Pathogenic Avian Influenza Subtype Research Articles

A simple model for simulating immunity rate dynamics in a tropical free-range poultry population after avian influenza vaccination

In developing countries, vaccination against highly pathogenic avian influenza subtype H5N1 (HPAI) in free-range poultry flocks is usually implemented as periodic campaigns and newborn chicks are generally not vaccinated by farmers between vaccination passes. The demographic population turnover leads to a continuous decrease in the population immunity rate (PIR) over time. We present a simple Leslie matrix model for estimating population turnover and PIR dynamics in a hypothetical small-size vaccinated free-range poultry population. Four different vaccination scenarios were identified assuming necessary procedures to achieve immunity. The results indicate that high levels of population immunity are difficult to sustain. Assuming an animal immunity response of 80% after vaccination and a constant population size, PIR 4 months after vaccination was 30% in all the scenarios. Predictions averaged over time showed mean PIR between 36% and 48%, which is below the population immunity thresholds for eradication approximated from R0 estimates.

Risk of Introduction of H5N1 HPAI from Europe to Spain by Wild Water Birds in Autumn

Highly pathogenic avian influenza (HPAI) subtype H5N1 continues to circulate across Eurasia and Africa since its unprecedented rapid spread in 2005. Diffusion by wild bird movements has been evidenced in the European Union in 2006 and 2007. Spain is an important wintering quarter for aquatic birds from northern latitudes, so identifying the critical areas and species where an outbreak is prone to happen is necessary. This work presents an assessment of the risk of introduction of H5N1 HPAI in Spain by aquatic wild birds estimating a relative risk value per province. For this purpose, an assessment of the release and exposure to the risk of infection with H5N1 HPAI of 25 selected water bird species has been carried out. Parameters considered in the assessment include H5N1 HPAI notifications from 2006 to 2008 and factors that favour the occurrence or persistence of H5N1 HPAI (wetlands' surface, low temperatures), together with aquatic wild birds' movements parameters (departure, destination, stop-overs, abundance) and parameters relative to the susceptible population in Spain: poultry density and wild aquatic abundance. Results show the relative risk for each Spanish province of experiencing H5N1 HPAI introduced by wild aquatic birds helping to identify higher risk areas.

Possible explanation for no evidence of carditis in human H5N1 infection

Sir, influenza is an important respiratory viral infection. This viral infection can bring several complications. Viral carditis is documented as an important fatal complication of influenza [ [1] Feng X.M. Incidence of viral carditis in epidemic influenza. in: Zhonghua Xin Xue Guan Bing Za Zhi. vol. 12(3). Sep 1984: 177-179 Google Scholar ]. H5N1 influenza is a new emerging infectious disease with high fatality. This disease is of present surveillance. Unlike general influenza, the cardiac involvement in human H5N1 influenza virus infection is not documented in the literature [ [2] Wiwanitkit V. Humans infected with bird flu: is there evidence of cardiac disorder?. Can J Cardiol. 2006; 22: 661 Abstract Full Text PDF PubMed Scopus (1) Google Scholar ]. Here, the author uses basic theory to explain the possible reason for no carditis in H5N1 infection. A possible explanation is that the carditis in influenza is basically due to the immune complex process. However, in human H5N1 infection, there is no immune complex formation. This is mainly due to the fact that human beings fail to develop protective sterilising immune response to H5N1 particles [ [3] Kotwal G.J. Genetic diversity-independent neutralization of pandemic viruses (e.g. HIV), potentially pandemic (e.g. H5N1 strain of influenza) and carcinogenic (e.g. HBV and HCV) viruses and possible agents of bioterrorism (variola) by enveloped virus neutralizing compounds (EVNCs). Vaccine. Jun 6 2008; 26: 3055-3058 Crossref PubMed Scopus (52) Google Scholar ] therefore, there cannot be further formation of immune complex. Of interest, although there is a report indicating the possible carditis in human H5N1 infection but there is no confirmation from autopsy [ [4] Zhang W. Wen L.Y. Lu M. et al. Clinical characteristic analysis of the first human case infected by influenza A (H5N1) in Jiangxi Province. in: Zhonghua Jie He He Hu Xi Za Zhi. vol. 29(5). May 2006: 300-306 Google Scholar ]. This is totally different from avian cases that immune generation can occur and lead to carditis [ [5] Kwon Y.K. Sung H.W. Joh S.J. et al. An outbreak of highly pathogenic avian influenza subtype H5N1 in broiler breeders, Korea. J Vet Med Sci. Nov 2005; 67: 1193-1196 Crossref PubMed Scopus (16) Google Scholar ]. This article can support the evidence of no cardiac involvement in H5N1 virus infection.

Avian influenza surveillance in wild birds in the European Union in 2006.

Background Infections of wild birds with highly pathogenic avian influenza (AI) subtype H5N1 virus were reported for the first time in the European Union in 2006. Objectives To capture epidemiological information on H5N1 HPAI in wild bird populations through large‐scale surveillance and extensive data collection. Methods Records were analysed at bird level to explore the epidemiology of AI with regard to species of wild birds involved, timing and location of infections as well as the applicability of different surveillance types for the detection of infections. Results In total, 120,706 records of birds were sent to the Community Reference Laboratory for analysis. Incidents of H5N1 HPAI in wild birds were detected in 14 EU Member States during 2006. All of these incidents occurred between February and May, with the exception of two single cases during the summer months in Germany and Spain. Conclusions For the detection of H5N1 HPAI virus, passive surveillance of dead or diseased birds appeared the most effective approach, whilst active surveillance offered better detection of low pathogenic avian influenza (LPAI) viruses. No carrier species for H5N1 HPAI virus could be identified and almost all birds infected with H5N1 HPAI virus were either dead or showed clinical signs. A very large number of Mallards (Anas platyrhynchos) were tested in 2006 and while a high proportion of LPAI infections were found in this species, H5N1 HPAI virus was rarely identified in these birds. Orders of species that appeared to be very clinically susceptible to H5N1 HPAI virus were swans, diving ducks, mergansers and grebes, supporting experimental evidence. Surveillance results indicate that H5N1 HPAI virus did not establish itself successfully in the EU wild bird population in 2006.

Phylogenetics and Pathogenesis of Early Avian Influenza Viruses (H5N1), Nigeria

Three highly pathogenic avian influenza subtype H5N1 and 4 Newcastle disease viruses were isolated from sick or dead chickens in southwestern Nigeria. Sequencing and phylogenetic analysis placed them within H5N1 subclade 2.2.2. Intravenous and intranasal pathogenicity tests produced systemic disease with vascular endothelial cell tropism in chickens.

Detection of human virulence signatures in H5N1

A method for detecting the emergence of potential pandemic-causing influenza strains has been developed. The system first uses real-time RT-PCR to detect H5, the highly pathogenic avian influenza subtype most likely to cause a pandemic. Pyrosequencing is then employed to scan for codon changes encoding amino acids known to define human influenza versus avian influenza signatures. The pyrosequencing assays were developed to screen at the nucleotide level for 52 amino acid changes defined as avian- or human-specific. A library has been built to screen the sequence data generated and properly identify the strain in question as a potential threat. This method can be used to screen samples for influenza and to determine if the detected virus contains mutations that may make the virus more infective or virulent to humans, potentially thwarting a pandemic outbreak.

Estimation of the basic reproductive number (R0) for epidemic, highly pathogenic avian influenza subtype H5N1 spread

Three different methods were used for estimating the basic reproductive number (R0) from data on 110 outbreaks of highly pathogenic avian influenza (HPAI) subtype H5N1 that occurred in village poultry in Romania, 12 May to 6 June 2006. We assumed a village-level infectious period of 7 days. The methods applied were GIS-based identification of nearest infectious neighbour (based on either Euclidean or road distance), the method of epidemic doubling time, and a susceptible-infectious (SI) modelling approach. In general, the estimated basic reproductive numbers were consistent: 2.14, 1.95, 2.68 and 2.21, respectively. Although the true basic reproductive number in this epidemic is unknown, results suggest that the use of a range of methods might be useful for characterizing epidemics of infectious diseases. Once the basic reproductive number has been estimated, better control strategies and targeted surveillance programmes can be designed.

Environmental and anthropogenic risk factors for highly pathogenic avian influenza subtype H5N1 outbreaks in Romania, 2005−2006

The association between highly pathogenic avian influenza (HPAI) subtype H5N1 outbreak risk in poultry in 161 Romanian villages (October 2005 to June 2006) and environmental and anthropogenic factors was investigated. Village outbreak risk was associated with a village being <5 km from a major road (odds ratio [OR] 5.27, 95% confidence interval [CI] 1.21-22.9) or a river/stream (OR 1.97, 95% CI 1.06-3.72). Outbreak risk in the first part of the epidemic was associated with a village being <5 km from a major road (OR 3.31, 95% CI 1.10-9.98) or a regularly flooded land area (OR 5.08, 95% CI 1.08-23.9); whereas outbreak risk in the second part of the epidemic was associated with a village being <5 km from a river/stream (OR 5.5, 95% CI 1.69-18.9). Results suggest that both environmental and anthropogenic factors influence the risk of HPAI subtype H5N1 outbreaks in village poultry populations.

Geostatistical visualisation and spatial statistics for evaluation of the dispersion of epidemic highly pathogenic avian influenza subtype H5N1

The aim of this study was to evaluate a range of statistical and geostatistical methods for their usefulness in providing insights into how highly pathogenic avian influenza (HPAI) subtype H5N1 might spread through a national population of village poultry. The insights gained allow the generation of disease dispersion hypotheses. The case study data set consisted of 161 outbreaks of HPAI subtype H5N1 in village poultry reported in Romania between October 2005 and June 2006. Reports of village outbreaks (%) occurred in three waves: October-December (14%), February-March (16%), and May-June (68%). Risk mapping - based on variography and kriging - was used to visualize the evolution of the epidemic. Outbreaks first appeared in eastern and southern Romania, particularly within an area that forms part of the Danube River Delta. The largest phase of the epidemic affected villages in all parts of central, southern, and eastern Romania, but outbreaks were clustered in central Romania. Outbreaks spread in an east to west direction. By using geostatistical visualisation and spatial statistics, the evolution of the epidemic could be characterised into two parts: disease introduction, local spread, and sporadic outbreaks, and long-distance disease spread with rapid epidemic propagation. This is consistent with the hypothesis that the environment and landscape (specifically the Danube River Delta) played a critical role in the introduction and initial spread of HPAI subtype H5N1 during the autumn and winter of 2005, and that the movement of poultry might have introduced the infection into central Romania during the spring and summer of 2006. Further research focusing on the spatio-temporal interface between the two parts of the epidemic might reveal how and why it progressed from a confined, local epidemic to a large, national epidemic. Such information would assist efforts to limit the global spread of HPAI subtype H5N1.

The indirect immunofluorescence assay using cardiac tissue from chickens, quails and ducks for identification of influenza A virus during an outbreak of highly pathogenic avian influenza virus (H5N1): A rapid and simple screening tool for limited resource settings

Here we describe the diagnostic utility of the indirect immunofluorescence assay (IFA) during a recent outbreak of highly pathogenic avian influenza (HPAI) subtype H5N1 virus in southern Thailand and demonstrate the usefulness of the cardiac tissue from infected chickens, quail, and ducks for diagnosis. The most reliable sample for IFA diagnosis of influenza A virus was cardiac tissue (83.0%; 44/53) which when divided by species (chicken, quail and duck cardiac tissues) gave respective positivity rates of 88% (22/25), 88.9% (16/18) and 60.0% (6/10). Cardiac tissue also gave the highest IFA intensity for the three species. We believe that the IFA method has wide applicability in developing countries or remote settings where clinically similar avian diseases with high morbidity and mortality such as Newcastle disease and fowl cholera are common and could be rapidly excluded thereby conserving valuable reference laboratory capacity for true HPAI outbreaks.

An outbreak of avian influenza subtype H9N8 among chickens in South Korea

Low pathogenic avian influenza subtype H9N8 was diagnosed on a Korean native chicken farm in Gyeonggi province, South Korea, in late April 2004. Clinical signs included moderate respiratory distress, depression, mild diarrhoea, loss of appetite and a slightly elevated mortality (1.4% in 5 days). Pathologically, mucopurulent tracheitis and air sacculitis were prominently found with urate renal deposition. The isolated A/chicken/Kr/164/04 (H9N8) had an Ala-Ser-Gly-Arg (A/S/G/R) motif at the cleavage site of haemagglutinin, which has been commonly found in H9N2 isolated from Korean poultry. Phylogenetic analysis of the haemagglutinin and neuraminidase genes of the H9N8 avian influenza virus (AIV) isolate showed that reassortment had occurred. Its haemagglutinin gene was similar to that of Korean H9N2 AIVs, but its neuraminidase gene was closely related to that of A/WBF/Kr/KCA16/03 (H3N8) isolated from the faeces of wild birds in Korea. The pathogenicity of the isolate was tested on 6-week-old specific pathogen free chickens. The inoculated virus (H9N8) was recovered from most tested organs, including the trachea, lung, kidney, spleen, and caecal tonsil. This is the first report of an outbreak of low pathogenic avian influenza in chickens caused by AIV subtype H9N8.

Highly pathogenic avian influenza virus subtype H5N1 in Mute swans in the Czech Republic

In order to determine the actual prevalence of avian influenza viruses (AIV) in wild birds in the Czech Republic extensive surveillance was carried out between January and April 2006. A total of 2101 samples representing 61 bird species were examined for the presence of influenza A by using PCR, sequencing and cultivation on chicken embryos. AIV subtype H5N1 was detected in 12 Mute swans ( Cygnus olor). The viruses were determined as HPAI (highly pathogenic avian influenza) and the hemagglutinin sequence was closely similar to A/mallard/Italy/835/06 and A/turkey/Turkey/1194/05. Following the first H5N1 case, about 300 wild birds representing 33 species were collected from the outbreak region and tested for the presence of AIV without any positive result. This is the first report of highly pathogenic avian influenza subtype H5N1 in the Czech Republic. The potential role of swan as an effective vector of avian influenza virus is also discussed.

SEROPREVALENCE OF H9N2 SUBTYPE AVIAN INFLUENZA IN CHICKEN FARMS IN SAUDI ARABIA

A total number of 3511 serum samples were collected from chicken farms in Saudi Arabia during summer of 2004 and was tested for the presence of antibodies against type A specific antigen of avian influenza virus using commercial enzyme linked immunosorbent assay (ELISA) kits. Total positive samples represented 45.81%. Broiler positive samples represented 12.73%. While in layers, positive samples were 30.19%. Tissue samples were also taken from 5 chicken farms suffering from high mortality and respiratory signs and the H9N2 and Newcastle disease viruses were isolated and identified from these samples. These results indicate that the mild pathogenic avian influenza subtype H9N2 virus is widespread in poultry flocks in Saudi Arabia and is circulating undetected in most cases. Infection with H9N2 may pass unnoticed unless exacerbated by other co-infections like Mycoplasma gallisepticum or infectious bronchitis virus. Presence of H9N2 virus requires continuous monitoring and surveillance for possible occurrence of mutations and the risk of avian-to-human transmission.

An Outbreak of Highly Pathogenic Avian Influenza Subtype H5N1 in Broiler Breeders, Korea

Highly pathogenic avian influenza (HPAI) was diagnosed in broiler breeders, submitted to the National Veterinary Research and Quarantine Service in South Korea. Grossly, the dead breeders had lesions consistent with HPAI, including pancreatic mottling, splenomegaly, pulmonary edema and congestion, and hemorrhages in the mucosa of the proventriculus, gizzard and small intestine, and on the serosal surface. Microscopically, there were necrotized hepatitis and pancreatitis, lymphocytic meningoencephalitis, myocarditis, and interstitial pneumonia. Influenza viral antigen was demonstrated in areas closely associated with histopathologic lesions. The AI virus was isolated from cecal tonsils, feces, trachea, and kidney of the chickens. The isolated virus was identified as the highly pathogenic H5N1, with a hemagglutinin proteolytic cleavage site deduced amino acid sequences of QREKRKKR/GLFGAGLFGAIAG. In order to determine the pathogenicity of the isolate, eight 6-week-old specific pathogen free chickens were inoculated intravenously with the virus, and all the birds died within 24 hr after inoculation. This is the first report of an outbreak of HPAI in the chickens in South Korea.

Vaccination of chickens against H5N1 avian influenza in the face of an outbreak interrupts virus transmission

Vaccination of chickens with a commercially available killed H5N2 vaccine was being evaluated as an additional tool to enhanced biosecurity measures and intensive surveillance for control of highly pathogenic avian influenza subtype H5N1 disease in Hong Kong in 2002. In December 2002 to January 2003, there were outbreaks of H5N1 disease in waterfowl in two recreational parks, wild water birds, several poultry markets and five chicken farms. In addition to quarantine, depopulation of the affected sheds and increased biosecurity, vaccination of the unaffected sheds and surrounding unvaccinated farms was undertaken on three farms. In at least two farms, infection spread to the recently vaccinated sheds with low rates of H5N1 mortality in sheds when the chickens were between 9 and 18 days post-vaccination. However, after 18 days post-vaccination no more deaths from H5N1 avian influenza occurred and intensive monitoring by virus culture on these farms showed no evidence of asymptomatic shedding of the virus. This provides evidence that H5 vaccine can interrupt virus transmission in a field setting.

Detection of highly pathogenic and low pathogenic avian influenza subtype H5 (Eurasian lineage) using NASBA

Nucleic acid sequence-based amplification (NASBA) is a technique that allows the rapid amplification of specific regions of nucleic acid obtained from a diverse range of sources. It is especially suitable for amplifying RNA sequences. A NASBA technique has been developed that allows the detection of avian influenza A subtype H5 from allantoic fluid harvested from inoculated chick embryos. The amplified viral RNA is detected by electrochemiluminescence. The NASBA technique described below is rapid and specific for the identification of influenza A subtype H5 viruses of the Eurasian lineage. More importantly, it can be used to distinguish highly pathogenic and low pathogenic strains of the H5 subtype.