[Show abstract][Hide abstract] ABSTRACT: Orientia tsutsugamushi is the causative agent of scrub typhus, a major cause of febrile illness in rural area of Asia-Pacific region. A multi-locus sequence typing (MLST) analysis was performed on strains isolated from human patients from 3 countries in Southeast Asia: Cambodia, Vietnam and Thailand. The phylogeny of the 56-kDa protein encoding gene was analyzed on the same strains and showed a structured topology with genetically distinct clusters. MLST analysis did not lead to the same conclusion. DNA polymorphism and phylogeny of individual gene loci indicated a significant level of recombination and genetic diversity whereas the ST distribution indicated the presence of isolated patches. No correlation was found with the geographic origin. This work suggests that weak divergence in core genome and ancestral haplotypes are maintained by permanent recombination in mites while the 56-kDa protein gene is diverging in higher speed due to selection by the mammalian immune system.
[Show abstract][Hide abstract] ABSTRACT: Laboratory capacity is needed in central Viet Nam to provide early warning to public health authorities of respiratory outbreaks of importance to human health, for example the outbreak of influenza A(H1N1) pandemic in 2009. Polymerase chain reaction (PCR) procedures established as part of a capacity-building process were used to conduct prospective respiratory surveillance in a region where few previous studies have been undertaken.
Between October 2008 and September 2010, nose and throat swabs from adults and children (approximately 20 per week) presenting with an acute respiratory illness to the Ninh Hoa General Hospital were collected. Same-day PCR testing and result reporting for 13 respiratory viruses were carried out by locally trained scientists.
Of 2144 surveillance samples tested, 1235 (57.6%) were positive for at least one virus. The most common were influenza A strains (17.9%), with pandemic influenza A(H1N1) 2009 and seasonal H3N2 strain accounting for 52% and 43% of these, respectively. Other virus detections included: rhinovirus (12.4%), enterovirus (8.9%), influenza B (8.3%), adenovirus (5.3%), parainfluenza (4.7%), respiratory syncytial virus (RSV) (3.9%), human coronavirus (3.0%) and human metapneumovirus (0.3%). The detection rate was greatest in the 0-5 year age group. Viral co-infections were identified in 148 (6.9%) cases.
The outbreak in 2009 of the influenza A(H1N1) pandemic strain provided a practical test of the laboratory's pandemic plan. This study shows that the availability of appropriate equipment and molecular-based testing can contribute to important individual and public health outcomes in geographical locations susceptible to emerging infections.
[Show abstract][Hide abstract] ABSTRACT: Scrub typhus is an acute infectious disease caused by an obligate intracellular bacterium Orientia tsutsugamushi following the bite of infected trombiculid mites of the genus Leptotrombidium. This zoonotic disease is a major cause of febrile illness in the Asia-Pacific region, with a large spectrum of clinical manifestations from unapparent or mild disease to fatal disease. O. tsutsugamushi is characterized by a very high genomic plasticity and a large number of antigenic variants amongst strains. The 56-kDa type specific antigen (TSA) gene, encoding the major antigenic protein, was used as reference to investigate the genetic relationships between the strains and to genotype O. tsutsugamushi isolates. The open reading frame of the 56-kDa TSA gene of 41 sequences (28 Cambodian and 13 Vietnamese strains) from patient samples were sequenced and used for genotyping. The 28 Cambodian isolates clustered into 5 major groups, including Karp (43.5%), JG-v (25%), Kato/TA716 (21.5%), TA763 (3.5%) and Gilliam (3.5%). Karp (77%), TA763 (15.5%) and JG-v (7.5%) strains were identified amongst the 13 Vietnamese isolates. This is the first countrywide genotyping description in Cambodia and in Central Vietnam. These results demonstrate the considerable diversity of genotypes in co-circulation in both countries. The genotyping result might raise awareness amongst Cambodian and Vietnamese clinicians of the high genetic diversity of circulating O. tsutsugamushi strains and provides unique and beneficial data for serological and molecular diagnosis of scrub typhus infections as well as raw materials for future studies and vaccine development.
Infection, genetics and evolution: journal of molecular epidemiology and evolutionary genetics in infectious diseases 01/2011; 15. DOI:10.1016/j.meegid.2011.01.004 · 3.02 Impact Factor