dc.description.abstract | East Coast Fever is a tick-borne disease of economic importance in bovines caused
by Theileria parva, a protozoan parasite transmitted transstadially by a three-host
tick, Rhipicephalus appendiculatus. The control of ECF requires integrated pest management,
including vaccine development. Theileria parva Marikebuni vaccine is a live parasite vaccine
used to immunize cattle against ECF. At present, there is no information on the effect of this
vaccine on the feeding and reproductive success of R. appendiculatus. This study investigated
the interaction between the T. parva vector and its immunized host,cattle. Three groups of ECF
naïve calves aged between 3-12 months were selected for the study, each having six
calves. Calves in the first group, the “immunized group”, received 1 ml of Marikebuni vaccine
and a long-acting oxytetracycline blocking agent at 30ml/kg body weight. The 2nd group,
“Control Group 1” received uninfected tick material and the blocking agent while the 3rd group,
“Control Group 2” received the uninfected tick material only. Ticks were counted and weighed
before and after application to calves. Incubation of ticks was done at 27-28 ⁰C optimum
temperature and 80% -85% humidity. The number of ticks that fed successfully, the mean
blood meal weight, and the number of successfully molted nymphs were analyzed to indicate
the feeding success of R. appendiculatus. The mean egg mass weight, number of egg batches
and clutch sizes of eggs indicated oviposition success. The number of live larvae hatched
determined the egg viability. Data were compared using linear regression, an ANOVA test, and
a binary logistic regression model using R statistical software Version 4.1.3 (2022-03-10), at a
p<0.05 significance level. The outcomes of this study showed that the number of fed nymph
ticks (OR = 0.996; p-value = 0.29); nymph blood meal weight (OR = 0.712; p-value = 0.34);
number of successfully molted nymphs (OR = 1.004, p value = 0.36); number of successfully
fed adult female ticks (OR = 1.05; p-value = 0.93); and the adult female tick blood meal weight
(OR = 0.32, p value = 0.48; F = 3.26, p-value = 0.11)did not differ significantly between R.
appendiculatus that fed on immunized calves and those that fed on controls. The egg mass
weight differed significantly between the ticks that fed on immunized calves and controls (F =
7.993; p-value = 0.023), and a significant pairwise average difference of 1.34 was detected
between the ticks that fed on immunized and control group 2 calves and between those that fed
on control groups 1and 2 (adjusted p-value =0.03). Other parameters determining oviposition
success did not differ significantly between the ticks fed on the immunized group and the
controls: clutch sizes of eggs (OR = 1.0, P-value = 0.40); number of egg batches (OR = 0.08,
p-value = 0.35). The number of live larvae that hatched successfully did not differ significantly
between the immunized and control groups (OR = 0.99; p-value = 0.33). In conclusion, the
blood feeding success of Rhipicephalus appendiculatus was not significantly altered by the
vaccine, despite the observed differences (p >0.05). The oviposition success of the tick vector
was altered by the vaccine, reducing the egg mass weight in ticks that fed on the immunized
group significantly (p<0.05). The viability of eggs from R. appendiculatus ticks was not
significantly impacted by the vaccine, despite the observed differences (p > 0.05). The findings
of this work shed light on the efficacy of the Marikebuni vaccine against R. appendiculatus.
Significantly reduced egg mass weight on ticks fed on cattle immunized with Marikebuni
vaccine shows that the vaccine indirectly leads to some degree of vector control. The
production and distribution of this vaccine in ECF endemic regions of sub-Saharan Africa
should therefore be increased. | en_US |