Loop-mediated isothermal amplification for influenza A (H5N1) virus.
We describe a 1-step reverse-transcription loop-mediated isothermal i·so·ther·mal
Of, relating to, or indicating equal or constant temperatures.
having the same temperature. amplification assay for detection of highly pathogenic avian influenza A (H5N1) viruses. The assay was tested by using a panel of highly pathogenic H5N1 subtypes isolated over the past 10 years and clinical specimens. The assay produced negative results for all non-H5N1 subtypes.
Highly pathogenic avian influenza A (H5N1) virus has had a significant global effect on the poultry industry, human healthcare, and many other sectors (1). Several molecular tests have been developed for the rapid detection of influenza (H5) virus subtypes (2), but they often require sophisticated equipment (e.g., PCR PCR polymerase chain reaction.
polymerase chain reaction
Polymerase chain reaction (PCR) machine) and are difficult for researchers and clinicians to perform in resource-limited settings. Loop-mediated isothermal amplification (LAMP) provides a molecular testing option for this scenario (3). The LAMP mechanism has been described (3,4). Using this approach, nucleic acids are amplified under isothermal conditions (e.g., in a water bath) with high specificity, efficiency, and speed (3). The assay is highly specific due to recognition of target DNA DNA: see nucleic acid.
or deoxyribonucleic acid
One of two types of nucleic acid (the other is RNA); a complex organic compound found in all living cells and many viruses. It is the chemical substance of genes. by 6 independent sequences. An attractive feature of LAMP is its ability to generate large amounts of white magnesium pyrophosphate pyrophosphate /py·ro·phos·phate/ (-fos´fat) a salt of pyrophosphoric acid.
n. Abbr. PP
A salt or ester of pyrophosphoric acid. precipitate in positive reactions (4). Examples of positive and negative reactions are shown in online Appendix Figure 1 (available from www.cdc.gov/ EID/content/13/6/899-appG1.htm). LAMP enables easy visual identification of positive reactions (4,5) and avoids additional cost and labor for postamplification analysis. This closed-tube method can also minimize the problem of carryover contamination in less controlled environments.
[FIGURE 1 OMITTED]
We aimed to develop a reverse transcription (RT) LAMP assay that could detect a variety of highly pathogenic influenza (H5N1) viruses. For primer design, we used highly pathogenic influenza (H5N1) sequences publicly available from the Influenza Sequence Database (www. flu.lanl.gov/index.html) in August 2006. We used hemagglutinin hemagglutinin /he·mag·glu·ti·nin/ (-gloo´ti-nin) an antibody that causes agglutination of erythrocytes.
cold hemagglutinin one which acts only at temperatures near 4° C. (HA) from an influenza (H5N1) prototype vaccine strain (A/Vietnam/1203/2004, GenBank accession no. AY651334) as the reference for this study. The sequences included highly pathogenic influenza (H5N1) viruses identified in the past 2 years. In addition, sequences from all the other HA subtypes (e.g., 1,127 for H1 and 1,472 for H3) in the above database were used for the analysis. Because highly pathogenic influenza (H5N1) gene sequences are genetically diverse, all studied H5 sequences (n = 711) were aligned, and a highly conserved region at the 5' end of HA2 encoding sequence (corresponding to nt 1,065-1,298 of the reference sequence) was selected as the target (online Appendix Figure 2A, available from www.cdc.gov/EID/ content/13/6/899-appG2.htm, and online Appendix Figure 3, available from www.cdc.gov/EID/content/13/6/899-app G3.htm). Of all the downloaded highly pathogenic influenza (H5N1) sequences, 115 did not contain the target site and were excluded from analysis. The GenBank accession numbers for the highly pathogenic influenza (H5N1) sequences used for the primer design are listed in the online Appendix Table (available from www.cdc.gov/EID/ content/13/6/899-appT.htm).
Previous demonstration that degenerate primers could be used in LAMP assays (6) led us to use the same approach for designing a set of degenerate primers for the targeted region (online Appendix Figure 2B). Our HA sequence analysis also showed that HA sequences from influenza (H5N2) viruses of North American lineage and other viruses with other HA subtypes contain extensive mismatches to the primers used in the LAMP assay (online Appendix Figure 2A, B). In the initial phase of the study, we used the reference strain (A/Vietnam/1203/2004) to determine the sensitivity of the assay. Purified RNA RNA: see nucleic acid.
in full ribonucleic acid
One of the two main types of nucleic acid (the other being DNA), which functions in cellular protein synthesis in all living cells and replaces DNA as the carrier of genetic from a viral supernatant with a known titer was serially diluted and subjected to the LAMP assay. As shown in the Figure, panel A, the detection limit of the assay was found to be 2 x [10.sup.-3] plaque-forming units (pfu) per reaction. The sensitivity of this assay was also compared with that of an optimized RT-PCR RT-PCR
reverse transcriptase-polymerase chain reaction. See PCR1. assay recommended by the World Health Organization (7). As shown in the Figure, panel A, the detection limit of the RT-PCR assay was identical to that from the LAMP assay. We also spiked various amounts of influenza (H5) viruses into non-H5 nasopharyngeal nasopharyngeal
pertaining to the nasal and pharyngeal cavities.
see nasopharyngeal meatus.
see reverse sneeze. aspirate as·pi·rate
To take in or remove by aspiration.
A substance removed by aspiration.
The removal by suction of a fluid from a body cavity using a needle. samples and tested the purified RNA from these clinical specimens by the LAMP and RT-PCR assays. The results from these assays were identical (data not shown). These findings are in accordance with previous findings that the sensitivity of LAMP assays is comparable to that of conventional PCR methods (5,6,8). In addition, all positive reactions were visually examined for the presence of white precipitate at the end of the reaction incubation. As expected, all results correlated exactly with those deduced by the real-time turbidity turbidity /tur·bid·i·ty/ (ter-bid´i-te) cloudiness; disturbance of solids (sediment) in a solution, so that it is not clear.tur´bid
The cloudiness or lack of transparency of a solution. meter (data not shown).
We also tested the feasibility of using this assay to detect influenza (H5) viruses in clinical specimens from a patient with influenza (H5). RNA from 2 different postmortem postmortem /post·mor·tem/ (post-mort´im) performed or occurring after death.
Relating to or occurring during the period after death.
See autopsy. lung tissue samples from a patient infected with influenza A/HK/212/03 was subjected to the LAMP assay. As shown in the Figure, panel B, both RNA samples had positive results for the influenza (H5) viruses.
To evaluate the specificity of the LAMP assay for influenza (H5) viruses, a comparative study including all 16 HA subtypes and a variety of H5N1 strains was performed (Table). All 14 H5N1 strains isolated from different geographic regions during the past 10 years were positive, whereas none of the non-H5 samples were positive (Table). All the reactions were visually examined, and the results corresponded with those generated from the real -time turbidity meter. Influenza A/chicken/Wajo/BBVM/2005, A/duck/Vietnam/568/2005, and A/bar-headed goose/Qinghai/5/2005 are clade clade Cladus, subtype Genetics A branch of biological taxa or species that share features inherited from a common ancestor; a single phylogenetic group or line. See Inheritance, Species. 2 influenza (H5N 1) viruses that have recently emerged from different geographic regions (9), and these 3 viruses are phylogenetically phy·lo·ge·net·ic
1. Of or relating to phylogeny or phylogenetics.
2. Relating to or based on evolutionary development or history: a phylogenetic classification of species. distinct (10,11). Our results demonstrate that this assay is applicable to a wide variety of highly pathogenic influenza (H5N1) viruses. In addition, other virus reassortants with the HA of this lineage are expected to be positive in the assay.
We previously demonstrated that heat-treated blood samples could be directly tested by a LAMP assay specific for DNA of a bloodborne pathogen (5). These modifications could avoid the need for nucleic acid purification, thereby reducing the cost and turnaround time for molecular diagnosis. We tested the feasibility of detecting the H5 sequence from viral cultures without RNA extraction. In a Biosafety Level 3 facility, 50 gL of viral culture of the prototype virus was heat inactivated inactivated
rendered inactive; the activity is destroyed.
treated so that they are no longer able to produce evidence of growth or damaging effect on tissue. (99[degrees]C for 10 min), the heat-treated sample was serially diluted with standard viral culture medium, and 2 [micro]L of serially diluted samples was added to the LAMP assay. As shown in the Figure, panel C, and in online Appendix Figure 1, H5N1 subtype could still be detected by the assay. However, the detection limit (9.6 pfu/reaction) was [approximately equal to] 1,000 x less sensitive than the limit with purified RNA as an input.
The RT-LAMP assay is highly specific, and its sensitivity is comparable to that of an optimized RT-PCR assay for influenza (H5N 1) viruses. The detection limit is equivalent to that of a similar LAMP assay (12), but our assay was extensively tested by using a wide variety of influenza (H5) viruses, including recent clade 2 influenza (H5) viruses (9). LAMP does not require thermocyclers and gel electrophoresis. Reactions can simply be incubated in a water bath or heating block, and the results can be confirmed by direct visual inspection. Because early identification of influenza (H5) is crucial for the containment of the disease, this novel assay can provide an efficient option for the preliminary molecular detection of highly pathogenic influenza (H5) viruses in basic laboratory or clinical settings. Combined with the use of a turbidity meter, which costs much less than a real-time RT-PCR system, RT-LAMP can provide quantitative data for viral load studies. In conclusion, the LAMP assay is a promising tool for the detection of influenza (H5) viruses.
We thank Bonnie W.Y. Wong for her technical assistance.
We acknowledge research funding from Public Health Research Grant A195357 from the US National Institutes of Health, the Research Grant Council of Hong Kong (HKU HKU University of Hong Kong
HKU Hogeschool voor de Kunsten Utrecht (Utrecht School of The Arts, The Netherlands)
HKU Hot Key Users 7530/06M), and the Seed Funding Programme for Basic Research from HKU.
(1.) Perez DR, Sorrell EM, Donis RO. Avian influenza: an omnipresent pandemic threat. Pediatr Infect Dis J. 2005;24:S208-16.
(2.) Brown IH. Advances in molecular diagnostics for avian influenza. Dev Biol (Basel). 2006;124:93-7.
(3.) Notomi T, Okayama H, Masubuchi H, Yonekawa T, Watanabe K, Amino N, et al. Loop-mediated isothermal amplification of DNA. Nucleic Acids Res. 2000;28:e63.
(4.) Mori Y, Nagamine K, Tomita N, Notomi T. Detection of loop-mediated isothermal amplification reaction by turbidity derived from magnesium pyrophosphate formation. Biochem Biophys Res Commun. 2001;289:150-4.
(5.) Poon poon
Any of several trees of the genus Calophyllum, of southern Asia, having light hard wood used for masts and spars.
[Sinhalese p LLM LLM
Latin Legum Magister (Master of Laws)
LLM Master of Laws [Latin Legum Magister]
Noun 1. , Wong BWY BWY British Wheel of Yoga (national governing body for yoga in Britain) , Ma EHT EHT Egg Harbor Township (New Jersey)
EHT Extra High Tension (spectrometry)
EHT Essential Hypertension
EHT Ek Hasina Thi (movie, India)
EHT Electrothermal Hydrazine Thruster , Chan KH, Chow LMC LMC Large Magellanic Cloud (also see SMC)
LMC Library Media Center
LMC Lees-McRae College (Banner Elk, NC)
LMC Lutheran Medical Center
LMC League of Minnesota Cities
LMC Local Medical Committee , Abeyewickreme W, et al. Sensitive and inexpensive molecular test for falciparum malaria fal·cip·a·rum malaria
Malaria caused by Plasmodium falciparum and characterized by severe malarial paroxysms that recur about every 48 hours and often by acute cerebral, renal, or gastrointestinal manifestations. : detecting Plasmodium falciparum DNA directly from heat-treated blood by loop-mediated isothermal amplification. Clin Chem. 2006;52:303-6.
(6.) Poon LLM, Leung CSW CSW Commission on the Status of Women
CSW Christian Solidarity Worldwide
CSW Clinical Social Worker
CSW College of the Southwest (New Mexico)
CSW Cambridge SoundWorks (audio manufacturer) , Chart KH, Lee JHC JHC Jesus H Christ
JHC Journal of Higher Criticism
JHC Jubilee House Community (North Carolina)
JHC Joint Hull Committee
JHC Jacketed Hollow Cavity (type of bullet)
JHC John Henry Company , Yuen KY, Guan guan: see curassow. Y, et al. Detection of human influenza A viruses by loop-mediated isothermal amplification. J Clin Microbiol. 2005;43:427-30.
(7.) World Health Organization. Recommended laboratory tests to identify avian influenza A virus in specimens from humans. 2005 [cited 2006 September 24]. Available from http://www.who.int/csr/disease/avian influenza/guidelines/avian_labtests2.pdf
(8.) Parida M, Posadas Posadas (pōsä`thäs), city (1991 pop. 211,297), capital of Misiones prov., NE Argentina, a port on the upper Paraná River. Its industries include woodworking and metallurgy. G, Inoue S, Hasebe F, Morita K. Real-time reverse transcription loop-mediated isothermal amplification for rapid detection of West Nile virus West Nile virus, microorganism and the infection resulting from it, which typically produces no symptoms or a flulike condition. The virus is a flavivirus and is related to a number of viruses that cause encephalitis. . J Clin Microbiol. 2004;42:257-63.
(9.) Webster RG, Govorkova EA. H5NI influenza--continuing evolution and spread. N Engl J Med. 2006;355:2174-7.
(10.) Chen H, Smith GJD GJD Great Japanese Dog , Li KS, Wang J, Fan XH, Rayner JM, et al. Establishment of multiple sublineages of H5N1 influenza virus in Asia: implications for pandemic control. Proc Natl Acad Sci U S A. 2006; 103:2845-50.
(11.) Smith G J, Naipospos TS, Nguyen TD, de Jong MD, Vijaykrishna D, Usman TB, et al. Evolution and adaptation of H5N1 influenza virus in avian and human hosts in Indonesia and Vietnam. Virology virology, study of viruses and their role in disease. Many viruses, such as animal RNA viruses and viruses that infect bacteria, or bacteriophages, have become useful laboratory tools in genetic studies and in work on the cellular metabolic control of gene expression . 2006;350:258-68.
(12.) Imai M, Ninomiya A, Minekawa H, Notomi T, Ishizaki T, Tashiro M, et al. Development of H5-RT-LAMP (loop-mediated isothermal amplification) system for rapid diagnosis of H5 avian influenza virus infection. Vaccine. 2006;24:6679-82.
Shanthi Jayawardena, * Chung Y. Cheung, * Ian Barr, ([dagger]) Kwok H. Chan, * Honglin Chen, * Yi Guan, * J.S. Malik Peiris, * and Leo L.M. Poon *
* The University of Hong Kong The University of Hong Kong (commonly abbreviated as HKU, pronounced as "Hong Kong U") is the oldest tertiary institution in Hong Kong. Its motto is "Sapientia et Virtus" in Latin, and " , Hong Kong Special Administrative Region A special administrative region may be:
Ms Jayawardena is a PhD student in the Department of Microbiology of The University of Hong Kong. Her research interests mainly relate to the molecular biology of influenza viruses.
Address for correspondence: Leo L.M. Poon, Department of Microbiology, The University of Hong Kong, Queen Mary Hospital There are several Queen Mary Hospitals in the world:
Table. RT-LAMP assay results for highly pathogenic influenza A (H5N1) * Virus subtype Strain Result H1 A/H K/54/98 - H2 A/Singapore/57 - H3 A/HK/1174/99 - H4 A/duck/HK/MPA892/06 - H5N1 A/H K/483/97 + H5N1 A/H K/486/97 + H5N1 A/chicken/HK/61.9/2002 + H5N1 A/goose/HK/739.2/2002 + H5N1 A/HK/213/03 + H5N1 A/H K/212/03 + H5N1 A/Thailand/MK2/04 + H5N1 A/Vietnam/1203/04 + H5N1 A/chicken/Indoneasia/4/2004 + H5N1 A/chicken/Thailand/1/2004 + H5N1 A/chicken/Vietnam/33/2004 + H5N1 A/chicken/Wajo/BBVM/2005 + H5N1 A/duck/Vietnam/568/2005 + H5N1 A/bar-headed goose/Qinghai/5/2005 + H6 A/teal/HKNV312/97 - H7 A/env/HK/MPB127/05 - H8 A/duck/HK/MP4275/2005 - H9 A/duck/HK/G1/97 - H10 A/env/HK/MPB839/05 - H11 A/env/HK/MPB1679/06 - H12 A/red necked stint/WA/5745/1984 - H13 A/gull/Maryland/704/1977 - H14 A/mallard/Gurjev/244/1982 - H15 A/shelduckNVA/1762/1979 - H16 A/gull/Denmark/68110/2002 - * RT-LAMP, reverse transcription loop-mediated isothermal amplification; -, negative; +, positive.