- Research article
- Open Access
Asymmetric competitive suppression between strains of dengue virus
© Pepin et al; licensee BioMed Central Ltd. 2008
- Received: 12 August 2007
- Accepted: 08 February 2008
- Published: 08 February 2008
Within-host competition between strains of a vector-borne pathogen can affect strain frequencies in both the host and vector, thereby affecting viral population dynamics. However little is known about inter-strain competition in one of the most genetically diverse and epidemiologically important mosquito-borne RNA virus: dengue virus (DENV). To assess the strength and symmetry of intra-host competition among different strains of DENV, the effect of mixed infection of two DENV serotypes, DENV2 and DENV4, on the replication of each in cultured mosquito cells was tested. The number of infectious particles produced by each DENV strain in mixed infections was compared to that in single infections to determine whether replication of each strain was decreased in the presence of the other strain (i.e., competition). The two DENV strains were added to cells either simultaneously (coinfection) or with a 1 or 6-hour time lag between first and second serotype (superinfection).
DENV2 and DENV4 showed significantly reduced replication in mixed infection relative to single infection treatments. In superinfection treatments, replication was suppressed to a greater extent when the interval between addition of each strain was longer, and when a strain was added second. Additionally, competitive effects were asymmetric: although both strains replicated to similar peak population sizes in single infections, DENV2 was more suppressed than DENV4 in mixed infections. Superinfection treatments yielded significantly lower combined virus titers than coinfection or single infection treatments.
Competition between DENV strains in cultured mosquito cells can cause a significant decrease in peak viral population sizes, which could translate to decreased transmission by the vector. Effects of competition were asymmetric between DENV2 and DENV4, probably reflecting significant variation in the competitive ability of DENV strains in nature. Competition was strongest in superinfection treatments, suggesting that colonization of new DENV strains could be impeded in areas where numerous mosquitoes are infected with endemic DENV strains.
- Mixed Infection
- Dengue Hemorrhagic Fever
- Single Infection
- Dengue Shock Syndrome
- Total Titer
Infection of a single host by multiple strains of a pathogen may result in competition for host resources . Such intra-host competition is predicted to shape a variety of pathogen traits such as virulence, transmissibility, and resource partitioning, that could affect epidemiology and virus population dynamics [2–9]. However, empirical data demonstrating the action of intra-host competition among pathogens have been scarce, particularly for medically-relevant organisms [10, 11]. Among viruses, the magnitude of competition is sensitive to the order and interval of infection by different strains. For example, when two strains of Cydia pomonella granulomavirus infect a codling moth host at the same time (coinfection) replication of both strains is decreased , yet coinfection of disparate strains of vaccinia virus in cultured monkey cells does not result in decreased replication . However, in the vaccinia system, when one strain infects four hours after the other (superinfection), replication of the second strain is suppressed, and with a ten-hour lag time between infections, the second strain is unable to replicate at all (superinfection exclusion). Similar patterns, albeit over different timescales, have been observed in vivo for Borna disease virus infection of rats , LaCrosse virus infection of mosquitoes , and bluetongue virus infection of midges . Notably, competitive suppression is not an inevitable outcome of mixed-strain infection. Avirulent strains of murine cytomegalovirus and herpes simplex virus may experience enhanced replication and virulence in mixed-genotype relative to single-genotype infections [17, 18]. Thus, while inter-strain interactions appear to significantly impact the population dynamics of viruses, their outcome varies across biological systems. In order to understand and predict the evolutionary epidemiology of medically important viruses that exist as mixed-strain assemblages, it is important to study the interactions within those particular systems.
Dengue viruses (DENV, genus Flavivirus, family Flaviviridae), the mosquito-borne human pathogens that cause dengue fever, have increased in geographic range, prevalence, and disease severity in recent decades. DENV is currently considered the most significant emerging threat to global public health of any vector-borne virus . Genetic variation within this diverse group of RNA viruses has been categorized as follows: antigenically and genetically distinctserotypes (DEN1–4) are each comprised of numerous distinct genotypes, which are in turn subdivided into multiple sub-groups or types . Genome sequence data and phylogenetic analyses suggest that strain replacement, apparently mediated by competitive displacement, is widespread in DENV epidemiology [20–25]. Most prominently, the Southeast Asian genotype (SA) of DENV2 invaded the Americas in the late twentieth century and has subsequently displaced the endemic American (Am) DENV2 genotype across much of the New World [20, 26]. This displacement has had substantial impacts on the epidemiology of DENV because the SA genotype is associated with the most severe manifestations of DENV disease, dengue hemorrhagic fever and dengue shock syndrome, whereas the Am genotype is not [26, 27]. At present, there are no licensed vaccines or antiviral therapies available to control DENV, and vector control has proved ineffective at limiting the global spread of the virus . In order to develop new control strategies and effectively deploy existing ones, it will be necessary to gain a better understanding of the factors that shape the ecology and evolution of this virus.
For within-host competition among pathogen strains to happen, multiple strains must occur in the same geographic location, infect the same host, and target the same cells within that host. DENV meets all three of these criteria. The four DENV serotypes co-circulate across most of the geographic range of the virus [29–32] and co-infection of individual humans and vectors by multiple DENV strains occurs in nature [33–36], and even appears to be common in some outbreaks . In the mosquito vector, all four dengue serotypes use the same putative receptor in the mosquito midgut, the initial site of DENV replication , and initial infection of the mosquito midgut appears to involve only a few individual cells . The same may be true in human hosts, but the initial stages of DENV infection in humans have proven difficult to characterize. One significant difference between vector and human infection is that the former persists for life whereas the latter is transient because it is cleared by the host immune response. This may expand the opportunities for competition in vectors relative to humans.
To date only one study has explicitly considered the role of competition within the vector on the epidemiological dynamics of wild type DENV strains: among Aedes aegypti mosquitoes fed on bloodmeals containing equal quantities of the Am and SA genotype of DENV2, more mosquitoes were infected with the SA genotype . However this study did not include single genotype infections for comparison. Since the Am genotype also has lower infectivity in single infections , it is unclear whether the differences in the coinfection study are due to competition within the vector or whether they are simply inherent differences among the genotypes that act independently in mixed infections. While variation between the Am and SA genotypes in their intrinsic ability to infect mosquitoes does appear to contribute to the competitive displacement of the former , coinfection studies conducted with the appropriate single infection controls are needed to characterize the role of direct competition among DENV strains infecting a single host.
Data from vaccine research provides the only other experimental evidence suggesting that heterologous DENV strains can interfere with each other's replication during coinfection; studies of the replication of live-attenuated tetravalent vaccine formulations (containing all four serotypes) in humans have shown that the replication of individual serotypes appears to be sensitive to the identity and concentration of coinfecting serotypes [42, 43]. Although these data suggest that interference between serotypes can cause decreased replication, it is unclear whether these effects are due to direct competition or whether they are mediated indirectly through the immune system.
To test the hypothesis that competition between dengue virus strains occurs within the mosquito vector, we compared replication of two dengue serotypes (DENV2 and DENV4) in single relative to mixed infections in cultured Aedes albopictus mosquito cells (C6/36), a model for replication in one of the primary DENV vectors. Serotypes infected alone (single infections), or together (mixed infections) by either coinfection, where both serotypes were added simultaneously, or by superinfection, where the second serotype was infected either one or six hours after the first. Viral progeny output was measured at three designated time points. Single infections served as controls for interpreting effects of mixed infections. We predicted that if competition occurs: (l) a given serotype would replicate to higher titers in single infections relative to mixed infections, (2) the serotypes, which have similar replication rates in single infections, would be suppressed similarly in mixed infections, and (3) superinfection would affect the degree of competitive suppression such that the longer the interval between the introduction of two serotypes, the more disproportionate the suppression of the serotype infecting second. While predictions 1 and 3 were borne out by our results, we detected intriguing asymmetries in the response of the two serotypes to competition. Our results highlight that intra-host competition could affect transmission of different DENV serotypes and that the degree of suppression depends on time interval between infection of the two serotypes as well as their identity.
Description of Experimental Design.
Superinfection Interval (hrs)
2 and 4
2 then 2
4 then 4
2 then 4
4 then 2
2 and 4
2 then 2
4 then 4
2 then 4
4 then 2
Results of repeated measures ANOVA.
Single-strain: MOI 5 vs MOI 10
Single-strain MOI 5 vs all mixed-strain (1 level)
Single-strain MOI 5 vs each mixed-strain (5 levels)
P > F
P > F
P > F
Ti × Tr
Ti × Sub(Grp)
Ti × Tr
Ti × Sub(Grp)
To test the prediction that DENV serotypes in mixed infections would replicate to lower titers than DENV serotypes in single infections, titers for each serotype in single infection treatments were compared to those in mixed infection treatments (i.e., with individual mixed treatments pooled as a single effect). DENV2 showed decreased titers in mixed versus single infections, and the magnitude of this effect increased with time (Fig. 1 and Table 2, middle). Interestingly, competition did not appear to affect replication rate during most of the exponential growth phase (compare slopes from 32 to 72 hours in Fig. 1). DENV4, in contrast, showed no significant difference in replication in single versus mixed-strain infections (Fig. 1 and Table 2, middle). However, a separate analysis of the effect of each individual mixed-serotype treatment showed that treatment-type explained a significant amount of variation in DENV4 titers (Fig. 1 and Table 2, right).
Results of ANCOVA.
P > F
TRC × DENV
To examine whether competition between DENV serotypes can occur, we tested whether high dose infections with two serotypes in cultured mosquito cells affected progeny output for either serotype relative to its output in single-serotype infections. Aedes albopictus is one of the major vectors of dengue worldwide , and while cultured cells are not a perfect model for infection in vivo they offer a tractable system for assessing the potential effects of mixed-serotype infections. We found that replication can indeed be suppressed during mixed infections with two serotypes, and that the magnitude of suppression of a given serotypeis stronger for serotypes infecting cells that already have established infections with a different serotype. This is the first study that quantitatively demonstrates competitive suppression between dengue serotypes. Since DENV isolation studies have suggested that mixed-serotype infections in both hosts and vectors occur, and may even be common in some circumstances, our data indicate that further investigation of the interactions between dengue serotypes is important for understanding dengue epidemiology.
Although competition affected final titers, population growth rate during most of the exponential phase was similar between single infection and mixed infection treatments. Thus, competitive suppression occurred late in infection, once virus populations had approached a plateau in concentration. A similar late-acting effect was observed when a wild type strain of foot-and-mouth disease virus (FMDV) was co-infected with engineered strains carrying 1–3 point mutations in either the capsid, a structural protein, or the polymerase, a non-structural protein responsible for replication of the genome . Wild type virus replication was not suppressed within the first 3–5 hours after introduction to cells, but at later sampling time points the wild type had produced significantly fewer infectious progeny relative to single infection controls. Furthermore, in FMDV suppression of wild type virus replication was not always observed, but rather the outcome depended on the particular mutations carried by the competitor. Replication ability of the competitor mutants was characterized in separate treatments (in single infections), which showed that while some mutants were incapable of producing infectious progeny, others were almost as fit as the wild type. Of the three competitors carrying mutations in the polymerase, only the mutant that produced high levels of polymerase and infectious progeny caused suppression of the wild type. Interestingly, some of the competitors carrying capsid mutations produced large quantities of capsid protein early in infection and actually enhanced the production of infectious particles of wild type early in infection. Taken together, the results suggest that competitive success may depend upon a strain's ability to monopolize its own replication machinery and structural proteins and to acquire those of its competitors late in infection. Our finding that DENV serotypes are suppressed later in infection is consistent with the idea that competition is mediated by the intracellular density of virus genome templates and copies of virus proteins, perhaps through competition for polymerase or capsid proteins [45–48]. Under this hypothesis, a virus strain that experienced high levels of coinfection with other strains, such as a new strain invading an area with an endemic virus population, would benefit from a rapid escalation of RNA replication early in infection. Our results support this notion by the finding that the magnitude of suppression depended upon the superinfection interval. Serotypes that infected earlier had an advantage, whereas those that infected later had the most extreme disadvantage.
The two serotypes of DENV used in this study, which showed similar rates of replication in isolation, nonetheless showed significant variation in competitive ability, suggesting that similar variation may occur in nature. A second implication of this asymmetry is that traits conferring competitive ability in mixed infection may be de-coupled from those that enable high replication rates in single infections. For example, a virus strain may replicate rapidly when it has sole access to homologous viral polymerase but poorly in a mixed population of genomes competing for heterologous polymerases. Importantly, these results underscore that the outcome of within-host competition is not predictable from replication rates in single infections. This finding could also be relevant in the design and development of a tetravalent vaccine, which must contain all four serotypes. If one serotype is better able to usurp polymerase in a coinfected cell, then the production of neutralizing antibodies may be unbalanced, resulting in an ineffective vaccine. In this context, however, the total dose of virus is low enough that opportunity for inter-serotype interference within cells may be limited to peripheral cells co-infected at the injection site.
The fact that total titers were significantly lower in superinfections when compared to single infections of the same MOI shows that interspecific competition was stronger than intraspecific competition, further suggesting that competition-related traits are available to selection in this system. Thus, under the hypothesis that competition for viral proteins mediates suppression, we predict that strains isolated from regions where serotypes frequently coinfect mosquitoes should have the strongest ability to utilize and compete for genetically different polymerase or capsid proteins (i.e., generalists). However, with regard to differences in total titers in single versus mixed infections, there is a slight inconsistency; total titers in coinfections were not significantly lower than single infections while those in superinfections were. Theoretically, in the two treatments the frequencies of cells infected with particular numbers of each serotype would have been similar. The difference is that viruses that superinfect could be at a numerical disadvantage since those that infect first have already begun progeny production and thus could outnumber the second serotype once resources become limiting. Our result that superinfection decreases overall virus production significantly more that coinfection, indicates that competition resulted in disproportionately more severe effects on the total population when one of the strains had a headstart in the infection. This is consistent with our suspicion that the mechanism of competition may be density-dependent (i.e., each serotype is suppressed relatively more when the other serotype is more frequent). Experiments to test this prediction are ongoing.
Our results demonstrate that competition between serotypes can affect virus titers in mixed infections in mosquito cells, suggesting that competitive suppression could act to decrease transmission. To better understand the role of inter-serotype competition in emergence of dengue, future research should aim to identify predictor variables of suppression, to examine the effects of mixed-serotype infections on replication throughout both stages of the virus life cycle (vector and host), and to quantify these effects in an epidemiological framework. It would also be useful to examine these effects in live mosquitoes. Recent studies of single strain infections in Aedes aegypti have highlighted that viruses must replicate in, and disseminate to, several different vector tissues before infecting the salivary glands and disseminating to the saliva for transmission [39, 49]. The nature of this pathway and our finding that competitive abilities were uncoupled from performance in single infections highlight that there is potential for interaction effects between serotypes at several stages during vector infection, which could complicate prediction of the effects of mixed serotype infection. Lastly, our results underscore that within-host competition in the mosquito vector may have dramatic effects on both emergence and long-term virus persistence, and these potential effects should be explored in the context of other important factors of dengue virulence such as the host immune system.
Cells and viruses
Aedes albopictus epithelial cells (C6/36) [50, 51] were maintained in minimal essential media (Invitrogen, Grand Island, NY) supplemented with 10% fetal bovine serum, 2 mM L-glutamine (Invitrogen), 2 mM non-essential amino acids (Invitrogen), and 50 μg/ml gentamycin at 32°C (hereafter termed C6/36 media), 5% CO2, and 88% RH. DENV-2-DOO-0372 (DENV2) was originally isolated in Thailand in 1988 from a Type III DHF case and subsequently passaged in C6/36 seven times, with a final titer of 5 × 108 pfu/ml. DENV-4-Thai85-052 (DENV4) was isolated in Thailand (associated disease unknown) and passaged in C6/36 three times, with a final titer of 4 × 108 pfu/ml.
Infections and titering
To test the impact of mixed infection on replication, designated viruses were added to ~80% confluent monolayers of C6/36 cells in 6-well tissue culture-treated plates (BD Falcon™) at a multiplicity of infection (MOI) of 5 (5 plaque forming units, pfu, per cell). Media was first removed from cell monolayers, cells were washed in 2 ml fresh C6/36 media, and 1 ml of C6/36 media containing the appropriate number of virus particles was added. Cells were then incubated at 32°C for 20 minutes, washed with 2 ml of fresh media, and 3 ml of fresh media was added. For the second infection in the superinfection treatments, media was removed and the virus solution suspended in fresh media was added directly to the monolayer, omitting the wash step that was done in the first infection. Cells were again incubated for 20 minutes, then washed in 2 ml of fresh media, and fed 3 ml of fresh media. All treatments were incubated at 32°C, 5% CO2, and 88% humidity; supernatant samples (1 ml) were collected at 32, 72, and 120 hours after the last virus sample was added. This means that in 1-hour superinfection experiments, samples were collected at 33, 73, and 121 hours after the initial infection time, while in 6-hour superinfection experiments, samples were collected at 38, 78, and 126 hours. The 1 ml samples were immediately replaced with fresh media.
Table 1 summarizes the experimental design. DENV serotypes were infected as single infections (DENV2 or DENV4) or mixed infections (DENV2 and DENV4), the latter including: 1) coinfection in which both strains were added simultaneously, and 2) superinfection in which one strain was added after the other. Two superinfection intervals, 1 hour or 6 hours, and both superinfection orders (DENV2 first or DENV4 first) were used. Each treatment was replicated three times for a total of four independent infections. In one of these replicates, treatments were conducted in duplicate or triplicate in order to assess whether within-treatment effects (e.g., measurement noise from the titering protocol) contributed significant variability to between-treatment effects. A repeated-measures nested ANOVA with treatment as the repeated factor and the within- versus between-replicate effect nested within treatment, showed that there was a significant effect of treatment for both DENV2 and DENV4 (F4,96 = 8.5, P < 0.0001; F4,96 = 16.4, P < 0.0001; respectively) but no significant variation from the nested factor (F5,96 = 0.4, P < 0.86; F5,96 = 1.1, P < 0.4; for DENV2 and 4 respectively). Thus, we concluded that measurement noise from our experimental methods was negligible compared to effects from the imposed treatments. In the replicate where treatments were conducted in multiple-fold, we took the means from the multiple data points to represent the titer of each treatment in that replicate.
All titer data were log-transformed and analyzed by repeated measures factorial ANOVA with assay as the repeated main effect, time as a main effect, and assay × time as an interaction term using StatView (version 5.0.1, SAS Institute Inc.). Since single infection controls and coinfection treatments were not significantly different between the two experiments (1 hour versus 6 hour; [Additional file 1]) these data were pooled as follows: 1+8, 2+9, 4+11, 5+12, and 3+10, where numbers correspond to the treatment labels in Table 1. To test whether serotypes replicated to higher titers when infection was initiated with a greater concentration of virus, single infections of each serotype at MOI 5 were compared to single-serotype superinfections, which had a total MOI of 10 (i.e., 1+8 data versus 4+11 data). To test whether mixed-serotype infection explained a significant amount of variation in titers, the titer of each serotype in single infection treatments of MOI 5 were compared to the titer of that serotype in all mixed infection treatments pooled (e.g., for DENV2: 1+8 versus 3+6+7+10+13+14). Finally, to test the impact of each treatment type on the titer of each serotype, single infection treatments of MOI 5 were compared to each mixed infection treatment considered individually (e.g., for DENV2: 1+8 versus 3+10 versus 6 versus 13 versus 7 versus 14).
The impact of the interval of mixed infections were analyzed by ANCOVA using JMP (Version 5.1, SAS Institute Inc.), where the interval of mixed infection refers to the time that elapsed between addition of first and second serotype (see Table 1 for details). In this analysis, the titer at hour 120 was the dependent variable, the interval of mixed infection was the covariate, and DENV serotype was the discrete factor. To test whether the type of infection treatment influenced the total output of infectious virus (i.e., titers for both serotypes in mixed-strain infections), titers for DENV2 and DENV4 in each mixed infection assay were summed and then log-transformed to generate 'total titer' data. Total titers in coinfections (treatments: 3 and 10, Table 1) and superinfections (treatments: 13 and 14) were each compared to total titers in single-strain infections by t-tests using JMP. The single-strain infection category included both strains, but only the treatments where the total amount of virus added was equivalent to a MOI of 10 (treatments: 4, 5, 11 and 12), since the total MOI in the mixed-strain infection categories was also 10.
We thank Jeremy Yoder and Will Soto for helpful comments on the manuscript. Funding was provided by NIH-NM-INBRE (P20 RR016480-05), NIH-K22 (K22-A164193) and NSF-ADVANCE (SBE-123690).
- Read AF, Taylor LH: The ecology of genetically diverse infections. Science. 2001, 292 (5519): 1099-1102. 10.1126/science.1059410.View ArticlePubMedGoogle Scholar
- Bonhoeffer S, Holmes EC, Nowak MA: Causes of HIV diversity. Nature. 1995, 376 (6536): 125-10.1038/376125a0.View ArticlePubMedGoogle Scholar
- Bull JJ: Virulence. Evolution. 1994, 48 (5): 1423-1437. 10.2307/2410237.View ArticleGoogle Scholar
- Day T, Proulx SR: A general theory for the evolutionary dynamics of virulence. Am Nat. 2004, 163 (4): E40-63. 10.1086/382548.View ArticlePubMedGoogle Scholar
- Frank SA: Models of parasite virulence. Q Rev Biol. 1996, 71 (1): 37-78. 10.1086/419267.View ArticlePubMedGoogle Scholar
- May RM, Nowak MA: Coinfection and the evolution of parasite virulence. Proc Biol Sci. 1995, 261 (1361): 209-215. 10.1098/rspb.1995.0138.View ArticlePubMedGoogle Scholar
- Mosquera J, Adler FR: Evolution of virulence: a unified framework for coinfection and superinfection. J Theo Biol. 1998, 195 (3): 293-313. 10.1006/jtbi.1998.0793.View ArticleGoogle Scholar
- Nowak MA, May RM: Superinfection and the evolution of parasite virulence. Proc Biol Sci. 1994, 255 (1342): 81-89. 10.1098/rspb.1994.0012.View ArticlePubMedGoogle Scholar
- van Baalen M, Sabelis MW: The dynamics of multiple infection and the evolution of virulence. Am Nat. 1995, 146 (6): 881-910. 10.1086/285830.View ArticleGoogle Scholar
- de Roode JC, Helinski ME, Anwar MA, Read AF: Dynamics of multiple infection and within-host competition in genetically diverse malaria infections. Am Nat. 2005, 166 (5): 531-542. 10.1086/491659.View ArticlePubMedGoogle Scholar
- de Roode JC, Pansini R, Cheesman SJ, Helinski ME, Huijben S, Wargo AR, Bell AS, Chan BH, Walliker D, Read AF: Virulence and competitive ability in genetically diverse malaria infections. PNAS. 2005, 102 (21): 7624-7628. 10.1073/pnas.0500078102.PubMed CentralView ArticlePubMedGoogle Scholar
- Arends HM, Winstanley D, Jehle JA: Virulence and competitiveness of Cydia pomonella granulovirus mutants: parameters that do not match. J Gen Virol. 2005, 86 (Pt 10): 2731-2738. 10.1099/vir.0.81152-0.View ArticlePubMedGoogle Scholar
- Christen L, Seto J, Niles EG: Superinfection exclusion of vaccinia virus in virus-infected cell cultures. Virology. 1990, 174 (1): 35-42. 10.1016/0042-6822(90)90051-R.View ArticlePubMedGoogle Scholar
- Geib T, Sauder C, Venturelli S, Hassler C, Staeheli P, Schwemmle M: Selective virus resistance conferred by expression of Borna disease virus nucleocapsid components. J Virol. 2003, 77 (7): 4283-4290. 10.1128/JVI.77.7.4283-4290.2003.PubMed CentralView ArticlePubMedGoogle Scholar
- Sundin DR, Beaty BJ: Interference to oral superinfection of Aedes triseriatus infected with La Crosse virus. Am J Trop Med Hyg. 1988, 38 (2): 428-432.PubMedGoogle Scholar
- el Hussein A, Ramig RF, Holbrook FR, Beaty BJ: Asynchronous mixed infection of Culicoides variipennis with bluetongue virus serotypes 10 and 17. J Gen Virol. 1989, 70 (Pt 12): 3355-3362.View ArticlePubMedGoogle Scholar
- Cicin-Sain L, Podlech J, Messerle M, Reddehase MJ, Koszinowski UH: Frequent coinfection of cells explains functional in vivo complementation between cytomegalovirus variants in the multiply infected host. J Virol. 2005, 79 (15): 9492-9502. 10.1128/JVI.79.15.9492-9502.2005.PubMed CentralView ArticlePubMedGoogle Scholar
- Sedarati F, Javier RT, Stevens JG: Pathogenesis of a lethal mixed infection in mice with two nonneuroinvasive herpes simplex virus strains. J Virol. 1988, 62 (8): 3037-3039.PubMed CentralPubMedGoogle Scholar
- Mackenzie JS, Gubler DJ, Petersen LR: Emerging flaviviruses: the spread and resurgence of Japanese encephalitis, West Nile and dengue viruses. Nat Med. 2004, 10 (12 Suppl): S98-109. 10.1038/nm1144.View ArticlePubMedGoogle Scholar
- Rico-Hesse R: Microevolution and virulence of dengue viruses. Adv Virus Res. 2003, 59: 315-341.PubMed CentralView ArticlePubMedGoogle Scholar
- Foster JE, Bennett SN, Carrington CV, Vaughan H, McMillan WO: Phylogeography and molecular evolution of dengue 2 in the Caribbean basin, 1981–2000. Virology. 2004, 324 (1): 48-59. 10.1016/j.virol.2004.03.020.View ArticlePubMedGoogle Scholar
- Messer WB, Gubler DJ, Harris E, Sivananthan K, de Silva AM: Emergence and global spread of a dengue serotype 3, subtype III virus. Emerg Infect Dis. 2003, 9 (7): 800-809.PubMed CentralView ArticlePubMedGoogle Scholar
- Thu HM, Lowry K, Myint TT, Shwe TN, Han AM, Khin KK, Thant KZ, Thein S, Aaskov J: Myanmar dengue outbreak associated with displacement of serotypes 2, 3, and 4 by dengue 1. Emerg Infect Dis. 2004, 10 (4): 593-597.PubMed CentralView ArticlePubMedGoogle Scholar
- Wittke V, Robb TE, Thu HM, Nisalak A, Nimmannitya S, Kalayanrooj S, Vaughn DW, Endy TP, Holmes EC, Aaskov JG: Extinction and rapid emergence of strains of dengue 3 virus during an interepidemic period. Virology. 2002, 301 (1): 148-156. 10.1006/viro.2002.1549.View ArticlePubMedGoogle Scholar
- Zhang C, Mammen MP, Chinnawirotpisan P, Klungthong C, Rodpradit P, Monkongdee P, Nimmannitya S, Kalayanarooj S, Holmes EC: Clade replacements in dengue virus serotypes 1 and 3 are associated with changing serotype prevalence. J Virol. 2005, 79 (24): 15123-15130. 10.1128/JVI.79.24.15123-15130.2005.PubMed CentralView ArticlePubMedGoogle Scholar
- Rico-Hesse R, Harrison LM, Salas RA, Tovar D, Nisalak A, Ramos C, Boshell J, de Mesa MT, Nogueira RM, da Rosa AT: Origins of dengue type 2 viruses associated with increased pathogenicity in the Americas. Virology. 1997, 230 (2): 244-251. 10.1006/viro.1997.8504.View ArticlePubMedGoogle Scholar
- Watts DM, Porter KR, Putvatana P, Vasquez B, Calampa C, Hayes CG, Halstead SB: Failure of secondary infection with American genotype dengue 2 to cause dengue haemorrhagic fever. Lancet. 1999, 354 (9188): 1431-1434. 10.1016/S0140-6736(99)04015-5.View ArticlePubMedGoogle Scholar
- Whitehead SS, Blaney JE, Durbin AP, Murphy BR: Prospects for a dengue virus vaccine. Nat Rev Microbiol. 2007, 5 (7): 518-528. 10.1038/nrmicro1690.View ArticlePubMedGoogle Scholar
- Chareonsook O, Foy HM, Teeraratkul A, Silarug N: Changing epidemiology of dengue hemorrhagic fever in Thailand. Epid Inf. 1999, 122 (1): 161-166. 10.1017/S0950268898001617.View ArticleGoogle Scholar
- Gubler DJ: Perspectives on the prevention and control of dengue hemorrhagic fever. Kaoh J Med Sci. 1994, 10 (Suppl): S15-18.Google Scholar
- Gubler DJ: Dengue and dengue hemorrhagic fever. Clin Microbiol Rev. 1998, 11 (3): 480-496.PubMed CentralPubMedGoogle Scholar
- Nisalak A, Endy TP, Nimmannitya S, Kalayanarooj S, Thisayakorn U, Scott RM, Burke DS, Hoke CH, Innis BL, Vaughn DW: Serotype-specific dengue virus circulation and dengue disease in Bangkok, Thailand from 1973 to 1999. Am J Trop Med Hyg. 2003, 68 (2): 191-202.PubMedGoogle Scholar
- Aaskov J, Buzacott K, Thu HM, Lowry K, Holmes EC: Long-term transmission of defective RNA viruses in humans and Aedes mosquitoes. Science. 2006, 311: 236-238. 10.1126/science.1115030.View ArticlePubMedGoogle Scholar
- Gubler DJ, Kuno G, Sather GE, Waterman SH: A case of natural concurrent human infection with two dengue viruses. Am J Trop Med Hyg. 1985, 34 (1): 170-173.PubMedGoogle Scholar
- Lorono-Pino MA, Cropp CB, Farfan JA, Vorndam AV, Rodriguez-Angulo EM, Rosado-Paredes EP, Flores-Flores LF, Beaty BJ, Gubler DJ: Common occurrence of concurrent infections by multiple dengue virus serotypes. Am J Trop Med Hyg. 1999, 61 (5): 725-730.PubMedGoogle Scholar
- Wang WK, Chao DY, Lin SR, King CC, Chang SC: Concurrent infections by two dengue virus serotypes among dengue patients in Taiwan. J Microbiol Immunol Infect. 2003, 36 (2): 89-95.PubMedGoogle Scholar
- Thavara U, Siriyasatien P, Tawatsin A, Asavadachanukorn P, Anantapreecha S, Wongwanich R, Mulla MS: Double infection of heteroserotypes of dengue viruses in field populations of Aedes aegypti and Aedes albopictus (Diptera: Culicidae) and serological features of dengue viruses found in patients in southern Thailand. Southeast Asian J Trop Med Public Health. 2006, 37 (3): 468-476.PubMedGoogle Scholar
- Mercado-Curiel RF, Esquinca-Aviles HA, Tovar R, Diaz-Badillo A, Camacho-Nuez M, Munoz MdeL: The four serotypes of dengue recognize the same putative receptors in Aedes aegypti midgut and Ae. albopictus cells. BMC Microbiol. 2006, 6: 85-10.1186/1471-2180-6-85.PubMed CentralView ArticlePubMedGoogle Scholar
- Salazar MI, Richardson JH, Sanchez-Vargas I, Olson KE, Beaty BJ: Dengue virus type 2: replication and tropisms in orally infected Aedes aegypti mosquitoes. BMC Microbiol. 2007, 7: 9-10.1186/1471-2180-7-9.PubMed CentralView ArticlePubMedGoogle Scholar
- Cologna R, Armstrong PM, Rico-Hesse R: Selection for virulent dengue viruses occurs in humans and mosquitoes. J Virol. 2005, 79 (2): 853-859. 10.1128/JVI.79.2.853-859.2005.PubMed CentralView ArticlePubMedGoogle Scholar
- Armstrong PM, Rico-Hesse R: Efficiency of dengue serotype 2 virus strains to infect and disseminate in Aedes aegypti. Am J Trop Med Hyg. 2003, 68 (5): 539-544.PubMed CentralPubMedGoogle Scholar
- Guirakhoo F, Pugachev K, Zhang Z, Myers G, Levenbook I, Draper K, Lang J, Ocran S, Mitchell F, Parsons M, Brown N, Brandler S, Fournier C, Barrere B, Rizvi F, Travassos A, Nichols R, Trent D, Monath T: Safety and efficacy of chimeric yellow Fever-dengue virus tetravalent vaccine formulations in nonhuman primates. J Virol. 2004, 78 (9): 4761-4775. 10.1128/JVI.78.9.4761-4775.2004.PubMed CentralView ArticlePubMedGoogle Scholar
- Sabchareon A, Lang J, Chanthavanich P, Yoksan S, Forrat R, Attanath P, Sirivichayakul C, Pengsaa K, Pojjaroen-Anant C, Chokejindachai W, Jagsudee A, Saluzzo JF, Bhamarapravati N: Safety and immunogenicity of tetravalent live-attenuated dengue vaccines in Thai adult volunteers: role of serotype concentration, ratio, and multiple doses. Am J Trop Med Hyg. 2002, 66 (3): 264-272.PubMedGoogle Scholar
- Perales C, Mateo R, Mateu MG, Domingo E: Insights into RNA virus mutant spectrum and lethal mutagenesis events: replicative interference and complementation by multiple point mutants. J Mol Biol. 2007, 369 (4): 985-1000. 10.1016/j.jmb.2007.03.074.View ArticlePubMedGoogle Scholar
- Giachetti C, Holland JJ: Vesicular stomatitis virus and its defective interfering particles exhibit in vitro transcriptional and replicative competition for purified L-NS polymerase molecules. Virology. 1989, 170 (1): 264-267. 10.1016/0042-6822(89)90375-9.View ArticlePubMedGoogle Scholar
- Wu CA, Harper L, Ben-Porat T: Molecular basis for interference of defective interfering particles of pseudorabies virus with replication of standard virus. J Virol. 1986, 59 (2): 308-317.PubMed CentralPubMedGoogle Scholar
- Maloy ML, Whitaker-Dowling P, Youngner JS: Dominance of cold-adapted influenza A virus over wild-type viruses is at the level of RNA synthesis. Virology. 1994, 205 (1): 44-50. 10.1006/viro.1994.1618.View ArticlePubMedGoogle Scholar
- Kim GN, Kang CY: Utilization of homotypic and heterotypic proteins of vesicular stomatitis virus by defective interfering particle genomes for RNA replication and virion assembly: implications for the mechanism of homologous viral interference. J Virol. 2005, 79 (15): 9588-9596. 10.1128/JVI.79.15.9588-9596.2005.PubMed CentralView ArticlePubMedGoogle Scholar
- Linthicum KJ, Platt K, Myint KS, Lerdthusnee K, Innis BL, Vaughn DW: Dengue 3 virus distribution in the mosquito Aedes aegypti: an immunocytochemical study. Med Vet Entomol. 1996, 10 (1): 87-92.View ArticlePubMedGoogle Scholar
- Igarashi A: Isolation of a Singh's Aedes albopictus cell clone sensitive to Dengue and Chikungunya viruses. J Gen Virol. 1978, 40 (3): 531-544.View ArticlePubMedGoogle Scholar
- Singh KRP: Cell cultures derived from larvae of Aedes albopictus (Skuse) and Aedes aegypti (L.). Curr Sci. 1967, 36: 506-508.Google Scholar
- Durbin AP, Karron RA, Sun W, Vaughn DW, Reynolds MJ, Perreault JR, Thumar B, Men R, Lai CJ, Elkins WR, Chanock , Murphy BR, Whitehead SS: Attenuation and immunogenicity in humans of a live dengue virus type-4 vaccine candidate with a 30 nucleotide deletion in its 3'-untranslated region. Am J Trop Med Hyg. 2001, 65 (5): 405-413.PubMedGoogle Scholar
- Troyer JM, Hanley KA, Whitehead SS, Strickman D, Karron RA, Durbin AP, Murphy BR: A live attenuated recombinant dengue-4 virus vaccine candidate with restricted capacity for dissemination in mosquitoes and lack of transmission from vaccinees to mosquitoes. Am J Trop Med Hyg. 2001, 65 (5): 414-419.PubMedGoogle Scholar
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