Prevalence and Risk Factors of Chlamydia Infection in Domestic Sika Deer(Cervus nippon)in Northeastern China

U *

(1.General Station of Forest and Grassland Pest Management，National Forestry and Grassland Administration，Shenyang，110034；2.Northeast Forestry University，Harbin，150040；3.China Wildlife Conservation Association，Beijing，100714，China)

Abstract：Chlamydia is a zoonotic pathogen with a wide range of hosts which can cause abortion and other diseases in animals including sika deer(Cervus nippon).Epidemiological data regarding the distribution of Chlamydia infection in deer is limited in China.In this study，847 serum samples were randomly collected from 4 different cities(Chifeng，Harbin，Changchun and Jilin City).Eighty of the 847(9.5%)serum samples were seropositive for Chlamydia antibodies tested by the indirect hemagglutination assay(IHA).The prevalence of Chlamydia infection varied from 6.1% to 15.9% in different regions.Chlamydia infection in male and female deer was 9.4% and 9.5%，respectively.Chlamydia seroprevalences in those sika deer sampled in autumn and winter were 8.4% and 12.3%，respectively.According to forward stepwise logistic regression，season and gender were omitted from the final model because the logistic regression analysis detected no significant difference attributable to these factors(P> 0.05).Region，in contrast，was considered a major risk factor associated with Chlamydia infection in sika deer.Our results revealed the seroprevalence of Chlamydia infection in domestic sika deer in northeastern China.This could provide useful information for further analyses of the distribution and epidemic focus of Chlamydia in China.Our goal in this research was to provide useful basic data on which future research could be based for the eventual prevention of Chlamydia infection in sika deer.

Key words： Chlamydia；Sika deer；Prevalence；Indirect hemagglutination assay；Risk factor

1 Introduction

Chlamydia，the obligate intracellular gram-negative bacteria，is able to cause a series of severe diseases in humans and animals，including sika deer[1].Ovine enzootic abortion(OEA)is caused byChlamydiaabortus，associated with reproductive defects，abortion as well as enteric infections，even causing death[2].Chlamydiais considered as a zoonotic pathogen，because pregnant women can be infected through contacting with infected animals[3].

Several studies have reported the different seroprevalences ofChlamydiainfection in different species around the world such as India，Sweden，Poland，UK，Slovak Republic and USA[4-9].However，limited data aboutChlamydiainfection was available in China[1，10-11]，althoughChlamydiainfection were found in other animals such as in dogs[12]，cats[12]，pigs[13-14]，domestic geese(Anserdomestica)[15]，poultries[16]and birds[2].

Sika deer(Cervusnippon) is one of the most ancient members of the genusCervusand the number of domesticated sika deer in China is approximately 550 000.However，it is yet to know whether sika deer are infected withChlamydia.In this study，we investigated the seroprevalence ofChlamydiainfection in sika deer，northeastern China.The results provided “base-line” information for estimating the effectiveness of future control strategies against theChlamydiainfection in sika deer in China.

2 Materials and methods

2.1 Serum samples

A total of 847 serum samples were randomly collected from 4 different cities(Chifeng，Harbin，Changchun and Jilin)between 2012 and 2013.The blood samples were taken to the laboratory，and centrifuged at 3 000 g for 10 min and then serum was obtained，and stored at -20 ℃ until detected.

2.2 Detection reagents

Antibodies againstChlamydiawere examined using a commercial indirect hemagglutination assay(IHA)kit(Lanzhou Veterinary Research Institute，Chinese Academy of Agricultural Sciences，Lanzhou，China).The detection procedures were carried out as previously described[1，11].Samples were judged as positive forChlamydiainfection when antibody titers reacted 1∶16 or higher.Samples with antibody titers between 1∶4 and 1∶16 were considered dubious and need to be re-tested，positive，negative and blank controls were included in each test.

2.3 Statistical analysis

The variation inChlamydiaprevalence(y)of sika deer with different geographical location(x1)，gender(x2)，and season group(x3)was analyzed byχ2test using SAS version 9.1(SAS Institute Inc.，USA).Each of these variables was included in the binary Logit model as an independent variable base on the multivariable regression analysis.The best model was judged by Fisher’s scoring algorithm.All tests were two-sided，and values ofP<0.05 were considered statistically significant.Odds ratios(ORs)and their 95% confidence intervals(95% CIs)were estimated to explore the strength of the association betweenChlamydia-seropositivity and the conditions investigated.

3 Results

A total of 80 out of the 847(9.45%，95%[CI]7.48-11.42)deer serum samples were positive forChlamydiaantibody at the cut of 1∶16 examined by IHA test in sika deer in Northeast China(Tab.1).The seropositivity ofChlamydiawas 9.44%(95% CI 6.98-11.91)in male deer，which was not statistically different compared to the female deer(9.45%，95% CI 6.18-12.72，P>0.05)(Tab.1).The seroprevalence ofChlamydiawas 8.39% in autumn and 12.34% in winter，and the different was not statistically significant(P>0.05)(Tab.1).The prevalence ofChlamydiain four regions were varied from 6.35% to 15.87%，and the difference was statistically significant(P<0.05)(Tab.2).

Tab.1 Seroprevalence of Chlamydia infection in sika deer by indirect hemagglutination assay(IHA)

Tab.2 Odds ratios for geographical origin of sika deer are taken as risk factors for Chlamydia seroprevalence in sika deer

4 Discussion

The overall seroprevalence ofChlamydiain this study was lower than that reported in the fallow deer(Damadama)(30%)and red deer(24%)in Spain examined by ELISA[17]and higher than that reported in the fallow deer in Italy by complement fixation test[18]and in roe deer(Capreoluscapreolus)(1.4%)in Switzerland by ELISA[5].The sensitivity and specificity values of the testing kit have been validated by the ministry of agriculture of the People’s Republic of China(NY/T 562-2002)，and the sensitivity and specificity of the experiment are 100% and 95%，respectively.The different prevalence ofChlamy-diaexposure in deer was probably due to the differences in assay methods that can influence the positive values obtained.In addition，animal-welfare，sanitation，husbandry practices and ecological and geographical factors could be other reasons for the variation of prevalence.As shown in Tab.1，the antibody levels were varied from 1∶16 to 1∶256，including antibody titers of 1∶16 in 71，1∶64 in 5，1∶256 in 4.However，only 9 of the 80 positive deers each had an antibody titer higher than 1：16，which may be due to fewer contact withChlamydiain the surveyed regions.As a result，we need to pay more attention to this finding and avoid the situation getting worse.

In Northeast China，autumn is warmer and more humid compare to winter，thus，it is more suitable for the pathogen transmission.However，in the present study，the seroprevalence ofChlamydiainfection in sika deer collected in autumn was 8.39%(95% CI 6.21-10.57)which was a little lower than that in winter(12.34%，95% CI 8.06-16.61)，and the difference was not significant statistically(P>0.05)(Tab.1).In addition，the reason why we collected seasonal samples from sika deer is that mating season is mainly distributed in above seasons，which has important significant to evaluate the risk ofChlamydiainfection in sika deer.Moreover，the gender of sika deer is also not the risk factors associated withChlamydiaseroprevalence via logistic regression analysis(P>0.05).The results indicated that the climate and gender may not be the major risks forChlamydiaexpanding in sika deer in northeastern China.

Region was analyzed as a major risk factor in the logistic regression model，showing thatChlamydiaprevalence in Changchun(7.91%，95% CI 4.94-10.89)is similar with that in Chifeng(7.50%，95% CI 3.42-11.58)but higher than that in Jilin(6.13%，95% CI 2.45-9.82)，and lower than that in Harbin(15.87%，95% CI 10.90-20.83).Chlamydiainfection in sika deer in Harbin had a 2.99 times(OR=2.99，95 % CI 1.43-6.25，P=0.004)higher risk of being seropositive compared to that in sika deer in Jilin City described by the equationy=0.033x1+0.007(Tab.2).The difference may be due to the different animal welfares，living environments，feeding conditions and manage modes in different regions.Therefore，the difference among surveyed regions is the primary consideration of preventing and controlling theChlamydiatransmissions.

In China，the high quality meat and fur of the sika deer are popular in local area and other parts of China，which are transported to many parts of the country from deer farms in the surveyed region.Besides the meat and fur，most parts of the deer body can be used as traditional Chinese medicine[19-20].Sika deer could play an important role in the prevalence ofChlamydiaand more importantly，people acquring theChlamydiainfection is probably from the direct contact with the occupationally exposed persons，such as breeders，butchers，tanners and veterinarians.Results of the present study revealed a highChlamydiaseroprevalence in sika deer，which can cause significant economic losses to the local sika deer husbandry and breeding，and also pose a potential threat to the public health in these areas.Furthermore，all the samples were collected from adult-deer in autumn and winter during the slaughter seasons，therefore，more studies are needed to investigate the regularty of epidemic in season.