Low frequency of infection with avian influenza virus (H5N1) among poultry farmers, Thailand, 2004

T cell mediated immunity against influenza H5N1 nucleoprotein, matrix and hemagglutinin derived epitopes in H5N1 survivors and non-H5N1 subjects

Background

Protection against the influenza virus by a specific antibody is relatively strain specific; meanwhile broader immunity may be conferred by cell-mediated immune response to the conserved epitopes across influenza virus subtypes. A universal broad-spectrum influenza vaccine which confronts not only seasonal influenza virus, but also avian influenza H5N1 virus is promising.

Methods

This study determined the specific and cross-reactive T cell responses against the highly pathogenic avian influenza A (H5N1) virus in four survivors and 33 non-H5N1 subjects including 10 H3N2 patients and 23 healthy individuals. Ex vivo IFN-γ ELISpot assay using overlapping peptides spanning the entire nucleoprotein (NP), matrix (M) and hemagglutinin (HA) derived from A/Thailand/1(KAN-1)/2004 (H5N1) virus was employed in adjunct with flow cytometry for determining T cell functions. Microneutralization (microNT) assay was performed to determine the status of previous H5N1 virus infection.

Results

IFN-γ ELISpot assay demonstrated that survivors nos. 1 and 2 had markedly higher T cell responses against H5N1 NP, M and HA epitopes than survivors nos. 3 and 4; and the magnitude of T cell responses against NP were higher than that of M and HA. Durability of the immunoreactivity persisted for as long as four years after disease onset. Upon stimulation by NP in IFN-γ ELISpot assay, 60% of H3N2 patients and 39% of healthy subjects exhibited a cross-reactive T cell response. The higher frequency and magnitude of responses in H3N2 patients may be due to blood collection at the convalescent phase of the patients. In H5N1 survivors, the effector peptide-specific T cells generated from bulk culture PBMCs by in vitro stimulation displayed a polyfunction by simultaneously producing IFN-γ and TNF-α, together with upregulation of CD107a in recognition of the target cells pulsed with peptide or infected with rVac-NP virus as investigated by flow cytometry.

Conclusions

This study provides an insight into the better understanding on the homosubtypic and heterosubtypic T cell-mediated immune responses in H5N1 survivors and non-H5N1 subjects. NP is an immunodominant target of cross-recognition owing to its high conservancy. Therefore, the development of vaccine targeting the conserved NP may be a novel strategy for influenza vaccine design.

Serological evidence of human infections with highly pathogenic avian influenza A(H5N1) virus: a systematic review and meta-analysis

BACKGROUND

Highly pathogenic avian influenza A(H5N1) virus poses a global public health threat given severe and fatal zoonotic infections since 1997 and ongoing A(H5N1) virus circulation among poultry in several countries. A comprehensive assessment of the seroprevalence of A(H5N1) virus antibodies remains a gap and limits understanding of the true risk of A(H5N1) virus infection.

METHODS

We conducted a systematic review and meta-analysis of published serosurveys to assess the risk of subclinical and clinically mild A(H5N1) virus infections. We assessed A(H5N1) virus antibody titers and changes in titers among populations with variable exposures to different A(H5N1) viruses.

RESULTS

Across studies using the World Health Organization-recommended seropositive definition, the point estimates of the seroprevalence of A(H5N1) virus-specific antibodies were higher in poultry-exposed populations (range 0-0.6%) and persons exposed to both human A(H5N1) cases and infected birds (range 0.4-1.8%) than in close contacts of A(H5N1) cases or the general population (none to very low frequencies). Seroprevalence was higher in persons exposed to A(H5N1) clade 0 virus (1.9%, range 0.7-3.2%) than in participants exposed to other clades of A(H5N1) virus (range 0-0.5%) (p < 0.05). Seroprevalence was higher in poultry-exposed populations (range 0-1.9%) if such studies utilized antigenically similar A(H5N1) virus antigens in assays to A(H5N1) viruses circulating among poultry.

CONCLUSIONS

These low seroprevalences suggest that subclinical and clinically mild human A(H5N1) virus infections are uncommon. Standardized serological survey and laboratory methods are needed to fully understand the extent and risk of human A(H5N1) virus infections.

Avian influenza at animal-human interface: One-health challenge in live poultry retail stalls of Chakwal, Pakistan

Background

Live poultry retail stalls (LPRSs) are believed to be the source of human infection with avian influenza viruses (AIVs); however, little is known about epidemiology of these viruses in LPRSs of Pakistan.

Objectives

The current study was conducted to estimate the virological and serological prevalence of AIVs in humans and poultry and associated risk factors among seropositive butchers.

Methods

A field survey of LPRSs of Chakwal District was conducted between December 2015 and March 2016. In total, 322 samples (sera = 161 and throat swab = 161) from butchers and 130 pooled oropharyngeal swabs and 100 sera from birds were collected. Baseline sera (n = 100) from general population were also tested. Data were collected by structured questionnaires. Sera were tested by hemagglutination inhibition (HI) test further confirmed by micro‐neutralization test (MN). Swabs were processed by real‐time RT‐PCR. Logistic regression analyses were conducted to identify risk factors.

Results

In butchers, 15.5% sera were positive for antibodies against H9 virus using a cutoff of ≥40 in HI titer; 6% sera from general population were positive for H9. Seroprevalence in poultry was 89%, and only 2.30% swabs were positive for H9. Presence of another LPRS nearby and the number of cages in the stall were risk factors (OR > 1) for H9 seroprevalence in butchers.

Conclusions

This study provides evidence of co‐circulation of H9 virus in poultry and exposure of butchers in the LPRSs, which poses a continued threat to public health. We suggest regular surveillance of AIVs in occupationally exposed butchers and birds in LPRSs.

Serosurveillance of avian influenza A/H5N6 virus infection in poultry farmers, Gyeonggi Province, Republic of Korea, 2016-2017

OBJECTIVES

Between November 20, 2016 and April 17, 2017, outbreaks of highly pathogenic avian influenza (HPAI) A/H5N6 occurred on poultry farms in Gyeonggi Province in the Republic of Korea. A serosurvey was conducted among poultry farmers to identify the transmission of HPAI A/H5N6 virus to humans.

METHODS

A descriptive study of 870 poultry farmers in Gyeonggi Province in Korea was conducted during the 2016-2017 outbreaks. Serological testing was performed using a microneutralization (MN) assay for antibodies against influenza A/duck/ES2/Korea/2016 virus, which has antigenic properties similar to those of the HPAI A/H5N6 virus that caused this poultry outbreak.

RESULTS

Overall, 523 exposed poultry farmers were assessed by serological testing. Consequently, all tested negative for HPAI A/H5N6 virus via MN assay.

CONCLUSIONS

Based on serological assays, no transmission of HPAI A/H5N6 to humans was identified in this study cohort. Additional studies should be conducted to determine the possibility of poultry-to-human transmission of HPAI A/H5N6.

Environmental contamination and risk factors for transmission of highly pathogenic avian influenza A(H5N1) to humans, Cambodia, 2006-2010

BACKGROUND

Highly pathogenic avian influenza A (H5N1) virus has been of public health concern since 2003. Probable risk factors for A(H5N1) transmission to human have been demonstrated in several studies or epidemiological reports. However, transmission patterns may differ according to demographic characteristics of the population and local practices. This article aggregates these data from three studies with data collected in the previous surveys in 2006 and 2007 to further examine the risks factors associated with presence of anti-A(H5) antibodies among villagers residing within outbreak areas.

METHODS

We aggregated 5-year data (2006-2010) from serology survey and matched case-control studies in Cambodia to further examine the risks factors associated with A(H5N1) infection among villagers in the outbreak areas.

RESULTS

Serotesting among villagers detected 35 (1.5 % [0-2.6]) positive cases suggesting recent exposure to A(H5N1) virus. Practices associated with A(H5N1) infection among all ages were: having poultry cage or nesting area under or adjacent to the house (OR: 6.7 [1.6-28.3]; p = 0.010) and transporting poultry to market (OR: 17.6 [1.6-193.7]; p = 0.019). Practices found as risk factors for the infection among age under 20 years were swimming/bathing in ponds also accessed by domestic poultry (OR: 4.6 [1.1-19.1]; p = 0.038). Association with consuming wild birds reached borderline significance (p = 0.066).

CONCLUSION

Our results suggest that swimming/bathing in contaminated pond water and close contact with poultry may present a risk of A(H5N1) transmission to human.

Highly pathogenic Avian Influenza A(H5N1) virus infection among workers at live bird markets, Bangladesh, 2009-2010

Evidence of infection was low despite frequent exposure to infected poultry and low use of personal protective equipment.

The risk for influenza A(H5N1) virus infection is unclear among poultry workers in countries where the virus is endemic. To assess H5N1 seroprevalence and seroconversion among workers at live bird markets (LBMs) in Bangladesh, we followed a cohort of workers from 12 LBMs with existing avian influenza surveillance. Serum samples from workers were tested for H5N1 antibodies at the end of the study or when LBM samples first had H5N1 virus–positive test results. Of 404 workers, 9 (2%) were seropositive at baseline. Of 284 workers who completed the study and were seronegative at baseline, 6 (2%) seroconverted (7 cases/100 poultry worker–years). Workers who frequently fed poultry, cleaned feces from pens, cleaned food/water containers, and did not wash hands after touching sick poultry had a 7.6 times higher risk for infection compared with workers who infrequently performed these behaviors. Despite frequent exposure to H5N1 virus, LBM workers showed evidence of only sporadic infection.

Brief literature review for the WHO global influenza research agenda--highly pathogenic avian influenza H5N1 risk in humans

Highly pathogenic avian influenza A H5N1 viruses remain a significant health threat to humans given the continued rare occurrence of human cases with a high case fatality rate. This brief literature review summarizes available evidence of risk factors for H5N1 infection in humans and updates a recent systematic review published in early 2011. Several epidemiologic studies have been published to evaluate the risk factors for H5N1 infection in humans, including contact with poultry and poultry products and non-poultry-related contact such as from H5N1-contaminated water. While most H5N1 cases are attributed to exposure to sick poultry, it is unclear how many may be due to human-to-human transmission. The collective results of published literature suggest that transmission risk of H5N1 from poultry to humans may be highest among individuals who may have been in contact with the highest potential concentrations of virus shed by poultry. This suggests that there may be a threshold of virus concentration needed for effective transmission and that circulating H5N1 strains have not yet mutated to transmit readily from either poultry to human or from human to human. However, the mode of potential transmission can be quite varied throughout different countries and by study with exposures ranging from visiting a wet market, preparing infected poultry for consumption, to swimming or bathing in ponds frequented by poultry. Several important data gaps remain in the understanding of the epidemiology of H5N1 in humans and limit our ability to interpret the results of the available H5N1 seroepidemiologic studies.

Seroprevalence of antibodies against highly pathogenic avian influenza A (H5N1) virus among poultry workers in Bangladesh, 2009

We conducted a cross-sectional study in 2009 to determine the seroprevalence and risk factors for highly pathogenic avian influenza A (H5N1) [HPAI H5N1] virus antibodies among poultry workers at farms and live bird markets with confirmed/suspected poultry outbreaks during 2009 in Bangladesh. We tested sera by microneutralization assay using A/Bangladesh/207095/2008 (H5N1; clade 2.2.2) virus with confirmation by horse red blood cell hemagglutination inhibition and H5-specific Western blot assays. We enrolled 212 workers from 87 farms and 210 workers from three live bird markets. One hundred and two farm workers (48%) culled poultry. One hundred and ninety-three farm workers (91%) and 178 market workers (85%) reported direct contact with poultry that died during a laboratory confirmed HPAI H5N1 poultry farm outbreak or market poultry die-offs from suspected HPAI H5N1. Despite exposure to sick poultry, no farm or market poultry workers were seropositive for HPAI H5N1 virus antibodies (95% confidence interval 0-1%).

Assessment of serosurveys for H5N1

BACKGROUND

It has been suggested that the true case-fatality rate of human H5N1 influenza infection is appreciably less than the figure of approximately 60% that is based on official World Health Organization (WHO)-confirmed case reports because asymptomatic cases may have been missed. A number of seroepidemiologic studies have been conducted in an attempt to identify such missed cases.

METHODS

We conducted a comprehensive literature review of all English-language H5N1 human serology surveys with detailed attention to laboratory methodology used (including whether investigators used criteria set by the WHO to define positive cases), laboratory controls used, and the clades/genotypes involved.

RESULTS

Twenty-nine studies were included in the analysis. Few reported using unexposed control groups and one-third did not apply WHO criteria. Of studies that used WHO criteria, only 4 found any seropositive results to clades/genotypes of H5N1 that are currently circulating. No studies reported seropositive results to the clade 2/genotype Z viruses that have spread throughout Eurasia and Africa.

CONCLUSIONS

This review suggests that the frequency of positive H5 serology results is likely to be low; therefore, it is essential that future studies adhere to WHO criteria and include unexposed controls in their laboratory assays to limit the likelihood of false-positive results.

A serological survey of antibodies to H5, H7 and H9 avian influenza viruses amongst the duck-related workers in Beijing, China

The continued spread of highly pathogenic avian influenza (HPAI) viruses of H5 and H7 subtypes and low pathogenic avian influenza (LPAI) viruses of H5, H7 and H9 subtypes in birds and the subsequent infections in humans pose an ongoing pandemic threat. It has been proposed that poultry workers are at higher risk of exposure to HPAI or LPAI viruses and subsequently infection due to their repeated exposure to chickens or domestic waterfowl. The aim of this study was to examine the seroprevalence of antibodies against H5, H7 and H9 viruses amongst duck-related workers in Beijing, China and the risk factors associated with seropositivity. In March, 2011, 1741 participants were recruited from (1) commercial duck-breeding farms; (2) private duck-breeding farms; and (3) duck-slaughtering farms. Local villagers who bred ducks in their backyards were also recruited. A survey was administered by face-to-face interview, and blood samples were collected from subjects for antibody testing against H5, H7 and H9 viruses. We found that none of the subjects were seropositive for either H5 or H7 viruses, and only 0.7% (12/1741) had antibody against H9. A statistically significant difference in H9 antibody seroprevalence existed between the various categories of workers (P = 0.005), with the highest figures recorded amongst the villagers (1.7%). Independent risk factors associated with seropositivity toinfection with H9 virus included less frequent disinfection of worksite (OR, 5.13 [95% CI, 1.07-24.58]; P = 0.041; ≤ twice monthly versus>twice monthly) and handling ducks with wounds on hands (OR, 4.13 [95% CI, 1.26-13.57]; P = 0.019). Whilst the risk of infection with H5, H7 and H9 viruses appears to be low among duck-related workers in Beijing, China, ongoing monitoring of infection with the H9 virus is still warranted, especially amongst villagers who breed backyard ducks to monitor for any changes.

Avian influenza a (H5N1) virus antibodies in poultry cullers, South Korea, 2003-2004

Transmission of influenza (H5N1) virus from birds to humans is a serious public health threat. In South Korea, serologic investigation among 2,512 poultry workers exposed during December 2003-March 2004 to poultry with confirmed or suspected influenza (H5N1) virus infection found antibodies in 9. Frequency of bird-to-human transmission was low.

Seroevidence for H5N1 influenza infections in humans: meta-analysis

The prevalence of avian H5N1 influenza A infections in humans has not been definitively determined. Cases of H5N1 infection in humans confirmed by the World Health Organization (WHO) are fewer than 600 in number, with an overall case fatality rate of >50%. We hypothesize that the stringent criteria for confirmation of a human case of H5N1 by WHO do not account for a majority of infections but rather the select few hospitalized cases that are more likely to be severe and result in poor clinical outcome. Meta-analysis shows that 1 to 2% of more than 12,500 study participants from 20 studies had seroevidence for prior H5N1 infection.

Is H5N1 really highly lethal?

Medicine for Policymakers is a Journal column that provides decision makers with brief explanations of the meaning and implications for biosecurity of clinical issues. The articles describe, for a nonmedical audience, hospital practices, medical challenges, healthcare delivery issues, and other topics of current interest. Readers may submit ideas to the column's editor, Amesh A. Adalja, MD, through the Journal's editorial office at jfox@upmc-biosecurity.org .

Mammalian-transmissible H5N1 influenza: facts and perspective

Two recently submitted (but as yet unpublished) studies describe success in creating mutant isolates of H5N1 influenza A virus that can be transmitted via the respiratory route between ferrets; concern has been raised regarding human-to-human transmissibility of these or similar laboratory-generated influenza viruses. Furthermore, the potential release of methods used in these studies has engendered a great deal of controversy around publishing potential dual-use data and also has served as a catalyst for debates around the true case-fatality rate of H5N1 influenza and the capability of influenza vaccines and antivirals to impact any future unintentional or intentional release of H5N1 virus. In this report, we review available seroepidemiology data for H5N1 infection and discuss how case-finding strategies may influence the overall case-fatality rate reported by the WHO. We also provide information supporting the position that if an H5N1 influenza pandemic occurred, available medical countermeasures would have limited impact on the associated morbidity and mortality.

No evidence of infection with avian influenza viruses among US poultry workers in the Delmarva Peninsula, Maryland and Virginia, USA

Industrial poultry workers may be at elevated risk of avian influenza infection due to intense occupational contact with live poultry. Serum samples from poultry workers and community members in the Delmarva Peninsula, one of the densest regions of poultry production in the United States, were analyzed for antibodies to strains of five avian influenza subtypes using microneutralization assays. No evidence of infection was found, suggesting inefficient transmission to humans or the absence of virus in these premises. Continued serological surveillance of workers in industrial food animal facilities is necessary to prevent the transmission of influenza A viruses.

Serological response to the 2009 pandemic influenza A (H1N1) virus for disease diagnosis and estimating the infection rate in Thai population

Background

Individuals infected with the 2009 pandemic virus A(H1N1) developed serological response which can be measured by hemagglutination-inhibition (HI) and microneutralization (microNT) assays.

Methodology/Principal Findings

MicroNT and HI assays for specific antibody to the 2009 pandemic virus were conducted in serum samples collected at the end of the first epidemic wave from various groups of Thai people: laboratory confirmed cases, blood donors and health care workers (HCW) in Bangkok and neighboring province, general population in the North and the South, as well as archival sera collected at pre- and post-vaccination from vaccinees who received influenza vaccine of the 2006 season. This study demonstrated that goose erythrocytes yielded comparable HI antibody titer as compared to turkey erythrocytes. In contrast to the standard protocol, our investigation found out the necessity to eliminate nonspecific inhibitor present in the test sera by receptor destroying enzyme (RDE) prior to performing microNT assay. The investigation in pre-pandemic serum samples showed that HI antibody was more specific to the 2009 pandemic virus than NT antibody. Based on data from pre-pandemic sera together with those from the laboratory confirmed cases, HI antibody titers ≥40 for adults and ≥20 for children could be used as the cut-off level to differentiate between the individuals with or without past infection by the 2009 pandemic virus.

Conclusions/Significance

Based on the cut-off criteria, the infection rates of 7 and 12.8% were estimated in blood donors and HCW, respectively after the first wave of the 2009 influenza pandemic. Among general population, the infection rate of 58.6% was found in children versus 3.1% in adults.

Highly pathogenic avian influenza (H5N1): pathways of exposure at the animal-human interface, a systematic review

BACKGROUND

The threat posed by highly pathogenic avian influenza A H5N1 viruses to humans remains significant, given the continued occurrence of sporadic human cases (499 human cases in 15 countries) with a high case fatality rate (approximately 60%), the endemicity in poultry populations in several countries, and the potential for reassortment with the newly emerging 2009 H1N1 pandemic strain. Therefore, we review risk factors for H5N1 infection in humans.

METHODS AND FINDINGS

Several epidemiologic studies have evaluated the risk factors associated with increased risk of H5N1 infection among humans who were exposed to H5N1 viruses. Our review shows that most H5N1 cases are attributed to exposure to sick poultry. Most cases are sporadic, while occasional limited human-to-human transmission occurs. The most commonly identified factors associated with H5N1 virus infection included exposure through contact with infected blood or bodily fluids of infected poultry via food preparation practices; touching and caring for infected poultry; [corrected] exposure to H5N1 via swimming or bathing in potentially virus laden ponds; and exposure to H5N1 at live bird markets.

CONCLUSIONS

Research has demonstrated that despite frequent and widespread contact with poultry, transmission of the H5N1 virus from poultry to humans is rare. Available research has identified several risk factors that may be associated with infection including close direct contact with poultry and transmission via the environment. However, several important data gaps remain that limit our understanding of the epidemiology of H5N1 in humans. Although infection in humans with H5N1 remains rare, human cases continue to be reported and H5N1 is now considered endemic among poultry in parts of Asia and in Egypt, providing opportunities for additional human infections and for the acquisition of virus mutations that may lead to more efficient spread among humans and other mammalian species. Collaboration between human and animal health sectors for surveillance, case investigation, virus sharing, and risk assessment is essential to monitor for potential changes in circulating H5N1 viruses and in the epidemiology of H5N1 in order to provide the best possible chance for effective mitigation of the impact of H5N1 in both poultry and humans.

DISCLAIMER

The opinions expressed in this article are those of the authors and do not necessarily reflect those of the institutions or organizations with which they are affiliated.

Zoonotic transmission of avian influenza virus (H5N1), Egypt, 2006-2009

During March 2006-March 2009, a total of 6,355 suspected cases of avian influenza (H5N1) were reported to the Ministry of Health in Egypt. Sixty-three (1%) patients had confirmed infections; 24 (38%) died. Risk factors for death included female sex, age > or = 15 years, and receiving the first dose of oseltamivir >2 days after illness onset. All but 2 case-patients reported exposure to domestic poultry probably infected with avian influenza virus (H5N1). No cases of human-to-human transmission were found. Greatest risks for infection and death were reported among women > or = 15 years of age, who accounted for 38% of infections and 83% of deaths. The lower case-fatality rate in Egypt could be caused by a less virulent virus clade. However, the lower mortality rate seems to be caused by the large number of infected children who were identified early, received prompt treatment, and had less severe clinical disease.

Kinetics of neutralizing antibodies in patients naturally infected by H5N1 virus

BACKGROUND

Little is known about the kinetics of anti-H5 neutralizing antibodies in naturally H5N1-infected patients with severe clinical illness or asymptomatic infection.

METHODS

Using H5N1 microneutralisation (MN) and H5-pseudotype particle-based microneutralisation assays (H5pp) we analyzed sera sequentially obtained from 11 severely ill patients diagnosed by RT-PCR (follow-up range 1-139 weeks of disease onset) and 31 asymptomatically infected individuals detected in a sero-epidemiological study after exposure to H5N1 virus (follow-up range: 1-2 month-11 months after exposure).

RESULTS

Of 44 sera from 11 patients with H5N1 disease, 70% tested positive by MN (antibody titre > or = 80) after 2 weeks and 100% were positive by 3 weeks after disease onset. The geometric mean MN titers in severely ill patients were 540 at 1-2 months and 173 at 10-12 months and thus were higher than the titers from asymptomatic individuals (149 at 1-2 months, 62.2 at 10-12 months). Fractional polynomial regression analysis demonstrated that in all severely ill patients, positive titers persisted beyond 2 years of disease onset, while 10 of 23 sera collected 10-11 months after exposure in asymptomatically infected individuals tested negative.

CONCLUSIONS

Our results indicate that people with asymptomatic H5N1 infection have lower H5N1 antibody titres compared to those with severe illness and that in many asymptomatically infected patients the antibody titer decreased to levels below the threshold of positivity within one year. These data are essential for the design and interpretation of sero-epidemiological studies.

What is the evidence of a role for host genetics in susceptibility to influenza A/H5N1?

The apparent family clustering of avian influenza A/H5N1 has led several groups to postulate the existence of a host genetic influence on susceptibility to A/H5N1, yet the role of host factors on the risk of A/H5N1 disease has received remarkably little attention compared to the efforts focused on viral factors. We examined the epidemiological patterns of human A/H5N1 cases, their possible explanations, and the plausibility of a host genetic effect on susceptibility to A/H5N1 infection. The preponderance of familial clustering of cases and the relative lack of non-familial clusters, the occurrence of related cases separated by time and place, and the paucity of cases in some highly exposed groups such as poultry cullers, are consistent with a host genetic effect. Animal models support the biological plausibility of genetic susceptibility to A/H5N1. Although the evidence is circumstantial, host genetic factors are a parsimonious explanation for the unusual epidemiology of human A/H5N1 cases and warrant further investigation.

Prevalence of antibodies against avian influenza A (H5N1) virus among Cullers and poultry workers in Ho Chi Minh City, 2005

BACKGROUND

Between 2003 and 2005, highly pathogenic avian influenza A (H5N1) viruses caused large scale outbreaks in poultry in the Ho Chi Minh City area in Vietnam. We studied the prevalence of antibodies against H5N1 in poultry workers and cullers who were active in the program in Ho Chi Minh City in 2004 and 2005.

METHODOLOGY/PRINCIPAL FINDINGS

Single sera from 500 poultry workers and poultry cullers exposed to infected birds were tested for antibodies to avian influenza H5N1, using microneutralization assays and hemagglutination inhibition assay with horse blood. All sera tested negative using microneutralization tests. Three samples showed a 1ratio80 titer in the hemagglutination inhibition assay.

CONCLUSIONS/SIGNIFICANCE

This study provides additional support for the low transmissibility of clade 1 H5N1 to humans, but limited transmission to highly exposed persons cannot be excluded given the presence of low antibody titers in some individuals.

Seroprevalence of antibodies to avian influenza virus A (H5N1) among residents of villages with human cases, Thailand, 2005

No evidence of influenza virus A (H5N1) neutralizing antibodies was found in residents of 4 villages where human cases had occurred the previous year.

In 2005, we assessed the seroprevalence of neutralizing antibodies to avian influenza virus A (H5N1) among 901 residents of 4 villages in Thailand where at least 1 confirmed human case of influenza (H5N1) had occurred during 2004. Although 68.1% of survey participants (median age 40 years) were exposed to backyard poultry and 25.7% were exposed to sick or dead chickens, all participants were seronegative for influenza virus (H5N1).

Avian influenza A H5N1 infections in Bali Province, Indonesia: a behavioral, virological and seroepidemiological study

Background  Bali Province was affected by avian influenza H5N1 outbreaks in birds in October 2003. Despite ongoing circulation of the virus, no human infection had been identified by December 2005.

Objectives  To assess behavioral patterns associated with poultry rearing in Bali, and to identify potential risk factors for H5N1 infection in humans and in household chickens, ducks and pigs.

Methods  A behavioral, virological and seroepidemiologic survey in 38 villages and three live bird markets was completed in December 2005. A multi‐stage cluster design was used to select 291 households with 841 participants from all nine districts in Bali. Specimens were collected from participants as well as a maximum of three pigs, chickens and ducks from each household. Eighty‐seven market vendors participated, where specimens were collected from participants as well as chickens and ducks.

Results  Twenty out of the 38 villages sampled had H5N1 outbreaks. Despite exposure to H5N1 outbreaks, none of the participants from villages or markets were seropositive for H5N1. None of the pigs tested were positive for H5N1. Virus isolation rate in ducks and chicken in markets was higher than in households. Transport of poultry in or out of villages was a risk factor for outbreaks in household chickens and ducks.

Conclusions  The study highlighted that the market chain and associated behaviors may play a role in maintaining the virus in household flocks. The study adds evidence that transmission of H5N1 to humans remains a rare event despite high level handling of both healthy and sick birds.

Evidence for avian influenza A infections among Iowa's agricultural workers

BACKGROUND

Identifying risk factors for zoonotic influenza transmission may aid public health officials in pandemic influenza planning.

OBJECTIVES

We sought to evaluate rural Iowan agriculture workers exposed to poultry for previous evidence of avian influenza virus infection.

METHODS

In 2004 we enrolled 803 rural adult Iowans in a 2-year prospective study of zoonotic influenza transmission. Their enrollment data and sera were compared with those from 66 adult controls enrolled at the University of Iowa in 2006 by proportional odds modeling.

RESULTS

The 803 participants were 58.8% male with a mean age of 55.6 yrs. Forty-eight percent reported previous poultry exposure. Sera were studied by microneutralization techniques for antibodies against avian H4, H5, H6, H7, and H9 viruses. Touching live birds was associated (OR = 1.2; 95% CI 1.02-1.8) with increased antibody titer against H5 virus. Similarly, participants who reported hunting wild birds had increased antibody titers against H7 virus (OR = 2.8; 95%CI = 1.2-6.5) and subjects who reported recent work with poultry had increased antibody titers against H6 (OR = 3.4; 95% CI 1.4-8.5) and H7 viruses (OR = 2.5, 95% CI = 1.1-5.7). There was no evidence of elevated antibody against avian H4 or H9 viruses.

CONCLUSIONS

These data suggest that hunting and exposure to poultry may be important risk factors for avian influenza virus infection among rural US populations. Agriculture workers should be included in influenza pandemic plans.

The public health impact of avian influenza viruses

Influenza viruses with novel hemagglutinin and 1 or more accompanying genes derived from avian influenza viruses sporadically emerge in humans and have the potential to result in a pandemic if the virus causes disease and spreads efficiently in a population that lacks immunity to the novel hemagglutinin. Since 1997, multiple avian influenza virus subtypes have been transmitted directly from domestic poultry to humans and have caused a spectrum of human disease, from asymptomatic to severe and fatal. To assess the pandemic risk that avian influenza viruses pose, we have used multiple strategies to better understand the capacity of avian viruses to infect, cause disease, and transmit among mammals, including humans. Seroepidemiologic studies that evaluate the frequency and risk of human infection with avian influenza viruses in populations with exposure to domestic or wild birds can provide a better understanding of the pandemic potential of avian influenza subtypes. Investigations conducted in Hong Kong following the first H5N1 outbreak in humans in 1997 determined that exposure to poultry in live bird markets was a key risk factor for human disease. Among poultry workers, butchering and exposure to sick poultry were risk factors for antibody to H5 virus, which provided evidence for infection. A second risk assessment tool, the ferret, can be used to evaluate the level of virulence and potential for host-to-host transmission of avian influenza viruses in this naturally susceptible host. Avian viruses isolated from humans exhibit a level of virulence and transmissibility in ferrets that generally reflects that seen in humans. The ferret model thus provides a means to monitor emerging avian influenza viruses for pandemic risk, as well as to evaluate laboratory-generated reassortants and mutants to better understand the molecular basis of influenza virus transmissibility. Taken together, such studies provide valuable information with which we can assess the public health risk of avian influenza viruses.

Genetic susceptibility and resistance to influenza infection and disease in humans and mice

Although genetic risk factors for influenza infection have not yet been defined in people, differences in genetic background and related variation in the response to infection, as well as viral virulence, are all likely to influence both the likelihood of infection and disease severity. However, apart from characterization of viral binding sites in avian and mammalian hosts, relatively little investigation has focused on host genetic determinants of susceptibility or resistance to infection, or the severity of the associated disease in humans or other species. Similarly, the role of genetic background in the generation of an efficacious immune response to either infection or vaccination has not been extensively evaluated. However, genetic influences on susceptibility and resistance to numerous infectious agents and on the resultant host inflammatory and immune responses are well established in both humans and other animals. Mouse-adapted strains of human influenza viruses and the use of inbred strains of laboratory mice have supported extensive characterization of the pathogenesis and immunology of influenza virus infections. Like individual humans, inbred strains of mice vary in their reactions to influenza infection, particularly with regard to the inflammatory response and disease severity, supporting the potential use of these mice as a valuable surrogate for human genetic variation. Relying heavily on what we have learned from mice, this overview summarizes existing animal, human and epidemiologic data suggestive of host genetic influences on influenza infection.