J. Henning

Farm- and flock-level risk factors associated with Highly Pathogenic Avian Influenza outbreaks on small holder duck and chicken farms in the Mekong Delta of Viet Nam.

After 11 consecutive months of control, the Mekong Delta in Viet Nam experienced a wave of Highly Pathogenic Avian Influenza (HPAI) H5N1 outbreaks on small holder poultry farms from December 2006 to January 2007. We conducted a retrospective matched case-control study to investigate farm- and flock-level risk factors for outbreak occurrence during this period. Twenty-two case farms were selected from those where clinical signs consistent with HPAI H5N1 had been present and HPAI H5N1 had been confirmed with a positive real-time PCR test from samples obtained from affected birds. For every case farm enrolled, two control farms were selected matched on time of outbreak occurrence, farm location and species. Veterinarians conducted interviews with farmers, to collect information on household demographics, farm characteristics, husbandry practices, trading practices, poultry health, vaccination and biosecurity. Exact stratified logistic regression models were used to assess putative risk factors associated with a flock having or not having a HPAI outbreak. Nested analyses were also performed, restricted to subsets of farms using scavenging, confinement or supplementary feeding practices. Risk of an outbreak of HPAI H5N1 was increased in flocks that had received no vaccination (odds ratio (OR)=20.2; 95% confidence interval (CI): 1.0, +infinity) or only one vaccination (OR=85.2; 95% CI: 6.5, +infinity) of flocks compared to two vaccinations, and in flocks on farms that had family and friends visiting (OR=8.2; 95% CI: 1.0, +infinity) and geese present (OR=11.5; 95% CI: 1.1, +infinity). The subset analysis using only flocks that scavenged showed that sharing of scavenging areas with flocks from other farms was associated with increased risk of an outbreak (OR=10.9; 95% CI: 1.4, 492.9). We conclude that none or only one vaccination, visitors to farms, the presence of geese on farms and sharing of scavenging areas with ducks from other farms increase the risk of HPAI H5N1 outbreaks in poultry flocks in Viet Nam.

Risk factors and characteristics of H5N1 Highly Pathogenic Avian Influenza (HPAI) post-vaccination outbreaks

Highly pathogenic avian influenza (HPAI) virus H5N1 is now endemic in South-East Asia but HPAI control methods differ between countries. A widespread HPAI vaccination campaign that started at the end of 2005 in Viet Nam resulted in the cessation of poultry and human cases, but in 2006/2007 severe HPAI outbreaks re-emerged. In this study we investigated the pattern of this first post-vaccination epidemic in southern Viet Nam identifying a spatio-temporal cluster of outbreak occurrence and estimating spatially smoothed incidence rates of HPAI. Spatial risk factors associated with HPAI occurrence were identified. Medium-level poultry density resulted in an increased outbreak risk (Odds ratio (OR) = 5.4, 95% confidence interval (CI): 1.6–18.9) but also climate-vegetation factors played an important role: medium-level normalised difference vegetation indices during the rainy season from May to October were associated with higher risk of HPAI outbreaks (OR = 3.7, 95% CI: 1.7–8.1), probably because temporal flooding might have provided suitable conditions for the re-emergence of HPAI by expanding the virus distribution in the environment and by enlarging areas of possible contacts between domestic waterfowl and wild birds. On the other hand, several agricultural production factors, such as sweet potatoes yield, increased buffalo density, as well as increased electricity supply were associated with decreased risk of HPAI outbreaks. This illustrates that preventive control measures for HPAI should include a promotion of low-risk agricultural management practices as well as improvement of the infrastructure in village households. Improved HPAI vaccination efforts and coverage should focus on medium poultry density areas and on the pre-monsoon time period.

Scavenging ducks and transmission of highly pathogenic avian influenza, Java, Indonesia.

These ducks may be a source of infection for chickens and humans.

Highly pathogenic avian influenza (H5N1) in ducks and in-contact chickens in backyard and smallholder commercial duck farms in Viet Nam

Scavenging ducks are thought to play an important role in the maintenance and transmission of highly pathogenic avian influenza (HPAI) H5N1 virus among domesticated and wild bird populations in South East Asia, but detailed field epidemiological results describing the infection status of domestic ducks and in-contact chickens have not been published. We conducted a longitudinal study, monitoring ducks and in-contact chickens in 80 flocks in the Mekong Delta of Viet Nam with bi-monthly testing from May 2007 until May 2008. Because H5 vaccination campaigns are conducted at regular intervals in poultry flocks in Viet Nam, both unvaccinated sentinel and H5 vaccinates were monitored. On each farm, a total of 10 birds were selected: 7 ducks (4 unvaccinated and 3 vaccinated) and 3 chickens (2 unvaccinated and 1 vaccinated) that were in close contact with the ducks. Blood samples were tested for H5 antibodies using the hemagglutination inhibition test, with H5 antibody titers ≥2(4) considered to indicate past exposure to H5 field or vaccine virus. Titers of vaccinated birds were analyzed for samples collected more than 3 weeks post-vaccination. Pooled oropharyngeal and cloacal swabs were assessed for H5 viral RNA using real-time PCR. Bird- and flock-level prevalences were estimated accounting for sampling fractions and clustering under the multi-stage sampling design with birds being sampled within flocks within villages in four different provinces. In total, serum and swab samples from 5409 birds-samplings were analyzed. Bird-level seroprevalence was 17.5% (95% CI: 14.1, 20.9) amongst unvaccinated ducks and 10.7% (95% CI: 7.4, 14.4) amongst unvaccinated in-contact chickens. Flock-level seroprevalence (proportion of flock-visits with at least one unvaccinated bird test positive) was 42.6% (95% CI: 38.0, 47.2) for ducks and 19.0% (95% CI: 13.6, 24.4) for chickens. Only 54.3% (95% CI: 39.2, 69.3) of vaccinated ducks and 55.5% (95% CI: 46.8, 64.2) of vaccinated in-contact chickens had H5 antibodies at more than 3 weeks post-vaccination. At about 40% and 48% of flock-visits, less than 50% of sampled vaccinated ducks and chickens, respectively, had positive titers. The flock-level virus prevalence (proportion of flocks with at least one bird positive for H5 virus of the vaccinated and unvaccinated birds tested) was 0.7% (95% CI: 0.0, 2.1). No HPAI outbreaks or mortality suspected to be due to HPAI occurred in study flocks during the observation period. Our results indicate that a substantial proportion of ducks and in-contact chickens were exposed to H5 virus during the study period. In the face of this widespread exposure to H5 virus, and despite only moderate proportions of birds developing positive titers post-vaccination, flocks were not affected by HPAI outbreaks during our study period. The higher bird-level seroprevalence in ducks compared to in-contact chickens may be due to greater durations of antibody persistence in ducks or greater rates of H5 virus exposure. These findings indicate that ducks are potentially an important source of H5 virus for other bird species.

Survival of rabbit haemorrhagic disease virus (RHDV) in the environment

A study was conducted to investigate the persistence of rabbit haemorrhagic disease virus (RHDV) in the environment. Virus was impregnated onto two carrier materials (cotton tape and bovine liver) and exposed to environmental conditions on pasture during autumn in New Zealand. Samples were collected after 1, 10, 44 and 91 days and the viability of the virus was determined by oral inoculation of susceptible 11- to 14-week-old New Zealand White rabbits. Evidence of RHDV infection was based on clinical and pathological signs and/or seroconversion to RHDV. Virus impregnated on cotton tape was viable at 10 days of exposure but not at 44 days, while in bovine liver it was still viable at 91 days. The results of this study suggest that RHDV in animal tissues such as rabbit carcasses can survive for at least 3 months in the field, while virus exposed directly to environmental conditions, such as dried excreted virus, is viable for a period of less than 1 month. Survival of RHDV in the tissues of dead animals could, therefore, provide a persistent reservoir of virus, which could initiate new outbreaks of disease after extended delays.

Calf-Level Factors Associated with Bovine Neonatal Pancytopenia – A Multi-Country Case-Control Study

Bovine neonatal pancytopenia (BNP), a high fatality condition causing haemorrhages in calves aged less than 4 weeks, was first reported in 2007 in Germany and subsequently observed at low incidence in other European countries and New Zealand. A multi-country matched case-control study was conducted in 2011 to identify calf-level risk factors for BNP. 405 BNP cases were recruited from 330 farms in Belgium, France, Germany and the Netherlands by laboratory confirmation of farmer-reported cases. Up to four calves of similar age from the same farm were selected as controls (1154 calves). Risk factor data were collected by questionnaire. Multivariable modelling using conditional logistic regression indicated that PregSure®BVD (PregSure, Pfizer Animal Health) vaccination of the dam was strongly associated with BNP cases (adjusted matched Odds Ratio - amOR 17.8 first lactation dams; 95% confidence interval – ci 2.4, 134.4; p = 0.005), and second or more lactation PregSure-vaccinated dams were more likely to have a case than first lactation vaccinated dams (amOR 2.2 second lactation; ci 1.1, 4.3; p = 0.024; amOR 5.3 third or more lactation; ci 2.9, 9.8; p = <0.001). Feeding colostrum from other cows was strongly associated with BNP if the dam was not PregSure-vaccinated (amOR 30.5; ci 2.1, 440.5; p = 0.012), but the effect was less if the dam was PregSure-vaccinated (amOR 2.1; ci 1.1, 4.0; p = 0.024). Feeding exclusively dam’s milk was a higher risk than other types of milk (amOR 3.4; ci 1.6, 7.5; p = 0.002). The population attributable fractions were 0.84 (ci 0.68, 0.92) for PregSure vaccination, 0.13 (ci 0.06, 0.19) for feeding other cows’ colostrum, and 0.15 (ci 0.08, 0.22) for feeding dam’s milk. No other calf-level factors were identified, suggesting that there are other important factors that are outside the scope of this study, such as genetics, which explain why BNP develops in some PregSure-colostrum-exposed calves but not in others.

Village, chicken production in Myanmar - purpose, magnitude and major constraints

The main objective of this work was to describe the characteristics of and major constraints to village chicken production in Myanmar. Data on village chicken production, health, husbandry and marketing were collected in 296 households in 10 villages in the Yangon division of Myanmar in November 2003. The average flock size in the study area was about 30 birds, comprising 12 chicks, 12 growers, 4 hens and 2 cocks. Disease as a cause of mortality was more prominent in growers and adults, while predation and exposure to unfavourable environmental conditions were major causes of mortality in chicks. The main predators identified were: birds, rats, snakes, dogs and cats in 32, 31, 17, 15 and 3% of households respectively. Two main strategies were identified to improve village chicken production: vaccination as a means of protecting birds against Newcastle disease and confinement rearing and supplementary feeding of chicks, as a means of reducing the attrition rate of young chicks. This is the first survey conducted describing village chicken population structure and productivity in Myanmar.

Mortality rates adjusted for unobserved deaths and associations with Newcastle disease virus serology among unvaccinated village chickens in Myanmar.

Village chickens are an important livestock for many rural families in Myanmar and other developing countries. Village chickens are kept under free-ranging conditions, with confinement only at night. Therefore, it is likely that some deaths are not observed by farmers. We conducted a longitudinal study from November 2003 until May 2004 to describe temporal patterns of mortality of village chickens in 10 villages in Myanmar. Field veterinarians first identified the numbers of birds in all chicken-owning households in each village. We then selected 307 households randomly with stratification by flock size. Each study household was then visited once monthly at which time questionnaires were completed recording current flock structure and numbers of hatchings, mortalities, sales and birds consumed since the previous visit. In addition, sera were collected from a sample of adult birds and growers. Depending on month and age group of chicken, from 71 to 231 (out of 290-307) households had discrepancies in the counts of birds. For chicks, at least one-quarter of the households had unobserved losses of at least 5 chicks per household (maximum 66 chicks); unobserved losses were less for growers and adult chickens. The median month-specific, village-specific mortality rates per 1000 bird-days at risk (counting missing birds as deaths) ranged from 0.8 to 1.7 for adults, from 0.4 to 4.7 for growers and from 8.0 to 16.5 for chicks. Across all birds, the prevalence of protective titres against Newcastle disease virus was 79% (95% confidence interval 74, 84); higher prevalences of protective titres were associated with reduced mortality rates in the following months.

A molecular and antigenic survey of H5N1 highly pathogenic avian influenza virus isolates from smallholder duck farms in Central Java, Indonesia during 2007-2008

BackgroundIndonesia is one of the countries most severely affected by H5N1 highly pathogenic avian influenza (HPAI) virus in terms of poultry and human health. However, there is little information on the diversity of H5N1 viruses circulating in backyard farms, where chickens and ducks often intermingle. In this study, H5N1 virus infection occurring in 96 smallholder duck farms in central Java, Indonesia from 2007-2008 was investigated and the molecular and antigenic characteristics of H5N1 viruses isolated from these farms were analysed.ResultsAll 84 characterised viruses belonged to H5N1 clade 2.1 with three virus sublineages being identified: clade 2.1.1 (1), clade 2.1.3 (80), and IDN/6/05-like viruses (3) that did not belong to any of the present clades. All three clades were found in ducks, while only clade 2.1.3 was isolated from chickens. There were no significant amino acid mutations of the hemagglutinin (HA) and neuraminidase (NA) sites of the viruses, including the receptor binding, glycosylation, antigenic and catalytic sites and NA inhibitor targets. All the viruses had polybasic amino acids at the HA cleavage site. No evidence of major antigenic variants was detected. Based on the HA gene, identical virus variants could be found on different farms across the study sites and multiple genetic variants could be isolated from HPAI outbreaks simultaneously or at different time points from single farms. HPAI virus was isolated from both ducks and chickens; however, the proportion of surviving duck cases was considerably higher than in chickens.ConclusionsThe 2.1.3 clade was the most common lineage found in this study. All the viruses had sequence characteristic of HPAI, but negligible variations in other recognized amino acids at the HA and NA proteins which determine virus phenotypes. Multiple genetic variants appeared to be circulating simultaneously within poultry communities. The high proportion of live duck cases compared to chickens over the study period suggests that ducks are more likely to survive infection and they may better suit the role of long-term maintenance host for H5N1. As some viruses were isolated from dead birds, there was no clear correlation between genetic variations and pathogenicity of these viruses.

Influence of weather conditions on fly abundance and its implications for transmission of Rabbit Haemorrhagic Disease Virus in the North Island of New Zealand

Abstract.  Blowflies (Diptera: Calliphoridae) and flesh flies (Diptera: Sarcophagidae) are potential vectors of rabbit haemorrhagic disease virus (RHDV) in New Zealand. The associations between habitat and weather factors on the abundance of these flies were investigated. Between October 1999 and June 2001, flies were trapped on open pasture and in dense vegetation patches on farmland in the Himatangi area of the North Island. Five calliphorid species were trapped commonly at scrub edges and the most abundant sarcophagid, Oxysarcodexia varia Walker, was trapped mainly on open pasture. An abundance peak of O. varia was probably associated with the occurrence of a rabbit haemorrhagic disease (RHD) outbreak in the study area. Overall abundance of flies varied according to habitat and species, and species numbers differed between seasons and years. The all‐day minimum temperature 3 weeks before trapping was a significant variable in all models of fly abundance, whereas average rainfall did not affect fly abundance. The all‐day temperature range was significant only for O. varia. The influence of other climatic factors varied between fly species. Climate dependent variations in fly abundance may contribute to the risk of transmission of RHD, which occurred intermittently on the site during the study period.