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Enteric campylobacterios is a common zoonotic infection
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In December 2008, the National Public Health Service for Wales published an 11-page “final report” titled, “The investigation of an outbreak of diarrheal illness in participants of the Builth Wells Mountain Bike Marathon, July 2008.”
More than 660 mountain bikers from all over Great Britain took part in the event July 5-6, 2008, in Powys, Wales. On July 17, the National Public Health Service for Wales (NPHSW) was alerted by a participant who knew of eight people who had become unwell following the event. The same individual also reported that there were many others complaining of similar symptoms on a post-event Internet discussion forum.
An internet-based questionnaire was launched to investigate the outbreak. A total of 355 responses were received, with 161 cyclists reporting symptoms such as diarrhea and vomiting. Ten cyclists reported having stool samples which were positive for Campylobacter.
Investigation
Following an investigation by health experts, the muddy mountain cycle course was found to be heavily contaminated with sheep droppings. The report concluded that, “although microbiological confirmation has not been received for the majority of participants, the results of the study are consistent with a point source Campylobacter outbreak.”
The investigators said the outbreak was likely caused by campylobacter spread to the cyclists by mud that was contaminated with sheep feces. “Heavy overnight rain is likely to have contributed to the outbreak by increasing the amount of liquid mud on the course,” the researchers wrote. “Cyclists are believed to have been affected by eating meals and snacks during the event without washing their hands first.”
The NPHSW report obtained wide publicity. Other reports of similar events due to other enteric pathogens do exist, but this stands alone in the proposed mechanism of transmission and to its alleged zoonotic nature (“sheep droppings”). Reviewing the zoonotic aspects of enteric campilobacteriosis seems therefore to be well-timed.
Campylobacter jejuni, a Gram negative, microaerophilic bacterium is associated, similarly to C. coli, with enteritis in domestic animals and humans. Some strains of C. jejuni cause infertility and abortions in sheep and cattle. Both species are found worldwide. In this review, another, third campylobacter species, C. fetus, which affects mainly ruminants, will not be discussed.
Campylobacter species do not tolerate drying or heat but can often survive for a time in moist environments. C. jejuni can survive a few weeks to a few months under moist, reduced-oxygen conditions at 4°C, but only a few days at room temperature.
This species may also remain viable for up to nine days in feces, three days in milk and two to five days in water. It can survive in vaginal discharges on bedding or pasture for several days under field conditions. Both C. jejuni and C. coli can remain infective in moist poultry litter for prolonged periods.
Infections in animals
C. jejuni and C. coli can infect cattle, sheep, chickens, turkeys, dogs, cats, mink, ferrets, pigs, non-human primates and other species. Enteritis is caused in dogs, cats, calves, sheep, mink, ferrets, poultry and some species of laboratory animals. Both bacteria are transmitted by the fecal-oral route; they can be spread by direct contact and on fomites including food or water. Asymptomatic carriers are seen in many species of domestic animals. Enteritis is more common in young animals but stress or concurrent disease increase the risk of disease in adults. In dogs, the symptoms can include diarrhea, decreased appetite, vomiting and sometimes fever.
The symptoms generally last three to seven days, but some animals may have intermittent diarrhea for weeks and occasionally for months. Calves typically have a thick, mucoid diarrhea with occasional flecks of blood, either with or without a fever. Mucoid, watery and sometimes bloody diarrhea is also seen in cats, primates, mink and ferrets. Newly hatched chicks and poults develop acute enteritis, with rapid onset of diarrhea and death; poultry chicks over a week old do not usually become ill.
Campylobacter species are readily transmitted between animals or from animals to humans. The organism spreads very rapidly in poultry; all of the birds in a broiler flock can become infected within 72 hours. Organisms are present in feces, vaginal discharges and abortion products and can be spread by direct contact, on fomites and by arthropods acting as mechanical vectors. Contaminated food and water is often the source of infections.
Antibiotics may be useful for some cases of enteritis in animals, though information on efficacy is limited. No vaccination is available for campylobacter-related enteritis in animals.
Among animals, asymptomatic carriage of intestinal Campylobacter is more common than enteric disease. The carriage of Campylobacter in small animals is highly variable, ranging from 0% to 45% in cats and 1.6% to 75% in dogs. The prevalence of infection is low in household pets but high in animal shelters, pet shops and laboratory colonies, as well as in strays and rural animals exposed to livestock. Among livestock, C. jejuni has been isolated from the feces of 25% to 100% of asymptomatic cattle and, in one study, the gallbladders of 11% of healthy sheep. Various studies have noted a particularly high incidence of infection in poultry, with Campylobacter in 100% of the ceca of turkeys, 83% of chicken droppings and 88% of duck droppings. C. jejuni contamination has also been seen in approximately 30% of chicken meat and 5% of red meat samples.
Gastrointestinal campylobacteriosis is usually self-limiting in mammals; however, up to 32% mortality may be seen with highly pathogenic isolates in chicks.
In humans
According to CDC explanatory data, Campylobacter is one of the most common causes of diarrheal illness in the United States. The vast majority of cases occur as isolated, sporadic events.
Active surveillance through FoodNet indicates that about 13 cases are diagnosed each year for each 100,000 people. Many more cases go undiagnosed or unreported, and campylobacteriosis is estimated to affect more than 2.4 million people every year, or 0.8% of the population, occurring much more frequently in the summer months than in the winter. The organism is isolated from infants and young adults more frequently than from people in other age groups and from males more frequently than females. Fatality is rare. Most cases of campylobacteriosis are associated with eating raw or undercooked poultry meat or from their cross-contamination with other foods. Infants may get the infection by contact with poultry packages in shopping carts.
According to Danish data, the marked increase in consumption of fresh, unfrozen poultry in Denmark during the 1990s likely contributed substantially to the increasing incidence of human campylobacteriosis in this period; the risk from eating other poultry, including previously frozen chicken, was lower.
Outbreaks of Campylobacter can also be associated with unpasteurized milk or contaminated water. Some human cases have acquired their infection from contact with the stool of an ill dog or cat. The organism is not usually spread from one person to another, though exceptions occur.
Epilogue
The conclusion of the Welsh Public Health Service, attributing the recent outbreak amongst the Marathon cyclists to contaminated sheep droppings, is in need of supportive evidence. Such need is illuminated by the significant findings reported by Champion et. al. in the 2005 study, Comparative phylogenomics of the food-borne pathogen Campylobacter jejuni reveals genetic markers predictive of infection source, PNAS 102 (44), 16043–16048:
“In this study 111 C. jejuni strains were examined by genomotyping isolates from humans with a spectrum of C. jejuni-associated disease (70 strains), chickens (17 strains), bovines (13 strains), ovines (five strains), and the environment (six strains). From these data, the Bayesian phylogeny of the isolates revealed two distinct clades unequivocally supported by Bayesian probabilities (P=1); a livestock clade comprising 31/35 (88.6%) of the livestock isolates and a ‘‘nonlivestock’’ clade comprising further clades of environmental isolates. Several genes were identified as characteristic of strains in the livestock clade… Surprisingly these studies show that the majority (39/70, 55.7%) of C. jejuni human isolates were found in the nonlivestock clade, suggesting that most C. jejuni infections may be from nonlivestock (and possibly nonagricultural) sources. This study has provided insight into a previously unidentified reservoir of C. jejuni infection that may have implications in disease-control strategies.”
For more information:
- Arnon Shimshony, DVM, is Associate Professor at the Koret School of Veterinary Medicine Hebrew University of Jerusalem, Rehovot, and is the ProMED-mail Animal Diseases and Zoonoses Moderator. Dr. Shimshony was Chief Veterinary Officer, State of Israel, from 1974 to 1999.
- Additional information about the NPHSW report is available online at www.cfsph.iastate.edu/Factsheets/pdfs/campylobacteriosis.pdf.