DIAGNOSTIC AND THERAPEUTIC EVALUATIONS OF DEMODICOSIS IN DOGS
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Date
2019-08-05
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COLLEGE OF VETERINARY AND ANIMAL SCIENCES, POOKODE WAYANAD
Abstract
The present study on “Diagnostic and therapeutic evaluation of demodicosis in
dogs” was carried out in the Department of Veterinary Clinical Medicine, Ethics and
Jurisprudence, College of Veterinary and Animal Sciences, Pookode and other
veterinary hospitals in Wayanad district, Kerala during the period from September
2018 to June 2019 with clinical signs like hair loss, erythema, skin lesions specific for
demodicosis were screened and included in the study group. Apparently healthy dogs
were selected from those animals presented to the TVCC for wellness check-up or
vaccination. These animals were subjected to detailed signalment, anamnesis and
clinical examination with special emphasis on integumentary system. Deep skin
scrapings, tape impression smears and hair plucks were collected and subjected to
microscopical examination for diagnosing Demodex spp. mites based on
morphometry. The haematological parameters evaluated include Haemoglobin,
VPRC, Total Erythrocyte count, Total Leucocyte count, Platelet count, Mean
corpuscular volume, Mean corpuscular haemoglobin, Mean corpuscular haemoglobin
concentration. Serum biochemical parameters like ALT, ALP, total bilirubin, albumin
and globulin were also evaluated. Hair/skin samples were collected and stored under -
20°C in phosphate buffered saline for DNA extraction. Polymerase chain reaction
(PCR) was performed using primers specific for 16S rRNA of Demodex spp.
Amplicons were sequenced and analysed. Dogs with demodicosis were divided in to
three groups for comparing standard miticidal therapeutic protocols involving oral
ivermectin, ivermectin injection and doramectin injection respectively. Therapeutic
responses in each group were recorded on weekly basis.
The prevalence of demodicosis in dogs under study was found to be 21.6 per
cent. Among Demodex spp. positive cases, prevalence of localized form was 81.48
per cent, and that of generalized form was found to be 18.51 per cent. The highest
occurrence of demodicosis was recorded in dogs aged less than 1.5 years i.e 71.78 per
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cent followed by 18.51 per cent in age group of 1.5-4 years and lowest occurrence in
age group of > 4 years with 3.7 per cent. The prevalence of demodicosis in different
breeds of dogs under study was found to be highest in German shepherd with 22.2 per
cent, followed by Labrador retriever with 14.8 per cent. No significant difference was
found in prevalence of demodicosis between male and female dogs. The predominant
primary skin lesions noticed in dogs with demodicosis included papules in 63 per
cent, and patch in 14.8 per cent. The major secondary lesions observed were pustules,
hyperpigmentation and scales in each 63 per cent, hyperkeratosis, lichenification and
crust in 14.8 percent, erosion in 11.1 per cent and ulcer, excoriation, comedones and
epidermal collarettes in one each 3.7 per cent. Upon hematological examination
significant elevation of TLC (p ≤ 0.05) was observed in diseased animals whereas
TEC, haemoglobin and VPRC values showed a significant reduction (p ≤ 0.01) in
comparison to control group. Serum biochemical evaluation of diseased animals
revealed significant decrease in total serum protein and albumin (p ≤ 0.05) levels
when compared to healthy animals. The concentration of ALP was significantly
elevated (p ≤ 0.01) in affected animals. PCR, deep skin scraping method, and
trichography showed 100 per cent, 92.59 per cent, and 74.07 per cent sensitivity in
diagnosing demodicosis respectively. On morphometrical analysis, there was
significant reduction in mean total body length, opisthosoma, gnathosoma podosoma
and ratio of length opisthosoma length to body length, significant increase in ratio of
prosoma to opisthosoma, ratio of total body length and opisthosoma length and in
Demodex cornei than Demodex canis. Genus specific PCR of Demodex DNA yielded
a specific product of 340 bp with primer pair P1F and P2R in twenty seven positive
samples. The ten PCR products were sent for sequencing. Sequences were analyzed
in BLAST to confirm specificity of 16S gene of Demodex
(http://www.ncbi.nlm.nih.gov/BLAST). Ten sequences of Demodex spp. DNA were
submitted to the genbank and got accession numbers (MN161400- 161409). On
phylogenetic analysis nine Demodex canis and one Demodex cornei isolates were
found to be identical with china, USA and spain isolates. In therapeutic evaluation
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mite reduction in every week in three groups were evaluated. Chisqaure value showed
non-significant efficacy in three groups, but doramectin was found to be faster in
reducing mite count at second week. The study was concluded with findings which
include, morphometry can be used as an effective tool in differentiating different
species of mites, Demodex cornei is identical to Demodex canis in phylogeny,
Demodex cornei is a morphological variant of Demodex canis and doramectin can be
used for faster recovery in demodicosis in dogs.