Seroconversion to avian influenza virus in free-range chickens in the Riverland region of Victoria.

BACKGROUND: Since 2005, H5N1 avian influenza (AI) has spread from South-East Asia to over 60 different countries, resulting in the direct death or slaughter of over 250,000,000 poultry. Migratory waterfowl have been implicated in this spread and in Australia there have been numerous isolations of low-pathogenicity AI virus from wild waterfowl and shorebirds. The Department of Human Services, Victoria maintains 10 sentinel free-range chicken flocks in the Riverland at locations that are populated by large numbers of waterfowl known to carry a range of strains of AI. OBJECTIVE: This study analysed historical samples collected in 1991-94 and 2003-06 from the library of serum samples for antibodies against AI to assess the potential for transfer of AI virus from wild waterfowl to free-range poultry. RESULTS: Of the 2000 serum samples analysed, 17 were positive for antibodies against AI and 87 were suspect, with a clustering of positive and suspect results in the years 1994, 2003 and 2004. There was also a clustering of positive samples at the site of the Barmah flock. Nine sequential sets of sera from individual chickens with at least one positive result were identified. Analysis of these sequential sets showed that infection was acquired on site but that the antibody response to AI infection was short-lived and was no longer detectable at 8 weeks after the positive finding. CONCLUSION: The surveillance of sentinel chickens is a potential avenue for monitoring the circulation of AI viruses and could provide an early warning system for the commercial poultry industries.

Disease suspected to be caused by Ross River virus infection of horses.

Ross River Virus (RRV) was believed to be the cause of acute illness in four horses around the Bellarine peninsula in south-west Victoria, Australia. The horses presented with clinical signs including petechial haemorrhages, lymphadenopathy, distal limb swelling and reluctance to move. Fibrinogen was also elevated in three of the four horses. Whilst no virus was isolated, serological testing revealed elevated RRV IgM titres in all horses indicating acute infection. The outbreak occurred at a time when a known RRV vector, the mosquito Aedes camptorhynchus was recorded at very high levels in the region. This report is one of very few to attribute specific signs of disease to RRV in horses in conjunction with serological evidence of infection.

Isolation of Ross River virus from mosquitoes and from horses with signs of musculo-skeletal disease.

OBJECTIVE: To report clinical and clinicopathological findings in horses naturally infected with Ross River virus (RRV) and identify likely mosquito arbovirus vector species. PROCEDURES: Veterinarians submitted serum samples from 750 horses because they suspected Ross River virus (RRV) infection. The samples were tested for the presence of IgM and IgG antibody to RRV and for the presence of virus. Mosquitoes were trapped, differentiated to species level and tested for the presence of RRV by virus isolation. RESULTS: RRV was isolated from six species of mosquitoes (Ochlerotatus camptorhyncus, Culex globocoxitus, Cx. australicus, Cx. annulirostris, Cx. quinquefasciatus, Anopheles annulipes) and from 13 horses with clinical signs of musculo-skeletal disease. Antibody to RRV was detected in 420 of the 750 serum samples; 307 contained IgG only; 76 contained both IgM and IgG and 37 contained only IgM antibody to RRV. Virus was isolated from horses with IgM antibody only. CONCLUSIONS: RRV can be isolated from infected horses during the short time period when there is an overlap of clinical signs, positive IgM serology and viraemia. Early spring infections of horses may occur if RRV infected mosquito vectors are present. RRV has not been shown to cause clinical disease in horses. This is the first report of isolation of RRV from Oc. camptorhyncus in the Murray region and indicates a potential for infection of humans and animals in autumn as well as in spring.

Polymerase chain reaction tests for the identification of Ross River, Kunjin and Murray Valley encephalitis virus infections in horses.

OBJECTIVE: To develop and validate specific, sensitive and rapid diagnostic tests using RT-PCR for the detection of Ross River virus (RRV), Kunjin virus (KV) and Murray Valley encephalitis virus (MVEV) infections in horses. METHODS: Primer sets based on nucleotide sequence encoding the envelope glycoprotein E2 of RRV and on the nonstructural protein 5 (NS5) of KV and MVEV were designed and used in single round PCRs to test for the respective viruses in infected cell cultures and, in the case of RRV, in samples of horse blood and synovial fluid. RESULTS: The primer pairs designed for each of the three viruses amplified a product of expected size from prototype viruses that were grown in cell culture. The identity of each of the products was confirmed by nucleotide sequencing indicating that in the context used the RT-PCRs were specific. RRV was detected in serums from 8 horses for which there were clinical signs consistent with RRV infection such that an acute-phase serum sample was taken and submitted for RRV serology testing. The RRV RT-PCR was analytically sensitive in that it was estimated to detect as little as 50 TCID50 of RRV per mL of serum and was specific in that the primer pairs did not amplify other products from the 8 serum samples. The RRV primers also detected virus in three independent mosquito pools known to contain RRV by virus isolation in cell culture. Samples from horses suspected to be infected with KV and MVEV were not available. CONCLUSION: Despite much anecdotal and serological evidence for infection of horses with RRV actual infection and associated clinical disease are infrequently confirmed. The availability of a specific and analytically sensitive RT-PCR for the detection of RRV provides additional opportunities to confirm the presence of this virus in clinical samples. The RT-PCR primers for the diagnosis of KV and MVEV infections were shown to be specific for cell culture grown viruses but the further validation of these tests requires the availability of appropriate clinical samples from infected horses.

Communicable diseases surveillance

Communicable diseases surveillance highlights (vaccine preventable diseases, arboviruses, respiratory viruses), and surveillance outcomes from several reporting series as follows: National Notifiable Diseases Surveillance System tables, 14 October to 10 November 1998; Laboratory Serology and Virology Reporting Scheme tables, 8 October to 4 November 1998; Australian Sentinel Practice Research Network report tables, weeks 40 to 43, 1999; Gonococcal surveillance, reporting period 1 April to 30 June 1998; Sentinel chicken surveillance program, reporting period September 1998; HIV and AIDS surveillance, reporting period 1 to 30 June 1998, assessed as at 30 September 1998; Australian childhood immunisation coverage, 1 April to 30 June 1998 cohort, assessed as at 30 June 1998.

Sequential studies of endochondral ossification and serum 1,25-dihydroxycholecalciferol in broiler chickens between one and 21 days of age.

Two commercial broiler flocks of two distinct strains (A and B) were studied at weekly intervals from day old to 21 days, to assess the progressive endochondral ossification of the proximal tibiotarsus and the serum concentration of 1,25-dihydroxycholecalciferol (1,25(OH)2D3). The incidence of defects of endochondral ossification was different in the two strains, strain B having an incidence of tibial dyschondroplasia (TD) of 10 to 70 per cent and strain A an incidence of 10 to 20 per cent. In strain B, 40 per cent of the bone samples collected at 14 days of age also had lesions of calcium deficiency rickets. The concentration of 1,25(OH)2D3 in the two flocks was similar in the day-old chicks, but was 40 to 50 per cent lower at seven, 14 and 21 days of age in strain B, during the development of the rachitic and dyschondroplastic lesions. These results suggest that TD in some broiler strains is related to an inherent predisposition to rickets and to lower serum concentrations of 1,25(OH)2D3.

Evidence of vertical transmission of Ross River and Sindbis viruses (Togaviridae: Alphavirus) by mosquitoes (Diptera: Culicidae) in southeastern Australia.

Ross River and Sindbis viruses were isolated from Aedes camptorhynchus adults reared from immatures collected from a salt marsh in coastal Victoria, indicating the existence of field vertical transmission. These first isolations of an arbovirus from adult mosquitoes reared from field-collected immatures in Australia indicates one mechanism for arbovirus maintenance in temperate regions.

Serum total calcium, phosphorus, 1,25-dihydroxycholecalciferol, and endochondral ossification defects in commercial broiler chickens.

The research described in this paper relates the changes in serum concentration of calcium, phosphorus, and 1,25-dihydroxycholecalciferol [1,25(OH)2D3] to changes in tibial ash percentage and the incidence of endochondral ossification defects (EOD) in flocks of commercially reared broiler chickens at 14 d of age. Sequential studies of six Australian broiler flocks representing three major genetic lines were undertaken at weekly intervals from 1 to 28 d of age. Serum collected from birds was analyzed for total calcium, inorganic phosphorus, and 1,25(OH)2D3. Tibial ash percentage was also determined at weekly intervals, and the incidence of EOD was determined at 14 d of age by examining sagittal sections of the proximal tibiotarsus. The EOD observed in the 14-d-old broiler chickens were characterized by enlarged zones of proliferating chondrocytes, similar to that which occurs during calcium- or vitamin D-dependent rickets. Three flocks had a 50% incidence of EOD at 14 d of age and were classified as severely affected. The other three flocks had incidences ranging from 12 to 16% and were classified as mildly affected. Broiler flocks severely affected with EOD (50% incidence at Day 14) had lower (P < or = .05) concentrations of 1,25(OH)2D3 than flocks mildly affected (12 to 16% incidence). Tibial ash percentages were lower (P < or = .05) in the severely affected flocks between Days 14 to 28, and it is likely that a lower rate of ash accretion between Days 7 to 14 precedes the development of the EOD.(ABSTRACT TRUNCATED AT 250 WORDS)

The iodine status of grazing sheep as monitored by concentrations of iodine in milk.

The iodine nutrition of grazing ewes was assessed from milk iodine concentrations. In 54 flocks sampled throughout Victoria, the mean milk iodine concentrations in ewes ranged from 79 to 1831 micrograms/l. In 2 flocks where newborn lambs had goitre the concentrations in ewes ranged from 45 to 98 micrograms/l. A marked seasonal variation was apparent when ewes in a flock were sampled at monthly intervals over 2 years. Milk iodine concentrations were highest at the end of summer, and were lowest in spring. In grazing ewes the milk iodine concentrations remained relatively constant throughout the day. In ewes given single oral doses of up to 2 mg iodine, milk iodine concentrations increased to maximum within 5 h, the increment being related to the dose administered, and decreased to pretreatment concentrations within 24 h. Milk iodine concentrations in ewes given 1 ml iodised oil intramuscularly remained significantly higher than untreated ewes in the same flock for 16 months after treatment. The effectiveness of the single injection was still apparent after 2 consecutive pregnancies in the ewes.