Prevention of transmission of Babesia canis by Dermacentor reticulatus ticks to dogs after topical administration of fluralaner spot-on solution
Hypothesis
Fluralaner rapidly kills ticks within 12 h after tick attachment 1], and the prevention of Babesia canis transmission by oral treatment with fluralaner chewable tablets was already shown
2]. Recently, a new formulation of fluralaner as Bravecto™ Spot-on Solution became available
3]. Thus, the potential of topically administered fluralaner to prevent B. canis transmission was tested.
Methods and study set-up
The same methodology as already described by Taenzler et al.2] was applied to investigate the prevention of B. canis transmission by topical fluralaner treatment and, therefore, methods and study set-up
are only briefly summarized below. Ethical approval was obtained by the ClinVet Animal
Ethics Committee (CAEC) before study start.
Animal details
Sixteen healthy mixed breed dogs (eight males, eight females; 1–8 years, 13.8–26.9 kg)
tested negative for B. canis by polymerase chain reaction (PCR) and immunofluorescence assay test (IFAT), were
randomly allocated to two study groups of eight dogs each. Dogs were individually
housed indoors, and fed a standard commercially available dry dog food once daily;
drinking water was provided ad libitum.
Treatment
On day 0 (i.e. day of treatment), dogs in the treatment group were treated once topically
with fluralaner spot-on solution according to the manufacturer’s label instructions.
There was no evidence of mis-dosing such as spillage or run-off/drip-off in any treated
animal. Dogs in the control group remained untreated.
Tick infestations and assessments
On days 2, 28, 56, 70 and 84, all dogs were infested with 50 (± 4) adult, unfed D. reticulatus ticks (European origin, sex ratio 1:1). Prior to each infestation, the presence of
B. canis was confirmed by PCR using 50 ticks of the respective batch. Tick in situ thumb counts
were performed 48?±?4 h after each infestation. On day 90, all remaining ticks on
each dog were removed and counted.
Animal health
After treatment, the health status of each animal was monitored by physical examinations
on a 7-day interval and the rectal body temperature of each dog was measured thrice
weekly. General health observations, noting the dog as normal or abnormal, were performed
once daily starting 7 days prior to treatment until day 112 after treatment. If a
dog was noted as abnormal or the rectal body temperature was above or equal to 39.4 °C,
an additional physical examination was performed.
Blood analysis
If, one or more parameters during physical examination were abnormal, a blood smear
was made. Blood samples for serum analysis for antibodies to B. canis (IFAT) and for B. canis DNA detection (PCR) were collected on a 14-day interval and on a 7-day interval after
treatment, respectively 2].
Rescue treatment and replacement
Dogs confirmed positive for B. canis by blood smear were rescue treated using imidocarb and diminazene 2] and remained part of all health observations, but were not subjected to subsequent
tick infestations. PCR and IFAT were performed on blood samples and after confirmation
of a babesial infection by both analyses; these dogs were finally excluded from the
study. B. canis positive control dogs were replaced by a B. canis negative replacement dog to ensure a sufficient number of control dogs for tick infestations/counting.
In total, 19 replacement dogs (ten males, nine females) were used; thus, in the control
group a total of 27 dogs were included.
Efficacy evaluation
The statistical analysis was performed using the software package SAS® (SAS Institute
Inc., Cary, NC, USA, release 9.3). The experimental unit was the individual dog.
The percentage of efficacy against ticks was calculated for the treatment group at
each assessment time point using geometric means with Abbott’s formula:
Efficacy (%)?=?100 × (M
C
– M
T
)/M
C,
where M
C
is the mean number of total live attached ticks on untreated control dogs and M
T
the mean number of total live attached ticks on treated dogs. Log-transformed counts
(xi?=?ln(xi?+?1)) of live attached ticks were used to confirm the efficacy calculation.
Significant differences were assessed between the log-transformed counts of live attached
ticks in the treated group at each assessment time point compared to the log-transformed counts
of the untreated control group using a linear mixed model including study group as
a fixed effect and block as a random effect. The two-sided level of significance was
declared when p???0.05.
The percentage preventive effect against B. canis transmission for the treatment group was calculated as follows: Preventive effect
(%)?=?100 × (T
C
– T
T
)/T
C
, where T
C
is the total number of infected dogs in the untreated group and T
T
is the total number of infected dogs in the treated group. A dog was regarded infected
with B. canis, if it was tested positive by both IFAT and PCR. Study groups were compared using
the Fisher’s exact test.