Thursday 01 April 2010
Wind sparks Q fever outbreak Outbreaks of Q fever in people raise concerns over lack of surveillance for pathogen in UK farm animals
Source: SXC/hanspeta
At least 30 people contracted Q fever in the UK town of Cheltenham in 2007. A model1 published in Eurosurveillance suggests that Q fever bacteria blew into the town from nearby infected sheep farms.
Experts say this outbreak, and an ongoing epidemic in the Netherlands, hint that disease surveillance in livestock should be stepped up to protect human health.
Q fever is a bacterial disease caused by Coxiella burnetti. It usually affects sheep, goats and cows causing them to abort foetuses. The disease is thought to be endemic in UK livestock. People can develop Q fever after coming into contact with infected animals, and vets and farm workers are thought to be at highest risk. An ongoing epidemic of the disease in the Netherlands has so far affected more than 3000 people since 2007. Over 10 weeks of the same year, 30 people came down with Q fever in Cheltenham, England. Local authorities suspected the outbreak was caused by windblown bacteria from infected farms and investigated the possibility using a mathematical tool that can model the dispersion of bacteria into the atmosphere.
The researchers mapped the farms in the Cheltenham area and assessed the risk that each of them was the source of the outbreak. They based this risk assessment on interviews with farmers about signs of Q fever among their animals and farming practices that may increase the risk of bacteria being released into the atmosphere, as well as data from the UK’s national weather service about wind directions during the outbreak. Three farms were deemed to be high risk possible sources and included in the model along with weather and geographical data. A separate epidemiological investigation ruled out a common exposure among the people infected with Q fever bacteria in the town, such as visiting a local farm or meat market. “Dispersion modelling… showed that air from each of the suspected farms may have exposed the town to the bacterium at some point over the study period,” write Anders Wallensten, from the UK Health Protection Agency, and colleagues.
Wim van den Hoek, from the National Institute for Public Health and the Environment in the Netherlands, believes that windborne bacteria are behind the majority of human Q fever cases in the ongoing Dutch outbreak too. To date, the wind has not blown the bacteria into neighbouring countries. But public health authorities in Belgium and Germany are on the look out for cases in people, he says.
Research published by van den Hoek and colleagues last month in BMC Infectious Diseases suggests that people who live within five kilometres of an infected farm run the highest risk of catching Q fever bacteria caught up in the wind.
There are two reasons C. burnetii can travel in the wind, explains Conall McCaughey of the Regional Virus Laboratory in Belfast, Northern Ireland. Firstly, the bacteria can exist as spores that do not dry out and can survive for long periods of time in a dry environment. An outbreak of Q fever affecting 95 people in Newport, South Wales, in 2002 was sparked by the release of C. burnetii from strawboard building materials thought to have been contaminated with the bacteria 50 years earlier, he says. Secondly it takes just one C. burnetii organism to infect a person.
British authorities do not know how widespread C. burnetii infection is in livestock as there is are no monitoring systems in place. Currently, Q fever is not a notifiable animal disease in the country and infections are only uncovered during in depth investigations into outbreaks of abortions in animals. But this looks set to change, according to McCaughey. “I think that the surveillance of Q fever in farmed ruminants has been, to some extent, neglected in the past.” The size of the Netherlands outbreak has changed this, he explains. “There is a lot of international focus on the situation and national authorities [in European countries] have been focusing on the implications for their own countries.”
Pointing to a report2 published last month by the UK government Department for Environment, Food and Rural Affairs (DEFRA), McCaughey suspects there are plans for surveillance in the UK, which would be very useful for defining and managing the risk of outbreaks in people. Writing in Eurosurveillance, Wallensten and colleagues point out that the existing tests used to diagnose C. burnetii infection in farm animals are “of limited value”. But DEFRA appears to be investigating ways to improve diagnosis and surveillance for C. burnetii in animals. In 2008, the UK Veterinary Laboratory Agencies (VLA) investigated molecular Q fever diagnosic methods and compared several commercially available immunological testing kits. “The VLA is also organising a proficiency testing exercise with several other European laboratories,” write DEFRA in the report.
van den Hoek notes that unlike the UK, some European countries have Q fever surveillance systems in place to monitor livestock. “However [these] activities are highly viable and not comparable between countries.” A harmonised system is “highly desirable”, he adds.
References and link
1. Wallensten A, Moore P, Webster H, Johnson C, van de Burgt G, Pritchard G, et al. Q fever outbreak in Cheltenham, United Kingdom, in 2007 and the use of dispersion modelling to investigate the possibility of airborne spread. Euro Surveill 2010, 15. Article
2. DEFRA. Zoonosis Report United Kingdom 2008. Report
European Centre for Disease Prevention and Control information about Q fever
http://www.eht-forum.org/news.html?fileId=news100401063119&from=home&id=0