Influenza viruses circulating in Thailand in 2004 and 2005.

Determining the local circulating strain of influenza is essential to prevent and control epidemics. In the years 2004 and 2005, the National Influenza Center of Thailand received 3,854 and 3,834 specimens, respectively, from patients throughout the country, including submissions from 4 established influenza surveillance sentinel sites. In 2004, of 539 influenza-positive specimens, 461 were positive for influenza A and 78 were positive for influenza B by isolation. Influenza A subtyping revealed that 249, 197, and 15 isolates were H1N1, H3N2, and H5N1, respectively. In 2005, of 748 influenza-positive specimens, 492 were influenza A and the remaining 256 were influenza B. The results of influenza A subtyping indicated that 55, 437, and 5 isolates were H1N1, H3N2, and H5N1. All isolated strains of subtype H1N1 were A/New Caledonia/20/99-like. The isolated strains of H3N2 were A/Fujian/411/2002-like in the first half of the year 2004, while those in the latter half of 2004 gradually drifted to a mixture of A/Wellington/1/2004-like, A/California/7/2004-like, and A/Wisconsin/67/2005-like, and this mixture continued through the end of 2005. The influenza B strains were B/Sichuan/379/99-like, B/Hong Kong/330/2001-like, B/Shanghai/361/2002-like and B/Malaysia/2506/2004-like. The strains circulating in the years 2004 and 2005 were antigenically similar to the vaccine formulas recommended in the same period by WHO. Our results underscore that local influenza surveillance plays an important role in responding to epidemics and potential pandemics.

Higher in vitro susceptibility of human T cells to H5N1 than H1N1 influenza viruses.

Patients infected with H5N1 influenza A virus, who had a severe or fatal outcome, exhibited several characteristic clinical manifestations including lymphopenia. In this study, human CD4(+) T-cell lines and healthy donor-derived peripheral blood mononuclear cells (PBMCs) were examined for susceptibility to infection with Thai isolates of H5N1 in comparison to those of H1N1. Although cellular levels were variable between H5N1 and H1N1 in T-cell lines and PBMCs, rates of production of progeny virions were significantly higher in H5N1 infections, suggesting a more efficient release of virions. In addition, cytopathogenicity in PBMCs, leading to a decline in CD4(+) T-cell numbers, were much severer with H5N1 than H1N1. Thus, human T cells could be an important target for infection with H5N1.

Highly pathogenic avian influenza H5N1 viruses elicit an attenuated type i interferon response in polarized human bronchial epithelial cells.

The unparalleled spread of highly pathogenic avian influenza A (HPAI) H5N1 viruses has resulted in devastating outbreaks in domestic poultry and sporadic human infections with a high fatality rate. To better understand the mechanism(s) of H5N1 virus pathogenesis and host responses in humans, we utilized a polarized human bronchial epithelial cell model that expresses both avian alpha-2,3- and human alpha-2,6-linked sialic acid receptors on the apical surface and supports productive replication of both H5N1 and H3N2 viruses. Using this model, we compared the abilities of selected 2004 HPAI H5N1 viruses isolated from humans and a recent human H3N2 virus to trigger the type I interferon (IFN) response. H5N1 viruses elicited significantly less IFN regulatory factor 3 (IRF3) nuclear translocation, as well as delayed and reduced production of IFN-beta compared with the H3N2 virus. Furthermore, phosphorylation of Stat2 and induction of IFN-stimulated genes (ISGs), such as MX1, ISG15, IRF7, and retinoic acid-inducible gene I, were substantially delayed and reduced in cells infected with H5N1 viruses. We also observed that the highly virulent H5N1 virus replicated more efficiently and induced a weaker IFN response than the H5N1 virus that exhibited low virulence in mammals in an earlier study. Our data suggest that the H5N1 viruses tested, especially the virus with the high-pathogenicity phenotype, possess greater capability to attenuate the type I IFN response than the human H3N2 virus. The attenuation of this critical host innate immune defense may contribute to the virulence of H5N1 viruses observed in humans.

Influenza viral infection in 2005-2006 in Samitivej Hospital.

OBJECTIVE: Set an alarm system for early detection of respiratory viral infection. MATERIAL AND METHOD: The authors prospectively investigated avian flu and SARS between March 2005 and April 2006. Specimens from a nasopharyngeal swab or bronchial washing were analyzed for influenza A, B, parainfluenza, adenovirus, respiratory syncytial virus and avian flu and SARS by using technique of PCR and immunofluorescence by the Department of Medical Sciences. RESULTS: Eighty-nine patients who were enrolled in the present study. Peak of the incidence was 43% on April 2005 and there was no incidence of the influenza from December 2005 till April 2006. This may be due to the mass campaign of influenza vaccination or seasonal variation. CONCLUSION: Vaccination remains the primary strategy for the prevention of influenza, and the broadened recommendations should lead to protection of a larger portion of the population.

Influenza-associated hospitalization in urban Thai children.

BACKGROUND: Studies in North America and Europe have shown that young children are at increased risk of serious complications and hospitalization from influenza infection. In Thailand, however, influenza is commonly considered a mild infection that rarely requires hospitalization. An improved understanding of the burden of serious complications from influenza infection in young children is needed to inform clinical treatment and vaccination guidelines. METHODS: We conducted a prospective study of children 0-5 years of age with lower respiratory tract infection or influenza-like illness admitted to a pediatric tertiary-care hospital in Bangkok, Thailand during July 2004 to July 2005. All respiratory specimens were tested for influenza using a rapid antigen test and tissue cell culture. RESULTS: Thirty-nine of 456 (8.6%) hospitalized children had culture-positive influenza. Eighty percent of hospitalized influenza patients had no underlying chronic illnesses. Nineteen (49%) influenza patients required hospital stays of 5 days or more and two patients required mechanical ventilation. Influenza activity demonstrated bimodal seasonal variation with peak activity from August to October and January to April. Cough was present in 38 (97%) cases and fever >38.5 degrees C was significantly associated with influenza. CONCLUSION: Influenza is an important cause of hospitalization in children <5 years of age in Thailand. Children <5 years should be considered as a target group when establishing clinical guidelines for antiviral treatment and influenza vaccination.

Avian influenza (H5N1) viruses isolated from humans in Asia in 2004 exhibit increased virulence in mammals.

The spread of highly pathogenic avian influenza H5N1 viruses across Asia in 2003 and 2004 devastated domestic poultry populations and resulted in the largest and most lethal H5N1 virus outbreak in humans to date. To better understand the potential of H5N1 viruses isolated during this epizootic event to cause disease in mammals, we used the mouse and ferret models to evaluate the relative virulence of selected 2003 and 2004 H5N1 viruses representing multiple genetic and geographical groups and compared them to earlier H5N1 strains isolated from humans. Four of five human isolates tested were highly lethal for both mice and ferrets and exhibited a substantially greater level of virulence in ferrets than other H5N1 viruses isolated from humans since 1997. One human isolate and all four avian isolates tested were found to be of low virulence in either animal. The highly virulent viruses replicated to high titers in the mouse and ferret respiratory tracts and spread to multiple organs, including the brain. Rapid disease progression and high lethality rates in ferrets distinguished the highly virulent 2004 H5N1 viruses from the 1997 H5N1 viruses. A pair of viruses isolated from the same patient differed by eight amino acids, including a Lys/Glu disparity at 627 of PB2, previously identified as an H5N1 virulence factor in mice. The virus possessing Glu at 627 of PB2 exhibited only a modest decrease in virulence in mice and was highly virulent in ferrets, indicating that for this virus pair, the K627E PB2 difference did not have a prevailing effect on virulence in mice or ferrets. Our results demonstrate the general equivalence of mouse and ferret models for assessment of the virulence of 2003 and 2004 H5N1 viruses. However, the apparent enhancement of virulence of these viruses in humans in 2004 was better reflected in the ferret.

Probable person-to-person transmission of avian influenza A (H5N1).

BACKGROUND: During 2004, a highly pathogenic avian influenza A (H5N1) virus caused poultry disease in eight Asian countries and infected at least 44 persons, killing 32; most of these persons had had close contact with poultry. No evidence of efficient person-to-person transmission has yet been reported. We investigated possible person-to-person transmission in a family cluster of the disease in Thailand. METHODS: For each of the three involved patients, we reviewed the circumstances and timing of exposures to poultry and to other ill persons. Field teams isolated and treated the surviving patient, instituted active surveillance for disease and prophylaxis among exposed contacts, and culled the remaining poultry surrounding the affected village. Specimens from family members were tested by viral culture, microneutralization serologic analysis, immunohistochemical assay, reverse-transcriptase-polymerase-chain-reaction (RT-PCR) analysis, and genetic sequencing. RESULTS: The index patient became ill three to four days after her last exposure to dying household chickens. Her mother came from a distant city to care for her in the hospital, had no recognized exposure to poultry, and died from pneumonia after providing 16 to 18 hours of unprotected nursing care. The aunt also provided unprotected nursing care; she had fever five days after the mother first had fever, followed by pneumonia seven days later. Autopsy tissue from the mother and nasopharyngeal and throat swabs from the aunt were positive for influenza A (H5N1) by RT-PCR. No additional chains of transmission were identified, and sequencing of the viral genes identified no change in the receptor-binding site of hemagglutinin or other key features of the virus. The sequences of all eight viral gene segments clustered closely with other H5N1 sequences from recent avian isolates in Thailand. CONCLUSIONS: Disease in the mother and aunt probably resulted from person-to-person transmission of this lethal avian influenzavirus during unprotected exposure to the critically ill index patient.

Seroprevalence of anti-H5 antibody among Thai health care workers after exposure to avian influenza (H5N1) in a tertiary care center.

After the initial atypical presentation of a patient with avian influenza (H5N1) infection, paired acute-phase and convalescent-phase serum samples obtained from 25 health care workers (HCWs) who were exposed to the patient were compared with paired serum samples obtained from 24 HCWs who worked at different units in the same hospital and were not exposed to the patient. There was no serologic evidence of anti-H5 antibody reactivity or subclinical infection in either of the groups.

Influenza in Thailand: a case study for middle income countries.

Recent studies in Hong Kong and Singapore suggest that the annual impact of influenza in these wealthy tropical cities may be substantial, but little is known about the burden in middle-income tropical countries. We reviewed the status of influenza surveillance, vaccination, research, and policy in Thailand as of January 2004. From 1993 to 2002, 64-91 cases of clinically diagnosed influenza were reported per 100,000 persons per year. Influenza viruses were isolated in 34% of 4305 specimens submitted to the national influenza laboratory. Vaccine distribution figures suggest that less than 1% of the population is immunized against influenza each year. In January 2004, Thailand reported its first documented outbreak of influenza A H5N1 infection in poultry and the country's first human cases of avian influenza. Thailand's growing economy, well-developed public health infrastructure, and effective national immunization program could enable the country to take more active steps towards influenza control.

Early containment of severe acute respiratory syndrome (SARS); experience from Bamrasnaradura Institute, Thailand.

BACKGROUND: On March 11, 2003, a World Health Organization (WHO) physician was admitted to Bamrasnaradura Institute, after alerting the world to the dangers of severe acute respiratory syndrome (SARS) in Vietnam and developing a fever himself. Specimens from the first day of his admission were among the first to demonstrate the novel coronavirus, by culture, reverse transcription-polymerase chain reaction (RT-PCR), and rising of specific antibody, but proper protective measures remained unknown. The authors instituted airborne, droplet and contact precautions from the time of admission, and reviewed the efficacy of these measures. MATERIAL AND METHOD: A specific unit was set up to care for the physician, beginning by roping off an isolated room and using a window fan to create negative pressure, and later by constructing a glass-walled antechamber, designated changing and decontamination areas, and adding high-efficiency particulate air (HEPA) filters. The use of personal protective equipment (PPE) was consistently enforced by nurse managers for all the staff and visitors, including a minimum of N95 respirators, goggles or face shields, double gowns, double gloves, full head and shoe covering, and full Powered Air Purifying Respirator (PAPR) for intubation. To assess the adherence to PPE and the possibility of transmission to exposed staff a structured questionnaire was administered and serum samples tested for SARS coronavirus by enzyme-linked immunosorbent assay (ELISA). Exposure was defined as presence on the SARS ward or contact with laboratory specimens, and close contact was presence in the patient's room. RESULTS: The WHO physician died from respiratory failure on day 19. 112 of 129 exposed staff completed questionnaires, and the 70 who entered the patient's room reported a mean of 42 minutes of exposure (range 6 minutes-23.5 hours). 100% reported consistent handwashing after exposure, 95% consistently used a fit-tested N95 or greater respirator, and 80% were fully compliant with strict institutional PPE protocol. No staff developed an illness consistent with SARS. Serum samples from 35 close contacts obtained after day 28 had a negative result for SARS coronavirus antibody. CONCLUSIONS: Hospitalization of one of the earliest SARS patients with documented coronavirus shedding provided multiple opportunities for spread to the hospital staff, but strict enforcement of conservative infection control recommendations throughout the hospitalization was associated with no transmission.

Atypical avian influenza (H5N1).

We report the first case of avian influenza in a patient with fever and diarrhea but no respiratory symptoms. Avian influenza should be included in the differential diagnosis for patients with predominantly gastrointestinal symptoms, particularly if they have a history of exposure to poultry.

Isolation and identification of influenza virus strains circulating in Thailand in 2001.

Local influenza surveillance plays an important role in preparing for, and responding to, epidemics and pandemics. Between January and December 2001, the National Institute of Health of Thailand collected a total of 711 throat swab specimens from outpatients affected with acute respiratory symptoms from several centers throughout Thailand, of which 374 were virus-positive. Of these, 338 (90.4%) were positive for influenza virus by immunofluorescence testing. By hemagglutination-inhibition (HI) testing, 155 of the type A viruses were found to be subtype H1N1 strains closely related to A/New Caledonia/20/99, and 70 were subtype H3N2 A/Moscow/ 10/99-like viruses. For type B, the isolates were antigenically B/Sichuan/379/9-like by HI, although a number of the strains could be shown to be more closely related to earlier influenza B strains by genetic analysis. The strains circulating in Thailand were antigenically similar to strains isolated worldwide during the same period and to strains recommended by the WHO for inclusion in the vaccines for use in 2001-2002.

The out of Africa model of varicella-zoster virus evolution: single nucleotide polymorphisms and private alleles distinguish Asian clades from European/North American clades.

Until 1998, varicella-zoster virus (VZV) was generally considered sufficiently stable to allow the use of a single sequenced virus (VZV-Dumas) as a consensual representation of the world VZV genotype. But recent investigations have uncovered a gE mutant virus called VZV-MSP with a second genotype and a distinguishable accelerated cell spread phenotype. A subsequent study suggested that single nucleotide polymorphisms (SNPs) could be applied toward the genetic analysis of the VZV genome. To further assess the scope of genetic variation in the VZV genome on a worldwide basis, we carried out an extensive SNP analysis of structural glycoprotein genes gB, gE, gH, gI, gL, as well as the IE62 regulatory gene in viruses collected from Western Europe, North America and Asia, including the VZV vaccine strain. The SNP data showed segregation of viral isolates of Asian origin from those of Western ancestry into distinct phylogenetic clades. Unexpectedly, however, VZV from Thailand segregated with VZV from Iceland and the United States, i.e. it was more Western than Asian in nature. Further, SNP analysis disclosed strikingly unusual genotypes, e.g. gH genes with up to five missense mutations and gL genes with insertions of an in-frame methionine codon. In summary, these VZV genomic analyses have shown that individual VZV strains, like closely related human beings, have distinctive SNP profiles containing private alleles within just five VZV genes (gB, gH, gE, gL and IE62) that provide a fingerprint to localize ancestry of the viral strain.