Salmonella and E.coli O157 have always commanded attention, much more so than campylobacter. Yet while its name might not be so familiar, it has crept into prominence as the biggest cause of food-borne diarrhoea among humans in the developed world.
In Britain campylobacter cases outnumber salmonella cases by a factor of three. The Food Safety Authority of Ireland is worried that a rise in food-borne infection here, at a time when salmonella cases are declining, may be largely attributable to campylobacter in its various forms.
The past 30 years have "witnessed the rise of campylobacter enteritis (diarrhoea) from virtual obscurity to notoriety", according to Dr John Moore of Belfast City Hospital. It is a straightforward sort of microbe, easily killed and not very robust, yet succumb to it and you will know all about it in the form of often bloody diarrhoea for about a week. It can cause more severe effects including inflammatory arthritis and GuillainBarre syndrome, which impairs peripheral nerves and causes limb weakness and paralysis.
Campylobacter transmission to humans can be from contact with animals, dairy products (especially unpasteurised milk and birdpecked milk) or water, but transfer between humans is uncommon. There is always a "spring surge" in cases, said Dr Moore. A quarter of UK cases are linked to foreign travel - the natural habitat of most campylobacters is the intestine of warm-blooded animals, notably pigs and poultry.
Dr Moore is working with Dr Martin Cormican of NUI Galway and Dr Shay Fanning of Cork Institute of Technology in a project that applies genetic fingerprinting techniques to the organism. This will make it possible to determine the relationship between various environments and the spread of pathogens.
Dr Cyril Carroll of NUI Galway department of microbiology is also involved in important work on serotyping and genomic typing crucial to proper identification. The problem is there are no internationally accepted standards on typing methods, which makes comparison of results difficult. Equally, he said, not enough is known about its mode of transmission.
It is known campylobacters have idiosyncrasies. They don't cause large outbreaks and do not multiply in food, despite a high number of sporadic cases. But research is showing they can survive inside other simple microbes known as protozoans and, despite campy lobacter's vulnerability, it can evade disinfection while hidden in the protozoans. Moreover, some waterborne forms cannot be cultured in a lab, so they live in suspended animation, only to reemerge later with their infectivity intact.
US Researchers at the College of Veterinary Medicine in Georgia have established the ability of campylobacters to survive chlorination treatment in a number of protozoans such as amoebae. Microbiologists there suggest the ability to survive ingestion by bacteria was an evolutionary mechanism developed prior to getting the ability to cause disease. Today it is a mechanism for survival of bacteria in dilute and inhospitable aquatic environments.
Prof Tom Humphrey, head of the food microbiology research unit in Exeter, believes protozoans are becoming important ecological niches not only for campylobacter but also for E.coli O157. His work on campylobacter jejuni is focusing on the environment around chicken houses, and on why within two days tests on poultry can change from all negatives to all positives for the bug.
He doesn't think a vaccine will be effective with such large-scale contamination but is more hopeful about encouraging a good blend of microbes known as "competitive flora" within the birds to inhibit campylobacter.
FSAI chief executive Dr Patrick Wall is worried about a trend of campylobacters showing increasing resistance to fluroquinolones, commonly used to treat severe infectious diarrhoea, often before the cause is identified.
Resistance is also showing up with the front line (and closely related) drug ciprofloxacin. "This suggests the issue of overuse of these antibiotics in clinical practice and animal husbandry has to be addressed."
From an Irish perspective, he said it was worrying that the exact number of cases was not known and current monitoring was not as extensive as it should be, though the National Disease Surveillance Centre is arranging for electronic reporting of cases.
In Britain, where free GP services are available and there is a greater tradition of submitting samples for testing, better track of microbes is achieved. "God only knows how many campylobacter we have," he said.