Risk of Introduction in Northern Vietnam of HPAI Viruses from China: Description, Patterns and Drivers of Illegal Poultry Trade.

Poultry movement is known to contribute to the dissemination of highly pathogenic avian influenza (HPAI) viruses. In Northern Vietnam, the illegal trade of poultry from China is a source of concern and is considered as responsible for the regular introduction of new H5N1 viruses. The general objective of this study was to get a better understanding of this illegal trade (organization, volume, actors involved and drivers) to propose adequate preventive and control options. The information was also used to qualitatively evaluate the risk of exposure of susceptible poultry to HPAI H5N1 virus introduced from China by illegally traded poultry. We found that the main products imported from China are spent hens, day-old chicks (DOCs) and ducklings; spent hens being introduced in very large number. The drivers of this trade are multiple: economic (especially for spent hens) but also technical (demand for improved genetic potential for DOC and ducklings). Furthermore, these introductions also meet a high consumer demand at certain periods of the year. We also found that spatial dispersion of a batch of poultry illegally introduced from China is extensive and rapid, making any prediction of possible new outbreaks very hazardous. Finally, a risk mitigation plan should include measures to tackle the drivers of this trade or to legally organize it, to limit the threat to the local poultry sector. It is also essential for traders to be progressively better organized and biosecure and for hygienic practices to be enforced, as our study confirmed that at-risk behaviours are still very common among this profession.

Evaluation of the vaccination efficacy against H5N1 in domestic poultry in the Red River Delta in Vietnam.

The domestic poultry population in Vietnam has been vaccinated against highly pathogenic avian influenza (HPAI) H5N1 since 2005. Since then, outbreaks have continued to occur without a clear understanding of the mechanisms involved. The general objective of this study was to understand the epidemiology of the disease in the context of vaccination and to draw some conclusions about vaccination efficacy in the domestic poultry population of the Red River Delta area. Five cross-sectional surveys to measure the serological and virological prevalence in vaccinated and unvaccinated poultry were performed from the end of 2008 to June 2010. The global seroprevalence was 24% (95% confidence interval 19·9-28·2). Determinants of vaccine immunogenicity were identified separately in chickens and ducks as well as determinants of the seroconversion in unvaccinated birds. The results highlight the difficulties in maintaining good flock immunity in poultry populations using inactivated vaccine in the field with two vaccination rounds per year, and in preventing circulation of virus in co-existing unvaccinated poultry.

Evaluation of serological tests for H5N1 avian influenza on field samples from domestic poultry populations in Vietnam: consequences for surveillance.

In Vietnam, serological post H5N1 vaccination surveillance using the HI test is applied to assess the efficiency of the vaccination in addition to virological monitoring. In this paper we report on the evaluations of the performances of the haemagglutination inhibition (HI) test and of a H5-ELISA, using chicken and duck field samples. The evaluations were conducted by comparison with a pseudotyped-based virus neutralization test (H5pp VNT) performed in a reference laboratory and considered as a "gold standard" and also by using methods developed for imperfect reference test. Their global accuracy and best cut-offs were also estimated. Results from the HI test for several haemagglutinin subtypes and from a commercial type A influenza competition ELISA were also compared. The results showed that performance of the HI test was very good in comparison with the H5pp VNT. Data also clearly supported the cut-off of ≥ 4 log(2) used for the HI test for chickens but, a 3 log(2) positivity cut-off would be more appropriate for ducks. When compared with the VNT, the H5-ELISA showed poor specificity when using the positivity cut-off specified by the manufacturer but could be used as a screening test if confirmed by the HI test or the H5ppVNT which presents some interests for large scale testing (no need for biosafety level 3 conditions and high performance). A general and highly sensitive pre-screening can also be achieved using the detection of NP-specific antibodies with a competition ELISA. This appears of little interest in a context of high subtypes diversity where only a subtype is targeted for surveillance and control.

Risk factors of highly pathogenic avian influenza H5N1 occurrence at the village and farm levels in the Red River Delta Region in Vietnam.

A case-control study at both village and farm levels was designed to investigate risk factors for highly pathogenic avian influenza H5N1 during the 2007 outbreaks in one province of Northern Vietnam. Data related to human and natural environments, and poultry production systems were collected for 19 case and 38 unmatched control villages and 19 pairs of matched farms. Our results confirmed the role of poultry movements and trading activities. In particular, our models found that higher number of broiler flocks in the village increased the risk (OR = 1.49, 95% CI: 1.12-1.96), as well as the village having at least one poultry trader (OR = 11.53, 95% CI: 1.34-98.86). To a lesser extent, in one of our two models, we also identified that increased density of ponds and streams, commonly used for waterfowl production, and greater number of duck flocks in the village also increased the risk. The higher percentage of households keeping poultry, as an indicator of households keeping backyard poultry in our study population, was a protective factor (OR = 0.95, 95% CI: 0.91-0.98). At the farm level, three risk factors at the 5% level of type I error were identified by univariate analysis: a greater total number of birds (P = 0.006), increase in the number of flocks having access to water (P = 0.027) and a greater number of broiler flocks in the farm (P = 0.049). Effect of vaccination implementation (date and doses) was difficult to investigate because of a poor recording system. Some protective or risk factors with limited effect may not have been identified owing to our limited sample size. Nevertheless, our results provide a better understanding of local transmission mechanisms of HPAI H5N1 in one province of the Red River Delta region in Vietnam and highlight the need to reduce at-risk trading and production practices.

Avian influenza vaccines: a practical review in relation to their application in the field with a focus on the Asian experience.

Vaccination can be a useful tool for the control of avian influenza (AI) outbreaks, but its use is prohibited in most of the countries worldwide because of its interference with AI surveillance tests and its negative impact on poultry trade. AI vaccines currently in use in the field increase host resistance to the disease but have a limited impact on the virus transmission. To control or eradicate the disease, a carefully conceived vaccination strategy must be accompanied by strict biosecurity measures. Some countries have authorized vaccination under special circumstances with contradictory results, from control and disease eradication (Italy) to endemicity and antigenic drift of the viral strain (Mexico). Extensive vaccination programmes are ongoing in South East Asia to control the H5N1 epidemic. This review provides practical information on the available AI vaccines and associated diagnostic tests, the vaccination strategies applied in Asia and their impact on the disease epidemiology.

High frequency ultrasonic detection of C-crack defects in silicon nitride bearing balls.

A non-destructive testing method for silicon nitride bearing balls based on ultrasonic resonance spectroscopy is proposed here. Through the theoretical study of their elastic vibrations, it is possible to characterize the balls using a vibration mode that is similar to surface wave propagation. The study of the influence of C-crack defects on the resonances of Rayleigh modes is presented here. These C-cracks are typically formed by impacts between balls during finishing or handling. They are frequently found on the surface of silicon nitride bearing balls and these C-cracks decrease the rolling contact fatigue life considerably. This kind of defect is difficult to detect because the C-shaped surface crack is very small and narrow (500 microm x 5 microm), and its depth does not exceed 50 microm. The proposed methodology can both excite spheroidal vibrations in the ceramic balls and detect such vibrations over a large frequency range. In particular, high frequency vibrations are considered because these are similar to the surface waves propagating in the cortical zone of the ceramic balls and consequently they can be used to detect C-crack defects.

HPAI surveillance programme in Cambodia: results and perspectives.

Cambodia has faced 15 confirmed highly pathogenic avian influenza (H5N1) outbreaks in different sectors of the poultry industry since January 2004. The country has very limited human and financial resources and, when the outbreak first began, the veterinary services were not equipped with the basic tools to collect accurate epidemiological information or to fight the disease. Therefore, different agencies, under the umbrella of the Food and Agriculture Organisation, are providing support to the Government to strengthen its capacity to diagnose, survey and control the avian influenza (AI) virus. Different surveillance tools are being tested, such as market monitoring and a sentinel villages' network, to offset the weakness of the national passive surveillance network. Several constraints were identified during the implementation of this programme, such as a lack of motivation among provincial staff, the limited capacity of the central team to compile and analyse the data generated, the reluctance of farmers to have their animals sampled, and weak diagnostic capacities. The sustainability of such a surveillance system once international support ends remains to be seen. Participatory epidemiology (PE) may be an appropriate complementary tool to track diseases. PE works on the principle that livestock keepers often possess detailed knowledge of animal diseases and can provide valuable diagnostics that could help in identifying AI outbreaks, particularly in remote areas.

Non-destructive testing of ceramic balls using high frequency ultrasonic resonance spectroscopy.

Although ceramic balls are used more and more for bearings in the aerospace and space industries, defects in this type of ceramic material could be dangerous, particularly if such defects are located close to the surface. In this paper, we propose a non-destructive testing method for silicon nitride balls, based on ultrasonic resonance spectroscopy. Through the theoretical study of their elastic vibrations, it is possible to characterize the balls using a vibration mode that is similar to surface wave propagation. The proposed methodology can both excite spheroidal vibrations in the ceramic balls and detect such vibrations over a large frequency range. Studying their resonance spectrums allows the balls' elastic parameters be characterized. Ours is an original method that can quickly estimate the velocity of surface waves using high frequency resonances, which permits surface and sub-surface areas to be tested specifically. Two applications are described in this paper. Both use velocity measurements to achieve their different goals, the first to differentiate between flawless balls from different manufacturing processes, and the second to detect small defects, such as cracks. Our method is rapid and permits the entire ceramic ball to be tested in an industrial context.