NORTH-SOUTH CENTRE - ETH - North-South Centre North-South ...

Exploring the effects of anti-tick vaccines
on the transmission of Theileria parva
Tick-borne diseases (TBD) affect approximately 80% of
the world’s cattle population. Anti-tick vaccines (ATV) serve
as a method for TBD control in cattle livestock systems
by decreasing the number of ticks in successive generations
thereby reducing the likelihood of infection with TBD.
This project aims at evaluating the merits of using ATV as
a control method for Rhipicephalus appendiculatus-transmitted
Theileria parva, the causative agent of East Coast
Fever in cattle.
The potential of recombinant Ra86, the R. appendiculatus
homologue of the commercially available ATV used to
control Boophilus microplus in cattle, was investigated as
a T. parva transmission-blocking agent. Parameters investigated
were the effect of vaccination on the biology of
nymph and adult ticks, as well as the ability of nymphs to
acquire T. parva parasites after feeding on infected cattle.
Eight friesian cattle were vaccinated with Ra86 while additional
eight were used as controls. After vaccination, we
experimentally infected all cattle with T. parva and applied
ticks for feeding.
Ra86 vaccination had no significant effect on the mortality
rate of ticks or the duration of tick feeding. Engorgement
weights in nymphs did not differ significantly. However, the
adult females showed a slightly lower engorgement weight
in the vaccinated group. For both groups, the egg laying capacity
of adult females was seen to decrease with an increase
in feeding duration, but the overall difference in egg
weight was not significant. In contrast, we observed a significant
difference between the hatching potential of eggs for
the last adult detach day. 48.5% of the vaccine groups eggs
failed to hatch compared to 18.7% in the control group. The
most significant effect of Ra86 vaccination was seen in the
moulting of T. parva infected nymphs to adults. A significantly
higher percentage of nymphs (14%) fed on Ra86
vaccinated animals failed to moult compared to 3.5% of
nymphs fed on control animals. This parameter is an important
factor in disease control as ticks infected in the nymph
instar are responsible for T. parva transmission during
subsequent adult feeding.
Experiments are ongoing in order to assess the T. parva
infection rates in tick salivary glands, thus determining
the effect of vaccination with Ra86 on the T. parva development
within the vector. In conclusion, we provide first
time evidence that recombinant Ra86 used to immunise
cattle resulted in a statistically significant reductive effect
on nymph moulting, a parameter that has clear implications
for T. parva transmission in the field.
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Research fellow
Cassandra Leah Olds, ILRI, Kenya
Supervisors
Claudia Daubenberger, STI, Switzerland;
Richard Bishop, ILRI, Kenya
Capacity development
Research fellowships
Collaborators
David Odongo, ILRI, Kenya;
Barend Mans, Onderstepoort Veterinary Institute,
South Africa
Duration
May 2008 – April 2011
Storage of ticks in temperature and humidity controlled
incubators at the ILRI tick unit facility, Kenya