Analysis of horse movements and events during the 2007 outbreak of equine influenza in New South Wales, Australia.

OBJECTIVE: To analyse horse event and horse movement registration data collected between September 2007 and December 2008 during the outbreak of equine influenza in New South Wales, Australia. RESULTS: A total of 9356 events were registered, involving 504,382 horses and 242,952 riders. Registered horse movements totalled 224,084, involving 349,327 horses (excluding mobs) travelling 34.4 million km with an average of 154 km per journey. The number of recorded events and movements were low while movement controls were most stringent, then increased from December 2007 as restrictions were eased, to peak in April 2008 with up to 290 events and 15,730 movements weekly, after which registrations declined as the disease was eradicated. The main types of events registered were pony clubs (38%), race meetings and trials (17%), competition (13%), and clinics and lessons (11%). CONCLUSIONS: Registration of horse events and movements allowed movement controls to be progressively eased while retaining the ability to trace the movements of large numbers of horses if needed. The number of recorded events, movements and distances travelled confirms the highly mobile nature of the recreational horse industries, helps to explain the rapid and widespread dispersal of the disease before movement restrictions were imposed, and also demonstrates the value of those restrictions as a control measure. The data provide a quantitative snap-shot of horse events and movements, albeit distorted by the prevailing movement restrictions as well as by limitations in the data recording that should be addressed when developing traceability systems for horses in future.

The serological responses of chickens to mass vaccination with a live V4 Newcastle disease virus vaccine in the field and in the laboratory. 1. Meat chickens.

Meat chickens on commercial broiler farms were vaccinated once at 1 to 15 days of age with a live V4 Newcastle disease virus (NDV) vaccine administered by drinking water, aerosol or coarse spray. Hatchmates were housed and similarly vaccinated in laboratory isolation pens. Samples of birds were bled at weekly to fortnightly intervals and the serums tested for haemagglutination inhibiting antibody to NDV. Log2 mean titres of up to 6.26, and assumed protection levels (based on the percentage of birds with log2 titres of 4 or greater) of up to 89%, were obtained in field trials within 4 weeks of vaccination. Differences were observed between the results obtained from parallel field and laboratory trials. The presence of maternal NDV antibody reduced the response to vaccination. The results show that this V4 vaccine can produce an adequate serological response following mass administration to Australian meat chickens housed under commercial conditions.

Natural infection of broiler breeder chickens with endemic apathogenic Newcastle disease virus and their subsequent response to vaccination with a live V4 Newcastle disease virus vaccine.

Flocks of broiler breeder chickens housed on a commercial farm were monitored from 13 w of age for natural infection with endemic lentogenic Newcastle disease virus (NDV). Seroconversion was first detected at 17 w. By 24 w, all 8 flocks had achieved peak log2 mean haemagglutination inhibiting antibody titres of up to 4.8. Antibody titres then declined and rose again over several months, suggesting cyclic reinfection with NDV. A lentogenic NDV indistinguishable from V4 was isolated from the cloaca of one bird at 18 weeks of age. At 54 weeks of age, 6 of 8 flocks were vaccinated en masse with live V4 NDV vaccine, 3 flocks by drinking water and 3 flocks by aerosol. All flocks were serologically monitored for a further 8 w. Drinking water vaccination induced an anamnestic response in 3 flocks, showing that flocks with pre-existing active immunity to NDV may be successfully vaccinated with V4. However, in all aerosol vaccinated flocks, the procedures failed to induce a response different to that observed in unvaccinated flocks. The serological response to vaccination was greater in sires than in dams.

The serological responses of chickens to mass vaccination with a live V4 Newcastle disease virus vaccine in the field and in the laboratory. 2. Layer pullets.

Layer chickens on a commercial started pullet farm were vaccinated once at 31 to 52 days of age by drinking water or aerosol with live V4 Newcastle disease virus (NDV) vaccine. Flockmates which had been rehoused in laboratory isolation pens shortly beforehand were similarly vaccinated. Samples of birds were bled at intervals and the serums tested for haemagglutination inhibiting antibody to NDV. Log2 mean titres of up to 4.88 and assumed protection levels (based on the percentage of birds with log2 titres of 4 or greater) of up to 81%, were obtained in the field trials within 4 weeks of vaccination. A subsequent laboratory trial further compared the response of different breeds of chicken to different routes of vaccination. Differences were observed between breeds, routes of vaccination, and parallel field and laboratory trials. The results show that this V4 vaccine can produce an adequate serological response following mass vaccination of Australian layer pullets housed under commercial conditions, and that care should be exercised in extrapolating results obtained under laboratory conditions.

The resistance of meat chickens vaccinated by aerosol with a live V4 Newcastle disease virus vaccine in the field to challenge with a velogenic Newcastle disease virus.

Meat chickens housed on a commercial broiler farm in Australia were vaccinated once at 10 to 11 days-of-age by aerosol with live V4 Newcastle disease virus (NDV) vaccine. Groups of vaccinated and unvaccinated birds were flown to Malaysia, where they were challenged with a virulent strain of NDV. Survival rates in vaccinated chickens challenged 7, 14, 21 or 31 d after vaccination were 0.47, 0.77, 0.97 and 0.92, respectively. All unvaccinated chickens died due to Newcastle disease (ND) following challenge. Chickens in Australia and Malaysia were bled and the serums tested for haemagglutination-inhibiting (HI) antibody to NDV. Many vaccinated birds with no detectable antibody, and all birds with a log2 titre of 2 or greater, survived challenge. The results showed that this V4 vaccine induced protective immunity in a significant proportion of chickens within 7 d of mass aerosol vaccination. This early immunity occurred in the absence of detectable circulating HI antibody. Non-HI antibody mediated immunity continued to provide protection up to 31 d after vaccination. Almost all vaccinated birds were protected within 3 w of vaccination. It is concluded that the V4 vaccine is efficacious and could be useful during an outbreak of virulent ND in Australia.

Isolation of Mycoplasma synoviae from infectious synovitis of chickens.

This report describes the first isolations of Mycoplasma synoviae from the synovial sheaths and joints of commercial chickens affected with synovitis in Australia. Over 4 years 3 separate outbreaks were investigated in which up to 20% of birds exhibited clinical signs of poor growth and "hot foot" syndrome (swollen inflamed footpads). Once an outbreak occurred, chronic infection of the farm usually ensued. Grossly the hocks and footpads were swollen by a purulent exudate and associated inflammatory changes with histological features of a severe acute synovitis. Seroconversion of the flocks occurred at the time of the development of lesions. M. synoviae specific antibodies were demonstrated by ELISA in the joint fluid of affected birds. It is concluded that the cases described are similar to avian infectious synovitis syndrome caused by M. synoviae previously described overseas.

A viral infection causing cytomegalic inclusion disease in the renal epithelium of the platypus (Ornithorhynchus anatinus).

Cytomegaly and intranuclear inclusion bodies were observed in the renal collecting duct epithelium in three of four wild caught platypuses (Ornithorhynchus anatinus) from New South Wales using light and electron microscopy during routine pathological studies. Non-enveloped, spherical virions measuring about 80 nm in diameter were present in the nucleus and cytoplasm of affected cells as well as in the lumen of the renal tubule. A single enveloped virion measuring about 150 nm in diameter was found. There was no serological evidence of infection with cytomegalovirus (AD169 antigen) or adenovirus (mammalian and avian group antigens) in any of the platypuses. Although the identity of the virus was not confirmed, it was probably an adenovirus based on morphological grounds. The infection appeared to have little effect on the host.

Ruptured yolk sac in turkey poults.

A problem of increased neonatal mortality in turkey poults was shown to be due to rupture of the yolk sac, as a result of trauma inflicted during vent-sexing.