6. Discussion
The incidence of human campylobacteriosis in New Zealand is among the highest in the developed world. The majority cases of campylobacteriosis in people are foodborne or waterborne (e.g. contaminated, raw or undercooked meat, unpasteurised milk, untreated contaminated water) and are linked to contact with farm animals. Recent research at No. 4 dairy farm, Massey University revealed a Campylobacter carriage rate of 15-52 percent in adult dairy cows, 82 percent in heifer and 22 percent in calves (Wu, 2001). The current study was carried out to examine the potential of wild birds, rodents and flies as a source of infection. Poultry is believed to be the main reservoir of Campylobacter for people and research both in New Zealand and overseas have recognized that consumption of undercooked poultry meat is a leading risk factor for human campylobacteriosis (Ikram et al., 1994., Eberhart-Phillips et al., 1996). However, the potential of cattle, wild birds, rodents and flies as a contributor to human infection has been attracting consumer’s attention.
The present study was undertaken to explore the sparrows, rodents and flies as potential reservoirs of Campylobacter spp for dairy cows and these species might act as links in the epidemiology of human campylobacteriosis. The result of this study indicates a prevalence of 53.8 percent of Campylobacter jejuni in dairy cows, which is comparable with 65 percent as reported by Wu (2001) in her first sampling on the same farm during the same month of year. However, Wu, (2001) reported 8 percent and 9 percent prevalence rate for C. jejuni in dairy cows in the subsequent second and third sampling during winter and spring season respectively. The increase in the prevalence rate in summer appears to correspond with the pattern of human clinical disease observed which increases in the summer months (Brieseman, 1990). Overall the results clearly shown that the dairy cows at No.4 dairy unit are still common asymptomatic carriers of Campylobacter infections.
In our study, the only Campylobacter spp isolated from dairy cows, sparrows, rodents and flies was C. jejuni. This is surprising because other species of Campylobacter (C. lari, C. hyointestinalis and C. upsaliensis) have been previously isolated on this farm (Wu, 2001). The reason remains obscure but could be associated with seasonal variance, microbial competition, strain dominance in wild life reservoirs or variation in accuracy of microbiological methods applied.
The prevalence of C. jejuni both in farm and urban sparrows was found to be 37.7 percent and 39.6 percent respectively. Of the other samples, two silage, two boots, one apron and two water samples were found positive for C. jejuni.
Little is known about the role of sparrows in the transmission of C. jejuni to livestock in New Zealand but overseas studies have suggested that wild birds may be an important source of C. jejuni for cows (Cabitra et al., 1992). Since sparrows commonly roost and feed around cow sheds and nearby pasture, chances of environmental contamination by bird’s faecal droppings must be high. Contamination of silage and stored concentrate and minerals fed to livestock is also a potential link in the transmission of Campylobacter from wild animal reservoirs to livestock.
It appears from the limited literature available that rodents and drinking water could be important reservoirs of Campylobacter spp (Cabrita et al., 1992). The results of the present study in which 10.8 percent rodents were carriers of C. jejuni and 100 percent of water samples contained C. jejuni support this hypothesis. Chlorination is the main method of disinfections of drinking water provided in the pasture area. However, changes in chlorine levels may occur if there are sudden increases in demands for water during periods of hot weather (Anon2, 2002). Chlorine breaks down in the presence of sunlight (UV) and chlorine gas readily leaves the water, reducing the bactericidal effect (Anon3, 2002)
The PFGE patterns of isolates obtained during the present study will be compared those of previous investigations and fully discussed in the thesis.
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