Genomic DNAs from 3 oocyst isolates of Hammondia sp. from foxes (Vulpes vulpes and V. lagopus) and 1 oocyst isolate of Hammondia heydorni from a dog, were examined by PCR and sequence analysis of 6 loci in order to determine whether the isolates were conspecific. Consistent genetic differences were found between the fox and dog isolates, respectively, at the ITS-2 region, the lsu rRNA gene, the alpha tubulin gene and the HSP70 gene, but not at the ssu rRNA gene or ITS-1 locus. Infection experiments established that dogs were unsuitable as definitive hosts for Hammondia sp. of foxes; hence this species is regarded as separate from H. heydorni of wolf-like canids, but probably identical with Isospora triffittae (syn. Isospora triffitti) previously reported from foxes. This species has therefore been named Hammondia triffittae n. comb. Reindeer, moose, sheep, goats, foxes and rabbits may act as intermediate hosts for H. triffittae. Muscle tissues of inoculated intermediate hosts were infectious for foxes from 16 days post-infection. Oocysts of H. triffittae were subspherical, averaging 12·5×10·9 μm in size. The lsu rRNA gene and the alpha tubulin gene seem to be suitable genetic markers for differentiating between H. triffittae and H. heydorni.

The gene coding for α tubulin has been isolated by the polymerase chain reaction and sequenced from 2 isolates of Neospora caninum (Nc-Liverpool and Nc-SweB1)The nucleotide sequence data reported in this paper are available from the GenBank database under the accession numbers AF508031 (N. caninum) and AY169962 (H. heydorni).. The data show that the gene, as in Toxoplasma gondii, is single copy and contains 3 exons and 2 introns and is identical in sequence in the 2 isolates studied. Comparison of the predicted protein sequence shows it to be identical to the α tubulin protein encoded by the T. gondii gene. The majority of the nucleotide substitutions that have occurred during the evolution of the T. gondii and N. caninum genes from their common ancestor have occurred in the third codon position. A partial coding sequence for α tubulin was also obtained from Hammondia heydorni and compared to other α tubulin sequences from Apicomplexa. The results show the sequences of the T. gondii, N. caninum and H. heydorni α tubulin genes to be similar but not identical in sequence, thereby providing new evidence that N. caninum and H. heydorni are genetically distinct species.