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Single Infections (single + infections)
Selected AbstractsPatterns of Multiple Virus Infections in the Conifer Pathogenic Fungi, Diplodia pinea and Diplodia scrobiculataJOURNAL OF PHYTOPATHOLOGY, Issue 11-12 2008Juanita De Wet Abstract Diplodia pinea and Diplodia scrobiculata are opportunistic pathogens associated with various disease symptoms on conifers that most importantly include die-back and stem cankers. Two viruses with dsRNA genomes, Sphaeropsis sapinea RNA virus 1 and 2 (SsRV1 and SsRV2) are found in D. pinea and an undescribed dsRNA element is known to occur in D. scrobiculata. We have partially characterized the putative RNA-dependent RNA polymerase (RdRp) of the undescribed dsRNA element and designed virus-specific primers from the RdRp regions of all three virus genomes. This made it possible to screen for the presence of the three viruses in a collection of D. pinea and D. scrobiculata isolates using real-time PCR. Triple infections with all three viruses occurred in D. pinea and D. scrobiculata. Co-infections with SsRV1 and SsRV2 were common but found only in D. pinea. Co-infection with SsRV1 and the undescribed dsRNA element was rare and observed only in D. pinea. Single infections with either SsRV1 or SsRV2 were equally common, while the undescribed dsRNA element never occurred alone. SsRV1 occurred alone in both D. pinea and D. scrobiculata while SsRV2 occurred alone only in D. pinea. There were only two instances where the undescribed dsRNA element was observed in D. pinea and it was otherwise found only in D. scrobiculata. This study highlights the complex interactions between the viruses found in the closely related plant pathogenic fungi, D. pinea and D. scrobiculata. It illustrates the importance of not only characterizing viruses infecting fungi but also of determining the interactions between mycoviruses and their fungal hosts. [source] Competitive interactions and persistence of two nematode species that parasitize Drosophila recensECOLOGY LETTERS, Issue 6 2001S.J. Perlman Drosophila recens is parasitized in the wild by two nematodes, Howardula aoronymphium, a host generalist, and Parasitylenchus nearcticus, a host specialist known only from D. recens. In order to understand how these two parasite species coexist, we compared their ability to infect and grow in D. recens, their effects on host fecundity and survival, and whether one parasite species was competitively superior in double infections. The specialist nematode P. nearcticus had greater rates of infection and reproduction than the generalist H. aoronymphium, and completely sterilized females in single and mixed infections. The specialist was competitively superior in mixed infections, as generalist motherworms were significantly smaller than in single infections. These results suggest that P. nearcticus might competitively exclude H. aoronymphium if D. recens were the only host available. It is likely that H. aoronymphium persists in D. recens by transmission from other, more suitable host species. [source] ON THE EVOLUTION OF SEXUAL REPRODUCTION IN HOSTS COEVOLVING WITH MULTIPLE PARASITESEVOLUTION, Issue 6 2010Rafal Mostowy Host,parasite coevolution has been studied extensively in the context of the evolution of sex. Although hosts typically coevolve with several parasites, most studies considered one-host/one-parasite interactions. Here, we study population-genetic models in which hosts interact with two parasites. We find that host/multiple-parasite models differ nontrivially from host/single-parasite models. Selection for sex resulting from interactions with a single parasite is often outweighed by detrimental effects due to the interaction between parasites if coinfection affects the host more severely than expected based on single infections, and/or if double infections are more common than expected based on single infections. The resulting selection against sex is caused by strong linkage-disequilibria of constant sign that arise between host loci interacting with different parasites. In contrast, if coinfection affects hosts less severely than expected and double infections are less common than expected, selection for sex due to interactions with individual parasites can now be reinforced by additional rapid linkage-disequilibrium oscillations with changing sign. Thus, our findings indicate that the presence of an additional parasite can strongly affect the evolution of sex in ways that cannot be predicted from single-parasite models, and that thus host/multiparasite models are an important extension of the Red Queen Hypothesis. [source] MINIMAL SELFING, FEW CLONES, AND NO AMONG-HOST GENETIC STRUCTURE IN A HERMAPHRODITIC PARASITE WITH ASEXUAL LARVAL PROPAGATIONEVOLUTION, Issue 3 2006Charles D. Criscione Abstract Little is known about actual mating systems in natural populations of parasites or about what constitutes the limits of a parasite deme. These parameters are interesting because they affect levels of genetic diversity, opportunities for local adaptation, and other evolutionary processes. We expect that transmission dynamics and the distribution of parasites among hosts should have a large effect on mating systems and demic structure, but currently we have mostly speculation and very few data. For example, infrapopulations (all the parasites in a single host) should behave as demes if parasite offspring are transmitted as a clump from host to host over several generations. However, if offspring are well mixed, then the parasite component population (all the parasites among a host population) would function as the deme. Similarly, low mean intensities or a high proportion of worms in single infections should increase the selfing rate. For species having an asexual amplification stage, transmission between intermediate and definitive (final) hosts will control the variance in clonal reproductive success, which in turn could have a large influence on effective sizes and rates of inbreeding. We examined demic structure, selfing rates, and the variance in clonal reproductive success in natural populations of Plagioporus shawi, a hermaphroditic trematode that parasitizes salmon. Overall levels of genetic diversity were very high. An a posteriori inference of population structure overwhelmingly supports the component population as the deme, rather than individual infrapopulations. Only a single pair of 597 adult individuals was identified as clones. Thus, the variance in clonal reproductive success was almost zero. Despite being hermaphroditic, P. shawi appears to be almost entirely outcrossing. Genetic estimates of selfing (<5%) were in accordance with the proportion of parasites from single infections. Thus, it appears that individual flukes outcross whenever possible and only resort to selfing when alone. Finally, our data support the hypothesis that aquatic transmission and the use of several intermediate hosts promotes high genetic diversity and well-mixed infrapopulations. [source] Cervical carcinoma in Algiers, Algeria: Human papillomavirus and lifestyle risk factorsINTERNATIONAL JOURNAL OF CANCER, Issue 3 2005Doudja Hammouda Abstract We conducted a hospital-based case-control study in Algiers, Algeria. A total of 198 cervical carcinoma (CC) cases (including 15 adeno- and adenosquamous carcinomas) and 202 age-matched control women were included. Human papillomavirus (HPV) DNA in cervical cells was evaluated using a PCR assay. Odds ratios and corresponding confidence intervals were computed by means of unconditional multiple logistic regression models. HPV infection was detected in 97.7% of CC cases and 12.4% of control women (OR = 635). Nineteen different HPV types were found. HPV 16 was the most common type in both CC cases and control women, followed by HPV 18 and 45. Twelve types (HPV 16, 18, 31, 33, 35, 39, 45, 51, 52, 56, 66 and 73) were found as single infections in CC cases. Multiple HPV infections did not show a higher odds ratio for CC than single infections. In addition to HPV infection, husband's extramarital sexual relationships with other women (OR = 4.8) or prostitutes (OR = 3.2), residing in a rural environment for most of one's life (OR = 4.9) and indicators of poor sanitation or poor hygiene were the strongest risk factors for CC. Oral contraceptive use was unrelated to CC risk, while multiparity emerged as a significant risk factor after adjustment for sexual habits. Intrauterine device users showed a lower CC risk than nonusers. The role of major risk factors, except inside toilet, was confirmed in the analysis restricted to HPV-positive women. The distribution of HPV types in CC cases and control women in Algeria is more similar to the one found in Europe than the one in sub-Saharan Africa, where HPV 16 is less prevalent. A vaccine against HPV 16 and 18 may be effective in more than 3/4 of CCs in Algeria. [source] Variation in human papillomavirus type-16 viral load within different histological grades of cervical neoplasiaJOURNAL OF MEDICAL VIROLOGY, Issue 9 2007A.N. Fiander Abstract The objective of this study was to investigate variation in human papillomavirus (HPV) type-16 load within histologically defined grades of cervical intraepithelial neoplasia. Two hundred and thirty-seven liquid based cytology samples were collected from women attending colposcopy clinics, DNA was extracted, and presence of virus determined by PCR-enzyme immunoassay. Quantitative real-time PCR was used to determine viral load for 70 HPV-16 positive single infections. Viral load was expressed as the ratio of copies of the viral L1 gene to copies of the human beta-globin gene. Measurements varied from 0.019 to 4,194 HPV genomes per cell. Our data demonstrate that in cervical neoplasia, HPV load tends to correlate with disease severity, but that the number of viral genomes/cell varies considerably within histological grades. This variation within disease grades currently limits the clinical utility of viral load measurement. [source] Epidemics of Tomato torrado virus, Pepino mosaic virus and Tomato chlorosis virus in tomato crops: do mixed infections contribute to torrado disease epidemiology?ANNALS OF APPLIED BIOLOGY, Issue 3 2010P. Gómez Torrado disease was first observed in protected tomato crops in the Murcia province of Spain in spring 2001, causing serious concern to regional tomato producers. The disease-causing agent was initially identified as a picorna-like bipartite plant RNA virus, now known as Tomato torrado virus (ToTV), but several additional torradoviruses inducing similar disease symptoms have been described more recently. We studied the incidence of torradoviruses between 2005 and 2008 in two parts of Murcia (Spain) where tomato crops are grown commercially. We also analysed the potential association among ToTV, Pepino mosaic virus (PepMV) and Tomato chlorosis virus (ToCV) in samples showing torrado symptoms of varying severity. ToTV was the only torradovirus found in the samples (predominantly as single infections), but double and triple infections comprising ToTV, PepMV and/or ToCV were also detected. There was no evidence of a specific association among the viruses as the frequencies of mixed infections did not deviate from those expected to occur by chance. Statistical analysis of the potential association between torrado symptoms and the type of infection (single or multiple) was inconclusive. To determine whether co-infections with ToTV and PepMV have any marked influence on the torrado disease, we analysed torrado symptom severity and virus accumulation in tomato plants experimentally infected with ToTV-CE, PepMV-Sp13 and PepMV-PS5 in single and mixed infections. The severity of the torrado symptoms was not affected by the presence of PepMV. In single infections, the ToTV titre remained very low, reaching its maximum in the early stages of infection and declining rapidly thereafter, whereas the disease symptoms became more severe over the same timescale. In mixed infections, the accumulation of both ToTV and PepMV was altered with respect to single infections, and the magnitude of this alteration appeared to be virus and strain specific. Therefore, ToTV and PepMV mixed infections may modulate the epidemiology of both viruses in a complex way by altering virus fitness. The impact of our studies on efforts to track and prevent the spread of torrado disease is discussed. [source] Multiple human papilloma virus types in cervical infections: competition or synergy?APMIS, Issue 5 2010NINA MEJLHEDE Mejlhede N, Pedersen BV, Frisch M, Fomsgaard A. Multiple human papilloma virus types in cervical infections: competition or synergy? APMIS 2010; 118: 346,52. Coinfection with multiple human papilloma virus (HPV) types is common in cervical HPV infection. To evaluate if infections with different HPV types occur independently, we examined 3558 women above 15 years of age suspected of cervical HPV infection. Among them, 1842 (52%) women were HPV negative and 1716 (48%) were HPV positive as analysed by a PCR-based commercial microarray assay for mucosal types. Of the HPV-positive samples, 824 (48%) had single infections, while 892 (52%) had multiple infections. Observed numbers of concurrent HPV types differed from expected numbers under the assumption of independence between infections by the various HPV types. Significant positive associations were observed for 16 pairs of HPV types in statistical analysis accounting for mass significance. Significant negative associations were also found, i.e. women with HPV-16 infection had 0.4 times the odds of having HPV-51 compared with women not infected with HPV-16. HPV-16 was the only type with odds ratios <1 for all pairwise combinations. While our findings of statistically significant coexistence do not prove biological dependence among HPV types, they do suggest that infections with some HPV types may depend on the existence of certain other HPV types. Any interaction between coexisting HPV types could either decrease or increase the efficacy of current HPV vaccines that offer mainly type-specific protection, depending on whether the types vaccinated against compete with other HPV types or not. [source] Detection of new respiratory viruses in hospitalized infants with bronchiolitis: a three-year prospective studyACTA PAEDIATRICA, Issue 6 2010C Calvo Abstract Aim:, We have designed a study with the objective of describing the clinical impact of other viruses different from the respiratory syncytial virus (RSV) in hospitalized infants with bronchiolitis. Methods:, A 3 year prospective study was conducted on infants admitted to the Paediatrics Department of the Severo Ochoa Hospital (Spain). We studied the frequency of 16 respiratory viruses. Clinical characteristics of RSV-only infections were compared with other single agent viral infections. Results:, Positive results were confirmed in 275 (86.5%) of the 318 children studied. A single virus was detected in 196 patients and 79 were dual or multiple viral infections. RSV was detected in 61.3% of total bronchiolitis. Rhinovirus (RV) was 17.4% of the identified virus, followed by human bocavirus (HBoV), adenovirus and metapneumovirus (hMPV). Only RV, HBoV and hMPV were significant as single infections. RSV patients were younger than HBoV (p > 0.0001) and hMPV (p = 0.025). Seasonality was clearly different between them. Children with RSV infection needed treatment in the intensive care unit more frequently than others. Conclusions:, In hospitalized infants, RSV was the most frequent agent in bronchiolitis in winter, but other viruses were present in 47% of the patients. RV, HBoV and hMPV had a significant proportion of single infections. Clinical characteristics were similar amongst them, but seasonality was clearly different. [source] | |||||||||||||