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The complete nucleotide sequence (1759 nt) of the ssDNA genome of porcine circovirus (PCV) was determined from a cloned dsDNA replicative form isolated from PCV-infected cells. Sequence analysis detected no significant nucleic acid or protein similarity with another animal circovirus, chicken anaemia virus (CAV) but, surprisingly, the highest protein similarity was obtained between the product of the largest predicted PCV ORF (ORF1 ; encoding a potential protein of 35n7 kDa) and a putative protein encoded by the plant circovirus banana bunchy top virus (BBTV). High protein similarity was also detected with the other plant circoviruses subterranean clover stunt virus (SCSV) and coconut foliar

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The isolation of a number of strains of infectious bursal disease (IBD) virus from fowl, turkeys and ducks is described. These isolates could be grouped into two serotypes using the neutralisation test. It is proposed that the cell culture adapted vaccine strain from fowl should be the prototype virus for serotype 1 and that the TY89 isolate from a turkey should be the prototype for serotype 2. The isolates in serotype 2 consisted of an antigenically homogeneous group of viruses from turkeys and fowl. However, within serotype 1, which represented isolates from fowl and ducks, some isolates showed only a 30% cross reaction with the vaccine strain. If cross protection mirrors cross neutralisation, then infection with viruses belonging to serotype 2 or with antigenically distant strains from serotype 1 provides one explanation for the apparent failure of the vaccine on certain sites. However, if cross protection does not mirror cross neutralisation, then a virus from serotype 2 could be used as a heterotypic vaccine for young birds with high levels of maternally derived antibody to serotype 1.

Chicken anaemia agent (CAA) is a small, unclassified, icosahedral DNA virus with a single-stranded, circular genome. It seems to have a worldwide distribution. Only one serotype of CAA has been found, and all isolates investigated so far are pathogenic for young chicks. CAA causes a syndrome in chickens characterised by increased mortality, anaemia associated with atrophy of the haematopoietic tissues in the bone marrow, subcutaneous and intramuscular haemorrhages, and atrophy of the lymphoid system. CAA spreads both vertically and horizontally. Vertical transmission occurs following primary infection of in-lay breeding stock, and results in clinical disease in their progeny around 2 weeks of age. Horizontal spread usually results in subclinical disease. Both clinical and subclinical disease cause economic loss. Current control measures often involve controlled exposure of breeding flocks to CAA during the rearing period. A vaccine is indicated.