Abstract:
Ehrlichia ruminantium, the causative organism of heartwater infections, places severe
economic constraint on the livestock industry wherever Amblyomma tick vectors are present.
Angora goats are particularly susceptible to this disease and the current live blood vaccine
cannot safely be used to protect these animals. An attenuated E. ruminantium
(Welgevonden) experimental vaccine has previously shown promising results in Merino
sheep and Boer goats. The vaccine was administered by intravenous route (i/v). The general
objective of this study was to test the efficacy and safety of the attenuated heartwater vaccine
E. ruminantium (Welgevonden) in Angora goats. The specific objectives were, firstly to
assess the intra-muscular route of administration of the attenuated vaccine as compared to the
standard i/v route and, secondly, to study the haematological changes in Angora goats before,
during and after vaccination under controlled conditions at the Onderstepoort Veterinary
Institute tick-free stables. A total of 55 Angora goats were used in this trial. They were
purchased from an area in South Africa which is known to be Amblyomma-free and
heartwater-free. Furthermore, on arrival, the goats were screened for E. ruminantium
infection by the immunofluorescent antibody (IFA) test to confirm their disease-free status.
The Angora goats were divided into 3 groups: In Group 1, ten were vaccinated by the
standard i/v route, in Group 2, 31 received the vaccine by i/m route and 10 served as
untreated controls for Group 3. Five of the 10 i/v vaccinated group, 20/31 of the i/m
vaccinated and 5 controls were challenged by feeding of known infected adult A hebreaum.
The other remaining animals within the three groups were challenged using a known infected
blood stabilate administered by the standard i/v route (dose 5xLD50). All animals were
challenged 42 days after vaccination.
The vaccine did not produce any inflammatory reactions at the site of injection. However,
3/31 (9.7%) of i/m and 7/10 (70%) of i/v vaccinated goats developed febrile reactions starting
on Day 11 post-immunisation and were treated. All vaccinated goats were fully protected
against either needle i/v or tick challenge, while the control non-vaccinated goats reacted
severely to the challenge materials and required oxytetracycline treatment. Despite
treatment, two of the unvaccinated goats died from the challenge material.
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Haematological values (packed cell volume, differential blood cells count) were obtained on
blood samples taken from the treatment and control groups at different times during the
course of the trial. Wide within group variations as shown by the high standard deviation
values were found. As no significant changes were found between vaccinated and control animals, it is likely that the attenuated vaccine does not cause significant clinical
haematological changes. This study has demonstrated that the attenuated E. ruminantium (Welgevonden) vaccine is
safe in 90.3% and efficacious (100% efficacy) for intramuscular administration in Angora
goats. However, further laboratory and on-farms studies are needed in order to establish the
lowest effective and safety dose, duration of immunity, and the vaccine’s safety in young and
pregnant animals.
