Sparrows, flies, and rodents as reservoirs of Campylobacter spp. on a dairy farm : a thesis presented in partial fulfilment of the requirements for the degree of Master of Veterinary Science in Veterinary Public Health and Meat Hygiene at Massey University, Palmerston North, New Zealand
The reported numbers of human Campylobacter jejuni infections have increased considerably in many countries during the last few years. In New Zealand, the current annual incidence rate (302.5 cases/100 000) of human campylobacteriosis is higher than that of any other notifiable disease, and surpasses the incidence of campylobacteriosis reported by other developed countries. Although Campylobacter jejuni has been isolated from poultry at high prevalence rates worldwide, poultry are probably not the only important source of human campylobacteriosis as it is well documented that many other animal species (sheep, pigs, cattle and free-living birds and mammals) can be carriers of zoonotic Campylobacters. The high incidence of the disease in people could be related to the consumption of poorly cooked meat, drinking contaminated water, overseas travel and animal contact. This study investigates the potential role of free-living animals (sparrows, rodents and flies) as potential reservoirs of Campylobacter spp. and was carried out at Massey University No. 4 dairy farm. We isolated Campylobacter from the faeces of cattle and from other samples, and used pulsed-field gel electrophoresis (PFGE) typing of the organisms to determine the similarity between isolates. This study also includes a comparision of the prevalence and genetic diversity of Campylobacter isolated from sparrow populations on the farm and from an urban environment. Based on the results of a previous study on the same farm, sample size of 52 were taken for the dairy cows in order to obtain results at the 90% confidence level within 10% accuracy. Faecal samples from 53 farm sparrows, 65 rodents and 56 flies were calculated and examined for the presence of thermophilic Campylobacter spp. Faecal samples were also collected from 53 urban sparrows from "The Square" in the central urban area of Palmerston North city about 7 km from the dairy farm. A convenient number of samples of five of grass silage and two from each of water, worker's boots and aprons were collected with the aim to determine the presence of Campylobacters in these samples. All samples were collected between the 5th April 2002 and 25th May 2002. Random samples of rectal contents from 52 Friesian dairy cows were collected during milking time. Rodents were trapped in the feed storage premises approximately 15m from the milking shed using standard spring loaded, baited traps. Flies were captured around the milking shed using standard fly-traps. Bird samples were collected from an 8x10 feet tarpaulin placed on the ground under a tree where sparrows were roosting about 50m from the milking shed. Feed was provided to attract the birds. The same method was used to collect sparrow droppings in the urban area about 7 km from the tarm. Campylobacter jejuni was the only Campylobacter species isolated from the 290 samples collected at the dairy farm and from sparrows in the urban area. The highest isolation rate was found in dairy cows (54%), followed by urban sparrows (40%), farm sparrows (38%), rodents (11%) and flies (9%). Other samples from the farm environment such as grass silage, water, worker's apron and boots were also found to be positive for C. jejuni. Most of the rodents caught during the study period were mice. The high isolation rate in this study of Campylobacter from dairy cows (54%) and sparrows (40%) supports the notation that these species are important reservoirs of infection. Overall the results of the present and previous study show that at least some dairy cows from the same farm can be asymptomatic carriers (intermittent or persistant) of Campylobacter jejuni for at least 24 months. Molecular characterisation of genomic DNA from 61 C. jejuni isolates from farm and urban sources obtained during the study was performed by PFGE after digestion with the enzyme Sma I. Of the 22 restriction patterns obtained seven were common to more than one source. The PFGE typing yielded seven, six, nine, six and three restriction patterns from dairy cows, farm sparrows, urban sparrows, rodents and flies respectively. PFGE analysis of the C. jejuni isolates shows a high degree of diversity of the organisms within a limited geographical area. But the finding of some common restriction patterns provides evidence of identical clones infecting cattle, sparrows, flies and rodents.