Joerg Henning

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.

A sparse rabbit population in New Zealand was monitored over 3 years to assess the temporal dynamics of rabbit mortality, in particular to understand the mortality patterns due to rabbit haemorrhagic disease (RHD). A total of 107 deaths were recorded, of which 93 could be classified by cause. The predominant cause of mortality was predation (47% of deaths), followed by RHD (20%). Deaths due to RHD were clustered in time (within 3 weeks), predation occurred most actively from late autumn to spring, while other causes of death did not show pronounced seasonal peaks. No differences in cause-specific death risk were observed between sexes. Predation was the main cause of death in younger animals, while RHD mortality occurred mainly in older rabbits. This study has shown that the impact of RHD can vary considerably between years, indicating that a variety of risk factors are required to initiate a RHD epidemic with a high mortality rate among rabbits.

ABSTRACT 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.

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.

AIM: To estimate over a 3-year period following the first release of rabbit haemorrhagic disease virus (RHDV) the prevalence of rabbit haemorrhagic disease (RHD) and the abundance of rabbits (Oryctolagus cuniculus) in an area that historically had low rabbit densities.METHODS: Three farms grazing predominantly sheep and beef cattle, located close together and with low initial rabbit densities, were selected for study. RHDV had been deliberately released on all farms in December 1997. Farms were visited 2–3 times per year between June 1998 and April 2001. At each visit, rabbits were shot with the aid of spotlights at night and blood samples were collected for detection of RHDV antibodies. Rabbit carcasses were necropsied and the age of the animals was determined. Rabbit abundance on each property was measured throughout the study using spotlight night counts. Logistic regression was used to identify factors associated with the risk of carcasses being seropositive for RHDV.RESULTS: Rabbit density differed initially between farms (8.2, 9.9, 2.3 rabbits per spotlight km in June 1998), and declined on all three properties over time (1.2, 2.4, 1.1 rabbits per spotlight km in November 2000). Highest antibody titres to RHDV were initially evident on the farm on which rabbits were most abundant. The average prevalence of seropositive rabbits overall was 21% (95% CI=15–28%). Female rabbits tended to be less likely to be seropositive for RHDV than males (OR=0.47; 95% CI=0.21–1.02). The odds of becoming seropositive were reduced for rabbits born in the breeding season of 1999–2000 (OR=0.17; 95% CI=0.05–0.64).CONCLUSIONS: The temporal pattern of outbreaks measured by peaks of seroprevalence differed between closely-spaced farms when they had different rabbit densities, but were similar when rabbit densities were similar. Microclimate and vegetation influencing abundance of insect vectors for RHDV and intrinsic population-related factors like rabbit breeding behaviour are also likely to be involved in local patterns of spread.

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.

... 1993; Lenghaus et al. 2000). Similar clinical findings, morphological similarities, and geographical distributions between RHDV and the European brown hare syndrome virus (EBHSV) in European hares suggested that RHDV may have developed from EBHSV (Capucci et al. ...

This study investigated whether exposure to inactivated rabbit haemorrhagic disease virus (RHDV) can produce an antigenic response in rabbits and protect them from a subsequent challenge with virulent virus. The aim was to determine if the spreading of baits containing RHDV, which is a common management practice in New Zealand to reduce rabbit numbers, could result in protective immunity in wild rabbits. RHDV was inactivated by ultraviolet (UV) light using an electronic UV crosslinker with a UV dose of 168.48 W-s/cm2 and a UV intensity of 0.0078 W/cm2. Two groups of four rabbits were then inoculated with inactivated virus via oral and intramuscular routes. Rabbits were monitored for 30 days post-inoculation and then challenged orally with virulent virus. No rabbit exposed to inactivated RHDV developed clinical signs of RHD or had antibodies at day 30 post-infection and all animals died within 82 h after challenge with virulent virus. No antibodies were detected at the time of death. These findings suggest that exposure to virus completely inactivated by UV light in the field or on baits will not protect rabbits against challenge with virulent virus.

In Java, Indonesia, during March 2007-March 2008, 96 farms with scavenging ducks that were not vaccinated against highly pathogenic avian influenza (HPAI) were monitored bimonthly. Bird-level (prevalence among individual birds) H5 seroprevalence was 2.6% for ducks and 0.5% for chickens in contact with ducks. At least 1 seropositive bird was detected during 19.5% and 2.0% of duck- and chicken-flock visits, respectively. Duck flocks were 12.4x more likely than chicken flocks to have seropositive birds. During 21.4% of farm visits, <or=1 sampled duck was H5 seropositive when all sampled in-contact chickens were seronegative. Subtype H5 virus was detected during 2.5% of duck-flock visits and 1.5% of chicken-flock visits. When deaths from HPAI infection occurred, H5 virus shedding occurred in apparently healthy birds on 68.8% of farms. Of 180 poultry deaths investigated, 43.9% were attributed to H5 virus. These longitudinal study results indicate that ducks are a source of infection for chickens and, potentially, for humans.

There is a variety of professions working with village chickens in developing countries, including farmers, veterinarians and chicken traders. People from all these occupations were involved in a participatory rural appraisal to investigate husbandry practices and trade of village chickens in Myanmar. Data were collected in two climatically different regions of the country, in the Yangon and in the Mandalay divisions. The breeding and training of fighting cocks was practised only in the Mandalay division, with well-trained birds sold for very high prices. Apart from this, chickens were raised in both regions mainly for small disposable income and were generally sold when money was needed, in particular during religious festivals. Chicken traders on bicycles, often called ‘middle men’, usually purchase birds from farmers in about 10 villages per day. Several ‘middle men’ supply birds to wealthier chicken merchants, who sell these birds at larger chicken markets. There is in general limited knowledge among farmers about the prevention of Newcastle disease via vaccination. Commercial indigenous chicken production is practised in Myanmar, but family poultry farming dominates indigenous chicken production in the country.

ABSTRACT A longitudinal capture-mark-recapture study was conducted to determine the temporal dynamics of rabbit haemorrhagic disease (RHD) in a European rabbit (Oryctolagus cuniculus) population of low to moderate density on sand-hill country in the lower North Island of New Zealand. A combination of sampling ( trapping and radio-tracking) and diagnostic (cELISA, PCR and isotype ELISA) methods was employed to obtain data weekly from May 1998 until June 2001. Although rabbit haemorrhagic disease virus ( RHDV) infection was detected in the study population in all 3 years, disease epidemics were evident only in the late summer or autumn months in 1999 and 2001. Overall, 20% of 385 samples obtained from adult animals older than 11 weeks were seropositive. An RHD outbreak in 1999 contributed to an estimated population decline of 26%. A second RHD epidemic in February 2001 was associated with a population decline of 52% over the subsequent month. Following the outbreaks, the seroprevalence in adult survivors was between 40% and 50%. During 2000, no deaths from RHDV were confirmed and mortalities were predominantly attributed to predation. Influx of seronegative immigrants was greatest in the 1999 and 2001 breeding seasons, and preceded the RHD epidemics in those years. Our data suggest that RHD epidemics require the population immunity level to fall below a threshold where propagation of infection can be maintained through the population.