Research Article: Prevalence of thermophilic Campylobacter species in Swedish dogs and characterization of C. jejuni isolates

Date Published: April 1, 2015

Publisher: BioMed Central

Author(s): Mia Holmberg, Thomas Rosendal, Eva O Engvall, Anna Ohlson, Ann Lindberg.

http://doi.org/10.1186/s13028-015-0108-0

Abstract

The aims of this study were to investigate the prevalence of Campylobacter species in Swedish dogs, to identify the species of the Campylobacter isolates and to genotype the C. jejuni isolates. Young and healthy dogs were targeted and the sampling was performed at 11 veterinary clinics throughout Sweden from October 2011 to October 2012. Faecal swab samples were collected and sent to the laboratory at the National Veterinary Institute (SVA) for isolation of Campylobacter, speciation and genotyping.

Campylobacter spp. were isolated from 67 of the 180 sampled dogs which yields an overall prevalence of 37%. The most prevalent species of Campylobacter among the participating dogs was C. upsaliensis with 52 of the 67 identified isolates. A lower prevalence was observed for C. jejuni with seven identified isolates and one isolate was identified as C. helveticus. Multi-locus sequence typing (MLST) was carried out on the seven C. jejuni isolates and all sequence types that were found are also commonly found in humans. The dogs were divided into three age groups; 1) under 12 months, 2) 12 to 23 months and 3) 24 months and older. The highest prevalence was found in the two younger age groups. Dogs shedding C. jejuni were between 3–12 months of age while dogs shedding C. upsaliensis were found in all ages.

The present investigation finds that Campylobacter spp. known to cause campylobacteriosis in humans are present in Swedish dogs. The results suggest an age predisposition where dogs under 2 years of age are more likely to shed Campylobacter spp. than older dogs. The most commonly isolated species was C. upsaliensis followed by C. jejuni, which was only detected in dogs up to 12 months of age. All C. jejuni isolates identified in the present study were of the same MLST types that have previously been described both in humans and in animals. The awareness of the Campylobacter risk of healthy young dogs may be an important way to reduce the transmission from dogs to infants, young children and immunocompromised adults.

Partial Text

Campylobacteriosis is the most commonly reported zoonotic disease and the most common cause of bacterial enteritis in humans in many countries throughout the world [1]. In 2013, there were 8114 notified human cases of campylobacteriosis in Sweden. Of these, 41% were considered to be domestically acquired [2]. Humans can be infected with Campylobacter by several routes and the bacteria are commonly found in a wide range of animals including cats and dogs. Especially in young dogs (<1 year), Campylobacter is often found in faecal samples and the dogs usually shed the bacteria without showing any clinical signs [3,4]. Several studies have reported the presence of Campylobacter spp. in both healthy dogs and dogs with diarrhoea, but Campylobacter is generally not considered to be pathogenic to dogs [5-8]. No association was found between presence of Campylobacter and diarrhoea in a Norwegian study on dogs [8] whereas a study in Canada found significant higher infection rate in diarrhoeic dogs compared with healthy dogs [5]. In an investigation of dogs in Ireland, diarrhoeic dogs were more likely to be Campylobacter positive than dogs without diarrhoea, but the dogs with diarrhoea also had concurrent gastrointestinal parasites, inflammatory bowel disease or diabetes [9]. A study of dogs in Barbados found no difference in clinical disease in dogs with and without presence of Campylobacter in the faeces, but indicated that co-infection with parvovirus and Campylobacter was common [10]. An association between occurrence of diarrhoea and Campylobacter infection was described in a previous Swedish investigation of dogs from 1979, and 63% of the dogs with diarrhoea also had antibodies to canine parvovirus [11]. The true role of Campylobacter in canine gastroenteritis is uncertain as the bacteria may be found in clinically healthy dogs or often as a co-infection or intestinal carriage in diseased dogs. In total, 180 dogs were sampled from the 11 participating veterinary clinics. The sampling period was from October 2011 to October 2012; however, two samples received in November 2012 were also included in the study. For practical reasons, the number of samples received per month varied between the participating clinics. One clinic only sent in samples from one month. The location of the clinics and number of sampled and positive dogs per clinic is illustrated in Figure 1. One of the positive samples lacked information about clinic on the referral form. Most samples were received during the first seven months of the sampling period (October – April). The highest proportion of positive samples occurred in the winter months with a peak in March 2012 (57%). The number of samples per month and positive samples per month are shown in Figure 2.Figure 1Spatial distribution of veterinary clinics where dogs were sampled. The height of the bars represents the number of sampled dogs (red = positive samples, green = negative samples).Figure 2Total number of samples and samples withCampylobacterspecies per month. Proportion positive samples is indicated by the red line. In this study, 37% of the tested dogs were found to be positive for Campylobacter. This proportion is similar to the previous prevalence estimates of other studies [6,9,27]. However, as we targeted young dogs and the mean age of the sampled dogs was 12 months this estimated prevalence may not be representative for the entire Swedish dog population. Moreover, the study design was such that each dog was only sampled once and only one isolate per dog was analysed. In longitudinal studies with another type of study design where dogs were sampled at several occasions considerably higher prevalences of 73-100% have been reported [3,28]. The most common Campylobacter species among the tested dogs (52/180 dogs) was by far C. upsaliensis which is in agreement with many previous studies on dogs where relatively high prevalences of C. upsaliensis have been found in many different populations and countries [5,7,9,22,28]. The lower prevalence (4%) that was observed for C. jejuni (7/180 dogs) is similar to some studies [12,27,29,30], but lower than in a previous Swedish study by Engvall et al. [4] where 11% of the dogs were positive for C. jejuni. However, in the previous study all samples were cultured on three selective plates (two CAT and one Preston agar plate). This probably contributed to the higher isolation rate compared to the present study. A recent study in Switzerland by Amar et al. [30] found a low prevalence of C. jejuni (6.3%) and an even lower prevalence (5.9%) of C. upsaliensis in healthy dogs. A higher prevalence of C. jejuni has been reported in stray dogs [10,28], which may be due to a different exposure to environmental sources of Campylobacter than what household dogs are normally exposed to. In a study from Spain, 19% (20/105) of dogs under 2 years of age living in a household, were found to have C. jejuni [22]. In the present study, one sample was identified as C. helveticus which is not so often identified in samples from dogs, but has previously been associated with cats [29]. The present investigation finds that Campylobacter spp. known to cause campylobacteriosis in humans are present in Swedish dogs. The results suggest an age predisposition where dogs under 2 years of age are more likely to shed Campylobacter spp. than older dogs. The most commonly isolated species was C. upsaliensis followed by C. jejuni, which was only detected in dogs up to 12 months of age. All C. jejuni isolates identified in the present study were the same MLST types as had been previously described both in humans and in animals. Further investigation is necessary to determine the similarity between these dog C. jejuni MLST types and those found in humans in Sweden during the same period. The awareness of the Campylobacter risk of healthy young dogs may be an important way to reduce the transmission from dogs to infants, young children and immunocompromised adults.   Source: http://doi.org/10.1186/s13028-015-0108-0