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Ctenocephalides felis (cat flea) infestation in neonatal dairy calves managed with deltamethrin pour-on in Australia.
Tsoi, F.M.B.; Šlapeta, J.; Reynolds...
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Objectives: Fleas are worldwide distributed hematophagous ectoparasites (Lawrence et al., 2019). The cat flea (ctenocephalides felis) is considered the most pervasive flea with veterinary significance principally centred around owned dogs and cats (Rust, 2017; Šlapeta et al., 2011). From the veterinary perspective, livestock are rarely recognised as cat flea hosts, or suffer from flea infestations (Araujo et al., 1998; Dryden et al., 1993; Kaal et al., 2006). Here we report on an outbreak of a flea infestation in neonatal dairy calves in eastern Australia.
Materials and Methods: The described events took place in April to June 2018 and included a group of calves (0–12 weeks) on a privately owned dairy farm in eastern New South Wales, Australia, under the care of the University Veterinary Teaching Hospital, Camden, Livestock Unit. The farm operates an all year round calving herd of 600 Holstein-Friesian cows and 400 youngstock.
All calves (n = 25) were individually restrained and their ear tag recorded for numerical identification. The body condition score (BCS) was assessed using the Penn State University method on a scale of 2–5, with 0.25 increments. A capillary refill time (CRT) was evaluated for each calf. Fleas were collected from the sternum and ventral inguinal area of the calves using a metal flea comb (JW Gripsoft Flea Comb, Australia). Each calf was combed for 90 seconds in each area, 3 minutes per calf. The total flea count for both sites was reported. A commercially available deltamethrin pour-on formula (Arrest Easy-Dose, Virbac Animal Health, Australia) was used according to the registered label (1.9mg/kg). A Flea count was performed immediately before each treatment, and two weeks after the last treatment and the geometric mean calculated for the BCS and flea burden present. The flea reduction post treatment was calculated as a percentage difference between the pre-treatment and post-treatment geometric mean count. Statitical analysis was undertaken using the Mann-Whitney test and exact P values calculated using GraphPad Prism 7.02 (GraphPad Software, CA) with significance level considered at P-value<0.05.
Results: In early April 2018 examination of 15 affected calves (age 0–4 weeks) revealed a geometric mean bur- den of 41.51 (15–75) fleas (treatment group TA at timepoint 1 {TA1}). The affected calves showed dull and quiet demeanour, with the geometric mean BCS of 2.67 (2–4). At eight weeks (TA4), all calves showed bright, alert and responsive demeanour. The affected treated calves mean BCS was 4.04 (3.75–4.5) and mean count at TA4 was 2.29 (0–2) fleas on affected treated calves (n = 10), representing a 94.8 % reduc- tion from TA1 count. In mid-April 2018, an examination of 10 calves (age<4 weeks) revealed a geometric mean burden of 9.32 (2–33) fleas (treatment group TB at timepoint 1 [TB1]). Demeanour of all calves was bright, alert and responsive. The geometric mean BCS was 3.79 (3–4.25). At four weeks (TB3), all 10 calves showed bright, alert and responsive demeanour. The calves mean BCS was 3.67 (3.25–4). The mean count at TB3 on the treated calves (n = 10) was 0.68 (0–4) fleas representing a 92.7 % reduction compared to TB1 counts.The initial flea burden between TA1 and TB1 (geometric mean) was reduced by 77.5 % in the youngest calf category with no clinical disease apparent and improved BCS from 2.67 to 3.79 in calves at TB1, 4 weeks post first application of pour-on deltamethrin. Both the flea count and BCS scores between TA1 and TB1 were significant (Mann-Whitney test, P-value<0.05).
Conclusion: Deltamethrin is a synthetic insecticide structurally based on natural pyrethrins (Mestres and Mestres, 1992) and causes rapid knockdown effect through paralysis of the insect nervous system. In cattle in Australia, deltame- thrin is used for the treatment of lice and flies (Mestres and Mestres, 1992). We took advantage of the existing registered pour-on formulation for cattle, therefore assuring safety, and the knowledge that that the cat flea (Ctenocephalides felis), is susceptible to its active ingredient based on previous studies in dogs. The application of deltamethrin pour-on achieved the objective of improving the health and welfare of the calves, through a reduction in the number of fleas.
Keywords: Fleas, Neonatal, Calves, Deltamethrin.
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Affiliation of the authors at the time of publication
Sydney School of Veterinary Science, Sydney, Australia
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