Antimicrobial resistance is a global health crisis and carbapenem-resistant Klebsiella pneumoniae(CRKp)is listed as one of the top high-priority pathogens by the World Health Organization.Meanwhile,hypervirulent K.pne...Antimicrobial resistance is a global health crisis and carbapenem-resistant Klebsiella pneumoniae(CRKp)is listed as one of the top high-priority pathogens by the World Health Organization.Meanwhile,hypervirulent K.pneumoniae(hvKp)causes severe community-associated infections,such as liver abscesses and meningitis,in otherwise healthy individuals.Both CRKp and hvKp infections are associated with high mortality rates.The convergence of carbapenem resistance and hypervirulence within a single bacterial strain may lead to significantly more severe clinical outcomes.展开更多
This manuscript is based on a recent study by Pillay et al that was published in recently.Liver abscesses can be caused by rare potentially life-threatening infections of either bacterial or parasitic origin.The incid...This manuscript is based on a recent study by Pillay et al that was published in recently.Liver abscesses can be caused by rare potentially life-threatening infections of either bacterial or parasitic origin.The incidence rate in Europe is lower than in developing countries,but it is a major complication with high morbidity,particularly in immunocompromised patients.They are most frequently caused by Enterobacterales infections,but hypervirulent Klebsiella strains are an emerging problem in Western countries.Amoebiasis has been a public health problem in Europe,primarily imported from other endemic foci.At the same time,this infection is becoming an emerging disease,as the number of infected patients who have not traveled to endemic areas is rising.Treatment options for hydatid liver cyst include chemotherapy,open or laparoscopic surgery,percutaneous treatment(percutaneous aspiration,re-aspiration and injection and its modification)and“wait and watch”strategy.Most hydatid liver cyst patients in Pillay et al’s study received surgical treatment,but several studies have confirmed the safety and efficacy of percutaneous aspiration,re-aspiration and injection.展开更多
BACKGROUND Klebsiella pneumoniae(K.pneumoniae)used to affect mainly people with compromised immunity or weakened by other infections,but recent emergence of hypervirulent strains has increased infections even in healt...BACKGROUND Klebsiella pneumoniae(K.pneumoniae)used to affect mainly people with compromised immunity or weakened by other infections,but recent emergence of hypervirulent strains has increased infections even in healthy individuals.These infections include liver abscess,pneumonia,bacteremia,meningitis,necrotizing fasciitis,and endophthalmitis.Although metastatic infection by hypervirulent K.pneumoniae(hvKP)is increasingly recognized,co-infection with Cryptococcus neoformans(C.neoformans)meningitis in immunocompetent hosts is rare but fatal.So,it is necessary to determine the risk factors,complications,and comorbidity of this disease.CASE SUMMARY This report describes a 58-year-old man with hvKP pulmonary abscess,bacteremia,and meningitis,accompanied by fatal Cryptococcus meningitis.This patient presented with fever for 1 wk and drowsiness for 3 d.Laboratory findings revealed pulmonary abscess and bacteremia of K.pneumoniae.He was given intravenous antibiotic therapy,and the infection was under control for about 1 wk.However,his condition deteriorated rapidly because of metastatic purulent meningitis.Although hvKP and C.neoformans were isolated and confirmed,the patient died of spontaneous respiratory and cardiac arrest caused by cerebral hernia.CONCLUSION HvKP has emerged as a cause of metastatic infections in immunocompetent hosts.polymicrobial co-infections should be taken into consideration when metastatic infection is present.展开更多
To determine passive haemagglutination (PHA) antibody titer that would protect chicks against Nigerian isolates of the Infectious Bursa Disease Virus (IBDV), five groups of chicks aged 30 days which had different anti...To determine passive haemagglutination (PHA) antibody titer that would protect chicks against Nigerian isolates of the Infectious Bursa Disease Virus (IBDV), five groups of chicks aged 30 days which had different antibody titers were challenged with a Nigerian isolate of virulent IBDV. Mortality rates of the different groups were plotted against their respective mean PHA antibody titers. A group with zero antibody titer had a mortality rate of 75% while those with PHA antibody titers of 185.6, 243.2, 256 and 307.2 had mortality rates of 40%, zero, zero and zero respectively. Linear equation generated for a line of best fit of the graph of mortality rates of the chicks on their IBD antibody titers gave antibody titer (X) at which mortality (Y) would be zero as 300. A mortality of 75% and the high antibody level needed to protect chicks suggest that the isolate may be a hypervirulent strain.展开更多
Hypervirulent Klebsiella pneumoniae(hvKp)is a major cause of severe community-acquired infection.A key plasmidencoded factor,regulator of mucoid phenotype A(RmpA),activates capsule locus gene expression to promote hyp...Hypervirulent Klebsiella pneumoniae(hvKp)is a major cause of severe community-acquired infection.A key plasmidencoded factor,regulator of mucoid phenotype A(RmpA),activates capsule locus gene expression to promote hypermucoviscosity,a phenotype that is strongly linked to increased pathogenicity.However,the precise regulatory mechanisms that control RmpA in hvKp remain poorly understood.In this study,we constructed a rmpA knockdown strain in hvKp using CRISPR interference and assessed the global regulatory role of RmpA through complementary multi-omic sequencing(RNA sequencing[RNA-seq]and chromatin immunoprecipitation sequencing[ChIP-seq]),promoter-gfp reporter assays,and phenotypic experiments.The functional role of RmpA was evaluated in Escherichia coli via heterologous expression.The RNA-seq analysis revealed that RmpA activates carbohydrate metabolism pathways,but represses pathways related to DNA replication,ribosome metabolism,and biofilm formation.The ChIP-seq analysis further confirmed the potential role of RmpA as a global regulator that enhances capsule production by activating transcripts within the capsule locus.It also upregulates genes involved in sugar metabolism and transport,which supplies essential precursors for capsule synthesis.RmpA modulates the phenotypic switch between hypermucoviscosity and biofilm formation by repressing type Ⅲ fimbriae genes.Notably,RmpA overexpression in E.coli induced changes in multiple metabolic pathways.These findings position RmpA as a latent central regulator in hvKp that orchestrates the metabolic pathways and phenotypic traits essential for virulence.展开更多
The emergence of hypervirulence(hv)and carbapenem resistance(CR)as distinct evolutionary directions for Klebsiella pneumoniae presents a significant threat in clinical settings.However,in recent years,there has been a...The emergence of hypervirulence(hv)and carbapenem resistance(CR)as distinct evolutionary directions for Klebsiella pneumoniae presents a significant threat in clinical settings.However,in recent years,there has been a growing identification of K.pneumoniae strains that integrate both phenotypes,resulting in severe clinical outcomes.Carbapenemresistant hypervirulent K.pneumoniae(CRhvKP)typically emerges through the acquisition of plasmids carrying either virulence or CR-encoded genes by carbapenem-resistant K.pneumoniae or hypervirulent K.pneumoniae.Furthermore,the acquisition of a hybrid plasmid can confer a combination of CR and hv.CRhvKP can cause a variety of infections,including pneumonia,urinary tract infections,bloodstream infections,liver abscesses,and other related conditions.While the sequence type 11(ST11)dominates the majority of CRhvKP strains in China,the molecular factors responsible for the success of ST11 CRhvKP largely remain unknown.Here,we provide an overview of the current understanding of the variation and distribution of crucial virulence determinants,the mechanisms driving the merging of hv and CR,and the potential molecular factors influencing the epidemiological success of ST11 CRhvKP.This research aims to contribute to a comprehensive understanding of the complexities surrounding CRhvKP.It is imperative to underscore the development of combination therapies,precision medicine,and vaccine strategies as pivotal approaches in effectively combating CRhvKP.Considering the widespread prevalence of CRhvKP,a prioritized,multifaceted approach encompassing infection control,active surveillance,and the development of innovative therapeutics is essential.展开更多
Pseudomonas aeruginosa is a significant pathogen mainly causing healthcare-associated infections(HAIs).Newly emerging high-risk clones of P.aeruginosa with elevated virulence profiles furtherly cause severe community-...Pseudomonas aeruginosa is a significant pathogen mainly causing healthcare-associated infections(HAIs).Newly emerging high-risk clones of P.aeruginosa with elevated virulence profiles furtherly cause severe community-acquired infections(CAIs).Usually,it is not common for P.aeruginosa to co-carry exoU and exoS genes,encoding two type III secretion system(T3SS)effectors.The pathogenicity mechanism of exoS+/exoU+strains of P.aeruginosa remains unclear.Here,we provide detailed evidence for a subset of hypervirulent P.aeruginosa strains,which abundantly co-express and secrete the T3SS effectors ExoS and ExoU.The exoS+/exoU+P.aeruginosa strains were available to cause both HAIs and CAIs.The CAI-associated strains could elicit severe inflammation and hemorrhage,leading to higher death rates in a murine acute pneumonia model,and had great virulence potential in establishing chronic infections,demonstrating hypervirulence when compared to PAO1(exoS+/exoU-)and PA14(exoS-/exoU+).Both ExoS and ExoU were co-expressed and co-secreted in abundance in exoS+/exoU+strains.Their abundant protein secretion could boost exoS+/exoU+strains’potentials for cytotoxicity in vitro and pathogenicity in vivo.Genomic evidence indicates that exoU acquisition is likely mediated by horizontal gene transfer(HGT)of the pathogenicity island PAPI-2,while deletion of exoU was sufficient to mitigate virulence in the exoS+/exoU+strains.Furthermore,bioinformatics analysis showed that such exoS+/exoU+P.aeruginosa strains turned out to be widely distributed across the globe.Overall,the research provide detailed evidence for the high virulence and epidemicity of exoS+/exoU+strains of P.aeruginosa,highlighting an urgent need for surveillance against these high-risk hypervirulent strains.展开更多
Importance Hypervirulent variants of Klebsiella pneumoniae(hvKp)are capable of causing life-threatening pyogenic liver abscesses(PLAs),but hvKp caused PLAs was seldom reported in pediatric populations.Hence,there is a...Importance Hypervirulent variants of Klebsiella pneumoniae(hvKp)are capable of causing life-threatening pyogenic liver abscesses(PLAs),but hvKp caused PLAs was seldom reported in pediatric populations.Hence,there is an urgent need to raise our awareness of this phenomenon in pediatric populations.Objective This study aimed to report the clinical characteristics of hvKp that caused fatal PLA complicated by bacteremia in an adolescent and further identify the microbiological and genomic features of the causative strain.Methods A 14-year-old boy with diabetes mellitus was admitted to our hospital with a diagnosis of PLA complicated by bacteremia.A hypermucoviscous hvKp strain,KPN_19-106,was isolated from the drainage fluid present within the liver abscess cavity and blood.The hypermucoviscosity phenotype of the causative strain was determined by string test.Its virulence was measured using serum resistance assay and Galleria mellonella larvae-killing assay.Antimicrobial susceptibility was determined by broth microdilution method.Genetic information was obtained by whole-genome sequencing and bioinformatics analysis.Results KPN_19-106 belonged to sequence type 380 and serotype K2 and exhibited stronger serum resistance and higher in vivo lethality than the well-characterized hvKp NTUH-K2044 strain.Although KPN_19-106 is susceptible to most antibiotics,no sign of improvement was observed during treatment with such drugs.Whole-genome sequencing revealed that the isolate had integrated multiple mobile genetic elements related to virulence.Interpretation Antibiotic-susceptible hvKp can cause fatal PLA complicated by bacteremia in adolescents,with no improvement during antimicrobial therapy.The causative strain in this case had integrated multiple virulence genes and thus exhibited higher virulence both in vitro and in vivo when compared with NTUH-K2044.展开更多
The global spread of hypervirulent Klebsiella pneumoniae(hvKp)poses a serious public health threat.In this study,we conducted genomic epidemiology analysis on 2097 global hvKp isolates,including our 900 isolates seque...The global spread of hypervirulent Klebsiella pneumoniae(hvKp)poses a serious public health threat.In this study,we conducted genomic epidemiology analysis on 2097 global hvKp isolates,including our 900 isolates sequenced through the Illumina platform(177 of them fully sequenced through PacBio platform),representing the most comprehensive genomic analysis of hvKp to date.Our results identified six dominant clonal groups(CGs),particularly including CG23 and CG258,and 17 major virulence determinant combinations(VDCs)comprising 10 virulence gene profiles(VGPs),four types of virulence plasmids,four ICEKp variants,Tn7399,and all_island.Each CG harbored distinct advantageous VDCs,indicating strong genomic correlation and co-evolution.Additionally,the phylogeny and evolutionary history of CG23 and CG258 were characterized in depth.Notably,41.58%of the 2097 isolates were multidrug-resistant and 33.29%were carbapenem-resistant,indicating serious antimicrobial resistance.Overall,our study provides a global genomic landscape of hvKp,emphasizing the genetic basis for their global dissemination and the need for precise prevention and control.展开更多
基金supported by the National Natural Science Foundation of China(grant numbers 81991531 to M.W.,82102440 to J.J.,and 32400149 to J.Z.).
文摘Antimicrobial resistance is a global health crisis and carbapenem-resistant Klebsiella pneumoniae(CRKp)is listed as one of the top high-priority pathogens by the World Health Organization.Meanwhile,hypervirulent K.pneumoniae(hvKp)causes severe community-associated infections,such as liver abscesses and meningitis,in otherwise healthy individuals.Both CRKp and hvKp infections are associated with high mortality rates.The convergence of carbapenem resistance and hypervirulence within a single bacterial strain may lead to significantly more severe clinical outcomes.
文摘This manuscript is based on a recent study by Pillay et al that was published in recently.Liver abscesses can be caused by rare potentially life-threatening infections of either bacterial or parasitic origin.The incidence rate in Europe is lower than in developing countries,but it is a major complication with high morbidity,particularly in immunocompromised patients.They are most frequently caused by Enterobacterales infections,but hypervirulent Klebsiella strains are an emerging problem in Western countries.Amoebiasis has been a public health problem in Europe,primarily imported from other endemic foci.At the same time,this infection is becoming an emerging disease,as the number of infected patients who have not traveled to endemic areas is rising.Treatment options for hydatid liver cyst include chemotherapy,open or laparoscopic surgery,percutaneous treatment(percutaneous aspiration,re-aspiration and injection and its modification)and“wait and watch”strategy.Most hydatid liver cyst patients in Pillay et al’s study received surgical treatment,but several studies have confirmed the safety and efficacy of percutaneous aspiration,re-aspiration and injection.
基金Supported by Science and Technology Planning Project of Guangdong Province of China,No.2017A020215177
文摘BACKGROUND Klebsiella pneumoniae(K.pneumoniae)used to affect mainly people with compromised immunity or weakened by other infections,but recent emergence of hypervirulent strains has increased infections even in healthy individuals.These infections include liver abscess,pneumonia,bacteremia,meningitis,necrotizing fasciitis,and endophthalmitis.Although metastatic infection by hypervirulent K.pneumoniae(hvKP)is increasingly recognized,co-infection with Cryptococcus neoformans(C.neoformans)meningitis in immunocompetent hosts is rare but fatal.So,it is necessary to determine the risk factors,complications,and comorbidity of this disease.CASE SUMMARY This report describes a 58-year-old man with hvKP pulmonary abscess,bacteremia,and meningitis,accompanied by fatal Cryptococcus meningitis.This patient presented with fever for 1 wk and drowsiness for 3 d.Laboratory findings revealed pulmonary abscess and bacteremia of K.pneumoniae.He was given intravenous antibiotic therapy,and the infection was under control for about 1 wk.However,his condition deteriorated rapidly because of metastatic purulent meningitis.Although hvKP and C.neoformans were isolated and confirmed,the patient died of spontaneous respiratory and cardiac arrest caused by cerebral hernia.CONCLUSION HvKP has emerged as a cause of metastatic infections in immunocompetent hosts.polymicrobial co-infections should be taken into consideration when metastatic infection is present.
文摘To determine passive haemagglutination (PHA) antibody titer that would protect chicks against Nigerian isolates of the Infectious Bursa Disease Virus (IBDV), five groups of chicks aged 30 days which had different antibody titers were challenged with a Nigerian isolate of virulent IBDV. Mortality rates of the different groups were plotted against their respective mean PHA antibody titers. A group with zero antibody titer had a mortality rate of 75% while those with PHA antibody titers of 185.6, 243.2, 256 and 307.2 had mortality rates of 40%, zero, zero and zero respectively. Linear equation generated for a line of best fit of the graph of mortality rates of the chicks on their IBD antibody titers gave antibody titer (X) at which mortality (Y) would be zero as 300. A mortality of 75% and the high antibody level needed to protect chicks suggest that the isolate may be a hypervirulent strain.
基金supported by the National Key Research and Development Program of China(grant number 2022YFC2303100 to J.F.)the International Partnership Program of the Chinese Academy of Sciences(grant number 079GJHZ2022033GC to J.F.).
文摘Hypervirulent Klebsiella pneumoniae(hvKp)is a major cause of severe community-acquired infection.A key plasmidencoded factor,regulator of mucoid phenotype A(RmpA),activates capsule locus gene expression to promote hypermucoviscosity,a phenotype that is strongly linked to increased pathogenicity.However,the precise regulatory mechanisms that control RmpA in hvKp remain poorly understood.In this study,we constructed a rmpA knockdown strain in hvKp using CRISPR interference and assessed the global regulatory role of RmpA through complementary multi-omic sequencing(RNA sequencing[RNA-seq]and chromatin immunoprecipitation sequencing[ChIP-seq]),promoter-gfp reporter assays,and phenotypic experiments.The functional role of RmpA was evaluated in Escherichia coli via heterologous expression.The RNA-seq analysis revealed that RmpA activates carbohydrate metabolism pathways,but represses pathways related to DNA replication,ribosome metabolism,and biofilm formation.The ChIP-seq analysis further confirmed the potential role of RmpA as a global regulator that enhances capsule production by activating transcripts within the capsule locus.It also upregulates genes involved in sugar metabolism and transport,which supplies essential precursors for capsule synthesis.RmpA modulates the phenotypic switch between hypermucoviscosity and biofilm formation by repressing type Ⅲ fimbriae genes.Notably,RmpA overexpression in E.coli induced changes in multiple metabolic pathways.These findings position RmpA as a latent central regulator in hvKp that orchestrates the metabolic pathways and phenotypic traits essential for virulence.
基金supported by the National Key Research and Development Program of China(2021YFC2300300)Key Research and Development Program of Zhejiang Province(2021C03068)+1 种基金National Natural Science Foundation of China(81971984 and 82202588)Shandong Provincial Laboratory Project(SYS202202).
文摘The emergence of hypervirulence(hv)and carbapenem resistance(CR)as distinct evolutionary directions for Klebsiella pneumoniae presents a significant threat in clinical settings.However,in recent years,there has been a growing identification of K.pneumoniae strains that integrate both phenotypes,resulting in severe clinical outcomes.Carbapenemresistant hypervirulent K.pneumoniae(CRhvKP)typically emerges through the acquisition of plasmids carrying either virulence or CR-encoded genes by carbapenem-resistant K.pneumoniae or hypervirulent K.pneumoniae.Furthermore,the acquisition of a hybrid plasmid can confer a combination of CR and hv.CRhvKP can cause a variety of infections,including pneumonia,urinary tract infections,bloodstream infections,liver abscesses,and other related conditions.While the sequence type 11(ST11)dominates the majority of CRhvKP strains in China,the molecular factors responsible for the success of ST11 CRhvKP largely remain unknown.Here,we provide an overview of the current understanding of the variation and distribution of crucial virulence determinants,the mechanisms driving the merging of hv and CR,and the potential molecular factors influencing the epidemiological success of ST11 CRhvKP.This research aims to contribute to a comprehensive understanding of the complexities surrounding CRhvKP.It is imperative to underscore the development of combination therapies,precision medicine,and vaccine strategies as pivotal approaches in effectively combating CRhvKP.Considering the widespread prevalence of CRhvKP,a prioritized,multifaceted approach encompassing infection control,active surveillance,and the development of innovative therapeutics is essential.
基金supported by the National Natural Science Foundation of China(32141001 and 31830001)the National Science Fund for Distinguished Young Scholars(32125003)the National Key R&D Program of China(2022YFC2303900 and 2022YFC3704700)。
基金supported by grants from the National Key R&D Program of China(2021YFC2302005)the Joint Funds of the International Development Research Center of Canada(109282-001)the National Key R&D Program of China(2021YFC2301004 and 2017YFE0125600).
文摘Pseudomonas aeruginosa is a significant pathogen mainly causing healthcare-associated infections(HAIs).Newly emerging high-risk clones of P.aeruginosa with elevated virulence profiles furtherly cause severe community-acquired infections(CAIs).Usually,it is not common for P.aeruginosa to co-carry exoU and exoS genes,encoding two type III secretion system(T3SS)effectors.The pathogenicity mechanism of exoS+/exoU+strains of P.aeruginosa remains unclear.Here,we provide detailed evidence for a subset of hypervirulent P.aeruginosa strains,which abundantly co-express and secrete the T3SS effectors ExoS and ExoU.The exoS+/exoU+P.aeruginosa strains were available to cause both HAIs and CAIs.The CAI-associated strains could elicit severe inflammation and hemorrhage,leading to higher death rates in a murine acute pneumonia model,and had great virulence potential in establishing chronic infections,demonstrating hypervirulence when compared to PAO1(exoS+/exoU-)and PA14(exoS-/exoU+).Both ExoS and ExoU were co-expressed and co-secreted in abundance in exoS+/exoU+strains.Their abundant protein secretion could boost exoS+/exoU+strains’potentials for cytotoxicity in vitro and pathogenicity in vivo.Genomic evidence indicates that exoU acquisition is likely mediated by horizontal gene transfer(HGT)of the pathogenicity island PAPI-2,while deletion of exoU was sufficient to mitigate virulence in the exoS+/exoU+strains.Furthermore,bioinformatics analysis showed that such exoS+/exoU+P.aeruginosa strains turned out to be widely distributed across the globe.Overall,the research provide detailed evidence for the high virulence and epidemicity of exoS+/exoU+strains of P.aeruginosa,highlighting an urgent need for surveillance against these high-risk hypervirulent strains.
基金Beijing Municipal Administration of Hospitals Clinical Medicine Development of Special Funding Support(grant number ZYLX201813).
文摘Importance Hypervirulent variants of Klebsiella pneumoniae(hvKp)are capable of causing life-threatening pyogenic liver abscesses(PLAs),but hvKp caused PLAs was seldom reported in pediatric populations.Hence,there is an urgent need to raise our awareness of this phenomenon in pediatric populations.Objective This study aimed to report the clinical characteristics of hvKp that caused fatal PLA complicated by bacteremia in an adolescent and further identify the microbiological and genomic features of the causative strain.Methods A 14-year-old boy with diabetes mellitus was admitted to our hospital with a diagnosis of PLA complicated by bacteremia.A hypermucoviscous hvKp strain,KPN_19-106,was isolated from the drainage fluid present within the liver abscess cavity and blood.The hypermucoviscosity phenotype of the causative strain was determined by string test.Its virulence was measured using serum resistance assay and Galleria mellonella larvae-killing assay.Antimicrobial susceptibility was determined by broth microdilution method.Genetic information was obtained by whole-genome sequencing and bioinformatics analysis.Results KPN_19-106 belonged to sequence type 380 and serotype K2 and exhibited stronger serum resistance and higher in vivo lethality than the well-characterized hvKp NTUH-K2044 strain.Although KPN_19-106 is susceptible to most antibiotics,no sign of improvement was observed during treatment with such drugs.Whole-genome sequencing revealed that the isolate had integrated multiple mobile genetic elements related to virulence.Interpretation Antibiotic-susceptible hvKp can cause fatal PLA complicated by bacteremia in adolescents,with no improvement during antimicrobial therapy.The causative strain in this case had integrated multiple virulence genes and thus exhibited higher virulence both in vitro and in vivo when compared with NTUH-K2044.
基金supported by the National Key R&D Program of China(2023YFC2605600 and 2023YFC2604400).
文摘The global spread of hypervirulent Klebsiella pneumoniae(hvKp)poses a serious public health threat.In this study,we conducted genomic epidemiology analysis on 2097 global hvKp isolates,including our 900 isolates sequenced through the Illumina platform(177 of them fully sequenced through PacBio platform),representing the most comprehensive genomic analysis of hvKp to date.Our results identified six dominant clonal groups(CGs),particularly including CG23 and CG258,and 17 major virulence determinant combinations(VDCs)comprising 10 virulence gene profiles(VGPs),four types of virulence plasmids,four ICEKp variants,Tn7399,and all_island.Each CG harbored distinct advantageous VDCs,indicating strong genomic correlation and co-evolution.Additionally,the phylogeny and evolutionary history of CG23 and CG258 were characterized in depth.Notably,41.58%of the 2097 isolates were multidrug-resistant and 33.29%were carbapenem-resistant,indicating serious antimicrobial resistance.Overall,our study provides a global genomic landscape of hvKp,emphasizing the genetic basis for their global dissemination and the need for precise prevention and control.
