Prevalence Of Avian Influenza Research Articles

Avian Influenza Surveillance in Pigs, Dogs, Chickens and Slaughter Slabs Biosecurity in Kaduna Metropolis, Nigeria

Avian influenza is a zoonotic disease likely to be exposed to dog, pig and poultry owners & their processors who are in close contact during processing of these animals in Kaduna Metropolis, Nigeria. The study assessed the biosecurity practice of processors in pig, poultry, and dog slaughter slabs; and the prevalence of Avian Influenza (H5 subtype) antibodies in dogs, pigs, and chickens in Kaduna Metropolis. The slaughter slab biosecurity practices were evaluated using questionnaires while the H5 antibodies surveillance was determined by hemagglutination inhibition test. Serum samples from 45 dogs, 104 pigs and 75 chickens were tested for H5 subtype. H5 subtype antibodies prevalence in dogs was 2.2% with a mean titre of 9.0 ± 0 log2 while prevalence and mean titre in chicken were 6.7% and 8.5 ± 0.32 log2 respectively. All pig sera tested were negative for H5 subtype antibodies. The chicken H5 subtype prevalence in central market and railway station live bird markets were 4.3% and 13% respectively. H5 subtype antibodies were present in dogs and chickens in Kaduna metropolis. There is the need for targeted surveillance of avian influenza in dogs and pigs should be incorporated in the national avian influenza surveillance program.

Prevalence of avian influenza in humans and different bird species in Indonesia: A review

Avian influenza, commonly called bird flu, is highly contagious and pandemic zoonosis of global importance, primarily affecting birds and other mammals, including humans. The present review is intended to highlight a report on the prevalence of avian influenza in humans and different bird species of Indonesia.The study is based on 27 scientific articles from 2004 to May 2021 in which the prevalence of avian influenza is determined mainly by the following molecular, virological, and serological tests: polymerase chain reaction (PCR), hemagglutination inhibition (HI), enzyme-linked immunosorbent assay (ELISA), and ®Rapid antigen detection test. A vast divergence in the prevalence of avian influenza was observed due to the diversity in sensitivity and specificity of the tests applied. The prevalence of avian influenza varies due to spatial and temporal factors, bird species, and breed differences. An average maximum prevalence (25%)) was found in poultry (domestic and commercial birds) as compared to ducks (20.13%) and other birds (10.66%). An average documented prevalence (16.3%) was found in humans. Birds sold in live bird markets showed maximum prevalence due to different geographical distribution. The already published studies dissection illustrates that avian influenza infects all types of birds and humans in Indonesia. A proper surveillance system, effective vaccination plan, and segregation and culling strategy regarding avian influenza-infected birds are desperately needed to eradicate avian influenza in Indonesia.

English

The present study is aimed at investigating clinical poultry diseases in an Upazila Government Veterinary Hospital of Bangladesh through passive surveillance and to know the frequency distribution of antimicrobial drugs prescription pattern. The study was conducted in Ramu Upazila Government Veterinary Hospital under Cox’s Bazar district of Bangladesh from February to March, 2016. A total of 180 cases including 73 broiler, 84 layer, 18 duck and 5 pigeon were included in this study. Diseases were diagnosed based on clinical history, clinical signs, post mortem lesions and rapid kit test. The most prevalent diseases were Newcastle disease (ND) 17.8% (95% CI 12-24%), colibacillosis 11.5% (95% CI 6-17%), infectious bursal disease (IBD) 10.8% (95% CI 6-16%) and aspergillosis 9.6% (95% CI 5-14%) in broiler and layer chickens; duck plague 69.6% (95% CI 49-90%) in duck and pigeon pox 13% (95% CI 0.2-24%) in pigeon. Regarding production type, the prevalence of colibacillosis, IBD and aspergillosis was significantly higher in broiler chickens (17.8, 19.2 and 16.4%) when compared with layer chickens (6.0, 3.6 and 3.6%) (p<0.05). On the contrary, ND and avian influenza (AI) were significantly greater in layer (27.4 and 10.7%) than broiler chickens (6.8 and 1.4%). Within age group, aspergillosis and omphalitis were higher at 1 to 10 days age groups while IBD and ND were greater in older age groups. In layer chickens, the prevalence of ND, AI, salmonellosis and fowl cholera were recorded higher in number between the ages of 9 and 83 weeks. Among the antibiotic drugs, ciprofloxacin (46.7%), colistin (42.2%), trimethoprim and sulphur drug (37.8%) were mostly prescribed to treat the diseases. Poor biosecurity practices and lack of appropriate laboratory diagnostic facilities are associated with these disease distributions in the study area. Strict biosecurity and continuous surveillance program can minimize the disease prevalence. Key words: Poultry diseases, veterinary hospital, antimicrobial drugs, Bangladesh, surveillance.

Prevalence of Avian Influenza in Live Bird Markets, Bird Gardens, and Zoos in Iran in 2015: A Cross-sectional Study.

Avian Influenza (AI) H9N2 is endemic in Iran; therefore, it is necessary to estimate the disease prevalence among birds in live bird markets (LBMs) and assess the risk spread across the country. Accordingly, this study aimed to estimate the prevalence of AI subtypes in LBMs, bird gardens, and zoos during October and November 2015 in Iran and investigate the associated risk factors. Data related to independent variables for birds and premises were collected using a prepared questionnaire which included items about previously known potential risk factors associated with avian influenza infection. Serological testing was carried out to detect the antibodies against H5, H7, and H9. Regarding H5 and H7, the antigens H5N2 and H7N1 were used in this study. Positive samples on the first test were examined with the second antigens, namely H5N1 and H7N7. Moreover, sera with titers &amp;ge;4 (i.e. log2) were considered positive and premises with at least one positive bird were considered as positive units. In total, 87 premises were included in this cross-sectional study. Serum samples were examined utilizing hemagglutination inhibition, and RT-PCR was conducted on swab samples. Regarding the molecular test, the RNA was extracted using the High Pure Viral RNA Kit (Roche, Germany). In addition, real-time RT-PCR was conducted based on the described method. The seroprevalence rates of H9N2 were 83.9% and 31.8% at the premises and bird levels, respectively. Totally, 9.2% of pooled swab samples were positive for H9N2. However, all sera and swab samples were negative for H5 and H7. Hot and humid weather (OR=0.13, 95% CI 0.02 &amp;ndash; 0.78) as well as bird-keeping condition (i.e., enclosed area) (OR=0.11, 95% CI 0.012 &amp;ndash; 1.02) were protective factors for H9N2. High seroprevalence rate of H9 indicates that the disease is endemic in Iranian LBMs. Active surveillance must be carried out in LBMs, especially in the northern provinces of Iran. In addition, cleanliness and improved hygiene would be useful to prevent the spread of disease in LBMs.

A delayed avian influenza model with avian slaughter: Stability analysis and optimal control

H7N9 avian influenza, a zoonotic disease caused by the transmission of the avian influenza A virus from poultry to humans, is low pathogenic for poultry but highly pathogenic for humans. Slaughter is an effective way to control the outbreak. In this paper, we consider the slaughter of avian population and the incubation periods of avian influenza A virus, and develop a poultry-to-human epidemiological model including time delays of being infectious for the avian and human populations after infection. By studying the dynamical behavior of this delay model, we obtain a threshold value for the extinction and prevalence of avian influenza, and show the local and global asymptotical properties of the two equilibria of the model. We further choose the slaughter intensity and the effect of education campaign as control variables, and formulate an optimal control problem to minimize the disease outbreak and control cost. We solve the optimal control problem and perform numerical simulations to illustrate the analytical results.

Dynamics Analysis of an Avian Influenza A (H7N9) Epidemic Model with Vaccination and Seasonality

H7N9 virus in the environment plays a role in the dynamics of avian influenza A (H7N9). A nationwide poultry vaccination with H7N9 vaccine program was implemented in China in October of 2017. To analyze the effect of vaccination and environmental virus on the development of avian influenza A (H7N9), we establish an avian influenza A (H7N9) transmission model with vaccination and seasonality among human, birds, and poultry. The basic reproduction number for the prevalence of avian influenza is obtained. The global stability of the disease‐free equilibrium and the existence of positive periodic solution are proved by the comparison theorem and the asymptotic autonomous system theorem. Finally, we use numerical simulations to demonstrate the theoretical results. Simulation results indicate that the risk of H7N9 infection is higher in colder environment. Vaccinating poultry can significantly reduce human infection.

Avian Influenza A (H7N9) Model Based on Poultry Transport Network in China

In order to analyze the spread of avian influenza A (H7N9), we construct an avian influenza transmission model from poultry (including poultry farm, backyard poultry farm, live-poultry wholesale market, and wet market) to human according to poultry transport network. We obtain the threshold value for the prevalence of avian influenza A (H7N9) and also give the existence and number of the boundary equilibria and endemic equilibria in different conditions. We can see that poultry transport network plays an important role in controlling avian influenza A (H7N9). Finally, numerical simulations are presented to illustrate the effects of poultry in different places on avian influenza. In order to reduce human infections in China, our results suggest that closing the retail live-poultry market or preventing the poultry of backyard poultry farm into the live-poultry market is feasible in a suitable condition.

Prevalence of avian influenza, Newcastle disease, and infectious bronchitis viruses in broiler flocks infected with multifactorial respiratory diseases in Iran, 2015-2016.

In this study, the prevalence and spatial distribution of Newcastle disease, infectious bronchitis, and avian influenza have been evaluated in commercial broiler farms in 31 provinces in Iran. In this survey, a total of 233 affected broiler chicken farms were sampled. The infectious bronchitis virus (alone) was detected with highest frequency in 60 farms, and separately or combined with other agents, in 110 farms; Newcastle disease virus, separately, was detected in 28 farms, and in 63 farms separately or combined with other infectious agents; and avian influenza H9N2 was detected in 22 farms separately and in 51 farms separately or concomitant with other infectious agents. The sample tested negative for all H5 serotypes. The results of the present study show that the most prevalent avian viral infectious disease contributing to respiratory syndromes in broiler farms in Iran was infectious bronchitis due to infectious bronchitis virus serotypes variant 2 and 793/B. On the other hand, combined with the alternation of dominant viruses and circulating strains, flocks are exposed to unremitting anamorphic viral infections. Thus, the permanent monitoring of cases that have occurred and the review of vaccination plans of affected flocks every year are some of the necessary measures needed for strategic control of respiratory syndrome in broilers. It is noteworthy that execution of epidemiologic examinations on the cogent factors of prevalence of this syndrome and defeat of vaccination strategy in the flocks is urgent and has to be fulfilled on the definite causes of time.

Risk factors for avian influenza virus in backyard poultry flocks and environments in Zhejiang Province, China: a cross-sectional study

BackgroundHuman infection of avian influenza virus (AIV) remains a great concern. Although live poultry markets are believed to be associated with human infections, ever more infections have been reported in rural areas with backyard poultry, especially in the fifth epidemic of H7N9. However, limited information is available on backyard poultry infection and surrounding environmental contamination.MethodsTwo surveillance systems and a field survey were used to collect data and samples in Zhejiang Province. In total, 4538 samples were collected by surveillance systems and 3171 from the field survey between May 2015 and May 2017, while 352 backyard poultry owners were interviewed in May 2017 by questionnaire to investigate factors influencing the prevalence of avian influenza A virus and other AIV subtypes. RT-PCR was used to test the nucleic acids of viruses. ArcGIS 10.1 software was used to generate maps. Univariate and logistic regression analyses were conducted to identify risk factors for AIV infection.ResultsOf the 428 poultry premises observed by the surveillance system, 53 (12.38%) were positive for influenza A virus. Of the 352 samples from poultry premises observed by field survey, 13 (3.39%) were positive for influenza A virus. The prevalence of AIV was unevenly distributed and the dominant subtype differed among cities. Eastern (Shaoxing and Ningbo) and southern (Wenzhou) cities exhibited a higher prevalence of AIV (16.33, 8.94, and 7.30% respectively). Contamination of AIV subtypes was most severe in January, especially in 2016 (23.26%, 70/301). The positive rate of subtype H5/H7/H9 was 2.53% (115/4538). Subtype H5 was the least prevalent, while subtypes H7 and H9 had similar positivity rates (1.50 and 1.32% respectively). Poultry flocks and environmental samples had a similar prevalence of AIV (4.46% vs 5.06%). The type of live birds was a risk factor and the sanitary condition of the setting was a protective factor against influenza A contamination.ConclusionsAIV subtypes were prevalent in backyard poultry flocks and surrounding environments in Zhejiang Province. The types of live birds and sanitary conditions of the environment were associated with influenza A contamination. These findings shine a light on the characteristics of contamination of AIV subtypes and emphasize the importance of reducing AIV circulation in backyard poultry settings.

A method to identify the areas at risk for the introduction of avian influenza virus into poultry flocks through direct contact with wild ducks.

Wild dabbling ducks are the main reservoir for avian influenza (AI) viruses and pose an ongoing threat to commercial poultry flocks. Combining the (i) size of that population, (ii) their flight distances and (iii) their AI prevalence, the density of AI-infected dabbling ducks (DID) was calculated as a risk factor for the introduction of AI viruses into poultry holdings of Emilia-Romagna region, Northern Italy. Data on 747 poultry holdings and on 39 AI primary outbreaks notified in Emilia-Romagna between 2000 and 2017 were used to validate that risk factor. A multivariable Bayesian logistic regression was performed to assess whether DID could be associated with the occurrence of AI primary outbreaks. DID value, being an outdoor flock, hobby poultry trading, species reared, length of cycle and flock size were used as explanatory variables. Being an outdoor poultry flock was significantly associated with a higher risk of AI outbreak occurrence. The probability of DID to be a risk factor for AI virus introduction was estimated to be 90%. A DID cut-off of 0.23 was identified to define high-risk areas for AI virus introduction. Using this value, the high-risk area covers 43% of the region. Seventy-four per cent of the primary AI outbreaks have occurred in that area, containing 39% of the regional poultry holdings. Poultry holdings located in areas with a high DID value should be included in a risk-based surveillance programme aimed at AI early detection.

Prevalence of avian influenza (H9N2) in commercial quail, partridge, and turkey farms in Iran, 2014-2015.

Avian influenza virus (AIV) H9N2 subtype is endemic in Iran and causes substantial economic loss to the growing poultry industry within the country. In this study, a cross-sectional analysis was carried out to determine the sero-prevalence of H9N2 in several commercial farms between the years 2014 and 2015. The comparison of the mean of serum titers and the ratio of sero-positive birds between all units were analyzed using one-way ANOVA test. In 2014, a total of 77 farms (58 turkey farms, 14 quail farms, and 5 partridge farms) and 894 birds (682 turkeys, 154 quails, and 58 partridges) were sampled while in 2015, a total of 69 farms (54 turkey farms, 8 quail farms, and 7 partridge farms) and 856 birds (675 turkeys, 105 quails, and 76 partridges) were sampled. Of that, 52 of 77 sampled farms (67.5%) and 437 of 894 samples (48.9%) were positive for H9N2 in 2014 while. Forty-one of 69 farms (59.4%) and 307 of 856 sera (35.9%) were positive in 2015. Furthermore, the mean titer of partridge farms was significantly lower than that of turkey farms (p<0.01) and the mean percentage of sero-positive turkey farms was significantly higher than partridge farms (p<0.01) in 2014. In 2015, no significant difference was observed between the mean sera titer amongst farms and percentage of sero-positive birds (p>0.05). Our results indicated that H9N2 is circulating in these farms. Since many more such farms are being established for operations, in addition to the threat of emergence and continuous reemergence of the disease in these farms, enhanced veterinary biosecurity measures on farms are required for mitigation.

Longitudinal Study of Avian Influenza and Newcastle Disease in Village Poultry, Mali, 2009–2011

Newcastle disease (ND) is endemic in West Africa, which has also experienced outbreaks of highly pathogenic avian influenza (AI) H5N1 since 2006. We aimed to estimate the prevalence and incidence of AI and ND in village poultry in Mali and to identify associated risk factors. A longitudinal serologic study was conducted between November 2009 and February 2011 using ELISA commercial kits to detect antibodies. Sera (5963) were collected from 4890 different poultry. AI was rare, with a seroprevalence of 2.9% (95% confidence interval [CI] 2.3-3.5) and a seroincidence rate of 0.7 birds per 100 bird-months at risk (95% CI 0.4-1.0). AI antibodies were short lived, with a seroreversion rate of 25.4 birds per 100 bird-months at risk (95% CI 19.0-31.7). Risk factors for AI were limited: temporal variation occurred, but proximity to a water body was a risk factor only when large populations of wild waterbirds were present. ND was very common, with seroprevalence of 68.9% (95% CI 61.9-76.0) and a seroincidence rate of 15.9 birds per 100 bird-months at risk (95% CI 11.9-19.8). ND seroreversion rate was 6.2 birds per 100 bird-months at risk (95% CI 3.6-8.9). Regarding risk factors for ND, temporal variations occurred, and ND was more likely to be present in the Sudanian agro-ecological zone than in the Sahelian zone, in chickens than in other species, in flocks with higher numbers of Guinea fowl, and in flocks that had access to a waterbody. Control efforts would benefit from further increasing the ND vaccination coverage of village poultry, although this was already quite high (54.9%) for an African country. Seroconversion seemed satisfactory in vaccinated poultry, since 90.0% (95% CI 87.6-92.4) of these had ND antibodies. Further research should investigate the apparent lack of an epidemiologic role of domestic ducks for AI in Mali (unlike in Southeast Asia) and the potential role of Guinea fowl as a reservoir for ND.

Avian influenza prevalence among hunter-harvested birds in a remote Canadian First Nation community.

Avian influenza virus (AIV) prevalence has been associated with wild game and other bird species. The contamination of these birds may pose a greater risk to those who regularly hunt and consumed infected species. Due to resident concerns communicated by local Band Council, hunter-harvested birds from a remote First Nation community in subArctic Ontario, Canada were assessed for AIV. Hunters, and especially those who live a subsistence lifestyle, are at higher risk of AIV exposure due to their increased contact with wild birds, which represent an important part of their diet. Cloacal swabs from 304 harvested game birds representing several species of wild birds commonly hunted and consumed in this First Nation community were analyzed for AIV using real-time reverse transcription polymerase chain reaction. Subtyping was performed using reverse transcription polymerase chain reaction. Sequences were assembled using Lasergene, and the sequences were compared to Genbank. In total, 16 of the 304 cloacal swab samples were positive for AIV. Of the 16 positive samples, 12 were found in mallard ducks, 3 were found in snow geese (wavies), and 1 positive sample was found in partridge. The AIV samples were subtyped, when possible, and found to be positive for the low pathogenic avian influenza virus subtypes H3 and H4. No samples were positive for subtypes of human concern, namely H5 and H7. This work represents the first AIV monitoring program results of hunter-harvested birds in a remote subsistence First Nation community. Community-level surveillance of AIV in remote subsistence hunting communities may help to identify future risks, while educating those who may have the highest exposure about proper handling of hunted birds. Ultimately, only low pathogenic strains of AIV were found, but monitoring should be continued and expanded to safeguard those with the highest exposure risk to AIV.

Recombinant Hemagglutinin of Avian Influenza Virus H5 Expressed in the Chloroplast of Chlamydomonas reinhardtii and Evaluation of Its Immunogenicity in Chickens.

Globally, avian influenza (AI) is a serious problem in poultry farming. Despite vaccination, the prevalence of AI in México highlights the need for new approaches to control AI and to reduce the economic losses associated with its occurrence in susceptible birds. Recombinant proteins from avian influenza virus (AIV) have been expressed in different organisms, such as plants. The present study investigated the feasibility of designing and expressing the HA protein of AIV in the transplastomic microalga Chlamydomonas reinhardtii as a novel approach for AIV control and taking advantage of culture conditions, its reproductive range, and safe use in consideration of the generally regarded as safe food ingredient regulatory classification. The results showed that the HA protein of AIV in C. reinhardtii presents antigenic activity by western blot test and through its application in chickens, demonstrating its feasibility as a recombinant antigen against AIV.

One Decade of Active Avian Influenza Wild Bird Surveillance in Belgium Showed a Higher Viroprevalence in Hunter-Harvested Than in Live-Ringed Birds

Active monitoring of avian influenza (AI) viruses in wild birds was initiated in Belgium in 2005 in response to the first highly pathogenic avian influenza (HPAI) H5N1 outbreaks occurring in Europe. In Belgium, active wild bird surveillance that targeted live-ringed and hunter-harvested wild birds was developed and maintained from 2005 onward. After one decade, this program assimilated, analyzed, and reported on over 35,000 swabs. The 2009-2014 datasets were used for the current analysis because detailed information was available for this period. The overall prevalence of avian influenza (AI) in samples from live-ringed birds during this period was 0.48% whereas it was 6.12% in hunter-harvested samples. While the ringing sampling targeted a large number of bird species and was realized over the years, the hunting sampling was mainly concentrated on mallard (Anas platyrhynchos) during the hunting season, from mid-August to late January. Even when using just AI prevalence for live-ringed A. platyrhynchos during the hunting season, the value remained significantly lower (2.10%) compared to that detected for hunter-harvested mallards. One explanation for this significant difference in viroprevalence in hunter-harvested mallards was the game restocking practice, which released captive-bred birds in the wild before the hunting period. Indeed, the released game restocking birds, having an AI-naïve immune status, could act as local amplifiers of AI viruses already circulating in the wild, and this could affect AI epidemiology. Also, the release into the wild of noncontrolled restocking birds might lead to the introduction of new strains in the natural environment, leading to increased AI presence in the environment. Consequently, the release of naïve or infected restocking birds may affect AI dynamics.

THE EVALUATION OF DOMESTIC DUCKS AS POTENTIAL RESERVOIR OF AVIAN INFLUENZA VIRUS IN POST HPAI H5N1 OUTBREAK AREA, SUNYANI MUNICIPALITY, BRONG AHAFO REGION OF GHANA.

Background:Avian influenza (AI) is an important zoonotic disease responsible for significant losses in most sub-Saharan countries. However, the role of poultry other than chicken in the epidemiology of the disease, especially after the first AI outbreak in Ghana, has not been fully elucidated. The obiective of this study is to determine whether the AI virus infection that was reported in the area in May 2007 was circulating silently in ducks in nine randomly selected farms in the Sunyani Municipality, Ghana.Materials and Methods:The sample size was calculated using Epi info version 3.4.1 at 95% confidence level, absolute precision of 5% and assuming 0.5 prevalence of Avian Influenza A virus in ducks. Samples collection was done simultaneously with questionnaire administration to farmers. A total of 526 samples made up of 384 cloacal swabs and 142 feather tissues from ducks from a commercial duck farm, seven backyard holdings and one live birds market in six randomly selected communities in the Sunyani Municipality, Brong Ahafo region of Ghana. The samples were processed and subjected to Influenza Type A Matrix Gene analysis using RRT-PCR.Results:All the 526 samples subiected to Influenza Type A Matrix Gene analysis using RRT-PCR were negative for Influenza Type A viruses. However, it was observed that bio-security practices which are keys to reintroduction of the virus in the area were not adhered to in 89 % of the sites investigated. Our finding also revealed that only the commercial farm investigated in this study complied with fifteen (78.9%) of the nineteen different farm practices observed.Conclusion:Though AI was not detected in the ducks sampled, there is the need for continuous surveillance and education of stakeholders on standard bio-security and farm management practices in the area.

Impact of Age, Season, and Flowing vs. Stagnant Water Habitat on Avian Influenza Prevalence in Mute Swan (Cygnus olor) in Belgium.

Due to their probable role in the spread of Asian highly pathogenic avian influenza (HPAI) H5N1 virus, and in order to explore its implication in the low pathogenic avian influenza (LPAI) virus epidemiology, mute swans represent one particular wild bird species specifically targeted in the avian influenza (AI) surveillance elaborated in Belgium. A total of 640 individual mute swans have been sampled during a 4-yr AI surveillance program (2007-2010) to determine the AI seroprevalence and viroprevalence in this species; all were analyzed through age, temporal, and habitat (flowing and stagnant water) factors. Using a nucleoprotein (NP)-based ELISA, a global antibody prevalence of 35% has been found and was characterized by two peaks in the winter and the summer that might be indicative of a greater LPAI virus circulation in the autumn than in the spring. A significantly higher antibody prevalence was detected in adult swans (53.8%) as compared to juveniles (15.5%). In contrast, a low prevalence of infection (2.7%) was found, mainly in juvenile mute swans and only during the autumn migration period. Interestingly, an impact of water habitat was observed based on the comparison of the antibody prevalence and prevalence of infection from swan populations living on stagnant water vs. flowing water, suggesting that stagnant water provides a more-favorable environment for LPAI persistence and transmission.

Avian Influenza Dynamics Under Periodic Environmental Conditions

Since wild birds are the major natural reservoir for all known influenza A viruses, understanding the ecology of avian influenza (AI) viruses circulating in wild birds is critical to predicting disease risk in wild and domestic birds and preventing transmission to humans. AI virus which is shed by infected birds into aquatic environments plays a pivotal role in the sustained transmission of AI. Recent laboratory experiments, however, show that viral persistence in water is highly sensitive to environmental conditions such as temperature, which varies seasonally and geographically. Here, we develop mathematical models to study the effects of time-varying environmental conditions on AI dynamics, deriving the effects of temperature on the basic reproductive number ($\mathcal{R}_0$), the final outbreak size, and the effective reproductive number ($\mathcal{R}_e$). For periodic environmental temperatures, we derive a mathematical formulation of an AI invasion threshold ($\mathcal{R}_i$) and conclude that apart from the mean temperature, the amplitude of the periodic temperature profile plays a significant role in the invasion of wild bird populations by AI. In particular, both higher means and higher amplitudes (warmer and more variable temperatures) reduce the likelihood of AI invasion. We also analyze the global dynamics of the model proving that AI is uniformly persistent in the wild bird population if $\mathcal{R}_i>1$. In numerical work, we fit the model to recent experimental data and field survey data from Northern Europe. Two important and robust quantitative conclusions emerge: that direct transmission is negligible compared to indirect and that immunity wanes within about 4 weeks. The latter conclusion is of particular interest since many previous models assume lifetime immunity. We also demonstrate that time-varying temperature may be the underlying cause of several features of AI dynamics which are observed in real data. In particular, AI prevalence is observed to peak in spring and fall but to wane in summer; this behavior naturally emerges from our model under a wide range of conditions.

Large-scale avian influenza surveillance in wild birds throughout the United States.

Avian influenza is a viral disease that primarily infects wild and domestic birds, but it also can be transmitted to a variety of mammals. In 2006, the United States of America Departments of Agriculture and Interior designed a large-scale, interagency surveillance effort that sought to determine if highly pathogenic avian influenza viruses were present in wild bird populations within the United States of America. This program, combined with the Canadian and Mexican surveillance programs, represented the largest, coordinated wildlife disease surveillance program ever implemented. Here we analyze data from 197,885 samples that were collected from over 200 wild bird species. While the initial motivation for surveillance focused on highly pathogenic avian influenza, the scale of the data provided unprecedented information on the ecology of avian influenza viruses in the United States, avian influenza virus host associations, and avian influenza prevalence in wild birds over time. Ultimately, significant advances in our knowledge of avian influenza will depend on both large-scale surveillance efforts and on focused research studies.

Understanding pathogen transmission dynamics in waterbird communities: At what scale should interactions be studied?

Pathogen transmission in animal populations is contingent on interactions between and within species. Often standard ornithological data (e.g. total counts at a wetland) are the only data available for assessing the risks of avian pathogen transmission. In this paper we ask whether these data can be used to infer fine-scale transmission patterns. We tested for non-randomness in waterbird assemblages and explored waterbird interactions using social network analysis. Certain network parameter values were then compared to a data set on avian influenza prevalence in southern Africa. Our results showed that species associations were strongly non-random, implying that most standard ornithological data sets would not provide adequate information on which to base models of pathogen spread. In both aquatic and terrestrial networks, all species regularly associated closely with other network members. The spread of pathogens through the community could thus be rapid. Network analysis together with detailed, fine-scale observations offers a promising avenue for further research and management-oriented applications.