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Poult Sci 2008. 87:838-843. doi:10.3382/ps.2007-00195
© 2008 Poultry Science Association
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ENVIRONMENT, WELL-BEING, AND BEHAVIOR

Development of Methods for Detection and Quantification of Avian Influenza and Newcastle Disease Viruses in Compost by Real-Time Reverse Transcription Polymerase Chain Reaction and Virus Isolation

J. Guan*,1, M. Chan*, B. Ma{dagger}, C. Grenier*, D. C. Wilkie*, J. Pasick{ddagger}, B. W. Brooks* and J. L. Spencer*

* Ottawa Laboratory (Fallowfield), Canadian Food Inspection Agency, 3851 Fallowfield Road, Nepean, Ontario, Canada, K2H 8P9; {dagger} Eastern Cereal and Oilseed Research Centre, Agriculture and Agri-Food Canada, Ottawa, Ontario, Canada, K1A 0C6; and {ddagger} National Centre for Foreign Animal Disease, Canadian Food Inspection Agency, 1015 Arlington Street, Winnipeg, Manitoba, Canada, R3E 3M4

1 Corresponding author: guanj{at}inspection.gc.ca


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 REFERENCES
 
Composting has been used for disposal of poultry carcasses and manure following outbreaks caused by avian influenza virus (AIV) and Newcastle disease virus (NDV), but methods are needed to test for survival of the viruses in compost to ensure biosecurity. Methods developed in the present study include extracting viruses from compost and purifying viral RNA. The extracted viruses were detected by virus isolation using embryonated chicken eggs, and the purified RNA was detected by real-time reverse transcription PCR (RRT-PCR). The virus isolation and the RRT-PCR methods were evaluated with 3 compost preparations that were produced from chicken manure mixed with corn silage, wood shavings, or wheat straw. The detection limits of both methods were 1,700 and 1,000 embryo lethal doses of AIV and NDV per gram of compost, respectively. The copy number of viral RNA quantified by RRT-PCR was highly correlated with the amount of virus in compost. The results suggested that the RRT-PCR method may be used as an alternative to the virus isolation method for rapid detection and accurate quantification of AIV and NDV in compost.

Key Words: detection • quantification • avian influenza virus • Newcastle disease virus • compost


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 REFERENCES
 
Avian influenza virus (AIV) belongs to the Influenzavirus A genus of the Orthomyxoviridae family; and Newcastle disease virus (NDV), formerly classified as serotype 1 avian paramyxovirus, belongs to the Avulavirus genus of the Paramyxoviridae family. Avian influenza virus and Newcastle disease virus can infect over 90 and 250 species of birds, respectively (Alexander, 2003; Swayne and Halvorson, 2003). Outbreaks caused by these disease viruses have resulted in severe losses to the poultry industry. Both AIV and NDV are able to survive for long periods in the environment, such as in feces and in water at temperatures lower than 20°C (Stallknecht et al., 1990; Lu et al., 2003; Kinde et al., 2004). Spread of disease could occur through feces carried by personnel and equipment (Henzler et al., 2003). To control disease spread, on-site composting was used in several AIV and NDV outbreaks in North America for safe disposal of the aftermath carcasses, feces, and other wastes (Kinde et al., 2004; Spencer, 2005; Wilkinson, 2007). Although previous studies demonstrated that AIV and NDV were inactivated in poultry carcasses and manure after composting for 10 to 12 d (Senne et al., 1994; Kinde et al., 2004), methods for sensitive detection of the viruses in compost are needed to ensure biosecurity.

Methods used to detect and quantify AIV and NDV in specimens from poultry and their feces include virus isolation in embryonated chicken eggs (ECE; Alexander, 1989; Beard, 1989), and molecular methods that are based on real-time reverse transcription PCR (RRT-PCR; Tan et al., 2004; Wise et al., 2004). However, the complex composition of compost presents challenges for detection and quantification of the viruses. Compost contains a broad range of microorganisms (Tiquia, 2005) along with numerous organic and inorganic compounds such as humic acids and polyphenols that may kill ECE and inhibit PCR (Lewis et al., 2000). Thus, sensitive detection of AIV and NDV in compost requires effective extraction of the viruses and removal of inhibitory substances. Monpoeho et al. (2001) evaluated methods that were mainly for extraction of nonenveloped viruses from environmental samples, including elution of viruses and reduction of microbial contaminants. However, these methods required the use of organic solvents or extremes in pH that would be harmful to enveloped viruses, such as AIV and NDV (Alexander, 2003; Swayne and Halvorson, 2003). The objectives of the present study were to develop methods for the detection and quantification of AIV and NDV in compost by RRT-PCR and virus isolation using ECE.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS AND DISCUSSION
 REFERENCES
 
Preparation of AIV and NDV Stocks
An AIV A/Tky/Mass/3740/65 (H6N2) strain and an NDV Clonevac-30R vaccine strain (Intervet Canada Ltd., Whitby, Ontario, Canada) were propagated in 9-d-old ECE as described by Alexander (1989) and Beard (1989). In brief, 200 µL of each virus suspension was inoculated into the allantoic sac of each ECE. The eggs were incubated at 37°C and 62% relative humidity. Allantoic fluids were collected and pooled 3 to 4 d postinoculation. The virus titer was determined by inoculating serial dilutions of the pooled fluids into ECE and determining the 50% embryo lethal dose (ELD50, Alexander, 1989; Beard, 1989). The fluids were stored at –80°C for later studies.

Composting Procedures
Composting was done in level 2 isolation facilities. Chicken manure used for the studies was collected from specific pathogen-free chickens maintained in cage layer facilities of the Canadian Food Inspection Agency. Chicken manure was mixed with corn silage (compost #1), wood shavings (compost #2), or wheat straw (compost #3). Carbon to nitrogen (C/N) ratios of these materials and their mixtures were determined as described by Lawson and Keeling (1999) and are shown in Table 1Go. Water was added to adjust the moisture content of the mixtures to approximately 65%, as measured with an IR-35 Moisture analyzer (Denver Instrument, Denver, CO). Approximately 0.3 m3 of each mixture was added to each of 3 compost bins, which were plastic barrels with a built-in center aeration pipe (D&P Industries Inc., Redmond, OR). For insulation, each of the bins was covered with a 30-cm-thick layer of wood shavings. Temperatures at 20, 50, and 80 cm from the bottom of the bins were recorded using type K thermocouples as described by Guan et al. (2004). Compost specimens were collected after 21 d of composting from the bottom of the bins where temperatures had risen above 50°C. The specimens were immediately stored at –80°C for later use.


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  		Table 1. Moisture content and carbon to nitrogen ratio (C/N) of compost materials and mixtures
 
Extraction of Viruses from Compost
Four extraction buffers were compared for their efficiency in eluting NDV from specimens of compost #1. The specimens collected after 21 d of composting were divided into 20-g portions. Each portion was inoculated with 100 µL of serially diluted allantoic fluid that contained 2.1 x 1010 ELD50 of NDV. To simulate natural contamination, the inoculated compost specimens were incubated at 23°C for 30 min to allow virus adsorption. The specimens were then suspended with 100 mL of one of the following extraction buffers (pH 8.0): 3% or 10% beef extract (BE, Becton, Dickinson and Co., Oakville, Ontario, Canada), brain heart infusion broth (Becton, Dickinson and Co.), or 10% tryptose phosphate broth (Becton, Dickinson and Co.) plus 0.05 M glycine (Sigma, St. Louis, MO). The suspension was agitated at 400 rpm for 30 min at 4°C to release the virus from compost, and then strained using a stainless-steel mesh with a pore size of 2 mm2. The filtrate was centrifuged at 5,000 x g for 60 min at 4°C for separation of compost debris. The supernatant was collected and 75 mL was mixed with an equal volume of 16% polyethylene glycol 6,000 (pH 7.2, Sigma) in 0.01 M PBS (pH 7.2). The mixture was incubated at 4°C overnight, followed by centrifugation at 10,000 x g for 90 min at 4°C to precipitate the viruses. The supernatant was discarded, and the pellet was suspended in 12 mL of PBS and treated with an antibiotic cocktail of streptomycin, vancomycin, nystatin, and gentamycin (SVNG) as described below.

Reduction of Microbial Contaminants
Four treatments were compared for reduction of contaminants present in the extracts of compost #1 specimens that were inoculated with NDV and prepared using 10% BE. The treatments were: 1) 2.7 mL of extract was incubated with 0.3 mL of the SVNG cocktail (1,000 µg/mL of streptomycin, 20 units/mL of vancomycin, 500 units/ mL of nystatin, and 500 units/mL of gentamycin in final concentrations) for 1 h at 23°C, followed by centrifugation at 2,000 x g for 20 min at 4°C; 2) 2.7 mL of extract was incubated with 0.3 mL of an antibiotic cocktail designated G-PSNPK (29.2 mg/mL of glutamine, 10,000 units/mL of penicillin, 10 mg/mL of spectinomycin, 5,000 units/ mL of nystatin, 1,500 unit/mL of polymixin B, 10 mg/ mL of kanamycin in final concentrations) for 1 h at 23°C, followed by centrifugation at 2,000 x g for 20 min at 4°C; 3) 3.0 mL of extract was mixed with 1.0 mL of chloroform by vortexing at maximal speed for 30 s, followed by centrifugation at 5,000 x g for 10 min at 4°C; 4) 3.0 mL of extract was passed through a durapore membrane filter with a pore size of 0.22 µm (Millipore, Nepean, Ontario, Canada). Supernatants or filtrates that resulted from the treatments were collected. All antibiotics and chemicals used in the above treatments were purchased from Sigma.

Isolation and Identification of Virus in ECE
Five 9-d-old ECE were each inoculated with 200 µL of the above supernatants or filtrates. The inoculated ECE were incubated at 37°C and 62% relative humidity for up to 7 d. Within 24 h of embryo death, allantoic fluid was collected and tested for AIV or NDV using hemagglutination and hemagglutinin inhibition assays as described by Alexander (1989) and Beard (1989). Reference antisera against A/turkey/Mass/1965 (H6N2) and A/chicken/ Penn/1370–1/1983 (H5N2) were used for identification of the AIV strain, and reference antisera against APMV-1 GB Texas, APMV-2 Yucaipa, APMV-3 Ty6661/67 were used for identification of the NDV strain.

RNA Extraction and Purification
Three commercial kits were compared for extraction and purification of NDV RNA from the extracts of compost #1 specimens that were prepared using 10% BE and with or without SVNG treatment. Viral RNA was extracted and purified from 200 µL of the treated or untreated compost extracts using one of the following kits: RNeasy Mini kit (Qiagen, Mississauga, Ontario), Mag-MAX viral RNA isolation kit (Ambion Inc., Austin, TX), or RiboPure kit (Ambion). The quantity of extracted RNA was determined using an ND-1000 spectrophotometer (NanoDrop Technologies, Wilmington, DE). Operations were carried out according to the manufacturer’s instructions.

Primers and Probes
Primers and probes used for detection of AIV and NDV were developed by Spackman et al. (2002) and Wise et al. (2004), respectively: M+25 5'AGATGAGTCTTC-TAACCGAGGTCG, M-124 5'TGCAAAAACATCTT-CAAGTCTCTG, and M+64 5'FAM-TCAGGCCCCCT-CAAAGCCGA-TAMRA for AIV; M+4100 5'AGTGATG-TGCTCGGACCTTC, M-4220 5'CCTGAGGAGAGGCAT TTGCTA, and M+4169 5'FAM-TTCTCTAGCAGTGGGA CAGCCTGC-TAMRA for NDV.

Construction of RNA Standards
For absolute quantification, RNA standards representing the matrix protein gene regions of AIV and NDV were generated by in vitro transcription. In brief, DNA fragments were amplified by reverse transcription PCR using primer pairs: M+4 5'AAAAGCAGGTAGATGTT-GAA and T7-M-986 5'TAATACGACTCACTATAGGGT-TCCAGCTCTATGTTGACA for AIV; M+3718 5'TGTGG CAAACAAATACTCAT and T7-M-4730 5'TAATAC-GACTCACTATAGGGATTCGGGAGGAGCTTAAC for NDV. The resultant PCR products were purified using a PCR clean-up kit (Fisher Scientific, Ottawa, Ontario, Canada), and the purified products were used as templates for in vitro transcription with a MEGAscript T7 kit (Ambion). The transcribed RNA standards were quantified spectrophotometrically following enzymatic removal of the DNA templates.

Real-Time Reverse Transcription PCR
The PCR reaction mixture had a final volume of 25 µL and contained 12.5 µL of 2 x QuantiTect probe reverse transcription PCR master mix (Qiagen); 12.5 and 10 pmol of each primer for AIV and NDV, respectively; 7.5 and 6 pmol of the probe for AIV and NDV, respectively; 13 units of RNase inhibitor (Ambion); and 5 µL of RNA extract or RNA standard. The PCR was performed with a 7500 real-time PCR system (Applied Biosystems, Foster City, CA). The reverse transcription was 30 min at 50°C for AIV and NDV. Following a 15-min activation of DNA polymerase at 95°C, cycling protocols for AIV were 45 cycles at 94°C for 5 s and at 60°C for 33 s; and for NDV were 40 cycles at 94°C for 10 s, at 52°C for 33 s, and at 72°C for 10 s.

Evaluation of Virus Isolation and RRT-PCR Methods
Each specimen of compost #1, #2, and #3 was inoculated with 100 µL of serially diluted allantoic fluid that contained 2.1 x 1010 ELD50 of NDV or 3.4 x 109 ELD50 of AIV. Virus was extracted from the inoculated specimens using 10% BE, and compost extracts were treated with SVNG before inoculation into ECE as described above. Viral RNA was extracted from the untreated compost extracts using the RiboPure kit and was detected by RRT-PCR as described above. The experiment was repeated twice.

Statistical Analysis
Chi-square tests of homogeneity were performed using Microsoft Excel software to assess the influence that various extraction buffers, antimicrobial treatments, and RNA extraction kits had on detection of NDV in compost #1 specimens (Daniel, 1999). Data were considered to be statistically significant when P < 0.05.


   RESULTS AND DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
REFERENCES
 
Extraction of Viruses from Compost
Four extraction buffers were compared for their efficiency in eluting NDV from specimens of compost #1, and of these, extraction with 10% beef extract was 10-fold more sensitive than with any of the other 3 buffers (Table 2Go). This was based on isolation of virus in ECE, which were incubated for 7 d to allow viral replication in allantoic cavities. Compared with other buffers tested, 10% beef extract provided higher concentrations of soluble organic matter that could compete with viruses for adsorption sites on compost particles and facilitate elution of viruses (Metcalf et al., 1995). Because NDV and AIV are enveloped viruses and are not stable at low pH (Lu et al., 2003; Kinde et al., 2004), both viruses were eluted from compost using 10% BE at pH 8.0 instead of using organic flocculation, which requires low pH for extraction of nonenveloped viruses from wastewaters, sludge, and other environmental samples (Monpoeho et al., 2001).


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  		Table 2. Comparison of extraction buffers for detection of Newcastle disease virus (NDV) in compost1
 
Reduction of Microbes from Compost
Following elution, the viruses were further concentrated by PEG precipitation, which has been used for recovery of human, animal, and plant viruses (Lewis and Metcalf, 1988). To reduce the contaminating organisms that were co-extracted with the viruses, the compost extracts were treated with antibiotic cocktails (SVNG or G-PSNPK). The isolation limit was at least 10-fold more sensitive with these antibiotic treatments than with the filtration or chloroform treatment (Table 3Go) because the filter membrane adsorbs large amounts of the viruses (Scott et al., 2002) and chloroform destroys the lipid envelop of the viruses (Alexander, 2003; Swayne and Halvorson, 2003). Humic acids derived from compost did not cause apparent damage to chicken embryos (data not presented), which was consistent with the finding that humic acids did not affect assays in cell cultures (Lewis et al., 2000).


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  		Table 3. Comparison of various treatments for detection of Newcastle disease virus (NDV) in compost suspensions1
 
Detection of Viruses in Compost Using RRT-PCR
Because compost contains large amounts of inhibitory substances of PCR (Lewis et al., 2000), extraction of viruses was required before using commercial kits to extract and purify viral RNA. Treatments for reduction of microbial contaminants in compost extracts compromised the RRT-PCR detection (data not presented). Thus, untreated extracts were used for RNA extraction and purification. When the RiboPure kit (Ambion) was used, the detection limit was 1,000 ELD50 of NDV per gram of compost #1 (Table 4Go), which was equivalent to 1.8 copies of NDV RNA per PCR reaction after consideration of dilution factors. Compared with the other RNA purification kits, the RiboPure kit was selected for its reliability in supporting sensitive detection of viral RNA in compost. Amplification efficiency of RNA derived from compost was similar to that of the RNA standards, and the similarity of their amplification curves is shown in Figure 1Go. This indicated that viral RNA was effectively extracted and purified from compost. Linear relationships were established between the quantities of viral RNA based on RRT-PCR and the amount of virus that was inoculated into compost (Figure 2A and 2BGo). The linearity ranges were from 3.0 to 7.0 log ELD50/g for NDV and from 3.2 to 7.2 log ELD50/g for AIV. The correlation coefficient (R2) for both viruses was 0.99 (Figure 2A and 2BGo), which means that the quantity of viral RNA was highly correlated with the amount of virus in compost. These findings indicated the feasibility of using RRT-PCR for accurate quantification of the viruses in compost.


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  		Table 4. Evaluation of commercial purification kits for detection of Newcastle disease virus (NDV) RNA in compost1
 

Figure 1
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  		Figure 1. The amplification plot of real-time reverse transcription PCR using templates: serially diluted Newcastle disease virus (NDV) RNA standard (solid lines) and NDV RNA obtained from compost #1 specimens that were inoculated with NDV virus (dash lines).

 

Figure 2
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  		Figure 2. Linear relationships between the quantities of viral RNA based on real-time reverse transcription PCR and the amounts of the virus [A, avian influenza virus (AIV); B, Newcastle disease virus (NDV)] that were inoculated into compost #1 specimens. Each value is the mean of 3 determinations and error bars represent 1 standard deviation.

 
Evaluation of Virus Isolation and RRT-PCR Methods
A combination of 10% beef extract and SVNG treatment was selected for isolation of AIV and NDV using ECE and was evaluated for detection of the viruses with specimens from the 3 compost preparations. The resultant compost extracts, before SVNG treatment, were used for evaluation of the RRT-PCR method. As low as 100 ELD50 of NDV per gram of compost #1 was detected, and this was equivalent to 1.25 ELD50 of NDV in each ECE after calculating the dilution factors. In compost #2 and #3, at least 1,000 ELD50 of NDV per gram of compost was required for reliable detection (Table 5Go). When specimens were inoculated with AIV, the detection limit was 1,700 ELD50 per gram for all 3 compost preparations (Table 5Go). Similar detection limits were obtained using the RRT-PCR method and they were 1,000 ELD50 of NDV and 1,700 ELD50 of AIV per gram for all 3 compost preparations (Table 5Go). These were equivalent to 1,670 copies of AIV RNA and 1,060 copies of NDV RNA per gram of compost based on the quantification by RRT-PCR. Isolation of viruses that were extracted from compost required up to 7 d of incubation of ECE. In comparison, viral RNA that was extracted and purified from compost could be detected by RRT-PCR within 4 h. Thus, RRT-PCR might be a feasible alternative to traditional virus titration methods for rapid detection and accurate quantification of AIV and NDV in compost.


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  		Table 5. Evaluation of methods for detection of Newcastle disease virus (NDV) and avian influenza virus (AIV) in 3 compost preparations by virus isolation and real-time reverse transcription PCR (RRT-PCR)1
 


   ACKNOWLEDGMENTS
 
This study is part of the CRTI04–0052RD project entitled "On site composting for bio-containment and safe disposal of infectious animal carcasses and manure in the event of a bio-terrorism attack", which is funded by the Canadian Chemical, Biological, Radiological, and Nuclear Research and Technology Initiative. Sincere appreciation is expressed to E. G. Brown at the University of Ottawa, Ottawa, Ontario, Canada, for providing the AIV strain.

Received for publication May 15, 2007. Accepted for publication January 16, 2008.


   REFERENCES
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 REFERENCES
 
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Alexander, D. J. 2003. Newcastle disease. Pages 64–87 in Diseases of Poultry. 11th ed. Y. M. Saif, H. J. Barnes, J. R. Glisson, A. M. Fadly, L. R. McDougald, D. E. Swayne, ed. Iowa State Press, Ames, IA.

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