Demodicosis caused by Demodex canis and Demodex cornei in dogs

Abstract

Two mongrel dogs aged between 7 and 9 months in a same house were presented to the clinics with a history of chronic dermatitis associated with pruritus. Clinical examination revealed presence of primary and secondary skin lesions on the face, around the ears, chin, neck, fore limbs and lateral abdomen. Examination of skin scrapings revealed Demodex cornei (majority) and D. canis (minority) in both the dogs. By using hair pluck examination D. canis were detected and by tape impression smears examination large number of adult short-tail Demodex mites were found. D. cornei was identified by based on the morphological characters including short opisthosoma with blind and round terminal end. Mean length of total body, opisthosoma of both types of the mites were differed statistically significant (P < 0.01) but gnathosoma and podosoma did not differ significantly (P > 0.05). Dogs were treated with daily oral ivermectin @ 500 μg/kg/day, external application of amitraz along with supportive therapy. After completion of 45 days of therapy dogs were recovered completely without any side effects.

Introduction

Canine demodicosis is one of the well known skin diseases encountered in veterinary practice. It is a dermatologic disease that occurs when mites colonize the hair follicles, sebaceous glands. Dermatological changes include erythema, alopecia, comedones, follicular hyperkeratosis, pustules, crusts and seborrhea. Often, a secondary pyoderma further complicates the disease (Scott et al. 2001). Demodex canis was the main causative agent of canine demodicosis and it is characterized by the presence of large numbers of Demodex mites. The three recognized canine Demodex mites are: Demodex canis, Demodexinjai, and the unnamed short-bodied mite. Demodex canis was the first to be identified and named the two additional Demodex mites may be mutations of Demodex canis, or separate species (Scott et al. 2001). Hillier and Desch (1997) described Demodex injai, a long bodies demodecid, where the male mites were more than twice the length of the males of D.canis (Desch and Hillier 2003). In another report an unusual mite was reported by Scarff (1988). Stubby form of the Demodex was described as being about one half of the length of the female of D.canis (Chesney 1999). Currently, the reports about D. cornei infestation in dogs are very few in India, although the first report was published in 1998 (Scott et al. 2001). This paper reports the occurrence of mixed Demodex infestation of D. cornei and D. canis in dogs and its management.

Materials and methods

Two mongrel dogs aged between 7 and 9 months belongs to a same house was brought to the Veterinary Hospital, Proddatur with a history of skin lesions associated with pruritus from One month. Upon clinical examination, dogs exhibited papules, pustules, erythema, alopecia, hyperpigmentation, erosions, lichenification and cellulitis. Distribution of lesions observed on face, around the eyes and ears, chin region, fore limbs, neck and lateral abdomen (Fig. 1). Skin scrapings, tape impression smears and hair plucks was collected from the affected dogs for laboratory examination. Scrapings were collected with scalpel blade dipped in liquid paraffin and collection of scrapings was continued until there was slight ooze of blood from dermal capillaries. Material was suspended in a few drops of liquid paraffin on a microscopic slide, a coverslip was applied and the preparation was examined under low and high power (10X, 40X) of microscope. The acetate tape impression smears was used to investigate superficial mites. The sticky surface of the tape was pressed on the suspected lesions, and tape was then mounted directly on a glass slide. The glass slides were examined under compound microscopes with 10X and 40X of magnification. Few tape impression smears were stained with new methylene blue for 1 min and examined under 100X (Rosenkrantz 2008).

Fig. 1.

Dog affected with Demodicosis—Periorbital lesions

Results and discussion

Skin scrapings collected from the head region, revealed different stages of Demodex mites (Fig. 2) along with few ovigerous female mites (Fig. 4a). D. canis were found in hair pluck examination technique. The tape impression technique of the dogs revealed more number of short-tail Demodex mites (D. cornei). Cytology of impression smears revealed cocci, cocci engulfed by neutrophils which indicate involvement of secondary bacterial infection. Based on the history, lesions and laboratory findings, the present case was diagnosed as generalized superficial demodicosis of D. cornei and generalized follicular demodicosis of D. canis with secondary bacterial pyoderma. Dogs were treated with oral ivermectin at 500 μg/kg/day for 45 days by regular monitoring for the side effects. Ampicillin at 25 mg/kg twice a day orally, BID for 14 days was given to control secondary bacterial infection. After one week of antibiotic therapy, amitraz (2 ml in 1 litre of water) was given weekly twice as topical application followed by bath with benzyl peroxide (petben) shampoo up to the recovery period. One week after therapy moist lesions and scales was disappeared and dogs had mild pruritus. 2 weeks after treatment, the number of surface Demodex mites detected by the tape preparation technique was gradually decreased and the dogs were free from pruritus, erythema, erosions, and ulcers. One month after treatment, the general skin condition was improved; absence of pruritus was noticed and number of surface Demodex mites was also decreased. Complete disappearance of mites and re-growth of hair was noticed after 45 days of after therapy.

Fig. 2.

Demodex mites in skin scrapings (10X)

Fig. 4.

Ventral view of the ovigerous female of adult D. canis in scrapings (20X)

Mites with short tail were identified as D. cornei based on other morphological characteristics. Mites present in the tape impression smears had elongated body with short stumpy legs on podosoma and shorter opisthosoma. The measurements were carried out on the gnathosoma length, podosoma length, opisthosoma length and total body length. The adult mites were measured in microns by using ocular and stage micrometers under compound microscope. Measurement data of twenty-six adult (males and females) D. cornei mites of this study were reported. Twenty-six mounted adults of D. canis were measured under the microscopes and the following measurement data were also recorded in Table 1. In the present study, the mean total body length (132.21 ± 14.6 μm) of D. cornei (Fig. 3) was much less than that of D. canis (Fig. 4) (214.32 ± 13.81 μm). The mean total body length of the mites obtained from deep skin scrapings i.e. D. canis was almost agreeable with Chesney (1999) (226.1 ± 11.68 μm) and Gortel (2006) (224 μm). The mean body length of D.cornei obtained from the tape impression smears (132.21 ± 14.6 μm) was in accordance with Tamura et al. (2001) who reported unidentified subspecies with a short opisthosoma, an obtuse end and with mean body length of 139 ± 21.6 μm. Similarly Lopez et al. (2011) and Chesney (1999) reported the mean length of D. cornei was 139.3 ± 10.4 μm and 122.6 ± 12.0 μm in their studies respectively. All the measurements of both types of mites were analyzed using Student’s t test. Lengths of total body and opisthosoma of both types of the mites differed statistically significant (P < 0.01) while podosoma and gnathosoma did not differ significantly (P > 0.05). Differentiation of the both the mites (D. cornei and D. canis) mainly based on their size, inhabitant or location of the mite and morphological difference. The mite collection technique can also give a useful diagnostic data, because D. cornei inhabits in stratum corneum of epidermis, the suitable collection technique for D. cornei is superficial skin scraping or using tape preparation techniques, while the habitat of D. canis is hair follicles and sebaceous glands which move deeper into layer of dermis, so it may concluded that the suitable collection techniques for D. canis are deep skin scraping or hair-plucking examination. From mite sizes, D. cornei is seemed obviously shorter than D. canis (Tamura et al. 2001; Patterson 2008; Tater and Patterson 2008). In the present study clinical manifestations of D. cornei infestation in dogs was in the form of a scaly and prurutic skin diseases, which was relevant to the previous report of Mason (1993) and Tater and Patterson (2008).

Table 1.

Micrometry of D. canis and D. cornei adult mites

Parameters	D. canis	Range	D. cornei	Range	P value
Gnathosoma	18.89 ± 0.18a	18–20	19.11 ± 0.14	18–20	0.141
Podosoma	60.98 ± 0.21a	59–62	61.06 ± 0.31	59–64	0.054
Opisthosoma	129.68 ± 3.34**	110–152	61.48 ± 2.4	49–76	0.001
Total body length	214.32 ± 13.81**	158–271	132.21 ± 14.6	96–152	0.001

* Significant (P < 0.05)

** Highly significant (P < 0.01)

^aNon significant (P > 0.05)

Fig. 3.

Ventral view of the adult D. cornei in tape impression smears (40X)

Conclusion

The short tailed Demodex mites collected from the two dermatitis dogs in this study were D. cornei. They had short opisthosoma and blunted posterior end when compared with D. canis. The mean total body length of short form of Demodex spp. was 132.21 microns while the mean total body length of D. canis was 214.32 microns.