Detection of human enteric viruses in oysters by in vivo and in vitro amplification of nucleic acids

Application of Concanavalin A-Linked Magnetic Beads for the Detection of Hepatitis A Virus

Prompt and inexpensive detection of hepatitis A virus (HAV) is essential to control acute hepatitis outbreaks associated with the consumption of contaminated raw or minimally processed food. In this study, various carbohydrate-binding lectins, including concanavalin A (Con A), wheat germ agglutinin, and soybean agglutinin, were compared for their binding affinity to HAV. Con A, which showed significantly higher binding affinity than other lectins, was used to develop an alternative and affordable method to conventional antibody-linked immunomagnetic separation prior to detection of HAV using reverse transcriptase PCR. This method, Con A-linked immunomagnetic separation combined with reverse transcriptase PCR, can detect HAV at a dilution concentration of 10^-4 of the virus stock (titer: 10⁴ median tissue culture infective dose per mL), indicating that Con A could be a promising candidate for concentrating HAV.

Foodborne viruses: Detection, risk assessment, and control options in food processing

In a recent report by risk assessment experts on the identification of food safety priorities using the Delphi technique, foodborne viruses were recognized among the top rated food safety priorities and have become a greater concern to the food industry over the past few years. Food safety experts agreed that control measures for viruses throughout the food chain are required. However, much still needs to be understood with regard to the effectiveness of these controls and how to properly validate their performance, whether it is personal hygiene of food handlers or the effects of processing of at risk foods or the interpretation and action required on positive virus test result. This manuscript provides a description of foodborne viruses and their characteristics, their responses to stress and technologies developed for viral detection and control. In addition, the gaps in knowledge and understanding, and future perspectives on the application of viral detection and control strategies for the food industry, along with suggestions on how the food industry could implement effective control strategies for viruses in foods. The current state of the science on epidemiology, public health burden, risk assessment and management options for viruses in food processing environments will be highlighted in this review.

The effect of storage time on Vibrio spp. and fecal indicator bacteria in an Isco autosampler

Monitoring concentrations of bacterial pathogens and indicators of fecal contamination in coastal and estuarine ecosystems is critical to reduce adverse effects to public health. During storm events, particularly hurricanes, floods, Nor'easters, and tropical cyclones, sampling of coastal and estuarine waters is not generally possible due to safety concerns. It is particularly important to monitor waters during these periods as it is at precisely these times that pathogenic bacteria such as Vibrio spp. and fecal indicator bacteria concentrations fluctuate, potentially posing significant risks to public health. Automated samplers, such as the Isco sampler, are commonly used to conduct remote sample collection. Remote sampling is employed during severe storm periods, thereby reducing risk to researchers. Water samples are then stored until conditions are safe enough to retrieve them, typically in less than 21h, to collect the samples. Concerns exist regarding potential "bottle effects", whereby containment of sample might result in altered results. While these effects are well documented in samples being held for 24h or more, there is little data on bottle effects occurring during the first 24h of containment, and less still on the specific effects related to this type of sampling regime. Estuarine water samples were collected in the fall of 2013, placed into an Isco autosampler and subsampled over time to determine the effects of storage within this type of autosampling device. Vibrio spp. and fecal indicator bacteria were quantified using replicated culture-based methods, including Enterolert™ and membrane filtration. The experiments demonstrated no significant impact of storage time when comparing concentrations of total Vibrio spp., Vibrio vulnificus, Vibrio parahaemolyticus, or Enterococcus spp. after storage compared to original concentrations. However, the findings also suggested that increased variability and growth can occur during the middle of the day. Therefore, if at all possible, analysis schedules should be modified to account for this variability, e.g. collection of samples after overnight storage should occur as early in the morning as practicable.

Preliminary Study to Assess the Performance of Mengovirus Elution from Sludge

In the virus detection protocol for sludge, the viral elution step from solids to solution is critical. In this study, mengoviruses were detected in artificially contaminated sludge with a qRT-PCR assay. The viral yields ranged between 19 and 66 % for 60 % sludge. This study demonstrates that mengovirus can be used as a sample process control for analysis of sewage sludge.

Comparative analysis of rodent tissue preservation methods and nucleic acid extraction techniques for virus screening purposes

The polymerase chain reaction (PCR) has become an essential method for the detection of viruses in tissue specimens. However, it is well known that the presence of PCR inhibitors in tissue samples may cause false-negative results. Hence the identification of PCR inhibitors and evaluation and optimization of nucleic acid extraction and preservation methods is of prime concern in virus discovery programs dealing with animal tissues. Accordingly, to monitor and remove inhibitors we have performed comparative analyses of two commonly used tissue storage methods and five RNA purification techniques using a variety of animal tissues, containing quantified levels of added MS2 bacteriophages as the indicator of inhibition. The results showed (i) no significant difference between the two methods of sample preservation, viz. direct storage at -80°C or 4°C in RNAlater, (ii) lung rodent tissues contained lower levels of inhibitor than liver, kidney and spleen, (iii) RNA extraction using the EZ1+PK RNA kit was the most effective procedure for removal of RT-PCR inhibitors.

New approaches for enhanced detection of enteroviruses from Hawaiian environmental waters

Health risks associated with sewage-contaminated recreational waters are of important public health concern. Reliable water monitoring systems are therefore crucial. Current recreational water quality criteria rely predominantly on the enumeration of bacterial indicators, while potentially dangerous viral pathogens often remain undetected. Human enteric viruses have been proposed as alternative indicators; however, their detection is often hindered by low viral concentrations present in the environment. Reported here are novel and effective laboratory protocols for viral concentration and highly sensitive and optimized RT-PCR for the efficient detection of enteroviruses, an important enteric virus subset, in Hawaiian environmental waters. Eighteen published enterovirus primer pairs were comparatively evaluated for detection sensitivity. The primer set exhibiting the lowest detection limit under optimized conditions, EQ-1/EQ-2, was validated in a field survey of 22 recreational bodies of water located around the island of Oahu, Hawaii. Eleven sites tested positive for enterovirus, indicating fecal contamination at these locations. As an additional means of viral concentration, shellfish were collected from 9 sample sites and subjected to dissection, RNA extraction, and subsequent RT-PCR. Shellfish tissue from 6 of 9 sites tested positive for enterovirus. The techniques implemented here are valuable resources to aid accurate reflection of microbial contamination in Hawaii’s environmental waters.

Human and bovine adenoviruses for the detection of source-specific fecal pollution in coastal waters in Australia

In this study, the host-specificity and -sensitivity of human- and bovine-specific adenoviruses (HS-AVs and BS-AVs) were evaluated by testing wastewater/fecal samples from various animal species in Southeast, Queensland, Australia. The overall specificity and sensitivity of the HS-AVs marker were 1.0 and 0.78, respectively. These figures for the BS-AVs were 1.0 and 0.73, respectively. Twenty environmental water samples were collected during wet conditions and 20 samples were colleted during dry conditions from the Maroochy Coastal River and tested for the presence of fecal indicator bacteria (FIB), host-specific viral markers, zoonotic bacterial and protozoan pathogens using PCR/qPCR. The concentrations of FIB in water samples collected after wet conditions were generally higher compared to dry conditions. HS-AVs was detected in 20% water samples collected during wet conditions and whereas BS-AVs was detected in both wet (i.e., 10%) and dry (i.e., 10%) conditions. Both Campylobacter jejuni mapA and Salmonella invA genes detected in 10% samples collected during dry conditions. The concentrations of Salmonella invA ranged between 3.5 × 10(2) and 4.3 × 10(2) genomic copies per 500 ml of water Giardia lamblia β-giardin gene was detected only in one sample (5%) collected during the dry conditions. Weak or significant correlations were observed between FIB with viral markers and zoonotic pathogens. However, during dry conditions, no significant correlations were observed between FIB concentrations with viral markers and zoonotic pathogens. The prevalence of HS-AVs in samples collected from the study river suggests that the quality of water is affected by human fecal pollution and as well as bovine fecal pollution. The results suggest that HS-AVs and BS-AVs detection using PCR could be a useful tool for the identification of human sourced fecal pollution in coastal waters.

Detection of naturally occurring enteroviruses in waters using direct RT-PCR and integrated cell culture-RT-PCR

Viruses detected by rapid molecular assays are not always infectious. In this study we compared enterovirus levels in natural waters using culture and reverse transcription-polymerase chain reaction (RT-PCR) techniques to determine whether molecular units of naturally occurring enteroviruses can be utilized to predict viral infectivity. Viruses were concentrated from 12 river water and effluent samples using 1 MDS filter-filtration and beef extract-elution. An integrated cell culture-RT-PCR (ICC-RT-PCR) was applied to the concentrates; and these waters contained up to 1.9 MPN of culturable (on BGM cells) viruses per litre (0.57 MPN/300 ml). Sample concentrates were also subjected to a direct 'molecular' approach using solvent-extraction, PEG-precipitation, and RNA-extraction before RT-PCR detection. The detection sensitivity of the direct RT-PCR was equivalent to 0.46 estimated (culturable) MPN/reaction, per 300 ml water. Two-thirds of the samples demonstrated consistent presence or absence of viruses by ICC-RT-PCR and direct RT-PCR. The direct RT-PCR approach resulted in over-estimation of naturally occurring infectious viruses as high as 91-fold in waters. Increased RT-PCR units may not reflect higher levels of culturable viruses in natural waters. The differences in virus levels detected by molecular and culture assays could be attributed to factors of volume of sample analyzed, different concentration schemes utilized that may affect the presence of residual inhibitors, and different stability exhibited by enterovirus strains/groups.

Human enteric viruses in groundwater from a confined bedrock aquifer

Confined aquifers are overlain by low-permeability aquitards that are commonly assumed to protect underlying aquifers from microbial contaminants. However, empirical data on microbial contamination beneath aquitards is limited. This study determined the occurrence of human pathogenic viruses in well water from a deep sandstone aquifer confined by a regionally extensive shale aquitard. Three public water-supply wells were each sampled 10 times over 15 months. Samples were analyzed by reverse transcription-polymerase chain reaction (RT-PCR) for several virus groups and by cell culture for infectious enteroviruses. Seven of 30 samples were positive by RT-PCR for enteroviruses; one of these was positive for infectious echovirus 18. The virus-positive samples were collected from two wells cased through the aquitard, indicating the viruses were present in the confined aquifer. Samples from the same wells showed atmospheric tritium, indicating water recharged within the pastfew decades. Hydrogeologic conditions support rapid porous media transport of viruses through the upper sandstone aquifer to the top of the aquitard 61 m below ground surface. Natural fractures in the shale aquitard are one possible virus transport pathway through the aquitard; however, windows, cross-connecting well bores, or imperfect grout seals along well casings also may be involved. Deep confined aquifers can be more vulnerable to contamination by human viruses than commonly believed.

Rapid virus detection procedure for molecular tracing of shellfish associated with disease outbreaks

Detection of pathogenic viruses in oysters implicated in gastroenteritis outbreaks is often hampered by time-consuming, specialist virus extraction methods. Five virus RNA extraction methods were evaluated with respect to performance characteristics and sensitivity on artificially contaminated oyster digestive glands. The two most promising procedures were further evaluated on bioaccumulated and naturally contaminated oysters. The most efficient method was used to trace the source in an outbreak situation. Out of five RNA extraction protocols, PEG precipitation and the RNeasy Kit performed best with norovirus genogroup III-spiked digestive glands. Analyzing 24-h bioaccumulated oysters revealed a slightly better sensitivity with PEG precipitation, but the RNeasy Kit was less prone to concentrate inhibitors. The latter procedure demonstrated the presence of human noroviruses in naturally contaminated oysters and oysters implicated in an outbreak. In this outbreak, in four out of nine individually analyzed digestive glands, norovirus was detected. In one of the oysters and in one of the fecal samples of the clinical cases, identical norovirus strains were detected. A standard and rapid virus extraction method using the RNeasy Kit appeared to be most useful in tracing shellfish as the source in gastroenteritis outbreaks, and to be able to make effective and timely risk management decisions.

Surrogates for the study of norovirus stability and inactivation in the environment: aA comparison of murine norovirus and feline calicivirus

Human noroviruses (NoVs) are the leading cause of food- and waterborne outbreaks of acute nonbacterial gastroenteritis worldwide. As a result of the lack of a mammalian cell culture model for these viruses, studies on persistence, inactivation, and transmission have been limited to cultivable viruses, including feline calicivirus (FCV). Recently, reports of the successful cell culture of murine norovirus 1 (MNV-1) have provided investigators with an alternative surrogate for human NoVs. In this study, we compared the inactivation profiles of MNV-1 to FCV in an effort to establish the relevance of MNV-1 as a surrogate virus. Specifically, we evaluated (i) stability upon exposure to pH extremes; (ii) stability upon exposure to organic solvents; (iii) thermal inactivation; and (iv) surface persistence under wet and dry conditions. MNV-1 was stable across the entire pH range tested (pH 2 to 10) with less than 1 log reduction in infectivity at pH 2, whereas FCV was inactivated rapidly at pH values < 3 and > 9. FCV was more stable than MNV-1 at 56 degrees C, but both viruses exhibited similar inactivation at 63 and 72 degrees C. Long-term persistence of both viruses suspended in a fecal matrix and inoculated onto stainless steel coupons were similar at 4 degrees C, but at room temperature in solution, MNV-1 was more stable than FCV. The genetic relatedness of MNV-1 to human NoVs combined with its ability to survive under gastric pH levels makes this virus a promising and relevant surrogate for studying environmental survival of human NoVs.

Comparaison de la culture cellulaire et de la RT–PCR pour la détection des entérovirus dans les eaux usées et les coquillages en Tunisie

Enteric viruses contaminating the environment represent a danger for public health notably enteroviruses that are excreted in stools and can contaminate wastewater and shellfish. The ability of enteroviruses to grow in cell culture and the development of techniques of molecular biology applied to their detection make these viruses a good marker of viral pollution of aquatic environment. The aim of our study was to develop a rapid and sensitive RT-PCR technique, able to detect enterovirus RNA in wastewater and shellfish. From 26 samples of wastewater and 56 samples of shellfish, 50.0 and 42.8% were found positive by RT-PCR, respectively, whereas 38.4 and 28.5% were positive by culture, respectively (P=0.077 by chi square test). The two techniques were found concordant in 57.3% of the 82 combined samples, whereas 23 samples (28.0%) were positive only by RT-PCR and that 12 samples (14.6%) were positive only by culture. These discrepancies illustrate the fact that the two techniques are not equivalent: the molecular technique allows the detection of not cultivable samples but is sensitive to PCR inhibitors that are present in large amounts in environmental samples.

Identification and sequence analysis of hepatitis A virus detected in market and environmental bivalve molluscs

In Italy in 1998, hepatitis A virus (HAV) was responsible for an infectious disease transmitted by contaminated bivalve molluscs. To determine the presence of HAV in the bivalves collected during a 1-year follow-up study, hepatitis A RNA was extracted and amplified by a nested reverse transcriptase-PCR method overlapping the VP1/2A region. The HAV genome was detected in 24 (14.1%) of 170 samples: 19 clams (Tapes decussates and Tapes semidecussatus), 1 oyster (Crossostea gigas), and 4 mussels (Mytillus galloprovincialis). Eleven positive samples were collected from marketing areas, and 13 positive samples were collected from growing areas. Seventeen of the 24 positive samples had been taken from domestic products, and 7 had been imported. Sequence analysis showed the presence of genotypes IA and IB. Our results suggest significant presence of HAV in bivalves from both marketing (public consumption) and environmental (growing) areas.

Molecular assays for targeting human and bovine enteric viruses in coastal waters and their application for library-independent source tracking

Rapid population growth and urban development along waterways and coastal areas have led to decreasing water quality. To examine the effects of upstream anthropogenic activities on microbiological water quality, methods for source-specific testing are required. In this study, molecular assays targeting human enteroviruses (HEV), bovine enteroviruses (BEV), and human adenoviruses (HAdV) were developed and used to identify major sources of fecal contamination in the lower Altamaha River, Georgia. Two-liter grab samples were collected monthly from five tidally influenced stations between July and December 2002. Samples were analyzed by reverse transcription- and nested-PCR. PCR results were confirmed by dot blot hybridization. Eleven and 17 of the 30 surface water samples tested positive for HAdV and HEV, respectively. Two-thirds of the samples tested positive for either HEV or HAdV, and the viruses occurred simultaneously in 26% of samples. BEV were detected in 11 of 30 surface water samples. Binary logistic regression analysis showed that the presence of both human and bovine enteric viruses was not significantly related to either fecal coliform or total coliform levels. The presence of these viruses was directly related to dissolved oxygen and streamflow but inversely related to water temperature, rainfall in the 30 days preceding sampling, and chlorophyll-a concentrations. The stringent host specificity of enteric viruses makes them good library-independent indicators for identification of water pollution sources. Viral pathogen detection by PCR is a highly sensitive and easy-to-use tool for rapid assessment of water quality and fecal contamination when public health risk characterization is not necessary.

Enteric viruses of humans and animals in aquatic environments: health risks, detection, and potential water quality assessment tools

Waterborne enteric viruses threaten both human and animal health. These pathogens are host specific and cause a wide range of diseases and symptoms in humans or other animals. While considerable research has documented the risk of enteric viruses to human health from contact with contaminated water, the current bacterial indicator-based methods for evaluation of water quality are often ineffectual proxies for pathogenic viruses. Additionally, relatively little work has specifically investigated the risk of waterborne viruses to animal health, and this risk currently is not addressed by routine water quality assessments. Nonetheless, because of their host specificity, enteric viruses can fulfill a unique role both for assessing health risks and as measures of contamination source in a watershed, yet the use of animal, as well as human, host-specific viruses in determining sources of fecal pollution has received little attention. With improved molecular detection assays, viruses from key host groups can be targeted directly using PCR amplification or hybridization with a high level of sensitivity and specificity. A multispecies viral analysis would provide needed information for controlling pollution by source, determining human health risks based on assessments of human virus loading and exposure, and determining potential risks to production animal health and could indicate the potential for the presence of other zoonotic pathogens. While there is a need to better understand the prevalence and environmental distribution of nonhuman enteric viruses, the development of improved methods for specific and sensitive detection will facilitate the use of these microbes for library-independent source tracking and water quality assessment tools.

Enteric viruses of humans and animals in aquatic environments: health risks, detection, and potential water quality assessment tools

Waterborne enteric viruses threaten both human and animal health. These pathogens are host specific and cause a wide range of diseases and symptoms in humans or other animals. While considerable research has documented the risk of enteric viruses to human health from contact with contaminated water, the current bacterial indicator-based methods for evaluation of water quality are often ineffectual proxies for pathogenic viruses. Additionally, relatively little work has specifically investigated the risk of waterborne viruses to animal health, and this risk currently is not addressed by routine water quality assessments. Nonetheless, because of their host specificity, enteric viruses can fulfill a unique role both for assessing health risks and as measures of contamination source in a watershed, yet the use of animal, as well as human, host-specific viruses in determining sources of fecal pollution has received little attention. With improved molecular detection assays, viruses from key host groups can be targeted directly using PCR amplification or hybridization with a high level of sensitivity and specificity. A multispecies viral analysis would provide needed information for controlling pollution by source, determining human health risks based on assessments of human virus loading and exposure, and determining potential risks to production animal health and could indicate the potential for the presence of other zoonotic pathogens. While there is a need to better understand the prevalence and environmental distribution of nonhuman enteric viruses, the development of improved methods for specific and sensitive detection will facilitate the use of these microbes for library-independent source tracking and water quality assessment tools.

Detection of infectious hepatitis A virus by integrated cell culture/strand-specific reverse transcriptase-polymerase chain reaction

AIMS

A novel integrated cell culture/strand-specific reverse transcriptase-polymerase chain reaction (RT-PCR) assay was established for detection of infectious hepatitis A virus (HAV).

METHODS AND RESULTS

The specificity of tagged RT-PCR was assessed using HAV genomic positive-strand RNA extracted from HAV virions as reference. Water samples artificially contaminated with infectious or formalin-inactivated HAV were subjected to integrated cell culture (ICC)/RT-PCR and ICC/strand-specific RT-PCR assays respectively. The tagged RT-PCR had high specificity for HAV negative-strand RNA. By demonstrating the formation of negative-strand RNA replicative intermediate, ICC/strand-specific RT-PCR can distinguish between infectious and non-infectious HAV. The described method detected infectious HAV at inoculation level of 10(0) TCID50 per flask within 4 days.

CONCLUSIONS

The ICC/strand-specific RT-PCR is a novel, rapid, sensitive and reliable method for detection of infectious HAV.

SIGNIFICANCE AND IMPACT OF THE STUDY

Coupled with a suitable virus concentration and purification system, ICC/strand-specific RT-PCR will provide a novel and rapid method for detection of infectious HAV in clinical, environmental and food samples. This assay may be used as an alternative method to test the effective inactivation of inactivated virus vaccines. It may also be adapted to assess the efficacy of disinfection of HAV and enteric viruses in foods and water.

Use of reverse transcription and PCR to discriminate between infectious and non-infectious hepatitis A virus

Hepatitis A virus (HAV) is a major cause of infectious hepatitis worldwide. Detection of HAV in contaminated food or water is a priority research area in laboratories worldwide. Our laboratory has reported previously the development of reverse transcription-polymerase chain reaction (RT-PCR) based detection and typing methods for HAV in contaminated shellfish and produce. It is commonly held that RT-PCR can detect viral genome, but cannot distinguish between infectious and inactivated virus. Therefore, signals obtained after PCR should be considered as false positives unless it can be shown that the sample contains virus capable of infecting a suitable host cell line in culture. We present data to show that this general assumption is not valid. Evidence is provided that demonstrate that signals generated after RT-PCR amplification of viral genome correlated well with the presence of infectious virus in the sample. Viral samples inactivated by heat or UV treatment produced significantly lower signal strength that paralleled infectivity of the sample in cultured cells. The loss of signal strength is most likely the result of damage to the viral RNA that renders it unsuitable for RT-PCR. The correlation between PCR signal and infectivity was better following UV inactivation than heat treatment. The procedure may be adapted to other viruses and inactivating agents.

Molecular surveillance of enterovirus and norwalk-like virus in oysters relocated to a municipal-sewage-impacted gulf estuary

An 18-month survey was conducted to examine the prevalence of enteric viruses and their relationship to indicators in environmentally polluted shellfish. Groups of oysters, one group per 4 weeks, were relocated to a coastal water area in the Gulf of Mexico that is impacted by municipal sewage and were analyzed for enteroviruses, Norwalk-like viruses (NLV), and indicator microorganisms (fecal coliform, Escherichia coli, and male-specific coliphages). The levels of indicator microorganisms were consistent with the expected continuous pollution of the area. Fourteen of the 18 oyster samples were found by reverse transcription (RT)-PCR to harbor NLV and/or enterovirus sequences. Of the four virus-negative oysters, three had exposure to water temperatures of >29 degrees C. Concomitant with these findings, two of these four oysters also accumulated the lowest levels of coliphages. PCR primers targeting pan-enteroviruses and the NLV 95/96-US common subset were utilized; NLV sequences were detected more frequently than those of enteroviruses. Within the 12-month sampling period, NLV and enterovirus sequences were detected in 58 and 42%, respectively, of the oysters (67% of the oysters tested were positive for at least one virus) from a prohibited shellfish-growing area approximately 30 m away from a sewage discharge site. Eight (4.6%) of the 175 NLV capsid nucleotide sequences were heterogeneous among the clones derived from naturally polluted oysters. Overall, enteric viral sequences were found in the contaminated oysters throughout all seasons except hot summer, with a higher prevalence of NLV than enterovirus. Although a high percentage of the oysters harbored enteric viruses, the virus levels were usually less than or equal to 2 logs of RT-PCR-detectable units per gram of oyster meat.

Detection of infectious adenovirus in cell culture by mRNA reverse transcription-PCR

We have developed and evaluated the reverse transcription (RT)-PCR detection of mRNA in cell culture to assay infectious adenoviruses (Ads) by using Ad type 2 (Ad2) and Ad41 as models. Only infectious Ads are detected because they are the only ones able to produce mRNA during replication in cell culture. Three primer sets for RT-PCR amplification of mRNA were evaluated for their sensitivity and specificity: a conserved region of late mRNA transcript encoding a virion structural hexon protein and detecting a wide range of human Ads and two primer sets targeting a region of an early mRNA transcript that specifically detects either Ad2 and Ad5 or Ad40 and Ad41. The mRNAs of infected A549 and Graham 293 cells were recovered from cell lysates with oligo(dT) at different time periods after infection and treated with RNase-free DNase to remove residual contaminating DNA, and then Ad mRNA was detected by RT-PCR assay. The mRNA of Ad2 was detected as early as 6 h after infection at 10(6) infectious units (IU) per cell culture and after longer incubation times at levels as low as 1 to 2 IU per cell culture. The mRNA of Ad41 was detected as soon as 24 h after infection at 10(6) IU per cell culture and at levels as low as 5 IU per cell culture after longer incubation times. To confirm the detection of only infectious viruses, it was shown that no mRNA was detected from Ad2 and Ad41 inactivated by free chlorine or high doses of collimated, monochromatic (254-nm) UV radiation. Detection of Ad2 mRNA exactly coincided with the presence of virus infectivity detected by cytopathogenic effects in cell cultures, but mRNA detection occurred sooner. These results suggest that mRNA detection by RT-PCR assay in inoculated cell cultures is a very sensitive, specific, and rapid method by which to detect infectious Ads in water and other environmental samples.

Virus-contaminated oysters: a three-month monitoring of oysters imported to Switzerland

Molluscan shellfish are known to be carriers of viral and bacterial pathogens. The consumption of raw oysters has been repeatedly linked to outbreaks of viral gastroenteritis and hepatitis A. Switzerland imports over 300 tons of oysters per year, 95% of which originate in France. To assess the level of viral contamination, a 3-month monitoring study was conducted. Therefore, the sensitivities of several previously described methods for virus concentration were compared, and one protocol was finally chosen by using dissected digestive tissues. Eighty-seven samples consisting of five oysters each were analyzed for Norwalk-like viruses (NLVs), enteroviruses, and hepatitis A viruses from November 2001 to February 2002. The oysters were exported by 31 French, three Dutch, and two Irish suppliers. Eight oyster samples from six French suppliers were positive for NLVs, and four samples from four French suppliers were positive for enteroviruses; two of the latter samples were positive for both viral agents. No hepatitis A viruses were detected. The sequences of NLV and enterovirus amplicons showed a great variety of strains, especially for the NLVs (strains similar to Bristol, Hawaii, Mexico, and Melksham agent). The data obtained indicated that imported oysters might be a source of NLV infection in Switzerland. However, further studies are needed to determine the quantitative significance of the risk factor within the overall epidemiology of NLVs.

Hepatitis A virus detection in oysters (Crassostrea gigas) in Santa Catarina State, Brazil, by reverse transcription-polymerase chain reaction

Shellfish are readily contaminated with viruses present in water containing sewage because of the concentration effect of filter feeding. Hepatitis A virus (HAV) is the main cause of acute hepatitis worldwide and may lead to severe illness or even death. It is transmitted through fecal and oral routes and causes widespread endemic and asymptomatic infections in young children. Here we describe a method for the detection of HAV RNA in shellfish involving the extraction of total RNA from oyster meat followed by reverse transcription-polymerase chain reaction (RT-PCR). Virus recovery from oyster extracts artificially seeded with HAV strain HM 175 was examined by RT-PCR. The minimum detection limit was 3.3 focus-forming units of HAV, and the recovery rate was 75.7%. This method was used to assess the viral contamination of four shellfish beds in Santa Catarina State, Brazil, over a 1-year period. Six (22%) of 27 samples collected in autumn and winter from one shellfish bed tested positive for HAV.

Detection of hepatitis A virus in mussels from different sources marketed in Puglia region (South Italy)

Hepatitis A virus (HAV) infection is endemic in Puglia (South Italy). Epidemiological studies indicate that shellfish consumption, particularly mussels, is a major risk factor for HAV infection, since these products are eaten raw or slightly cooked. Nested reverse transcriptase-polymerase chain reaction (RT-PCR) has been shown to be a sensitive technique for the detection of HAV in mussels. The aim of the present study was to detect the presence of HAV in a large sample of mussels by nested RT-PCR and to confirm the presence of infectious viral particles in positive samples by cell culture infection and RT-PCR confirmation. Two hundred and ninety samples of mussels from different sources were collected between December 1999 and January 2000. One hundred samples were collected before being subjected to depuration, 90 after depuration, and 100 were sampled in different seafood markets. HAV-RNA was detected in 20 (20.0%) of non-depurated mussels, in 10 (11.1%) of depurated samples, and in 23 (23.0%) of samples collected in the shellfish markets, without any significant difference in the prevalence of positive samples by collection sources (chi2 = 4.79, p = 0.09). Of the 53 samples found positive by nested RT-PCR, 18 (34.0%) resulted positive by cell culture assay. No relationship between viral contamination and bacterial contamination was found (p = 0.41). This study confirms the usefulness of molecular techniques in detecting HAV in shellfish and, thus, for the screening of a large sample of naturally contaminated mussels. Improved shellfish depuration methods are needed to obtain virus-safe shellfish and reduce the risk for public human health.

Development of a virus concentration method and its application to detection of enterovirus and norwalk virus from coastal seawater

We developed a new procedure for concentration of enteric viruses from water using a negatively charged membrane. Rinsing the membrane with 0.5 mM H(2)SO(4) (pH 3.0) in order to elute cations prior to viral elution with 1 mM NaOH (pH 10.5) promoted poliovirus recovery yields from 33 to 95% when applied to pure water and 38 to 89% when applied to natural seawater from Tokyo Bay, Japan, respectively. This method showed average recovery yields of spiked poliovirus of 62% (n = 8) from 1 liter of artificial seawater. This method showed higher recovery yields (>61%) than that of the conventional method using positively charged membrane (6%) when applied to seawater. This method is also free from beef extract elution, which has an inhibitory effect in the subsequent viral genome detection by reverse transcription-PCR. Naturally occurring Norwalk viruses from 2 liters of Tokyo Bay water in winter and infectious enteroviruses from 2 liters of recreational coastal seawater in summer were detected by using this viral concentration method.

Development of a virus concentration method and its application to detection of enterovirus and norwalk virus from coastal seawater

We developed a new procedure for concentration of enteric viruses from water using a negatively charged membrane. Rinsing the membrane with 0.5 mM H(2)SO(4) (pH 3.0) in order to elute cations prior to viral elution with 1 mM NaOH (pH 10.5) promoted poliovirus recovery yields from 33 to 95% when applied to pure water and 38 to 89% when applied to natural seawater from Tokyo Bay, Japan, respectively. This method showed average recovery yields of spiked poliovirus of 62% (n = 8) from 1 liter of artificial seawater. This method showed higher recovery yields (>61%) than that of the conventional method using positively charged membrane (6%) when applied to seawater. This method is also free from beef extract elution, which has an inhibitory effect in the subsequent viral genome detection by reverse transcription-PCR. Naturally occurring Norwalk viruses from 2 liters of Tokyo Bay water in winter and infectious enteroviruses from 2 liters of recreational coastal seawater in summer were detected by using this viral concentration method.

Improved detection of human enteric viruses in foods by RT-PCR

Human enteric viruses (including hepatitis A virus (HAV) and Norwalk-like viruses (NLVs)) are now recognized as common causes of foodborne disease. While methods to detect these agents in clinical specimens have improved significantly over the last 10 years, applications to food samples have progressed more slowly. In an effort to improve the sensitivity and speed of virus detection from non-shellfish food commodities by reverse transcription-polymerase chain reaction (RT-PCR), we (i) evaluated multiple RNA extraction methods; (ii) compared alternative NLV primer sets; and (iii) developed a one-step RT-PCR method. Hamburger and lettuce samples, processed for virus concentration using a previously reported filtration-extraction-precipitation procedure, were inoculated with HAV or NV. Several RNA extraction methods (guanidinium isothiocyanate, microspin column, QIAshredder Homogenizer, and TRIzol) and primer pairs were compared for overall RNA yield (microg/ml), purity (A(260)/A(280)), and RT-PCR limits of detection. The use of TRIzol with the QIAshredder Homogenizer (TRIzol/Shred) yielded the best RT-PCR detection limits (<1 RT-PCR amplifiable units/reaction for NV), and the NVp110/NVp36 primer set was the most efficient for detecting NV from seeded food samples. A one-step RT-PCR protocol using the TRIzol/Shred extraction method and the NVp110/NVp36 or HAV3/HAV5 primer sets demonstrated improved sensitivity (>10-fold) over the routinely used two-step method. HAV RNA was detected by RT-PCR at initial inoculum levels corresponding to <10 and <100 PFU per 300 microl sample concentrate (corresponding to 6 g food sample) for hamburger and lettuce, respectively. NV RNA was detected by RT-PCR at initial inoculum levels <5 and <50 RT-PCR amplifiable units per 300 microl concentrate (corresponding to 6 g food sample) for hamburger and lettuce, respectively. Residual RT-PCR inhibitors were effectively removed as evidenced by the ability to detect viral RNA in food concentrates without prior dilution. The methods reported here show promise for rapid, sensitive detection of human enteric viruses in foods.

Best viral elution method available for quantification of enteroviruses in sludge by both cell culture and reverse transcription-PCR

The aim of this study was to select one or several virus extraction techniques that enable simultaneous detection of enterovirus genomes and infectious particles in different types of urban sludge. Eight techniques were compared by using 16 different liquid and solid sludge samples. The numbers of infectious enteroviruses in cell cultures were determined by using the most-probable-number method. The enterovirus genome was quantified by a single-tube reverse transcription-PCR using TaqMan technology. The results were statistically analyzed by Friedman's test, a nonparametric test for analysis of randomized block data using only ranks in terms of extraction technique efficiency. Two techniques seemed to yield higher viral titers as determined by simultaneous detection by cell culture and PCR. The first involved a 10% beef extract solution at pH 9 and sonication; the second involved a 0.3 M NaCl-7% beef extract solution at pH 7.5 followed by Freon treatment. In solid sludge, no significant differences were observed among the eight techniques tested. Both of the best techniques can be used for simultaneous detection of infectious enterovirus particles and genomes in any type of urban sludge.

ICC/PCR detection of enteroviruses and hepatitis A virus in environmental samples

This study applied the integrated cell culture/polymerase chain reaction methodology (ICC/PCR) for rapid and specific detection of both cytopathogenic and noncytopathogenic viruses. Results of this study showed that the use of direct RT-PCR or conventional cell culture alone may yield erroneous results with the analysis of environmental samples. The purpose of this study was to compare cultural, molecular, and combined assays for the most effective method of virus detection in variable environmental samples. Using ICC/PCR, stock enterovirus inocula of [Formula: see text]10 PFU were PCR positive in at least 4/5 replicate flasks after only 5 h of incubation in cell culture, and in all flasks after [Formula: see text]10 h. An inoculum of one PFU was detected by PCR after 20 h of cell culture incubation while for concentrations of virus below one PFU, 25 h of incubation was sufficient. Similarly, hepatitis A virus (HAV) inocula of 100 MPN/flask, produced indeterminate CPE in cell culture, but were clearly detected by ICC/PCR following 48 h of incubation. Lower levels of HAV, 1 and 10 MPN, were detected by ICC/PCR after 96 to 72 h of incubation, respectively. Cell culture lysates from 11 environmental sample concentrates of sewage, marine water, and surface drinking water sources, were positive for enteroviruses by ICC/PCR compared to 3 positive by direct RT-PCR alone. Results from ICC/PCR eventually agreed with cell culture but required [Formula: see text]48 h of incubation, compared to as long as 3 weeks for CPE following incubation with BGM and FRhK cells.Key words: RT-PCR, cell culture, ICC/PCR, enterovirus, hepatitis A virus.

Human adenoviruses and coliphages in urban runoff-impacted coastal waters of Southern California

A nested-PCR method was used to detect the occurrence of human adenovirus in coastal waters of Southern California. Twenty- to forty-liter water samples were collected from 12 beach locations from Malibu to the border of Mexico between February and March 1999. All sampling sites were located at mouths of major rivers and creeks. Two ultrafiltration concentration methods, tangential flow filtration (TFF) and vortex flow filtration (VFF), were compared using six environmental samples. Human adenoviruses were detected in 4 of the 12 samples tested after nucleic acid extraction of VFF concentrates. The most probable number of adenoviral genomes ranged from 880 to 7,500 per liter of water. Coliphages were detected at all sites, with the concentration varying from 5.3 to 3332 PFU/liter of water. F-specific coliphages were found at 5 of the 12 sites, with the concentration ranging from 5.5 to 300 PFU/liter. The presence of human adenovirus was not significantly correlated with the concentration of coliphage (r = 0.32) but was significantly correlated (r = 0.99) with F-specific coliphage. The bacterial indicators (total coliforms, fecal coliforms, and enterococci) were found to exceed California recreational water quality daily limits at 5 of the 12 sites. However, this excess of bacterial indicators did not correlate with the presence of human adenoviruses in coastal waters. The results of this study call for both a reevaluation of our current recreational water quality standards to reflect the viral quality of recreational waters and monitoring of recreational waters for human viruses on a regular basis.

Detection of enterovirus and hepatitis A virus RNA in mussels (Mytilus spp.) by reverse transcriptase-polymerase chain reaction

AIMS

A simple and effective method of concentrating and purifying enteric viruses from mussel samples to be detected by nucleic acid extraction reverse transcriptase-polymerase chain reaction (RT-PCR) has been evaluated.

METHODS AND RESULTS

Seeded mussels were processed by alkaline elution, polyethylene glycol (PEG) precipitation, solvent extraction and PEG precipitation. Final concentrates were assayed by infectivity and RT-PCR after nucleic acid extraction. Two RNA extraction methods were comparatively evaluated for removing inhibitory substances: guanidinium thiocyanate extraction and Purescripttrade mark RNA isolation. Both procedures removed most inhibitors allowing the detection of viral RNA at inoculum levels as low as 4 pfu g(-1) for poliovirus type 1 and 1.8-18 most probable number of cytopathogenic units g(-1) for HAV. When inhibitors remained, they were efficiently removed by Sephadex column chromatography before RNA extraction.

CONCLUSION

The described method is effective for the detection of enteric viruses in mussels by RT-PCR. The use of Purescripttrade mark RNA isolation makes the method faster, safer and very easy to perform.

Concentration and detection of caliciviruses in water samples by reverse transcription-PCR

Human caliciviruses (HuCVs) cause waterborne outbreaks of gastroenteritis. Standard indicators of a safe water supply do not adequately predict contamination of water by viruses, including HuCVs. We developed a method to concentrate and detect HuCVs in water samples by using a cultivable primate calicivirus (Pan-1) as a model. Viable Pan-1 was seeded in different types of water and then filtered with a 1MDS filter, eluted with beef extract (BE), and reconcentrated by polyethylene glycol (PEG) precipitation. The viruses in the final samples were tested by plaque assay or by reverse transcription (RT)-PCR following extraction of the RNA with Trizol. Pan-1 was more sensitive to high-pH treatment than poliovirus was; a pH 9.0 BE solution was found to recover 35% more viable Pan-1 than a pH 9.5 BE solution recovered. Pan-1 was recovered from small volumes of deionized, finished, ground, and surface waters at efficiencies of 94, 73, 67, and 64%, respectively, when samples were assayed after elution without further concentration. When larger volumes of water (up to 40 liters) were tested after elution and concentration with PEG, 38, 19, and 14% of the seeded Pan-1 were recovered from finished, ground, and surface waters, respectively. The limit of detection of Pan-1 by RT-PCR was estimated to be 0.75 to 1.5 PFU in 40 liters of finished water. This method may be adapted for monitoring HuCVs in drinking water and other types of water for public health safety.

Three-year study to assess human enteric viruses in shellfish

The main pathogenic enteric viruses able to persist in the environment, such as hepatitis A virus (HAV), Norwalk-like virus (NLV), enterovirus (EV), rotavirus (RV), and astrovirus (AV), were detected by reverse transcription-PCR and hybridization in shellfish during a 3-year study. Oyster samples (n = 108), occasionally containing bacteria, were less frequently contaminated, showing positivity for AV (17%), NLV (23%), EV (19%), and RV (27%), whereas mussel samples, collected in areas routinely impacted by human sewage, were more highly contaminated: AV (50%), HAV (13%), NLV (35%), EV (45%), and RV (52%). Sequences obtained from HAV and NLV amplicons showed a great variety of strains, especially for NLV (strains close to Mexico, Snow Mountain Agent, or Norwalk virus). Viral contamination was mainly observed during winter months, although there were some seasonal differences among the viruses. This first study of virus detection over a fairly long period of time suggests that routine analysis of shellfish by a molecular technique is feasible.

Viruses and bivalve shellfish

The epidemiological data clearly demonstrates that filter feeding bivalve shellfish can, and do, act as efficient vehicles for the transmission of enteric viruses transmitted by the faecal-oral route. This identified hazard has been documented as a cause for concern by various international agencies and has a long history. Disease outbreaks can occur on an epidemic scale as graphically illustrated by an outbreak of Hepatitis A in Shanghai, China in 1988 involving about 300,000 cases. Improvement of harvesting area water quality offers the most sustainable route to improvement in the virological quality of bivalve shellfish sold live. However there is growing awareness, and concern, that current regulatory standards based on faecal coliform monitoring do not fully protect the shellfish consumer from viral infection. New viral test methods based on PCR, and the development of alternative more reliable faecal pollution indicators, offer new approaches for the further development of public health controls. However, further work is required to build a scientific consensus and to understand the implications of their introduction into legislation.

Detection of astroviruses, enteroviruses, and adenovirus types 40 and 41 in surface waters collected and evaluated by the information collection rule and an integrated cell culture-nested PCR procedure

We evaluated the use of an integrated cell culture-reverse transcription-PCR (ICC-RT-PCR) procedure coupled with nested PCR to detect human astroviruses, enteroviruses, and adenovirus types 40 and 41 in surface water samples that were collected and evaluated by using the Information Collection Rule (ICR) method. The results obtained with the ICC-RT-PCR-nested PCR method were compared to the results obtained with the total culturable virus assay-most-probable-number (TCVA-MPN) method, the method recommended by the U.S. Environmental Protection Agency for monitoring viruses in surface and finished waters. Twenty-nine ICR surface water samples were analyzed. Viruses were concentrated by using filter adsorption-beef extract elution and organic flocculation techniques, and then the preparations were evaluated for viruses by visualizing cytopathic effects in the Buffalo green monkey kidney (BGMK) cell line. In the ICC-RT-PCR-nested PCR technique we used Caco-2 cells to propagate astroviruses and enteroviruses (ICC step), and we used BGMK cells to propagate adenovirus types 40 and 41, as well as enteroviruses. Fifteen of the 29 samples (51.7%) were positive for astrovirus as determined by the ICC-RT-PCR-nested PCR method, and eight of these samples (27.5%) contained infectious astrovirus. Seventeen of the 29 samples (58.6%) were positive for enteroviruses when the BGMK cell line was used, and six (27.6%) of these samples were determined to be infectious. Fourteen of the 29 samples (48.3%) were positive for adenovirus types 40 and 41, and 11 (37.9%) of these samples were determined to be infectious. Twenty-seven of the 29 samples (93.1%) were positive for a virus, and 19 (68.9%) of the samples were positive for an infectious virus. Only 5 of the 29 samples (17.2%) were positive as determined by the TCVA-MPN method. The ICC-RT-PCR-nested PCR method provided increased sensitivity compared to the TCVA-MPN method.

Detection of norwalk-like virus in shellfish implicated in illness

In the 1990s, Norwalk-like viruses (NLVs) were identified in patient specimens as the primary pathogen associated with shellfish-borne gastroenteritis in the United States. Identification of these viruses from implicated shellfish has been difficult due to inefficient recovery of viruses, natural polymerase chain reaction (PCR) inhibitors in shellfish, and low virus contamination. Recent improvements to the method of detecting NLVs in shellfish include enhanced processing of virus and shellfish samples, application of nested PCR and nucleotide sequencing, and increased knowledge of NLV genetic diversity. Using a newly developed and sensitive method, an NLV G2 strain was identified in 2 oyster samples implicated in a 1998 California outbreak involving 171 cases. NLV capsid primers demonstrated a greater specificity of PCR detection than did polymerase primers. The 175-base viral capsid nucleotide sequences derived from oysters were 100% identical to those derived from a patient stool sample. This finding supports the epidemiologic associations indicating that contaminated shellfish serve as the vehicle for NLV transmission.

A method to detect low levels of enteric viruses in contaminated oysters

Direct isolation and identification of pathogenic viruses from oysters implicated in gastroenteritis outbreaks are hampered by inefficient methods for recovering viruses, naturally occurring PCR inhibitors, and low levels of virus contamination. In this study we focused on developing rapid and efficient oyster-processing procedures that can be used for sensitive PCR detection of viruses in raw oysters. Poliovirus type 3 (PV3) Sabin strain was used to evaluate the efficacy of virus recovery and the removal of PCR inhibitors during oyster-processing procedures. These procedures included elution, polyethylene glycol precipitation, solvent extraction, and RNA extraction. Acid adsorption-elution in which glycine buffer (pH 7.5) was used was found to retain fewer inhibitors than direct elution in which glycine buffer (pH 9.5) was used. RNA extraction in which a silica gel membrane was used was more effective than single-step RNA precipitation for removing additional nonspecific PCR inhibitors. The final 10-microl volume of RNA concentrates obtained from 2 g of oyster tissue (concentration factor, 200-fold) was satisfactory for efficient reverse transcription-PCR detection of virus. The overall detection sensitivity of our method was 1 PFU/g of oyster tissue initially seeded with PV3. The method was utilized to investigate a 1998 gastroenteritis outbreak in California in which contaminated oysters were the suspected disease transmission vehicle. A genogroup II Norwalk-like virus was found in two of three recalled oyster samples linked by tags to the harvest dates and areas associated with the majority of cases. The method described here improves the response to outbreaks and can be used for rapid and sensitive detection of viral agents in outbreak-implicated oysters.

Comparative study of techniques used to recover viruses from residual urban sludge

Eight virus extraction techniques were compared on three types of residual urban sludge for simultaneous detection of infectious enteroviruses, somatic coliphages, F-specific RNA bacteriophages and Bacteroides fragilis bacteriophages. The highest virus counts were found in extracts obtained using three extraction techniques described by respectively using a 10% beef extract solution at pH 9 and sonication, using a 0.3 M NaCl/7% beef extract solution at pH 7.5 and freon, and finally using a 0.1 M borate buffer/3% beef extract solution at pH 9 and sonication.

Recovery and detection of enterovirus, hepatitis A virus and Norwalk virus in hardshell clams (Mercenaria mercenaria) by RT-PCR methods

A method for recovery of enteric viruses from hardshell clams (Mercenaria mercenaria) has been developed and evaluated. Seeded 50-g samples of clam tissue homogenates were processed by adsorption elution precipitation, two fluorocarbon extractions and PEG precipitation. Clam concentrates were assayed by infectivity and by RT-PCR after guanidinium isothiocyanate (GIT) extraction and/or an indirect immunomagnetic capture (IC) of the virus using paramagnetic beads. GIT extraction removed PCR inhibitors and allowed a reliable RT-PCR detection of viral RNA. The detection sensitivity of GIT extraction-RT-PCR was < 1 PFU of poliovirus 1, < 10 PFU of HAV and 1-11 PCRU of Norwalk virus. IC was very effective for additional concentration and purification of enteric viruses from clam concentrates removing most RT-PCR inhibitors. The sensitivity of this method was comparable to the GIT extraction and the sample volume tolerance for PCR was increased about 10-fold. Both methods gave similar efficiency for virus detection in samples seeded with low virus levels. The procedure developed in this study is effective for enteric viruses detection in hardshell clams by RT-PCR.

Reverse transcriptase PCR detection of astrovirus, hepatitis A virus, and poliovirus in experimentally contaminated mussels: comparison of several extraction and concentration methods

Four methods of extraction and three methods of concentration of three enteric viruses from mussels were comparatively evaluated by reverse transcriptase PCR (RT-PCR). Shellfish were experimentally contaminated by immersion in seawater seeded with astrovirus, hepatitis A virus, or poliovirus. Sixty-gram samples of mussel tissues were processed by using borate buffer, glycine solution, saline beef, and saline beef-Freon extraction methods. The viruses were concentrated by precipitation with polyethylene glycol 6000 (PEG 6000) or PEG 8000 or by organic flocculation. RT-PCR was performed with RNA extracts from crude shellfish extracts and concentrates with and without Sephadex LH20 filtration. The glycine solution and borate buffer extraction methods resulted in significantly more RT-PCR-positive samples than the saline beef extraction method. We assessed the efficiency of 20 combinations of extraction and concentration methods. The borate buffer-organic flocculation, borate buffer-PEG 6000, and glycine solution-PEG 6000 combinations gave RT-PCR-positive results for all 27 samples analyzed for the three viruses. Detoxification of the samples by Sephadex LH20 filtration significantly decreased the efficiency of RT-PCR virus detection.

Epidemiology and detection as options for control of viral and parasitic foodborne disease

Human enteric viruses and protozoal parasites are important causes of emerging food and waterborne disease. Epidemiologic investigation and detection of the agents in clinical, food, and water specimens, which are traditionally used to establish the cause of disease outbreaks, are either cumbersome, expensive, and frequently unavailable or unattempted for the important food and waterborne enteric viruses and protozoa. However, the recent introduction of regulatory testing mandates, alternative testing strategies, and increased epidemiologic surveillance for food and waterborne disease should significantly improve the ability to detect and control these agents. We discuss new methods of investigating foodborne viral and parasitic disease and the future of these methods in recognizing, identifying, and controlling disease agents.