Physical structure of lakes constrains epidemics in Daphnia populations

Parasites are integral parts of most ecosystems, yet attention has only recently focused on how community structure and abiotic factors impact host-parasite interactions. In lakes, both factors are influenced by habitat morphology. To investigate the role of habitat structure in mediating parasitism in the plankton, we quantified timing and prevalence of a common microparasite (Metschnikowia bicuspidata) in its host, Daphnia dentifera, in 18 lakes that vary in basin size and shape. Over three years, we found substantial spatial and temporal variation in the severity of epidemics. Although infection rates reached as high as 50% in some lakes, they did not occur in most lakes in most years. Host density, often considered to be a key determinant of disease spread, did not explain a significant amount of variation in the occurrence of epidemics. Furthermore, host resistance does not fully explain this parasite's distribution, since we easily infected hosts in the laboratory. Rather, basin shape predicted epidemics well; epidemics occurred only in lakes with steep-sided basins. In these lakes, the magnitude of epidemics varied with year. We suggest that biological (predation) and physical (turbulence) effects of basin shape interact with annual weather patterns to determine the regional distribution of this parasite.     

Partitioning microbial respiration between jet fuel and native organic matter in an organic-rich long time-contaminated aquifer

The relative importance of jet fuel biodegradation relative to the respiration of natural organic matter in a contaminated organic-rich aquifer underlying a fire training area at Tyndall Air Force Base, Florida, USA was determined with isotopic measurements. Thirteen wells were sampled and analyzed for BTX (benzene, toluene, xylene), dissolved inorganic carbon (DIC) and CH4 concentrations, and delta13C and 14C of DIC. Results range from non-detectable to 3790 ppb, 1.4-24 mM, 0.2-776 microM, +5.8 per thousand to -22 per thousand, and from 52 to 99 pmc, respectively. Residual fuel was confined to two center wells underlying the fire training area. DIC and CH4 concentrations were elevated down-gradient of the contamination, but also at sites that were not in the apparent flow path of the contaminated groundwater. DIC exhibited greatest delta13C enrichment at highest DIC and CH4 concentrations indicating that CH4 production was an important respiration mode. Radiocarbon-depleted DIC was observed at sites with high hydrocarbon concentrations and down-gradient of the site. The results indicate that while natural attenuation was not rapidly reducing the quantity of free product overlying the aquifer at the site of contamination, it was at least constraining its flow away from the spill site. Apparently under the conditions of this study, BTX was degraded as rapidly as it was dissolved.     

The effect of hydrocarbon mixtures on adsorption of substituted naphthalenes by clay and sediment from water

Adsorption of methyl and dimethyl naphthalenes, and of these compounds as components of JP8 and synthetic jet fuel mixtures, has been measured on two sediments and montmorillonite clay in water. Isotherms were linear, and hydrocarbons of similar structure gave similar adsorption coefficients on a particular clay or sediment. Individual component adsorption coefficients were dependent upon mixture composition, but coefficients usually varied by less than a factor of two. This implies that single component adsorption coefficients may be adequate for use in environmental fate models of hydrocarbon mixtures.     

Heterogeneity of sorption and transport-related properties in a sand–gravel aquifer at Columbus, Mississippi

Properties related to sorption and transport of organic compounds have been determined on 126 sections of 17 cores taken in an aquifer at Columbus Air Force Base in Columbus, MS. Each core section was homogenized prior to analysis. Organic carbon content (OC), specific surface area (SA), distribution coefficient (K_d) for naphthalene, and particle size distribution were measured on each section. Hydraulic conductivity (K_h) for each section was calculated from the particle size distributions. K_h values obtained were comparable with those from earlier borehole flowmeter and pulse tracer tests. Frequency distributions for all properties were lognormal. The arithmetic means and standard deviations for all samples are: OC=0.028% (+0.031, −0.015), SA=4.02 m²/g (+3.95, −1.99), K_d=0.198 l/kg (+0.195, −0.098), K_h=0.00033 m/s (+0.00051, −0.00020). These standard deviations are asymmetrical about the mean because statistics were calculated using log-transformed data, and antilogarithms then taken to obtain the results in the units of property measurement. Variabilities, expressed as coefficients of variation, were similar for all properties. Correlations between the properties were investigated. A good correlation between naphthalene K_d and OC (r=0.78) was found, and other correlations were weak, thus indicating that organic carbon content may control sorption of nonpolar organic solutes in this low carbon aquifer. Autocorrelation (variogram) analysis indicated that, for all properties, correlation lengths were less than the distance between sample points, which were separated by about 20 m horizontally and 1 m vertically. Separate statistical analysis of two widely separated groups of wells showed the groups similar in all properties, except organic carbon. Large-scale inhomogeneity was not detected, although earlier tracer tests produced irregular plumes indicating inhomogeneity in observed solute transport. Implications of the results to site characterization, in situations where aquifers are heterogeneous on short length scales, are discussed.     

The discrepant epidemiology of Middle East respiratory syndrome coronavirus (MERS-CoV)

The Middle East respiratory syndrome coronavirus (MERS-CoV) is a newly emerged infection in humans affecting the Arabian Peninsula, Europe, and North Africa. The source and persistence of the infection in humans remains unknown. The aim of this paper was to apply a risk analysis approach to the epidemiology of MERS-CoV and to understand the source of ongoing infections. The epidemiology of MERS-CoV was reviewed and compared to SARS. Each observed feature of MERS-CoV epidemiology was summarized and fitted to either an epidemic or one of two sporadic scenarios (either animal or deliberate release). As of May 2014, MERS-CoV has infected over 681 people and killed a further 204 over 2 years. In contrast, there were 8,273 cases and 775 deaths from SARS within 8 months. MERS-CoV has a more sporadic pattern unlike the clear epidemic pattern seen with SARS, and an unusual concentration of cases in the Middle East, without epidemics in other countries to which it has spread. SARS, with a higher reproductive number (R0), was eliminated from humans within 8 months of emerging, yet MERS-CoV, with a low R0 has persisted in humans over a far more prolonged period. This is at odds with the expected behavior of a virus with a low R0, which theoretically should not persist unless there are ongoing introductions of infection into humans, and poses the question “what is the source of continuing infections in humans?” A hospital outbreak in Al Ahsa, the Kingdom of Saudi Arabia (KSA), had a classic epidemic pattern with some human-to-human transmission. However, 3 different strains were identified in that outbreak, an unexpected and unexplained finding for what appears to be a single source outbreak. Since this outbreak in April 2013, there has been a large increase in new cases, mainly in KSA in April and May 2014, with no corresponding epidemics in other countries. Yet MERS-CoV was present in KSA over several mass gatherings (which predispose to epidemics), including the Hajj pilgrimage, without an epidemic arising. Furthermore, although the virus has been identified in bats and camels, the mode of ongoing transmission to humans remains uncertain. Although some cases appear to be transmitted from human to human, and a few have animal or camel exposure, many cases have no history of contact with either animals or human cases. A high proportion of asymptomatic or otherwise undetected cases have been postulated as an explanation for the unusual epidemiology, yet active surveillance does not support this. When the observed data were fitted to different disease patterns, the features of MERS-CoV fit better with a sporadic pattern, with evidence for either deliberate release or an animal source. There are many discrepancies in the observed epidemiology of MERS-CoV, which better fits a sporadic than an epidemic pattern. Possible explanations of the unusual features of the epidemiology include human-to-human transmission with a large proportion of undetected cases; or sporadic ongoing infections from a non-human source; or a combination of both. Possible sources of ongoing sporadic infection in humans include animals (camels appear the most likely source), or deliberate release. The latter could explain 3 strains being present in a single hospital outbreak. Genetic testing should be conducted to determine whether the virus is evolving to be more transmissible. Better ascertainment of mild or asymptomatic cases is also needed. Finally, the discrepant epidemiology warrants critical analysis of all possible explanations, and involvement of all stakeholders in biosecurity, and deliberate release must be seriously considered and at least acknowledged as a possibility.     

International Standardisation of a Method for Detection of Human Pathogenic Viruses in Molluscan Shellfish

The viruses primarily associated with shellfish-borne illness are norovirus, causing gastroenteritis and hepatitis A virus (HAV). Recent years have seen a proliferation of publications on methods for detection of these viruses in shellfish using polymerase chain reaction (PCR). However, currently no standard harmonised procedures have been published. Standardisation is necessary before virus methods can be considered for adoption within a regulatory framework. A European standardisation working group is developing a two-part (quantitative and qualitative) standard method for virus detection in foodstuffs, including shellfish, which has the potential to be incorporated into EU legislation as a reference method. This article describes the development of the standard method and outlines the key methodology principles adopted, the controls and other quality assurance measures supporting the method and future necessary developments in the area.