-borne diseases pose a significant public health threat, particularly in densely populated urban areas. Climate change, urbanization, and global connectivity have fueled the expansion of mosquitoes and their associated pathogens, increasing the disease burden. Harris County, Texas, is among the most vulnerable regions in the United States for mosquito-borne disease outbreaks, underscoring the critical need for localized insights into mosquito population dynamics to inform vector surveillance and control strategies. This study provides a comprehensive analysis of the population dynamics of mosquito species in Harris County by exploring their species composition, spatial distribution, and seasonal patterns. Our findings reveal the extensive distribution of Culex quinquefasciatus and Aedes albopictus, with Aedes aegypti concentrated in highly urbanized areas. Notably, three of the five most abundant species are primary vectors of human pathogens, highlighting the urgent need for targeted interventions. By leveraging high-resolution surveillance data, this research deepens our understanding of mosquito dynamics and lays the groundwork for future studies investigating the effects of climate change, urbanization, and other environmental drivers on vector populations.

Spatial dynamics of Culex quinquefasciatus abundance: geostatistical insights from Harris County, Texas

Mosquito-borne diseases pose a significant public health threat, prompting the need to pinpoint high-risk areas for targeted interventions and environmental control measures. Culex quinquefasciatus is the primary vector for several mosquito-borne pathogens, including West Nile virus. Using spatial analysis and modeling techniques, we investigated the geospatial distribution of Culex quinquefasciatus abundance in the large metropolis of Harris County, Texas, from 2020 to 2022. Our geospatial analysis revealed clusters of high mosquito abundance, predominantly located in central Houston and the north-northwestern regions of Harris County, with lower mosquito abundance observed in the western and southeastern areas. We identified persistent high mosquito abundance in some of Houston's oldest neighborhoods, highlighting the importance of considering socioeconomic factors, the built environment, and historical urban development patterns in understanding vector ecology. Additionally, we observed a positive correlation between mosquito abundance and neighborhood-level socioeconomic status with the area deprivation index explaining between 22 and 38% of the variation in mosquito abundance (p-value < 0.001). This further underscores the influence of the built environment on vector populations. Our study emphasizes the utility of spatial analysis, including hotspot analysis and geostatistical interpolation, for understanding mosquito abundance patterns to guide resource allocation and surveillance efforts. Using geostatistical analysis, we discerned fine-scale geospatial patterns of Culex quinquefasciatus abundance in Harris County, Texas, to inform targeted interventions in vulnerable communities, ultimately reducing the risk of mosquito exposure and mosquito-borne disease transmission. By integrating spatial analysis with epidemiologic risk assessment, we can enhance public health preparedness and response efforts to prevent and control mosquito-borne disease.

Public health contributions of entomological surveillance of West Nile virus (WNV) and other mosquito-borne arboviruses in a context of climate change

Background

Climate change is likely to increase the risk of human transmission of arboviruses endemic to Canada, including West Nile virus (WNV), Eastern equine encephalitis virus (EEEV) and California serogroup virus (CSV), calling for enhanced surveillance, including entomological surveillance targeting mosquito vectors. A scoping review was carried out to document the public health contributions of entomological surveillance of arboviruses of importance in Canada.

Methods

The Ovid® and EBSCO platforms and the grey literature were searched to identify documents published between 2009 and 2023, in English or French, dealing with entomological surveillance of arboviruses of interest, conducted annually for human health purposes under the aegis of a government authority, with specified public health objectives and actions.

Results

The 42 selected publications mainly reported two public health objectives of adult mosquito surveillance: early warning of viral circulation and assessment of the level of risk of human transmission. Recommended actions included clinical preparedness, risk communication, promotion of personal protection measures and vector control. The main objectives of immature mosquito surveillance were to identify sites with high larval densities, in order to reduce/eliminate them and target the application of larvicides.

Conclusion

In a context of climate change favouring the spread of arboviruses, this study highlights the potential public health contributions of regular entomological surveillance of endemic arboviruses of importance in Canada. It helps support concrete actions to protect the health of the population from the risks of arboviral transmission.

Effective population size of Culex quinquefasciatus under insecticide-based vector management and following Hurricane Harvey in Harris County, Texas

Introduction: Culex quinquefasciatus is a mosquito species of significant public health importance due to its ability to transmit multiple pathogens that can cause mosquito-borne diseases, such as West Nile fever and St. Louis encephalitis. In Harris County, Texas, Cx. quinquefasciatus is a common vector species and is subjected to insecticide-based management by the Harris County Public Health Department. However, insecticide resistance in mosquitoes has increased rapidly worldwide and raises concerns about maintaining the effectiveness of vector control approaches. This concern is highly relevant in Texas, with its humid subtropical climate along the Gulf Coast that provides suitable habitat for Cx. quinquefasciatus and other mosquito species that are known disease vectors. Therefore, there is an urgent and ongoing need to monitor the effectiveness of current vector control programs. Methods: In this study, we evaluated the impact of vector control approaches by estimating the effective population size of Cx. quinquefasciatus in Harris County. We applied Approximate Bayesian Computation to microsatellite data to estimate effective population size. We collected Cx. quinquefasciatus samples from two mosquito control operation areas; 415 and 802, during routine vector monitoring in 2016 and 2017. No county mosquito control operations were applied at area 415 in 2016 and 2017, whereas extensive adulticide spraying operations were in effect at area 802 during the summer of 2016. We collected data for eighteen microsatellite markers for 713 and 723 mosquitoes at eight timepoints from 2016 to 2017 in areas 415 and 802, respectively. We also investigated the impact of Hurricane Harvey's landfall in the Houston area in August of 2017 on Cx. quinquefasciatus population fluctuation. Results: We found that the bottleneck scenario was the most probable historical scenario describing the impact of the winter season at area 415 and area 802, with the highest posterior probability of 0.9167 and 0.4966, respectively. We also detected an expansion event following Hurricane Harvey at area 802, showing a 3.03-fold increase in 2017. Discussion: Although we did not detect significant effects of vector control interventions, we found considerable influences of the winter season and a major hurricane on the effective population size of Cx. quinquefasciatus. The fluctuations in effective population size in both areas showed a significant seasonal pattern. Additionally, the significant population expansion following Hurricane Harvey in 2017 supports the necessity for post-hurricane vector-control interventions.

Characterizing Areas with Increased Burden of West Nile Virus Disease in California, 2009-2018

West Nile virus (WNV) is a mosquito-borne flavivirus that can cause severe neurological disease in humans, for which there is no treatment or vaccine. From 2009 to 2018, California has reported more human disease cases than any other state in the United States. We sought to identify smaller geographic areas within the 10 California counties with the highest number of WNV cases that accounted for disproportionately large numbers of human cases from 2009 to 2018. Eleven areas, consisting of groups of high-burden ZIP codes, were identified in nine counties within southern California and California's Central Valley. Despite containing only 2% of California's area and 17% of the state's population, these high-burden ZIP codes accounted for 44% of WNV cases reported and had a mean annual incidence that was 2.4 times the annual state incidence. Focusing mosquito control and public education efforts in these areas would lower WNV disease burden.

Development and Evaluation of Real-Time Reverse Transcription Recombinase Polymerase Amplification Assay for Rapid and Sensitive Detection of West Nile Virus in Human Clinical Samples

West Nile virus (WNV) causes West Nile fever and encephalitis worldwide. Currently, there are no effective drugs or vaccines available in the market to treat WNV infection in humans. Hence, it is of paramount importance to detect WNV early for the success of the disease control programs and timely clinical management in endemic areas. In the present paper, we report the development of real-time reverse transcription recombinase polymerase amplification (RT-RPA) assay for rapid and real-time detection of WNV targeting the envelope (env) gene of the virus. The RPA reaction was performed successfully at 39°C for 15 min in a real-time thermal cycler. The sensitivity of this assay was found similar to that of the quantitative real-time RT PCR (RT-qPCR) assay, which could detect 10 copies of the gene. The efficacy of the assay was evaluated with a panel of 110 WN suspected human samples showing the signs of retinitis, febrile illness and acute posterior uveitis. In comparison with RT-qPCR, RT-RPA showed a specificity of 100% (CI, 95.07–100%) and sensitivity of 96.15% (CI, 80.36–99.90%) with a negative (NPV) and positive predictive value (PPV) of 98.65 and 100%, respectively. The level of agreement between RT-RPA and reference RT-qPCR assay was shown to be very high. The turnaround time of real-time RPA assay is about 10-20 times faster than the RT-qPCR, which confirms its utility in the rapid and sensitive diagnosis of WNV infection. To the best of our knowledge, this is the first report which deals with the development of real-time RT-RPA assay for simple, rapid, sensitive, and specific detection of WNV in human clinical samples. The present RT-RPA assay proves to be a powerful tool that can be used for the rapid diagnosis of a large number of patient samples in endemic settings.

Detection of the Nav channel kdr-like mutation and modeling of factors affecting survivorship of Culex quinquefasciatus mosquitoes from six areas of Harris County (Houston), Texas, after permethrin field-cage tests

Culex quinquefasciatus is one of the most important mosquito vectors of arboviruses. Currently, the fastest approach to control disease transmission is the application of synthetic adulticide insecticides. However, in highly populated urban centers the development of insecticide resistance in mosquito populations could impair insecticide efficacy and therefore, disease control. To assess the effect of resistance on vector control, females of Cx. quinquefasciatus collected from six mosquito control operational areas in Harris County, Texas, were treated in field cage tests at three different distances with the pyrethroid Permanone® 31-66 applied at the operational rate. Females were analyzed by sequencing and/or diagnostic PCR using de novo designed primers for detecting the kdr-like mutation in the voltage-gated sodium channel (L982F; TTA to TTT) (house fly kdr canonical mutation L1014F). Females from the Cx. quinquefasciatus susceptible Sebring strain and those from the six operational areas placed at 30.4 m from the treatment source were killed in the tests, while 14% of field-collected mosquitoes survived at 60.8 m, and 35% at 91.2 m from the source. The diagnostic PCR had a with 97.5% accuracy to detect the kdr-like mutation. Pyrethroid resistant mosquitoes carrying the L982F mutation were broadly distributed in Harris County at high frequency. Among mosquitoes analyzed (n = 1,028), the kdr-kdr genotype was prevalent (81.2%), the kdr-s genotype was 18%, and s-s mosquitoes were less than 1% (n = 8). A logistic regression model estimated an equal probability of survival for the genotypes kdr-kdr and kdr-s in all areas analyzed. Altogether, our results point to a high-risk situation for the pyrethroid-based arboviral disease control in Harris County.

Infectious and Autoimmune Causes of Encephalitis in Children

BACKGROUND AND OBJECTIVES

Encephalitis can result in neurologic morbidity and mortality in children. Newly recognized infectious and noninfectious causes of encephalitis have become increasingly important over the past decade.

METHODS

We retrospectively reviewed medical records from pediatric patients in Houston diagnosed with encephalitis in both an urban and rural catchment area between 2010 and 2017. We conducted an investigation to understand the etiology, clinical characteristics, and diagnostic testing practices in this population.

RESULTS

We evaluated 231 patients who met the case definition of encephalitis, among which 42% had no recognized etiology. Among those with an identified etiology, the most common were infectious (73; 31%), including viral (n = 51; 22%), with the most frequent being West Nile virus (WNV; n = 12), and bacterial (n = 19; 8%), with the most frequent being Bartonella henselae (n = 7). Among cases of autoimmune encephalitis (n = 60; 26%), the most frequent cause was anti-N-methyl-D-aspartate receptor (NMDAR) encephalitis (n = 31). Autoimmune causes were seen more commonly in female (P < .01) patients. Testing for herpes simplex virus and enterovirus was nearly universal; testing for anti-NMDAR encephalitis, WNV, and Bartonella was less common.

CONCLUSIONS

WNV was the most common infectious cause of encephalitis in our pediatric population despite lower testing frequency for WNV than herpes simplex virus or enterovirus. Increasing testing for anti-NMDAR encephalitis resulted in frequent identification of cases. Increased awareness and testing for WNV and Bartonella would likely result in more identified causes of pediatric encephalitis. Earlier etiologic diagnosis of encephalitides may lead to improve clinical outcomes.

Influence of herd immunity in the cyclical nature of arboviruses

We review and contrast the evidence for an effect of amplifying host herd immunity on circulation and human exposure to arboviruses. Herd immunity of short-lived West Nile virus avian amplifying hosts appears to play a limited role in levels of enzootic circulation and spillover infections of humans, which are not amplifiers. In contrast, herd immunity of nonhuman primate hosts for enzootic Zika, dengue, and chikungunya viruses is much stronger and appears to regulate to a large extent the periodicity of sylvatic amplification in Africa. Following the recent Zika and chikungunya pandemics, human herd immunity in the Americas quickly rose to ∼50% in many regions, although seroprevalence remains patchy. Modeling from decades of chikungunya circulation in Asia suggests that this level of herd immunity will suppress for many years major chikungunya and Zika epidemics in the Americas, followed by smaller outbreaks as herd immunity cycles with a periodicity of up to several decades.

Two case reports of neuroinvasive West Nile virus infection in the Almaty region, Kazakhstan

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Population screening has confirmed circulation of West Nile virus in the southern region of Kazakhstan (Almaty region).

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We report two cases of meningoencephalitis of unknown etiology occurred in the rural area near Tekeli city, Kazakhstan, in August 2019.

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Retrospective analysis showed high titers of anti-WNV IgG in both patients’ serum specimens obtained on day 9 after the onset of symptoms.

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These are the first reports of West Nile virus infection in Kazakhstan.

Background

West Nile virus (WNV) is a member of the genus Flavivirus, which transmitted to humans mainly by mosquitoes. Recent pilot serosurveillance data from the Almaty region, Kazakhstan, suggest widespread WNV circulation in this area. This report includes two cases of neuroinvasive WNV infection in the same family living in a rural area near Tekeli city, Eskeldinsky district, Almaty region, Kazakhstan. Occurring concurrently and manifesting as WNV infection with febrile illness and symptoms of meningoencephalitis.

Methods

The study performed retrospective analysis of clinical histories and achieved serum samples obtained from patients with febrile and meningoencephalitic syndromes of unknown origin in the Almaty region spanning from April 1 to October 31, 2019. All sera samples obtained from patients with clinically suspected cases of acute WNV infection were retrospectively tested for WNV and tick-borne encephalitis virus by commercial immunoassays. Two cases were selected.

Cases presentation

We report two cases that occurred in August 2019 in a rural area near Tekeli city. Previously healthy 28- and 19-year-old husband and wife with febrile illness and neurological manifestations were hospitalized with the diagnosis of meningoencephalitis of unknown etiology and treated empirically. Retrospective serological analysis showed the presence of high titers of IgG against WNV on day 9 after onset of symptoms in cases.

Conclusions

This is the first report of aseptic meningitis with WNV infection in the background in Kazakhstan. The obtained data suggest circulation of WNV in the Almaty region and emphasize importance of laboratory testing for WNV in suspicious cases occurring in the region.

Scenario-based land abandonment projections: Method, application and implications

Land abandonment, e.g. agricultural land abandonment, can result in various social and ecological impacts. It would thus be helpful if the extent and spatial pattern of future land abandonment could be projected. However, the trajectory of future land abandonment generally depends on various factors, including biophysical conditions and future changes in socioeconomic indicators in the area. In this study, we developed a general framework for a scenario-based land abandonment projection, featuring a coupled regional economic and spatially explicit land change modeling approach. We applied this framework in selected municipalities in Fukushima Prefecture, Japan, under two socioeconomic development scenarios (2014-2050): low population and economic growth (LL scenario) and high population and economic growth (HH scenario). The case study results, which are also visualized through a set of hot spot maps, revealed that agricultural land abandonment would be more intense under the HH scenario due to the much higher future decline in farmer population driven by the shift in people's employment and main source of livelihood. Under the LL scenario, residential and urban land abandonment would be more profound because of the much higher future decline in total population. In general, our results provide insights into some plausible future socioeconomic changes, their interplay and their consequent land abandonment in the case study area, which would be useful in the context of forward-looking adaptive development planning. The proposed framework can be applied to other case study areas.

Evaluation of real-time reverse-transcription loop-mediated isothermal amplification assay for clinical diagnosis of West Nile virus in patients

Background & objectives

West Nile virus (WNV) is a mosquito-borne flavivirus. The disease can be diagnosed by isolation followed by fluorescent antibody tests, enzyme-linked immunosorbent assay and polymerase chain reaction (PCR) assay. These diagnostic methods are laborious and time-consuming. The present study was aimed to evaluate the real-time reverse-transcription loop-mediated isothermal amplification (RT-LAMP) method for rapid, early and accurate diagnosis of WNV.

Methods

A one-step single tube accelerated quantitative RT-LAMP assay was evaluated by targeting the Env gene of WNV. The gene amplification was accomplished by incubating the reaction mixture at 63°C for 60 min in both real time turbidimeter as well as routine laboratory water bath/dry heating bath. To rule out contamination issues, proper negative controls, including no template, no primer; and no enzyme, were always kept alongside each run. The RT-LAMP assay was evaluated on 105 clinical samples from individuals having ocular infection.

Results

Of the 105 samples tested, 27 were positive for WNV by RT-LAMP assay. The comparative evaluation with conventional RT-PCR revealed 100 per cent accordance with sensitivity and specificity of 100 and 95 per cent, respectively. The specificity of this assay was confirmed with serum samples obtained from patients with dengue and chikungunya.

Interpretation & conclusions

The RT-LAMP test seemed to be a sensitive and specific method for rapid detection of WNV infection and would be useful for rapid screening of a large number of clinical samples in endemic areas during outbreaks.

Widespread circulation of West Nile virus, but not Zika virus in southern Iran

West Nile virus (WNV) and Zika virus (ZIKV) are mosquito-borne viral infections. Over the past few decades, WNV has been associated with several outbreaks involving high numbers of neuroinvasive diseases among humans. The recent re-emergence of ZIKV has been associated with congenital malformation and also with Guillain-Barre syndrome in adults. The geographic range of arthropod-borne viruses has been rapidly increasing in recent years. The objectives of this study were to determine the presence of IgG specific antibodies and the genome of WNV and ZIKV in human samples, as well as WNV and ZIKV genomes in wild-caught mosquitoes in urban and rural areas of the Hormozgan province, in southern Iran. A total of 494 serum samples were tested for the presence of WNV and ZIKV IgG antibodies using ELISA assays. One hundred and two (20.6%) samples were reactive for WNV IgG antibodies. All serum samples were negative for ZIKV IgG antibodies. Using the multivariable logistic analysis, age (45+ vs. 1-25; OR = 3.4, 95% C.I.: 1.8-6.3), occupation (mostly outdoor vs. mostly indoor; OR = 2.4, 95% C.I.: 1.1-5.2), and skin type(type I/II vs. type III/IV and type V/VI; OR = 4.3, 95% C.I.: 1.7-10.8 and OR = 2.7, 95% C.I.: 1.3-5.5 respectively, skin types based on Fitzpatrick scale) showed significant association with WNV seroreactivity. We collected 2,015 mosquitoes in 136 pools belonging to 5 genera and 14 species. Three pools of Culex pipiens complex were positive for WNV RNA using real-time reverse transcription polymerase chain reaction (rtRT-PCR). ZIKV RNA was not detected in any of the pools. All WNV ELISA reactive serum samples were negative for WNV RNA. In conclusion, we provided evidence of the establishment of WNV in southern Iran and no proof of ZIKV in serum samples or in mosquito vectors. The establishment of an organized arbovirus surveillance system and active case finding strategies seems to be necessary.

Breaking the chain of zoonoses through biosecurity in livestock

Increases in global travel, trade and urbanisation are leading to greater incidence of zoonotic disease, and livestock are often a key link in the spread of disease to humans. As such, livestock vaccination strategies, as a part of broader biosecurity solutions, are critical to both animal and human health. Importantly, approaches that restrict infectious agents in livestock, not only protects their economic value but should reduce the potential for spill over infections in humans. Biosecurity solutions to livestock health can take a number of different forms and are generally heavily weighted towards prevention of infection rather than treatment. Therefore, vaccination can provide an effective component of a strategic approach, particularly as production economics dictate the use of cost effective solutions. Furthermore, in an evolving global environment there is a need for vaccines that accommodate for lower socioeconomic and rapidly emerging zoonotics.