Field evidence of the efficacy of vaccination to control low pathogenicity avian influenza in meat turkeys

This paper analyzes the efficacy of vaccination to control low pathogenicity avian influenza outbreaks using information collected during four epidemics occurring in Italy between 2000 and 2005. Different vaccination strategies and protocols for meat-turkey immunization are also considered.

An electronic learning course on avian influenza in Italy (2008)

The success of emergency intervention to control contagious animal diseases is dependent on the preparedness of veterinary services. In the framework of avian influenza preparedness, the Italian Ministry of Health, in cooperation with the National Reference Centers for Epidemiology and Avian Influenza, implemented an electronic learning course using new web-based information and communication technologies. The course was designed to train veterinary officers involved in disease outbreak management, laboratory diagnosis, and policy making. The "blended learning model" was applied, involving participants in tutor-supported self-learning, collaborative learning activities, and virtual classes. The course duration was 16 hr spread over a 4-wk period. Six editions were implemented for 705 participants. All participants completed the evaluation assignments, and the drop out rate was very low (only 4%). This project increased the number of professionals receiving high-quality training on AI in Italy, while reducing expenditure and maximizing return on effort.

Within-flock transmission of H7N1 highly pathogenic avian influenza virus in turkeys during the Italian epidemic in 1999-2000

Highly pathogenic avian influenza (HPAI) viruses show different disease dynamics between virus strains and host species, and therefore epidemic field data are very valuable. This study used field data of the HPAI H7N1 epidemic which affected Northern Italy in 1999-2000. Field mortality data was back-calculated into a S-I-format to estimate the transmission rate parameter beta, indicating the number of birds infected per infectious bird per time unit. The bird-infectious period was assumed to be 2 days, and all birds were assumed to die after this infectious period. The estimated beta for HPAI H7N1 virus transmission in turkeys was 1.43 (95% CI: 1.17-1.74). Farm risk factors such as flock size and age of the turkeys did not influence the estimated transmission rate parameter.

Evaluation of the risk of neighbourhood infection of H7N1 Highly Pathogenic Avian Influenza in Italy using Q statistic

Exposure to the risk of neighbourhood infection was estimated for the H7N1 Highly Pathogenic Avian Influenza (HPAI) epidemic that affected Northern Italy between 1999 and 2000. The two most affected regions (Lombardy and Veneto) were analyzed and the epidemic was divided into three phases. Q statistics were used to evaluate exposure to the risk of neighbourhood infection using two measures. First, a local Q statistic (Qikt) assessed daily exposure for each farm as a function of the number of neighbouring infected farms that were in their infectious period, weighted by the distance between farms. This allowed us to identify the daily time course of risk for each farm and, at any given time, local groups of farms defined by high risk. Second, for each farm a summary statistic of exposure risk within each phase (Qiph) was obtained by summing Qikt over the duration of each phase. This allowed identification of farms defined by persistent, high exposure risk within each phase of the epidemic. Statistical significance was evaluated using conditional Monte Carlo simulation, and significant values of Qiph were mapped to assess the variation of the risk of neighbourhood infection through the phases. Qikt was larger for farms in Lombardy and the reduction of exposed farms was more marked for Veneto. Although the highest value of Qiph was observed in Veneto, in each phase most of the significant values were in Lombardy. In the last phase of the epidemic, a large reduction in the number of farms significantly exposed to the risk of neighbourhood infection was observed in the Veneto region, along with generally low values of Qiph. This may be explained by differences in control measures in the two regions, including pre-emptive slaughtering of farms considered at high risk of infection. The Q statistic allowed us to quantify geographic, time-dynamic variations in exposure to neighbourhood infection, and to generate hypotheses on the efficacy of control measures.

Vaccination reduced the incidence of outbreaks of low pathogenicity avian influenza in northern Italy

When outbreaks of avian influenza (AI) occur in poultry populations, the main goal to achieve is the control and eradication of the infection. However, quantitative information on risk factors for AI spread and efficacy of AI control measures such as vaccination in the field is limited. From 2000 to 2005, H5 and H7 low pathogenicity (LP) AI viruses caused four epidemics in poultry in northeastern Italy. Italian veterinary authorities implemented emergency vaccination in the 2000-2001 and 2002-2003 LPAI epidemics and prophylactic vaccination from July 2004. The aim of this study is to quantitatively evaluate the efficacy of AI vaccination in the field, taking into account the different strategies (emergency and prophylactic) implemented. Moreover, risk factors for LPAI spread in domestic poultry were studied. By survival analysis, we observed a two-fold increase in survival probability for vaccinated poultry farms compared to unvaccinated ones. In meat turkeys, vaccination protocols changed in the different epidemics, and a relationship between protection and the number of vaccinations was observed; two or three vaccine administrations protected flocks from LPAI, whilst four administrations did not significantly reduce the risk of infection. In meat turkeys the risk of AI infection increased also with the increase in both farm size and proximity to an infected farm. In general, we observed a lower number of outbreaks and a faster eradication of the infection when LPAI viruses introduced in a preventively vaccinated poultry population. This study provides insights on LPAI vaccination efficacy and on risk factors involved in LPAI infection at farm level. To our knowledge, this is the first study which quantitatively evaluates AI vaccination efficacy and compares different vaccination strategies and protocols using field data.

Co-circulation of two sublineages of HPAI H5N1 virus in the Kingdom of Saudi Arabia with unique molecular signatures suggesting separate introductions into the commercial poultry and falconry sectors

Since early 2007, the Kingdom of Saudi Arabia (KSA) has experienced several highly pathogenic avian influenza (HPAI) H5N1 outbreaks in the falconry and poultry sectors. The public health threat associated with peculiar husbandry systems, requiring close contact between humans and birds of prey, highlights the need of an improved understanding of the epidemiology and of the viral characteristics of H5N1 viruses circulating in the region. Here we report molecular and phylogenetic analyses of H5N1 viruses isolated in the KSA in 2007 in distinct compartments of avian husbandry. From the results of our investigation it appears that two separate introductions into the different sectors occurred. The identification of specific amino acid mutations, which are described as genetic signatures of human influenza A viruses or known to confer resistance to antiviral drugs, raises concerns for the possible human health implications of the KSA H5N1 viruses.

Emergence of fox rabies in north-eastern Italy

Italy has been classified as rabies-free since 1997. In October 2008, two foxes have been diagnosed with rabies in the Province of Udine, north-east Italy. One case of human exposure caused by a bite from one of the foxes has occurred and was properly treated.

Emergence of fox rabies in north-eastern Italy

Italy has been classified as rabies-free since 1997. In October 2008, two foxes have been diagnosed with rabies in the Province of Udine, north-east Italy. One case of human exposure caused by a bite from one of the foxes has occurred and was properly treated.

Transmission parameters of highly pathogenic avian influenza (H7N1) among industrial poultry farms in northern Italy in 1999–2000

We estimated between-farm transmission parameters of the highly pathogenic avian-influenza (HPAI) epidemic that struck the poultry industry of northern Italy (including turkeys, layer hens, broilers, gamebirds, and waterfowl) from December 1999 through April 2000. We estimated the average number of susceptible farms that were infected with HPAI virus by each infectious farm during a day (beta) with a generalised linear model (GLM). The HPAI's reproductive ratios (R(h); the average number of new infected farms (IFs) that were caused by an infectious farm) were calculated separately for the regions of Lombardy and Veneto, where 382 out of 413 (92.5%) of IFs were located. In both regions, R(h) decreased to approximately 1 during the second month of the epidemic (showing that its containment had been initiated). Subsequently, during the last two months of the epidemic, beta and R(h) were reduced to 0.04/day and 0.6, respectively, in Veneto and to 0.07/day and 0.8 in Lombardy. The reduction of the susceptible population through strict control measures, including pre-emptive slaughter of at-risk poultry flocks, was implemented to a greatest extent in Veneto and this might have been associated with a more rapid control of the epidemic in this region than in Lombardy.

The challenge of controlling notifiable avian influenza by means of vaccination

Avian influenza (AI) is an Office International des Epizooties listed disease that has become a disease of great importance both for animal and human health. The increased relevance of AI in animal and human health has highlighted the lack of scientific information on several aspects of the disease, which has hampered the adequate management of some of the recent crises. Millions of animals have died, and there is growing concern over the loss of human lives and over the management of the pandemic potential. The present article reviews the currently available control methods for notifiable AI infections in poultry. The application of control policies, ranging from stamping out to emergency and prophylactic vaccination, is discussed on the basis of data generated in recent outbreaks and in light of new regulations, also in view of the maintenance of animal welfare. Poultry veterinarians working for the industry or for the public sector represent the first line of defense against the pandemic threat and for the prevention and control of this infection in poultry and in wild birds.

The use of vaccination in poultry production

Poultry vaccines are widely applied to prevent and control contagious poultry diseases. Their use in poultry production is aimed at avoiding or minimising the emergence of clinical disease at farm level, thus increasing production. Vaccines and vaccination programmes vary broadly in regard to several local factors (e.g. type of production, local pattern of disease, costs and potential losses) and are generally managed by the poultry industry. In the last decade, the financial losses caused by the major epidemic diseases of poultry (avian influenza and Newcastle disease) have been enormous for both the commercial and the public sectors. Thus, vaccination should also be applied in the framework of poultry disease eradication programmes at national or regional levels under the official supervision of public Veterinary Services. This paper provides insight on the use of vaccination for the control of poultry infections, with particular emphasis on the control of transboundary poultry diseases.

Intervention Strategies for Low-Pathogenic Avian Influenza Control in Italy

Italian poultry production was affected by several outbreaks of low-pathogenicity avian influenza (LPAI) between 2000 and 2005. Intervention measures (IM), such as stamping out of infected and suspected farms, controlled marketing, restocking bans, movement restriction, and emergency vaccination, were put into force in the most affected areas of Lombardia and Veneto regions. These two regions also showed differences in terms of measures applied and timeliness of application. In this study we describe the epidemics and discuss the effectiveness of the IM put into effect. The regional surveillance systems provided the data on the epidemics and the IM description. The IM effectiveness was compared between the different epidemics and the Lombardia and Veneto regions, considering the number of farms involved, the duration of the epidemics, and the extension of the area affected. With regard to the IM applied, reductions in the number of outbreaks (from 388 in 2002-03 to 15 in 2005), the duration of the outbreaks (from more than 1 yr to approximately 1 mo), and the spatial extension of the outbreaks (from 89 to 8 municipalities involved) were observed. The emergency vaccination, depopulation, and pre-emptive slaughtering reduced significantly the spread of the epidemic. Comparing the dynamics of the epidemics, more effective results were observed in the Veneto region, where the IM were applied to a greater extent. Emergency vaccination and depopulation were effective in the eradication of the disease during an epidemic, but vaccination and farm density reduction showed the most effective results in controlling the spread of LPAI.

Practicalities of the Implementation of a Vaccination Campaign for Avian Influenza

Emergency vaccination for avian influenza (AI) infections caused by viruses of the H5 or H7 subtypes has been used in several instances over the past years. It has been applied primarily in the chicken and turkey industry with the general objective of controlling, and in some instances eradicating, infection. The use of vaccination as a tool to eradicate AI requires the enforcement of a coordinated set of control and monitoring measures. In fact, only certain attempts at eradicating AI with the support of vaccination have been successful, and the outcome of the vaccination campaign has been shown to depend greatly on effective application of the field strategy that complemented the vaccination program. While it is taken for granted that the product and companion diagnostic test are suitable for that given situation, a monitoring system must be in place to promptly identify whether vaccinated birds have been field exposed, and the latter should be dealt with in an appropriate manner, avoiding the spread of infection to other premises. Prophylactic vaccination could also become a tool for AI management in the European Union, provided that its application is based on a systematic assessment of AI risk. The correct use of this tool can be a valuable support for the control of AI in poultry, with the added value of limiting the economic losses to the industry and to the taxpayer. Eventually, this will also reduce human exposure to potentially dangerous viruses.

Evaluation of the Efficacy of Intervention Measures and Vaccination for the Control of LPAI Epidemics in Verona Province (Veneto, Italy)

Meat-type turkey farms in Verona province (Veneto, Italy) have been affected by three low-pathogenicity avian influenza (LPAI) epidemics between 2000 and 2004. Control measures implemented ranged from stamping out to controlled marketing in conjunction with restocking bans and movement restriction on live poultry, vehicles, and personnel. These measures were complemented with two emergency vaccination programs (2000-01, 2002-03) started after the beginning of the epidemics, while 2004 outbreaks occurred in vaccinated farms. The three epidemics differed in the number of outbreaks, duration, and economic impact. The aim of the investigation was to estimate the risk of infection and the effect of vaccination on the LPAI epidemics affecting turkey farms in Verona province. Farm probability to avoid infection (Ps) was calculated by Kaplan-Meier for each epidemic. The vaccination effect was evaluated for the 2000-01 and 2002-03 epidemics considering different risk before or after the emergency vaccination. The epidemics and vaccination entered as predictors in a Cox regression model and hazard ratios (HR) were calculated. Ps values at the end of the epidemics were as follows: 2000-01 = 0.66, 2002-03 = 0.51, and 2004 = 0.91. Vaccination reduced dramatically the risk of infection. The measures implemented had different effects on the three epidemics. The lower probability of being infected during the 2004 epidemic was most likely related to the protection level of the vaccinated farms acquired before the beginning of the epidemic, which was also responsible for the reduced spread of infection.

The use of vaccination to combat multiple introductions of Notifiable Avian Influenza viruses of the H5 and H7 subtypes between 2000 and 2006 in Italy

Since 1999, Italy has been challenged by several epidemics of Notifiable Avian Influenza (NAI) of the H5 and H7 subtypes, occurring in the densely populated poultry areas of northern part of the country. Vaccination with a conventional vaccine containing a seed strain with a different neuraminidase subtype to the field virus was used to complement biosecurity and restriction measures as part of an overall eradication strategy. This vaccination technique, known as the "DIVA-Differentiating Infected from Vaccinated Animals" system, enabled, the identification of field exposed flocks and ultimately the eradication of H7N1, H7N3 and H5N2 infections. A bivalent H5/H7 prophylactic vaccination programme of defined poultry populations was introduced subsequently to increase their resistance to field infection. Retrospective analysis of the outbreaks identified important reservoir species such as quail, and demonstrated clearly the higher susceptibility of turkeys to infection. Data generated during 6 years of experience with vaccination against Avian Influenza (AI) indicate that it is a useful tool to limit secondary spread and possibly prevent the introduction of AI viruses in a susceptible population. The Italian AI control programme including vaccination was managed in a flexible manner and enabled the continuation of international trade. It is imperative that if vaccination is to be used to combat the current H5N1 epidemic it is used in conjunction with other measures and under official supervision. An extraordinary effort is required from international organisations to accredit control strategies so that harmonised and validated programs can be implemented. Transparency and sharing of field results from countries that are practising such programmes is crucial to the progressive control and ultimately the eradication of NAI infections in the animal reservoir.

Planning and executing a vaccination campaign against avian influenza

Vaccination against avian influenza infection caused by H5 or H7 virus subtypes has been used on several occasions in recent years to control and in some cases eradicate the disease. In order to contain avian influenza infection effectively, immunization should be combined with a coordinated set of control and monitoring measures. The outcome of an immunization campaign depends on the territorial strategy; whereas the capacity of the veterinary services in developed countries permits enforcement of strategies aimed at eradicating avian influenza, many countries currently affected by highly pathogenic avian influenza (HPAI) H5N1 viruses have a limited veterinary infrastructure and a limited capacity to respond to such epidemics. In these countries, resources are still insufficient to conduct adequate surveillance for identification and reaction to avian influenza outbreaks when they occur. When properly applied in this scenario, immunization can reduce mortality and production losses. In the long term, immunization might also decrease the prevalence of infection to levels at which stamping-out and surveillance can be applied. Countries should adapt their immunization programmes to local conditions in order to guarantee their efficacy and sustainability. In the initial emergency phase, human resources can be mobilized, with reliance on personal responsibility and motivation, thus compensating for potential shortcomings in organization. A more appropriate allocation of resources must be pursued in the long term, remembering that biosecurity is the main component of an exit strategy and must always be improved.

Control and prevention of avian influenza in an evolving scenario

Continuing outbreaks of highly pathogenic avian influenza (HPAI) across Eurasia and in Africa, caused by a type A influenza virus of the H5N1 subtype appear out of control and represent a serious risk for animal and public health worldwide. It is known that biosecurity represents the first line of defence against AI, although in certain circumstances strict hygienic measures appear to be inapplicable for social and economic conditions. The option of using vaccination against AI viruses of the H5 and H7 subtypes, has made its way in recent times--primarily as a tool to maximise the outcome of a series of control measures in countries that are currently infected, but also as a means of reducing the risk of introduction in areas at high risk of infection. In developing countries vaccination programmes in avian species have been recommended recently, however it will require concurrent management of local husbandry practices and industry compliance to eradicate the disease rather than the establishment of an endemic situation. Other key deliverables expected for this control strategy include maintaining a major source of food for rural communities and the preservation of the commercial viability of the local poultry industry. In developed countries vaccination is being used as a means of increasing resistance of susceptible animals to reduce the risk of introduction from the reservoir host or to reduce secondary spread in densely populated poultry areas. The recent joint OIE/FAO summits recommended applying vaccination, using the differentiating infected from vaccinated animals (DIVA) strategy when there is risk of major spread and depopulation is not feasible or desirable. Particularly in developing countries, stamping out of infected animals does not seem to be an appropriate means of reducing the spread of infection, if food supplies are to be guaranteed and economic consequences minimised. Crucial points to the success of a vaccination campaign are the implementation of complex territorial strategy involving upgraded biosecurity, monitoring vaccine efficacy, identification of field exposure and the appropriate management of infected flocks, regardless of vaccination status. Granting financial support for the compensation of farmers is also a key part of this strategy. Poultry veterinarians working for the industry or for the public sector represent the first line of defence against the pandemic threat and for the prevention and control of this infection in poultry and in wild birds.

Control of avian influenza in poultry

Avian influenza, listed by the World Organization for Animal Health (OIE), has become a disease of great importance for animal and human health. Several aspects of the disease lack scientific information, which has hampered the management of some recent crises. Millions of animals have died, and concern is growing over the loss of human lives and management of the pandemic potential. On the basis of data generated in recent outbreaks and in light of new OIE regulations and maintenance of animal welfare, we review the available control methods for avian influenza infections in poultry, from stamping out to prevention through emergency and prophylactic vaccination.