Prevalence of Demodex infection in pet dogs in Southern China

1 College of Veterinary Medicine, South China Agricultural University, Guangzhou, Guangdong Province 510642, PR China. 2 State Key Laboratory of Veterinary Etiological Biology, Key Laboratory of Veterinary Parasitology of Gansu Province, Lanzhou Veterinary Research Institute, CAAS, Lanzhou, Gansu Province 730046, PR China. 3 College of Animal Science and Technology, Yunnan Agricultural University, Kunming, Yunnan Province 650201, PR China. 4 College of Veterinary Medicine, Northwest A and F University, Yangling, Shaanxi Province 712100, PR China.

Nowadays, dogs are the most preferred pet animal in the world.However, they harbour a number of helminths and mites, which can result in significant health problems as well as financial losses globally (Morsy et al., 1995;Eguía-Aguilar et al., 2005;Sager et al., 2006;Rani et al., 2011).Canine demodicosis is mainly caused by Demodex canis (Jekl et al., 2006), and occasionally by short-or long-bodied unnamed Demodex (Alvarez et al., 2007;Ordeix et al., 2009).Demodex infection in dogs has been reported in different parts of the world among which are in Europe, Asia, America, Africa, and Latin America.In China, canine demodicosis cases have been reported in Kunming city (Yunan province) (Li et al., 1995), Zhengzhou city (Henan province) (Dong et al., 2009), Jinzhou city (Liaoning province) (Li and Zhao, 2008) and several dog farms (Ye et al., 2003).However, prior to the present study, there has been no published article on Demodex infection in pet dogs in southern China.
The objectives of the present investigation was to determine the prevalence of Demodex infection in pet dogs in Guangzhou City, Guangdong province, using microscopic examination of deep skin scraping, plucked hairs and skin biopsy, and to analyze the associations between prevalence and epidemiological factors (age, season, gender of pet dogs).

Study site
The study was conducted in Guangzhou city, southern China, which is located between latitudes of 22°26′-23°56′ N and longitudes of 112°57′-114°05′ E. Guangzhou is an urban centre and the capital of Guangdong province.This city covers an area of approximately 7434 m 2 , with a population of approximately 10.33 million people.

Collection and examination of dogs
From January to December 2009, a total of 3977 pet dogs admitted to 5 animal hospitals in Guangzhou City were used in the present investigation and they were examined in the animal hospitals for the presence of Demodex.The sex and age (estimated by dental examination and inquiries from owners) were recorded for each dog.The presence of Demodex in dogs examined was determined using the methods described by Chee et al. (2008).This involves microscopic examination of deep skin scrapings, plucked hairs and skin biopsy.Briefly, the presence of Demodex was detected by microscopic examination of deep skin scraping, plucked hairs and skin biopsy.Samples were collected from the head, pinna, ear canal, thoracic-abdominal areas, elbow or paws of each animal.Areas of the skin with dermatologic lesions were moistened with mineral oil and scraped with a scalpel blade until capillary bleeding was visible.The scrapings or hair follicles were placed on glass slides with a drop of 10% KOH solution and were examined microscopically for the presence of mites.The mites observed were identified as Demodex sp.based on morphological features and site of predilection (Wall and Shearer, 1997;Taylor et al., 2007).The presence of one mite at any developmental stage in dogs examined was considered to be a positive result.The number of mites collected from each infected dogs were estimated for the intensity of Demodex infection.This study was approved by the Animal Ethics Committee of South China Agricultural University.

Statistical analysis
Differences in the prevalence of Demodex infection in pet dogs between different months, sexes and age groups were analyzed using a Chi square test within the SPSS for Windows (Release 18.0 standard version, SPSS Inc., Chicago, Illinois) (Wu et al., 2011;Zhao et al., 2011).The differences were considered statistically significant when P < 0.05.

RESULTS
Of 3977 pet dogs examined, 977 (24.57%) dogs were observed to be positive for dermatosis, while Demodex infection was recorded in 130 (13.31%) of the dermopathic dogs (Table 1).The monthly prevalence of Demodex infection in dogs is shown in Table 1 with the highest prevalence of 4.15% recorded in March 2009 and the lowest prevalence of 1.39% in December 2009, however there was no significant difference in the prevalence of infection in different months (P> 0.05).The prevalence of Demodex in male dogs (3.67%) was higher than that in female dogs (2.74%), but the difference in prevalence was not statistically significant difference (P >0.05) (Table 2).Dogs of 1 to 5 years old were more commonly infected than other dogs, and the prevalence in pet dogs less than 1 yr old was higher than that in pet dogs more than 5 years old (Table 3), but the difference in prevalence among different age groups was not statistically significant (P >0.05).

DISCUSSION
The present study provides the first systematic assessment of Demodex infection in pet dogs in Guangzhou city, subtropical southern China.The results of the study revealed that Demodex infection accounts for 13.31% of canine dermatosis cases, which was similar to the findings of some previous studies (Nayak et al., 1997;Choi et al., 2000;Chee et al., 2008).
In the present study, the prevalence of Demodex infection was more frequent in male dogs than female dogs.This is consistent with the result of a previous study (Dong et al., 2009), but in contrasts to the findings of Nayak et al. (1997) and Rodriguez-Vivas et al. (2003), who reported that the females were more susceptible than males.These differences could not be easily explained, but may be attributed to epidemiological factors, such as weather, seasonal variations, geographical location, innate resistance, and particularly the age of the animals examined (Nayak et al., 1997;Chee et al., 2008).
Previous studies have shown that dogs less than 1 year old are more susceptible to ectoparasite infestations (Kwochka, 1987;Nayak et al., 1997;Chee et al., 2008), owing to their constant exposure to carrier mothers (Scott, 1979).However, in this study dogs aged 1 to 5 years were more commonly infected than dogs of other age groups.The possible explanation could be that the survey of canine demodicosis in our study included only dermatosis cases, whereas healthy dogs were also included in previous studies.

Conclusion
The present investigation revealed the prevalence of Demodex infection in pet dogs in Guangzhou City, subtropical southern China, which accounts for 13.31% of canine dermatosis cases.In view of the fact that canine demodicosis is a zoonotic disease based on the reports from previous studies, there is a need to educate dog owners and the general public regarding the public health importance of this disease.In addition, a control strategy should be put in place to reduce the prevalence of Demodex infection in the area of study.

Table 1 .
Prevalence of canine demodicosis in pet dogs in different months in 2009.

Table 2 .
Prevalence of Demodex infection in pet dogs by sex.

Table 3 .
Prevalence of Demodex infection in pet dogs by age.