Infections with pigeon circovirus (PiCV) occur in young racing pigeons and pigeons raised for meat production and have been reported worldwide, but relatively little is known about the disease induced by PiCV infection. The aim of this study was to investigate how PiCV is transmitted. Using a sensitive polymerase chain reaction (PCR) test, the presence of PiCV was investigated in a wide range of samples from adult pigeons, embryos, breeders and young birds, which were derived from a racing loft that had a clinical history of "young pigeon sickness" and in which PiCV had been previously been diagnosed. Using PCR, PiCV DNA was detected in tissues of 13/20 apparently healthy older birds, aged from 1 to 9 years. Viral DNA was most commonly detected in the respiratory organs, including the trachea, pharynx and lung, followed by tissues such as the spleen, kidney and liver. It was also detected in the ovary and/or testes of some birds. This finding, and the detection of viral DNA in tissues from 8/22 embryos, suggested that PiCV may be vertically transmitted. Testing of pharyngeal and cloacal swabs, and blood samples, collected immediately before the death of the adult pigeons, failed to detect all birds found to be infected at necropsy, suggesting that testing of potential breeding birds would not enable exclusion of infected birds from breeding programmes. Additional PCR testing of cloacal swab samples obtained sequentially from 19 young pigeons showed that while four were excreting virus when 15 days old, only one bird was excreting at the time of weaning (28 days old). The detection of viral DNA in cloacal swab samples from 15.8% of the birds when 37 days old and 100% of birds when 51 days old suggested that most young pigeons probably became infected in the rearing loft.

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Nineteen racing pigeons aged from one to five years were examined postmortem. pcr tests showed that the spleens of 16 of them were positive for pigeon circovirus, the livers of six were positive, and blood from one of them was positive for the virus. Five of 44 embryos in embryonated eggs collected from three lofts were positive by pcr, but swabs taken from the crops of 64 adult birds which were feeding one- to 10-day-old squabs in these three lofts were negative for the viral dna.

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Pigeon circovirus (picv) was detected in cloacal swab samples by means of a newly-developed, sensitive pcr. An initial investigation of 17 Belgian racing pigeons aged up to eight months showed that rates of detection of 88 per cent and above were achieved using samples of cloacal swab, blood and bursa of Fabricius. The sampling of 15 caged pigeons six times when they were from three to 31 weeks of age indicated that picv infections were more readily detected in cloacal swabs than in blood, and that the virus could be detected in cloacal swabs for longer periods after infection than in blood. picv infections were detected in cloacal swabs from 38 of 47 young pigeons aged from two to 31 weeks, from 12 racing lofts, which had clinical signs including diarrhoea and weight loss, regurgitation and respiratory signs. Samples from birds from two infected lofts indicated that picv could be detected in some birds for at least 27 weeks. Although nine of 14 pigeons aged from 32 to 45 weeks were virus-positive, picv was detected in only one of 18 adult pigeons that originated from four infected lofts.

SUMMARYThe immune response and resistance to PMV1 challenge of pigeons vaccinated with inactivated oil-emulsion (OE) or aqueous-suspension (AS) vaccines were compared. ASa was based on NDV LaSota strain, ASb on NDV Terumo strain, OEa on NDV Poletti strain and OEb on NDV Ulster 2C strain. Groups were each vaccinated subcutaneously with one of ASa (0.2ml), ASb (0.2ml), OEa (0.5ml), OEa (0.2ml) and OEb (0.5ml). An unvaccinated group was kept as control. The immune response measured by HI tests was the highest with the single 0.2ml dose of ASa vaccine. The single 0.2ml dose of OEa vaccine produced a poor HI response. Challenge with 'pigeon' PMV1 (intramuscular + intranasal/ocular) one month after vaccination resulted in the vast majority of unvaccinated pigeons excreting virus in the laryngeal secretions and the faeces and all . birds died. In comparison, virus shedding and morbidity-mortality were significantly reduced in the five challenged vaccinated groups. However, morbidity-mortality was higher in the OE groups than in the AS groups. No ASa vaccinated pigeon developed clinical signs and only one ASb vaccinated pigeon presented nervous signs. In contrast, morbidity-mortality reached 30 and 35% in the OE vaccinated groups.Only the inactivated aqueous-suspension vaccines, especially that prepared from NDV LaSota strain, gave, after one dose injection (0.2ml), high resistance to a severe challenge with 'pigeon' PMV1.

SUMMARYPigeons aged 3 weeks were vaccinated, subcutaneously, with an inactivated aqueous-suspension LaSota vaccine. Irrespective of the level of maternally-derived antibodies the single vaccination gave protection lasting 1 year as shown by resistance against an intramuscular challenge with a virulent 'pigeon' PMV-1 strain.