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FIGURE 1: Distribution of 1104 RRV cases in New South Wales. Dotted lines demarcate the biophysical zones:" far north coast (FNC); mid-north coast (MNC); central coast (CC); south coast (SC); northern tablelands (NT]; central tablelands (CT); southern tablelands (ST]; north-west slopes (NWS); central-west slopes (CWS); south-west slopes (SWS); north-west plains (NWP); far-west plains (FWP); and south-west plains (SWPj. • 1 -9 cases .10 -29 cases 030or more cases DGnffllh Shire 1257 cases]patient 12 were all considered to be diagnostic of RRV infection. As a general rule, neutralization tests (NT) were not employed except in some cases where similar HI antibody levels to both RRV and Sindbis virus rendered diagnosis difficult. The NT method used was as previously described." Clinical and epidemiological informationIn 92 of the 11% confirmed RRV cases in the statewide survey, insufficient details for useful analysis were provided. Of the remaining 1104 cases, 184 were useful only for the purpose of location ( Figure I) and were not analysed further. A full analysis of age, sex, location and onset of illness was performed for the remaining 920 cases. Clinical information for most of these patients was sparse, and in some cases the time of onset of illness had to be inferred from the date of the serum specimens and reports.

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Sentinel herds of large ruminants were established at five centres in Yunnan Province, Peoples Republic of China, between 1995 and 1997. The application of a sensitive antigen capture ELISA to facilitate virus isolation procedures led to the isolation of 108 strains of bluetongue (BLU) virus. Serotypes isolated included types 1, 2, 3, 4, 9, 11, 12, 15, 16, 21 and 23. Virus transmission occurred over a period of 1-3 months at each of the four positive sites, giving an overall BLU virus transmission period for the province of 5 months, from early June to early November. The greatest level of transmission took place in July and August. The duration of viraemia in individual animals varied from 1 to 7 weeks, with a mean calculated for each serotype between 6 and 20 days. The study represents the first detailed investigation of the epidemiology of BLU in China utilizing sentinel herds.

SUMMARYFollowing infection of chickens with infectious bronchitis virus (strain M41) viral antigens were detected by immunofluorescence in the basal layer of the trachéal mucosal epithelium for 44 days.The enzyme-linked immunosorbent assay (ELISA) first detected virusspecific antibody in tracheal washes 7 days after infection and at 10 days these antibodies reached a level that was maintained for at least 44 days, although there was considerable variation between chickens. In contrast a neutralisation test did not detect antibody until day 20 ; titres were in the range 2.2 to 3.2 log2 reaching a maximum at day 27. ELISA detected anti-viral IgA in tracheal washes only on day 7, whereas IgG was detected in all samples containing anti-viral antibody.Serum anti-viral antibodies were detected by ELISA at 7 days and reached peak titres at 10 days, which were maintained. In contrast, serum neutralising antibodies were first detected at 10 days and increased to peak titres on day 24.The implications of the differences between the results of ELISA and neutralisation tests are discussed. INTRODUCTIONThe mechanisms of immunity in chickens infected with avian infectious bronchitis virus (IBV) remain poorly understood (Darbyshire, 1981). Humoral antibodies develop and persist for lengthy periods but their titres often correlate poorly with protection against reinfection (Raggi and Lee, 1965). Similarly, cross-challenge experiments in vivo between different strains of the virus often indicate a greater degree of protection than would be expected from the relationships of such strains determined by neutralisation tests in vitro (Raggi and Lee, 1957;Winterfield and Hitchner, 1962).