The epidemiology of Neospora caninum

Latham, Sopia Maria (2003) The epidemiology of Neospora caninum. PhD thesis, University of Glasgow.

Abstract

A seroepidemiological study was undertaken in a pedigree dairy herd that had a
history of abortions due to neosporosis. The infection in this closed herd was thought
to have arisen from a point-source infection, after which sporadic abortions have
occurred. All cattle were bled twice, once in the winter and again the following
summer and antibodies to N. caninum measured using an ELISA. The overall
seroprevalence of Neospora was found to be 18 %. Three data sets; age-prevalence
data, dam-daughter pair analysis and family tree data showed vertical transmission to
be an important route of transmission of neosporosis in this herd. Analysis of anti-
Neospora antibody titres with respect to the stage in the breeding cycle of cows
appeared to show no association on a herd level. Data was collected on the number of
Artificial Insemination (AI) services per successful pregnancy which showed a
significantly greater number of Al services in Neospora-seropositive cattle compared
with Neospora-seronegative cattle. This is the first study to assess the effect of
neosporosis on cattle fertility in a quantitative manner and suggests that a wider study
is justified. N. caninum shares many similarities with T gondii and has widely been
assumed also to have a world-wide distribution. Two regions of Africa, Ghana in
West Africa and Tanzania in East Africa, were studied in a cross-sectional survey of
neosporosis in cattle indigenous to these areas. A prevalence of 8.1 % and 2% was
found in two different areas in cattle native to Tanzania. Despite sampling a
significant number of cattle in all three ecological zones of Ghana and of several
different breeds, no Neospora-seropositive cattle were found. Possible reasons for the
apparent absence of N. caninum in West Africa are discussed. To determine the
overall genetic diversity in laboratory isolates of N. caninum, RAPD and AFLP
methods were used. Genetic diversity was found to be low amongst Neospora
laboratory isolates, relative to T. gondii, but demonstrated that genetic heterogeneity
does exist within the species. Both RAPD and AFLP data were subjected to pair-wise
similarity and cluster analysis and showed that there was no clustering with respect to
host or geographical origin. The genetic similarity between cattle and dog isolates
suggests that these hosts are epidemiologically related. In order to exploit the genetic
heterogeneity in N. caninum to analyse a wider range of clinical field samples, several
methods were attempted to devise PCR-based sequence-specific typing approaches
that could be used on infected bovine tissue. Microsatellite markers were identified in N. caninum DNA sequences, however none of the microsatellite regions gave rise to
detectable size differences, although they remain to be tested on a wider range of field
samples. Laboratory isolates of N. caninum were also analysed for polymorphisms
with two conserved minisatellite probes, 33.6 and 33.15, but although hybridisation
occurred to digested parasite DNA, identical fingerprints were obtained for each
isolate. In a final attempt to identify sequence-specific polymorphic markers, intron
regions from two genes, actin and tubulin, were amplified and sequenced in both
laboratory and field isolates. This approach revealed a number of single nucleotide
polymorphisms (SNPs) that were able to differentiate between some isolates of N.
caninum and might serve as useful molecular markers. SNPs were found more
frequently in the clinical field samples, suggesting that the diversity of N. caninum is
greater than that represented by current laboratory isolates. Further genotyping of
field samples will enable the genetic population structure of N. caninum to be
determined to facilitate molecular epidemiological studies.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Subjects: Q Science > QR Microbiology; S Agriculture > SF Animal culture
• Colleges/Schools: College of Medical Veterinary and Life Sciences > School of Infection & Immunity
• Supervisor's Name: Supervisor, not known
• Date of Award: 2003
• Depositing User: Mrs Marie Cairney
• Unique ID: glathesis:2003-4239
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 02 May 2013 13:31
• Last Modified: 02 May 2013 13:35
• URI: https://theses.gla.ac.uk/id/eprint/4239