Studies on Neospora caninum and neosporosis in New Zealand cattle : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Animal Science, Massey University, Palmerston North, New Zealand

Abstract

The objective of this research was to investigate neosporosis in New Zealand cattle using experimental and molecular tools. The research also aimed to isolate and characterise an indigenous New Zealand isolate of Neospora caninum. A series of discrete projects were conducted to achieve the set objectives. A pilot study was first conducted and a wild-type strain of non-cytopathic bovine viral diarrhoea virus (BVDV) type 1 virus was isolated in vitro from a persistently infected heifer. The isolate was used to challenge heifers and the effect of experimental BVDV infection on heifers naturally infected with N. caninum was investigated. Results showed that heifers that were both BVDV and N. caninum seropositive produced 44.4% (8/ 18) damcalf pairs that were both BVDV and N caninum seropositive. Serologically, 66.7% (12/18) dam-calf pairs were seropositive to N. caninum antibodies, while 80% (8/10) dam-calf pairs were BVDV seropositive. A Polymerase Chain Reaction (PCR) study was also conducted and N. caninum DNA was detected in the blood of naturally infected aborting and pregnant heifers. Real-time quantification of N. caninum DNA in the blood of infected heifers showed a decrease of N. caninum DNA after abortion in the aborting group and an increase through gestation in the pregnant group. A study of antigenicity recognised 7 immunodominant (~18, ~25, ~33, ~35~36, ~45~46, ~47 and 60-62 kDa) and 5 minor antigens of N. caninum by cow sera. Three isolates of N. caninum (NcNZ 1 ,NcNZ 2 and NcNZ 3) were isolated from the brains of an infected cow, her calf and a stillborn calf. These isolates were confirmed as N. caninum by PCR, immunofluorescence antibody test and immunohistochemistry and were pathogenic to BALB/c mice.