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1.
Despite continuing research efforts, knowledge of the transmission of the highly pathogenic avian influenza (HPAI) virus still has considerable gaps, which complicates epidemic control. The goal of this research was to develop a model to back-calculate the day HPAI virus is introduced into a flock, based on within-flock mortality data. The back-calculation method was based on a stochastic SEIR (susceptible (S) - latently infected (E) - infectious (I) - removed (= dead; R)) epidemic model. The latent and infectious period were assumed to be gamma distributed. Parameter values were based on experimental H7N7 within-flock transmission data. The model was used to estimate the day of virus introduction based on a defined within-flock mortality threshold (detection rule for determining AI). Our results indicate that approximately two weeks can elapse before a noticeable increase in mortality is observed after a single introduction into a flock. For example, it takes twelve (minimum 11 - maximum 15) days before AI is detected if the detection rule is fifty dead chickens on two consecutive days in a 10 000 chicken flock (current Dutch monitoring rule for notification). The results were robust for flock size and detection rule, but sensitive to the length of the latent and infectious periods. Furthermore, assuming multiple introductions on one day will result in a shorter estimated period between infection and detection. The implications of the model outcomes for detecting and tracing outbreaks of H7N7 HPAI virus are discussed.  相似文献   

2.
珠三角地区H7N9禽流感传播途径具有复杂性和特殊性。为进一步明确传播途径,基于家禽产业链视角,在H7N9禽流感最为严重的广州市、深圳市、佛山市,采用分层抽样法选取有代表性且能反映整体情况的养殖场、批发市场、屠宰场、农贸市场,调查H7N9禽流感的动物防疫和个人防护情况。结果显示:养殖场的生物安全隔离仍不完善,存在活禽接触候鸟感染禽流感的风险;批发市场和屠宰场防疫水平高,人感染风险较低;农贸市场的动物防疫条件和个人防护不充分,易扩散病毒;最有可能的传播途径是与候鸟接触后携带病毒的活禽,通过"养殖—批发—零售"产业链蔓延。该结论在明确"禽传人"、"活禽市场环境暴露"观点上深化了产业链各环节间的传播路径。因此,珠三角地区H7N9禽流感的防控重点要加强养殖环节的生物安全隔离,并做好零售环节中活禽与人之间的防控。  相似文献   

3.
Low pathogenic avian influenza virus (LPAIV) exhibits an ecological climax with the aquatic ecosystem. The most widely prevalent subtype of LPAIV is H9N2. Wild aquatic birds being the natural reservoirs and ducks, the “Trojan horses” for Avian Influenza Virus (AIV), can contaminate the natural water bodies inhabited by them. The virus can persist in the contaminated water from days to years depending upon the environmental conditions. Various aquatic species other than ducks can promote the persistence and transmission of AIV; however, studies on the role of aquatic fauna in persistence and transmission of avian influenza virus are scarce. This experiment was designed to evaluate the survivability of H9N2 LPAIV in water with and without Atyopsis moluccensis (bamboo shrimp) for a period of 12 days. The infectivity and amount of virus in water were calculated and were found to be significantly higher in water with A. moluccensis than in water without A. moluccensis. The study also showed that A. moluccensis can accumulate the virus mechanically which can infect chicken eggs up to 11 days. The virus transmission potential of A. moluccensis requires further studies.  相似文献   

4.
Some outbreaks involving highly pathogenic avian influenza viruses (HPAIV) of subtypes H5 and H7 were caused by avian-to-human transmissions. In nature, different influenza A viruses can reassort leading to new viruses with new characteristics. We decided to investigate the impact that the NS-segment of H5 HPAIV would have on viral pathogenicity of a classical avian H7 HPAIV in poultry, a natural host. We focussed this study based on our previous work that demonstrated that single reassortment of the NS-segment from an H5 HPAIV into an H7 HPAIV changes the ability of the virus to replicate in mammalian hosts. Our present data show that two different H7-viruses containing an NS-segment from H5–types (FPV NS GD or FPV NS VN) show an overall highly pathogenic phenotype compared with the wild type H7–virus (FPV), as characterized by higher viral shedding and earlier manifestation of clinical signs. Correlating with the latter, higher amounts of IFN-β mRNA were detected in the blood of NS-reassortant infected birds, 48 h post-infection (pi). Although lymphopenia was detected in chickens from all AIV-infected groups, also 48 h pi those animals challenged with NS-reassortant viruses showed an increase of peripheral monocyte/macrophage-like cells expressing high levels of IL-1β, as determined by flow cytometry. Taken together, these findings highlight the importance of the NS-segment in viral pathogenicity which is directly involved in triggering antiviral and pro-inflammatory cytokines found during HPAIV pathogenesis in chickens.  相似文献   

5.
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6.
The stable carbon isotope technique has been widely used to infer the dietary ecology of a range of animal species; however calibration of the technique with animals fed known diets is essential for accurate back-calculation of dietary preferences. The aim of this study was to identify suitable samples and back-calculation methods to predict short-term (2 to 3 week) dietary selection by sheep among plants with C3 and C4 photosynthetic pathways. Variation in integration time of dietary carbon into plasma and faeces; diet-tissue discrimination of carbon isotopes (fractionation) and the importance of accounting for the digestible or indigestible components of the diet was investigated. The results indicate that faecal and rumen samples provided the most accurate prediction of short term dietary changes in sheep selecting between C3 and C4 plants. The most accurate back-calculation method for these samples used δ13C of the C3 and C4 plants and accounted for both diet-tissue discrimination and differences in the indigestibility between the C3 and C4 forage. For faecal samples, the organic matter content of the diet originating from C4 plants could be predicted with a mean error as low as 2.7%. Wool and plasma samples were not conducive to predicting proportion of C4 forage in the diet within 18 days after a change in diet; however plasma could be used to discriminate between animals fed 100% C3 and C4 diets after 3 days. The δ13C technique provides a valuable tool for researchers when designing pastures for dual environmental and production purposes. An understanding of what sheep select allows for development of appropriate grazing management strategies to optimise productivity and/or persistence of target species.  相似文献   

7.
Genetic changes in avian influenza viruses influence their infectivity, virulence and transmission. Recently we identified a novel genotype of H9N2 viruses in widespread circulation in poultry in Pakistan that contained polymerases (PB2, PB1 and PA) and non-structural (NS) gene segments identical to highly pathogenic H7N3 viruses. Here, we investigated the potential of these viruses to cause disease and assessed the transmission capability of the virus within and between poultry and wild terrestrial avian species. Groups of broilers, layers, jungle fowl, quail, sparrows or crows were infected with a representative strain (A/chicken/UDL-01/08) of this H9N2 virus and then mixed with naïve birds of the same breed or species, or different species to examine transmission. With the exception of crows, all directly inoculated and contact birds showed clinical signs, varying in severity with quail showing the most pronounced clinical signs. Virus shedding was detected in all infected birds, with quail showing the greatest levels of virus secretion, but only very low levels of virus were found in directly infected crow samples. Efficient virus intra-species transmission was observed within each group with the exception of crows in which no evidence of transmission was seen. Interspecies transmission was examined between chickens and sparrows and vice versa and efficient transmission was seen in either direction. These results highlight the ease of spread of this group of H9N2 viruses between domesticated poultry and sparrows and show that sparrows need to be considered as a high risk species for transmitting H9N2 viruses between premises.  相似文献   

8.
Highly pathogenic avian influenza (HPAI) viruses of the H5 and H7 subtype pose a major public health threat due to their capacity to cross the species barrier and infect mammals, for example dogs, cats and humans. In the present study we tested the capacity of selected H7 and H5 HPAI viruses to infect and to be transmitted from infected BALB/c mice to contact sentinels. Previous experiments have shown that viruses belonging to both H5 and H7 subtypes replicate in the respiratory tract and central nervous system of experimentally infected mice. In this study we show that selected H7N1 and H5N1 HPAI viruses can be transmitted from mouse-to-mouse by direct contact, and that in experimentally infected animals they exhibit a different pattern of replication and transmission. Our results can be considered as a starting point for transmission experiments involving other influenza A viruses with α 2-3 receptor affinity in order to better understand the viral factors influencing transmissibility of these viruses in selected mammalian species.  相似文献   

9.
With an extensive data set on visits made to control the H7N7 avian influenza epidemic in The Netherlands in 2003 we investigate the potential role of the persons involved in the control activities as vectors for disease transmission. We hypothesized that people can spread the virus on the same day mechanically, or till 10 days if they have become infected themselves. Taken into account was the estimated time of introduction of the virus into a poultry flock back-calculated from mortality data. We identified 19 visits from a person that went on the same day from an infected (source) farm to a (target) farm that was before infection and a further 197 visits were made to (target) farms that remained uninfected. Of the 19 visits, eight were made within 3 days before an infection started on the target farm. If we assume that these eight visits were the primary reason the visited farms became infected, then we can calculate an upper estimate for the probability of transmission by a person per visit of 0.037. In addition we identified visits were a person first visited an infected source farm and up to 10 days after visited a target farm that either remained uninfected or was before infection. Most visits to infected source farms were made just after infection. Animals on these farms were likely not yet symptomatic, thus escaping diagnosis. Such events may be difficult to prevent, although awareness of this possibility is already a major step towards prevention. Most of these visits involved tracing and screening and were made by a relatively small number of trained veterinarians. This makes it possible to focus training efforts specifically on these persons and make sure they stringently use the personal protective equipment and strictly follow the hygiene protocol, to protect them and prevent them from spreading the disease.  相似文献   

10.
On 31 March 2013, the National Health and Family Planning Commission announced that human infections with influenza A (H7N9) virus had occurred in Shanghai and Anhui provinces, China. H7N9 cases were later detected in Jiangsu and Zhejiang provinces. It was estimated that the virus first spread northward along the route taken by migratory birds and then spread to neighbouring provinces with the sale of poultry. Epidemiological studies were carried out on samples from the external environment of infected cases, transmission routes, farmers markets and live poultry markets. Phylogenetic study of viral sequences from human and avian infections in Zhejiang showed that those from Shanghai and Jiangsu provinces along Taihu Lake were highly homologous with those from the external environment. This suggests that avian viruses carried by waterfowl combined with the virus carried by migratory birds, giving rise to avian influenza virus H7N9, which is highly pathogenic to humans. It is possible that the virus was transmitted by local wildfowl to domestic poultry and then to humans, or spread further by means of trading in wholesale poultry markets. As the weather has turned warm, and with measures adopted to terminate poultry trade and facilitate health communication, the epidemic in the first half of the year has been kept under control. However, the infection source in the triangular area around Taihu Lake still remains. The H7N9 epidemic will probably hit the area later in the year and next spring when the migratory birds return and may even spread to other areas. Great importance should therefore be attached to the wildfowl in Taihu Lake as the repository and disseminator of the virus: investigation and study of this population is essential.  相似文献   

11.
旨在提高对禽流感病毒（avian influenza virus，AIV）检测效率，及时发现疫病。本研究通过分析M基因以及H5、H7和H9亚型的HA基因序列保守区域，设计并合成了相关探针和引物，建立了禽流感病毒（AIV）四重荧光RT-PCR检测方法，该方法可在检测禽流感病毒（AIV）的同时，确定病原是否为H5、H7和H9亚型。结果显示，该检测方法耗时短、特异性好、检测下限达到10-5 ng·μL-1。采用该方法检测临床采集的13个活禽交易市场的384份禽咽喉和泄殖腔双拭子样品，经检测，其中有60份样品为流感病毒阳性，且全部是H9亚型，该结果与行业标准方法（NY/T 772—2013）检测结果一致，κ值为1（P<0.001）。本方法能实现对禽流感病毒及H5、H7和H9亚型的高通量快速检测，将在AIV快速检测中发挥重要作用。  相似文献   

12.
Although the highly pathogenic avian influenza H5N1 virus continues to cause infections in both avian and human populations, the specific zoonotic risk factors remain poorly understood. This review summarizes available evidence regarding types of contact associated with transmission of H5N1 virus at the human–animal interface. A systematic search of the published literature revealed five analytical studies and 15 case reports describing avian influenza transmission from animals to humans for further review. Risk factors identified in analytical studies were compared, and World Health Organization‐confirmed cases, identified in case reports, were classified according to type of contact reported using a standardized algorithm. Although cases were primarily associated with direct contact with sick/unexpectedly dead birds, some cases reported only indirect contact with birds or contaminated environments or contact with apparently healthy birds. Specific types of contacts or activities leading to exposure could not be determined from data available in the publications reviewed. These results support previous reports that direct contact with sick birds is not the only means of human exposure to avian influenza H5N1 virus. To target public health measures and disease awareness messaging for reducing the risk of zoonotic infection with avian influenza H5N1 virus, the specific types of contacts and activities leading to transmission need to be further understood. The role of environmental virus persistence, shedding of virus by asymptomatic poultry and disease pathophysiology in different avian species relative to human zoonotic risk, as well as specific modes of zoonotic transmission, should be determined.  相似文献   

13.
H7N9 virus infection is a global concern, given that it can cause severe infection and mortality in humans. However, the understanding of H7N9 epidemiology, animal reservoir species and zoonotic risk remains limited. This work evaluates the pathogenicity, transmissibility and local innate immune response of three avian species harbouring different respiratory distribution of α2,6 and α2,3 SA receptors. Muscovy ducks, European quails and SPF chickens were intranasally inoculated with 105 embryo infectious dose (EID)50 of the human H7N9 (A/Anhui/1/2013) influenza isolate. None of the avian species showed clinical signs or macroscopic lesions, and only mild microscopic lesions were observed in the upper respiratory tract of quail and chickens. Quail presented more severe histopathologic lesions and avian influenza virus (AIV) positivity by immunohistochemistry (IHC), which correlated with higher IL‐6 responses. In contrast, Muscovy ducks were resistant to disease and presented higher IFNα and TLR7 response. In all species, viral shedding was higher in the respiratory than in the digestive tract. Higher viral shedding was observed in quail, followed by chicken and ducks, which presented similar viral titres. Efficient transmission was observed in all contact quail and half of the Muscovy ducks, while no transmission was observed between chicken. All avian species showed viral shedding in drinking water throughout infection.  相似文献   

14.
Natural infections with influenza viruses have been reported in a variety of animal species including humans, pigs, horses, sea mammals, mustelids and birds. Occasionally, devastating pandemics occur in domestic chickens (broiler and layers) and in humans. From November 2003 to March 2004 in many countries in Asia, there were outbreaks of H5N1 avian influenza virus, causing death of infected patients, and devastating the poultry industry. Some groups of Thai indigenous chickens survived and were therefore classified as resistant. These traits were related to immunogenetics, in particular, the major histocompatibility complex (MHC) class I and class II molecules. The chicken MHC class I were investigated as candidate genes for avian influenza virus disease resistance. Seven hundred and thirty Thai indigenous chickens from smallholder farms in the rural area of avian influenza virus disease outbreaks in the central part of Thailand were used in the present study. They were separated into two groups, 340 surviving chickens and 390 dead chickens (resistant and susceptible). Genomic DNA were precipitated from blood samples and feathers. The DNA were used to amplify the MHC class I gene. Data were analyzed using χ2 analysis to test significant differences of influences of MHC class I haplotypes on avian influenza virus disease traits. The results represented nine MHC class I haplotypes: A1, B12, B13, B15, B19, B21, B2, B6, and BA12, and included 10 of their heterozygotes. The homozygous B21 from these collected samples had a 100% survival rate and they were the major survival group. In addition, the heterozygous B21 also had a high survival rate because of co‐dominant expression of these genes. In contrast, the homozygous B13 had a 100% mortality rate and they were the major mortality group. These results confirmed that MHC class I haplotypes influence avian influenza virus disease‐resistant traits in Thai indigenous chicken. The MHC genes can be used as genetic markers to improve disease‐resistant traits in chicken.  相似文献   

15.
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16.
West Nile virus (WNV) and Usutu virus (USUV) are arboviruses that are maintained in enzootic transmission cycles between mosquitoes and birds and are occasionally transmitted to mammals. As arboviruses are currently expanding their geographic range and emerging in often unpredictable locations, surveillance is considered an important element of preparedness. To determine whether sera collected from resident and migratory birds in the Netherlands as part of avian influenza surveillance would also represent an effective source for proactive arbovirus surveillance, a random selection of such sera was screened for WNV antibodies using a commercial ELISA. In addition, sera of jackdaws and carrion crows captured for previous experimental infection studies were added to the selection. Of the 265 screened serum samples, 27 were found to be WNV–antibody‐positive, and subsequent cross‐neutralization experiments using WNV and USUV confirmed that five serum samples were positive for only WNV‐neutralizing antibodies and seven for only USUV. The positive birds consisted of four Eurasian coots (Fulica atra) and one carrion crow (Corvus corone) for WNV, of which the latter may suggest local presence of the virus, and only Eurasian coots for USUV. As a result, the screening of a small selection of serum samples originally collected for avian influenza surveillance demonstrated a seroprevalence of 1.6% for WNV and 2.8% for USUV, suggesting that this sustained infrastructure could serve as a useful source for future surveillance of arboviruses such as WNV and USUV in the Netherlands.  相似文献   

17.
The microbicidal activities of mixtures of quaternary ammonium compounds (QACs) and food additive grade calcium hydroxide (FdCa(OH)2) were evaluated in a suspension test at −20°C using an anti-freeze agent (AFA) containing methanol, or at 1°C, with varying contact time, toward avian influenza virus (AIV), Newcastle disease virus (NDV), fowl adenovirus (FAdV), avian reovirus (ARV), Salmonella Infantis (SI) and Escherichia coli (EC). At −20°C, the mixtures could inactivate AIV and NDV within 30 min, FAdV and ARV within 5 sec, and SI and EC within 3 min, respectively. AFA did not inactivate viruses and bacteria within 30 min and 10 min, respectively. At 1°C, the mixtures inactivated FAdV and ARV within 30 sec, AIV within 10 min, and NDV within 30 min. A mixture of slaked lime (SL) and QAC could inactivate FAdV and ARV within 30 sec, but could not inactivate AIV and NDV even after 60 min at 1°C. SL could not substitute FdCa(OH)2 in order to exert the synergistic effects with QAC. Thus, QACs microbicidal activities were maintained or enhanced by adding FdCa(OH)2. It is hence recommended to use QACs with FdCa(OH)2, especially in the winter season.  相似文献   

18.
Avian influenza outbreaks have occurred during winter months, and effective disinfection of poultry premises at freezing temperatures is needed. The commercial disinfectants Virkon and Accel, supplemented with an antifreeze agent [propylene glycol (PG), methanol (MeOH), or calcium chloride (CaCl2)], were evaluated for their effectiveness in killing avian influenza virus (AIV) at −20°C or 21°C. An AIV suspension was applied to stainless steel disks, air-dried, and covered with a disinfectant or antifreeze agent for 5 to 30 min. Virkon (2%) and Accel (6.25%) with 30% PG, 20% MeOH, or 20% CaCl2 inactivated 6 log10 AIV within 5 min at −20°C and 21°C. At these temperatures PG and MeOH alone did not kill AIV, but the 20% CaCl2 solution alone inactivated 5 log10 AIV within 10 min. The results suggested that CaCl2 is potentially useful to enhance the effectiveness of disinfection of poultry facilities after outbreaks of AIV infection in warm and cold seasons.  相似文献   

19.
This study investigated the immunoadjuvant effects of three types of bacterial genomic DNA and CpG oligonucleotides (CpG ODN) on the avian influenza virus (AIV) subtype H5N1 inactivated oil emulsion vaccine under two immunization strategies. The genomic DNA extracted from Escherichia coli O2, Staphylococcus aureus, Streptococcus faecalis FQ68, and synthetic CpG ODN were used as adjuvants, and their effects on the AIV oil emulsion vaccine were examined in chickens. The results indicated that when administered separately from the vaccine, adjuvants induced lower haemagglutination inhibition (HI) titres and serum IgG titres but resulted in higher concentrations of IFN-γ and IL-10. In contrast, when combined with the oil emulsion vaccine prior to inoculation, CpG ODN induced higher HI, IgG titres and IFN-γ concentration but resulted in lower IL-10 concentration. These data suggest that, depending on the immunization approaches, adjuvants may exert distinct immune effects in chickens receiving AIV H5N1 oil emulsion vaccine: the prior incorporation of CpG ODN into the vaccine may augment both the humoral and Th1 type immune responses, while separate inoculation of adjuvants has not shown better adjuvanticity.  相似文献   

20.
As part of the USA's National Strategy for Pandemic Influenza, an Interagency Strategic Plan for the Early Detection of Highly Pathogenic H5N1 Avian Influenza in Wild Migratory Birds was developed and implemented. From 1 April 2006 through 31 March 2009, 261 946 samples from wild birds and 101 457 wild bird fecal samples were collected in the USA; no highly pathogenic avian influenza was detected. The United States Department of Agriculture, and state and tribal cooperators accounted for 213 115 (81%) of the wild bird samples collected; 31, 27, 21 and 21% of the samples were collected from the Atlantic, Pacific, Central and Mississippi flyways, respectively. More than 250 species of wild birds in all 50 states were sampled. The majority of wild birds (86%) were dabbling ducks, geese, swans and shorebirds. The apparent prevalence of low pathogenic avian influenza viruses during biological years 2007 and 2008 was 9.7 and 11.0%, respectively. The apparent prevalence of H5 and H7 subtypes across all species sampled were 0.5 and 0.06%, respectively. The pooled fecal samples (n= 101 539) positive for low pathogenic avian influenza were 4.0, 6.7 and 4.7% for biological years 2006, 2007 and 2008, respectively. The highly pathogenic early detection system for wild birds developed and implemented in the USA represents the largest coordinated wildlife disease surveillance system ever conducted. This effort provided evidence that wild birds in the USA were free of highly pathogenic avian influenza virus (given the expected minimum prevalence of 0.001%) at the 99.9% confidence level during the surveillance period.  相似文献   

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