Coccidioidomycosis Dynamics in Relation to Climate in the Southwestern United States

Valley Fever: Environmental Risk Factors and Exposure Pathways Deduced from Field Measurements in California

Coccidioidomycosis, also known as Valley fever, has been reported among military personnel in Coccidioides-endemic areas of the southwestern United States since World War II. In this study, the prevalence of Coccidioides was confirmed in different soil and dust samples collected near three military bases in California using DNA extraction and Polymerase Chain Reaction (PCR) methods. Analyses of physical and chemical parameters revealed no significant differences between Coccidioides-positive and -negative sites. Soil samples collected in the Mojave Desert (near Twentynine Palms MCAGCC) showed the highest percentage of Coccidioides-positive soil and dust samples. Samples from the San Joaquin Valley (near NAS Lemoore) showed the lowest percentage of positive samples and were restricted to remnants of semi-natural areas between agricultural fields. Our results suggest that soil disturbance around all three military bases investigated poses a potential Coccidioides exposure risk for military personnel and the public. We conclude that once lands have been severely disturbed from their original state, they become less suitable for Coccidioides growth. We propose a conceptual framework for understanding exposure where disturbance of soils that exhibit natural or remnants of native vegetation (Creosote and Salt Bush) generate a high risk of exposure to the pathogen, likely during dry periods. In contrast, Coccidioides-positive sites, when undisturbed, will not pose a high risk of exposure.

Hospitalisations for mycoses as an indicator of socio-environmental vulnerability in the Brazilian Amazon-Savanna transition region

BACKGROUND

The infections caused by fungi represent a global concern and an important cause of hospital admissions in endemic areas. The influence of socio-environmental factors in infectious diseases has been documented; however, this phenomenon remains unclear regarding mycoses.

OBJECTIVES

This study aimed to analyse the spatio-temporal dynamics of hospitalisations for mycoses (HM) and the association with socio-economic and climate data in the Amazon-Savanna Transition Region in the state of Maranhão, Brazil.

METHODS

In this study, Spearman's correlation was applied to determine the correlation between HM, socio-economic and climatic data obtained from national databases in the period from 1998 to 2016. Hospitalisations for mycoses data were spatialised and analysed using the local Moran's index.

RESULTS

Our data revealed a negative and significant correlation between HM and socio-economic data regarding population, demographic density, human development index, health facilities and sanitary sewage. Significant correlations were observed between HM and precipitation, maximum temperature and minimum temperature. The main modulating climatic variable was the minimum temperature. The spatial autocorrelation analysis showed the dynamics of HM in municipalities belonging to the different regions of the state influenced by socio-economic conditions. We observed the presence of municipalities with high incidence of HM surrounded by others with low HM cases and vice versa.

CONCLUSIONS

Our results indicate that hospitalisations for mycoses represent an important indicator of socio-environmental vulnerability in the Amazon-Savanna transition region in Brazil. We encourage the adoption of measures to mitigate social and environmental impact on these diseases, especially in municipalities with low socio-economic status.

The mysterious desert dwellers: Coccidioides immitis and Coccidioides posadasii, causative fungal agents of coccidioidomycosis

The genus Coccidioides consists of two species: C. immitis and C. posadasii. Prior to 2000, all disease was thought to be caused by a single species, C. immitis. The organism grows in arid to semiarid alkaline soils throughout western North America and into Central and South America. Regions in the United States, with highest prevalence of disease, include California, Arizona, and Texas. The Mexican states of Baja California, Coahuila, Sonora, and Neuvo Leon currently have the highest skin test positive results. Central America contains isolated endemic areas in Guatemala and Honduras. South America has isolated regions of high endemicity including areas of Colombia, Venezuela, Argentina, Paraguay, and Brazil. Although approximately 15,000 cases per year are reported in the United States, actual disease burden is estimated to be in the hundreds of thousands, as only California and Arizona have dedicated public health outreach, and report and track disease reliably. In this review, we survey genomics, epidemiology, ecology, and summarize aspects of disease, diagnosis, prevention, and treatment.

Expansion of Coccidioidomycosis Endemic Regions in the United States in Response to Climate Change

Coccidioidomycosis (Valley fever) is a fungal disease endemic to the southwestern United States. Across this region, temperature and precipitation influence the extent of the endemic region and number of Valley fever cases. Climate projections for the western United States indicate that temperatures will increase and precipitation patterns will shift, which may alter disease dynamics. We estimated the area potentially endemic to Valley fever using a climate niche model derived from contemporary climate and disease incidence data. We then used our model with projections of climate from Earth system models to assess how endemic areas will change during the 21st century. By 2100 in a high warming scenario, our model predicts that the area of climate-limited endemicity will more than double, the number of affected states will increase from 12 to 17, and the number of Valley fever cases will increase by 50%. The Valley fever endemic region will expand north into dry western states, including Idaho, Wyoming, Montana, Nebraska, South Dakota, and North Dakota. Precipitation will limit the disease from spreading into states farther east and along the central and northern Pacific coast. This is the first quantitative estimate of how climate change may influence Valley fever in the United States. Our predictive model of Valley fever endemicity may provide guidance to public health officials to establish disease surveillance programs and design mitigation efforts to limit the impacts of this disease.

Communicating Risk for a Climate-Sensitive Disease: A Case Study of Valley Fever in Central California

Valley Fever, or Coccidioidomycosis, a fungal respiratory disease, is prevalent with increasing incidence in the Southwestern United States, especially in the central region of California. Public health agencies in the region do not have a consistent strategy for communication and health promotion targeting vulnerable communities about this climate-sensitive disease. We used the behavior adaptation communication model to design and conduct semi-structured interviews with representatives of public health agencies in five California counties: Fresno, Kern, Kings, San Luis Obispo, and Tulare County. While none of the agencies currently include climate change information into their Valley Fever risk messaging, the agencies discuss future communication methods similar to other health risk factors such as poor air quality days and influenza virus season. For political reasons, some public health agencies deliberately avoided the use of climate change language in communicating health risk factors to farmers who are particularly vulnerable to soil and dust-borne fungal spores. The effectiveness of health communication activities of the public health agencies has not been measured in reducing the prevalence of Valley Fever in impacted communities. Given the transboundary nature of climate influence on Valley Fever risk, a concerted and consistent health communication strategy is expected to be more effective than current practices.

Soil and climactic predictors of canine coccidioidomycosis seroprevalence in Washington State: An ecological cross-sectional study

Coccidioidomycosis is a predominantly respiratory infection of animals and humans caused by soil-dwelling fungi. Long known to be endemic to North American deserts, locally acquired human cases first emerged in Washington State in 2010. To inform development of an environmental niche map, we conducted an ecological cross-sectional study of the association between soil and climactic variables and canine seroprevalence in Washington State, at the zip code tabulation area level. Soil predictors included soil texture (per cent sand, silt and clay), pH, electrical conductivity and water storage capacity; climactic predictors included mean annual air temperature and liquid precipitation. Clustering was evaluated with Moran's I, and four modelling approaches were adopted a priori: two models without any smoothing (logistic regression and quasi-logistic regression) and two smoothing models (non-spatial and spatial smoothing). No evidence was found for clustering, and both smoothing models resulted in marked attenuation of all coefficients. Temperature was found to have a positive effect in the non-smoothing models (prevalence odds ratio, logistic model: 1.70, 95% confidence interval 1.02, 2.84). While no other significant associations were found, there was suggestive evidence of a positive effect for pH. Despite the limitations inherent to the ecological and cross-sectional nature of these data, these findings provide insight for the development of an environmental niche map in Washington State and demonstrate the utility of using data from an animal sentinel to predict human disease risk.

Utility of Whole-Genome Sequencing to Ascertain Locally Acquired Cases of Coccidioidomycosis, Washington, USA

Coccidioidomycosis is an emerging fungal infection in Washington, USA, and the epidemiology of the disease in this state is poorly understood. We used whole-genome sequencing to differentiate locally acquired cases in Washington on the basis of the previously identified phylogeographic population structure of Coccidioides spp. Clinical isolates from coccidioidomycosis cases involving possible Washington soil exposure were included. Of 17 human infections with epidemiologic evidence of possible local acquisition, 4 were likely locally acquired infections and 13 were likely acquired outside Washington. Isolates from locally acquired cases clustered within the previously established Washington clade of C. immitis. Genetic differences among these strains suggest multiple environmental reservoirs of C. immitis in the state.

Valley Fever on the Rise-Searching for Microbial Antagonists to the Fungal Pathogen Coccidioides immitis

The incidence of coccidioidomycosis, also known as Valley Fever, is increasing in the Southwestern United States and Mexico. Despite considerable efforts, a vaccine to protect humans from this disease is not forthcoming. The aim of this project was to isolate and phylogenetically compare bacterial species that could serve as biocontrol candidates to suppress the growth of Coccidioides immitis, the causative agent of coccidioidomycosis, in eroded soils or in areas close to human settlements that are being developed. Soil erosion in Coccidioides endemic areas is leading to substantial emissions of fugitive dust that can contain arthroconidia of the pathogen and thus it is becoming a health hazard. Natural microbial antagonists to C. immitis, that are adapted to arid desert soils could be used for biocontrol attempts to suppress the growth of the pathogen in situ to reduce the risk for humans and animals of contracting coccidioidomycosis. Bacteria were isolated from soil samples obtained near Bakersfield, California. Subsequently, pairwise challenge assays with bacterial pure cultures were initially performed against Uncinocarpus reesii, a non-pathogenic relative of C. immitis on media plates. Bacterial isolates that exhibited strongly antifungal properties were then re-challenged against C. immitis. Strongly anti-C. immitis bacterial isolates related to Bacillus subtilis and Streptomyces spp. were isolated, and their antifungal spectrum was investigated using a selection of environmental fungi.

Effects of Increasing Aridity on Ambient Dust and Public Health in the U.S. Southwest Under Climate Change

The U.S. Southwest is projected to experience increasing aridity due to climate change. We quantify the resulting impacts on ambient dust levels and public health using methods consistent with the Environmental Protection Agency's Climate Change Impacts and Risk Analysis framework. We first demonstrate that U.S. Southwest fine (PM2.5) and coarse (PM2.5-10) dust levels are strongly sensitive to variability in the 2-month Standardized Precipitation-Evapotranspiration Index across southwestern North America. We then estimate potential changes in dust levels through 2099 by applying the observed sensitivities to downscaled meteorological output projected by six climate models following an intermediate (Representative Concentration Pathway 4.5, RCP4.5) and a high (RCP8.5) greenhouse gas concentration scenario. By 2080-2099 under RCP8.5 relative to 1986-2005 in the U.S. Southwest: (1) Fine dust levels could increase by 57%, and fine dust-attributable all-cause mortality and hospitalizations could increase by 230% and 360%, respectively; (2) coarse dust levels could increase by 38%, and coarse dust-attributable cardiovascular mortality and asthma emergency department visits could increase by 210% and 88%, respectively; (3) climate-driven changes in dust concentrations can account for 34-47% of these health impacts, with the rest due to increases in population and baseline incidence rates; and (4) economic damages of the health impacts could total $47 billion per year additional to the 1986-2005 value of $13 billion per year. Compared to national-scale climate impacts projected for other U.S. sectors using the Climate Change Impacts and Risk Analysis framework, dust-related mortality ranks fourth behind extreme temperature-related mortality, labor productivity decline, and coastal property loss.

Investigating the Relationship Between Climate and Valley Fever (Coccidioidomycosis)

Valley fever (coccidioidomycosis) is a disease caused by inhalation of spores from the soil-dwelling Coccidioides fungal species. The disease is endemic to semiarid areas in the western USA and parts of Central and South America. The region of interest for this study, Kern County, California, accounts for approximately 14% of the reported valley fever cases in the USA each year. It is hypothesized that the weather conditions that foster the growth and dispersal of the fungus influence the number of cases in the endemic area. This study uses regression-based analysis to model and assess the seasonal relationships between valley fever incidence and climatic variables including concurrent and lagged precipitation, temperature, Palmer Drought Severity Index, wind speed, and PM₁₀ using data from 2000 to 2015. We find statistically significant links between disease incidence and climate conditions in Kern County, California. The best performing seasonal model explains up to 76% of the variability in fall valley fever incidence based on concurrent and antecedent climate conditions. Findings are consistent with previous studies, suggesting that antecedent precipitation is an important predictor of disease. The significant relationships found support the "grow and blow" hypothesis for climate-related coccidioidomycosis incidence risk that was originally developed for Arizona.