野生鸟类禽流感病毒感染情况的调查

为了解野生鸟类禽流感病毒(AIV)的携带感染情况,2006年～2010年,本研究在湖南省主要候鸟迁徙地收集115只野鸟组织或拭子样品、75份野鸟的新鲜粪便样品和72份血清样品。组织或拭子样品采用RT-PCR方法检测和鸡胚接种病毒分离鉴定,血清样品分别进行H5(含Re-5和Re-4)、H6、H7、H9、H10和H11抗体检测。结果表明,从斑鸠和绿头鸭组织中分别分离到H5N1亚型和H3N2亚型AIV;72份血清中有17份抗体为阳性,其中H5(Re-5)亚型5份、H5(Re-4)亚型1份、H6亚型1份、H7亚型2份和H9亚型8份,阳性率分别为6.94%、1.39%、1.39%、2.78%和11.11%。H10和H11亚型未检测到抗体阳性。     

Surveillance for highly pathogenic avian influenza in wild birds in the USA

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.     

Avian influenza viruses in wild birds: a moving target

The long-standing evolutionary and ecological relationships between wild birds and influenza A viruses has created a broad pool of viral genetic diversity and a reservoir of potentially transmissible viruses. An understanding of these relationships can help us identify and modify critical control points to reduce transmission of avian influenza viruses into animal and human populations.     

Surveillance for avian influenza virus in captive wild birds and indigenous chickens in Nigeria

Tropical Animal Health and Production - Several reports of avian influenza virus (AIV) have been made on commercial chickens and wild birds in sub-Saharan Africa, but there is paucity of...     

A global model of avian influenza prediction in wild birds: the importance of northern regions

Avian influenza virus (AIV) is enzootic to wild birds, which are its natural reservoir. The virus exhibits a large degree of genetic diversity and most of the isolated strains are of low pathogenicity to poultry. Although AIV is nearly ubiquitous in wild bird populations, highly pathogenic H5N1 subtypes in poultry have been the focus of most modeling efforts. To better understand viral ecology of AIV, a predictive model should 1) include wild birds, 2) include all isolated subtypes, and 3) cover the host’s natural range, unbounded by artificial country borders. As of this writing, there are few large-scale predictive models of AIV in wild birds. We used the Random Forests algorithm, an ensemble data-mining machine-learning method, to develop a global-scale predictive map of AIV, identify important predictors, and describe the environmental niche of AIV in wild bird populations. The model has an accuracy of 0.79 and identified northern areas as having the highest relative predicted risk of outbreak. The primary niche was described as regions of low annual rainfall and low temperatures. This study is the first global-scale model of low-pathogenicity avian influenza in wild birds and underscores the importance of largely unstudied northern regions in the persistence of AIV.     

Australian surveillance for avian influenza viruses in wild birds between July 2005 and June 2007

Objective   To identify and gain an understanding of the influenza viruses circulating in wild birds in Australia.
Design   A total of 16,303 swabs and 3782 blood samples were collected and analysed for avian influenza (AI) viruses from 16,420 wild birds in Australia between July 2005 and June 2007. Anseriformes and Charadriiformes were primarily targeted.
Procedures   Cloacal, oropharyngeal and faecal (environmental) swabs were tested using polymerase chain reaction (PCR) for the AI type A matrix gene. Positive samples underwent virus culture and subtyping. Serum samples were analysed using a blocking enzyme-linked immunosorbent assay for influenza A virus nucleoprotein.
Results   No highly pathogenic AI viruses were identified. However, 164 PCR tests were positive for the AI type A matrix gene, 46 of which were identified to subtype. A total of five viruses were isolated, three of which had a corresponding positive PCR and subtype identification (H3N8, H4N6, H7N6). Low pathogenic AI H5 and/or H7 was present in wild birds in New South Wales, Tasmania, Victoria and Western Australia. Antibodies to influenza A were also detected in 15.0% of the birds sampled.
Conclusions   Although low pathogenic AI virus subtypes are currently circulating in Australia, their prevalence is low (1.0% positive PCR). Surveillance activities for AI in wild birds should be continued to provide further epidemiological information about circulating viruses and to identify any changes in subtype prevalence.     

Humoral immune response to avian influenza vaccination over a six-month period in different species of captive wild birds

In December 2005, the four major Swiss zoos carried out the vaccination of selected zoo birds with the adjuvant inactivated vaccine H5N2 Nobilis influenza. Pre- and post-vaccination antibody titers were determined either by hemagglutination inhibition (HI) test (non-Galliformes) or by enzyme linked immunosorbent assay (ELISA) (Galliformes) at Week 0, 5, 10, and 26 (Day 0-1, 35-36, 70-71, and 182 respectively) to determine the humoral immune response to H5 antigen. After the first vaccination, the overall geometric mean titer of non-Galliformes was 65 (n = 142), which increased to 187 (n = 139) after booster vaccination and dropped to 74 (n = 65) six months after first vaccination. For the Galliformes group, the mean titers were found to be 2.09 at Week 5 (n = 119), 3.24 at Week 10 (n = 113), and 1.20 at Week 26 (n = 39). Within the non-Galliformes, significant differences in geometric mean titers were found among different species representatives. In general, the flamingos (Phoenicopteriformes) showed a strong response to vaccination, reaching a geometric mean titer of 659 at Week 10, while the Sphenisciformes did not show high antibody titers even after booster vaccination, reaching a maximum geometric mean titer of only 65. Based on the antibody titer profiles of all investigated species, we recommend at least annual revaccination for the species that we investigated.     

Risk-based surveillance for H5N1 avian influenza virus in wild birds in Great Britain

Recent outbreaks of the H5N1 strain of avian influenza in Europe have highlighted the need for continuous surveillance and early detection to reduce the likelihood of a major outbreak in the commercial poultry industry. In Great Britain (gb), one possible route by which H5N1 could be introduced into domestic poultry is through migratory wild birds from Europe and Asia. Extensive monitoring data on the 24 wild bird species considered most likely to introduce the virus into GB, and analyses of local poultry populations, were used to develop a risk profile to identify the areas where H5N1 is most likely to enter and spread to commercial poultry. The results indicate that surveillance would be best focused on areas of Norfolk, Suffolk, Lancashire, Lincolnshire, south-west England and the Welsh borders, with areas of lower priority in Anglesey, south-west Wales, north-east Aberdeenshire and the Firth of Forth area of Scotland. These areas have significant poultry populations including a large number of free-range flocks, and a high abundance of the 24 wild bird species.     

Infectivity and transmissibility of H9N2 avian influenza virus in chickens and wild terrestrial birds

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.     

Characterization of encephalitis in wild birds naturally infected by highly pathogenic avian influenza H5N1

During the outbreak of highly pathogenic avian influenza (HPAI) H5N1 in Sweden in 2006, disease and mortality were observed in a number of wild bird species. Encephalitis was one of the most consistent and severe findings in birds submitted for postmortem examination. However, the distribution and severity of the inflammation varied among individuals. This study characterized the encephalitis and the phenotype of the cellular infiltrate in brains of 40 birds of various species naturally infected with HPAI H5N1. Brain sections stained with hematoxylin and eosin and immunostained for influenza A viral antigen were evaluated in parallel to brain sections immunostained with antibodies against T lymphocytes (CD3+), B lymphocytes (CD79a+), macrophages (Lectin RCA-1+), and astrocytes expressing glial fibrillary acidic protein. The virus showed marked neurotropism, and the neuropathology included multifocal to diffuse areas of gliosis and inflammation in the gray matter, neuronal degeneration, neuronophagia, vacuolation of the neuropil, focal necrosis, perivascular cuffing, and meningitis. Broad ranges in severity, neuroanatomical distribution, and type of cellular infiltrate were observed among the different bird species. Since neurotropism is a key feature of HPAI H5N1 infection in birds and other species and because the clinical presentation can vary, the characterization of the inflammation in the brain is important in understanding the pathogenesis of the disease and also has important diagnostic implications for sample selection.     

Host range of avian influenza virus in free-living birds

Isolation of avian influenza virus (AIV) has been reported from 12 orders and 88 species of free-living birds. Most isolations are reported from species in the orders Anseriformes and Charadriiformes and it is recognized that species in Anseriformes represent important reservoirs of AIV. Morbidity and mortality among free-living birds attributable to AIV infection are rare, but differences in prevalence of AIV occur within and between avian species. Seasonal variation has been reported from free-living and sentinel ducks with peak AIV infection occurring in late summer and early fall. Prevalence of AIV is age-related, with highest isolation rates reported from juvenile birds. Differences in susceptibility to AIV infection among species have been demonstrated under experimental conditions. The dynamics and epidemiology of species-related variation in populations of free-living birds require further study.     

Prevalence of avian haematozoa in wild birds in a high-altitude forest in Japan

The infection dynamics of avian haematozoa, which includes the genera Plasmodium, Haemoproteus, and Leucocytozoon, are complicated by a variety of environmental factors and host-parasite interactions. In Japan, the prevalence of haematozoa in wild birds has recently been determined in several local areas. However, no information on the annual prevalence of avian haematozoa in a single study site has been reported. Here, we investigated the long-term infection dynamics of haematozoa in wild birds inhabiting a mountain forest of Japan. Blood samples were collected from 415 wild birds captured in the Chichibu mountains in Saitama Prefecture at an altitude of 1650 m between 2007 and 2010. All obtained samples were examined for haematozoan infection using nested polymerase chain reaction (PCR) of the cytochrome b (cytb) genes of haematozoa. A total of 62 out of 415 (14.9%) forest birds were PCR positive for haematozoa. Relatively high infection rates of Leucocytozoon were found among several bird species (Parus ater, 64.3%; Parus montanus, 81.8%) and may be due to the host preference of vector black flies and host nestling pattern in this forest. Phylogenetic analysis of amplified cytb sequences revealed for the first time that a variety of lineages of avian haematozoa are distributed among wild bird hosts in a high-altitude forest stand in Japan. Notably, significant seasonal changes of the prevalence of avian haematozoa were not observed; however, continuous investigation will likely provide detailed information on host-parasite interactions, including local environmental factors, that influence the dynamics of avian haematozoan infections.