Genetic and biological diversity among isolates of Neospora caninum

Neospora caninum is a protozoan parasite that causes bovine abortion. The e pidemiology of N. caninum is poorly understood and little is known about th e genetic diversity of the parasite, or whether individual isolates differ in virulence. Such diversity may, among other factors, underlie the range o f pathologies seen in cattle. In this study we analysed biological and gene tic variation in 6 isolates of N. caninum, originating from canine and bovi ne hosts by measurement of growth rate in vitro, Western blotting and rando m amplification of polymorphic DNA (RAPD). This comparative analysis of int raspecies diversity demonstrated that heterogeneity exists within the speci es. The relative growth rate in vitro, as assessed by (a)[H]uracil uptake, showed significant variation between isolates. However, no significant diff erences were detected between the antigenic profiles of each isolate by Wes tern blotting. RAPD-PCR was performed on DNA from the 6 Neospora isolates; 3 strains of Toxoplasma gondii, Sarcocystis sp. and Cryptosporidium parvum NY, ere also analysed. Twenty-six RAPD primers gave rise to 434 markers of which 222 were conserved between all the Neospora isolates and distinguishe d them from the other Apicomplexa, An additional 54 markets were unique for Neospora but were polymorphic within the species and able to differentiate between the individual isolates. The RAPD data were subjected to pair-wise similarity and cluster analysis and showed that the Neospora isolates clus tered together as a group, with T. gondii as their nearest neighbour. N. ca ninum isolates showed no clustering with respect either to host or geograph ical origin. The genetic similarity between Neospora isolates from cattle a nd dogs suggests that these hosts may be epidemiologically related, althoug h further analysis of bovine and canine field samples are required. The gen etic and biological diversity observed in this study may have important imp lications for our understanding of the pathology and epidemiology of neospo rosis.