The Dutch government’s battle against an ongoing epidemic of Q or ‘Query’ fever hit a roadblock yesterday as plans to cull thousands of potentially infected animals were reportedly put on hold after a parliamentary debate. The zoonotic disease continues to affect people across the country after emerging from the rural south in 2007 .

 

The move temporarily overturns an earlier decision, made by Health and Agriculture Ministers, to cull male goats and sheep in addition to thousands of pregnant females in infected farms. With a vaccine shortage and difficulties telling apart infected from healthy animals, the Ministers believe an expanded cull can minimise the risk of further spread.

 

Experts say the country is facing a long fight as many question marks remain over how the outbreak began, and what puts people at risk of getting infected with the Coxiella burnetti bacteria that cause the disease.

 

More than 3000 people across the Netherlands have been affected by the outbreak over the past three years, and at least six have died. Q-fever bacteria, classed as a “category B” bioterrorism agent in the USA, normally infect goats, sheep and cows, often leading to abortion in pregnant animals. Goats are believed to be the main culprit in this outbreak — dairy goat farms are abundant in the south of the country, and these animals shed more bacteria than others into the environment when giving birth.

 

According to data presented earlier this month to the European Union's Standing Committee on the Food Chain and Animal Health, a total of 29 Q-fever outbreaks in Dutch dairy goat farms were reported since 2005, when the disease was first detected in animals. Only two outbreaks were recorded in dairy sheep farms, one in 2006 and one in 2008.

 

But unconfirmed reports from local media this week suggest that the disease has been detected in a dairy sheep farm in the north of the country for the first time this year.

 

 

“Human infection by exposure to sheep is certainly plausible,” says Robert Massung, Chief of the Rickettsial Zoonoses Branch of the Division of Viral and Rickettsial Diseases at the US Centers for Disease Control and Prevention in Georgia.

 

But does a visitor to a sheep farm run the risk of catching Q fever? Alphons Horrevorts, from the Canisius Wilhelmina Hospital in Nijmegen, the Netherlands, says this is “very likely”. His team has investigated the case of a patient who became infected with the bacteria after having close contact with female sheep and cuddling a newborn lamb.

 

People may also be at risk of the disease without having direct exposure to infected animals. “Coxiella burnetti can be spread by air over a great distance,” Horrevorts points out. In the Dutch village of Herpen, where a human case of the disease was first spotted in 2007, “most patients were infected by inhalation of contaminated air.”

 

Massung explains that the bacteria have little trouble surviving in nature and can travel by wind for at least several kilometres. Inhaling these wind-borne pathogens, which are highly infectious, can then cause disease in people who live nowhere near a farm. “There have been many cases previously reported in humans not directly exposed to animals,” he says.

 

But little is clear about how Q fever spreads. The bacteria can also linger in water for long periods, leading some scientists to suggest contaminated water as a possible exposure route.

 

Massung believes that water and food are unlikely culprits. Annie Rodolakis, from the French National Institute for Agricultural Research in Paris, says exposure to water is a possibility. Whether it plays a role can be proven or disproven easily with molecular testing techniques, she says.

 

There is another possible explanation for the large number of infections seen in the Netherlands: a more virulent strain of Q-fever bacteria. Horrevorts and his team have suggested that several genotypes of C. burnetti are circulating in the country. “The virulence of the dominant strain could contribute to the extent of the disease,” says Rodolakis. Working with an animal model in the lab, Rodolakis is working with a colleague to shed some light on this question.

 

Massung believes there is no single answer to how the Dutch epidemic came to pass. “Unfortunately for the Netherlands, this appears to have been a ‘perfect storm’ scenario.”

 

A “unique combination” of factors created ideal conditions for the outbreak, explains Massung, beginning with a high density of commercial dairy goat farms after a rapid expansion of the goat farming industry over the past 15 years. These animals are often transferred among farms, he says, a practice that helps the spread of pathogens.

 

The same area that hosts animals that make up a ‘reservoir’ of Q-fever bacteria also hosts a dense human population with little or no existing immunity, explains Massung. A lack of awareness may also have helped the epidemic to pick up speed. Early on in the course of the outbreak, people probably had little knowledge of the disease, he says, which until then had affected mostly people who work on farms.

 

Research from Taiwan published recently in Zoonoses and Public Health suggests that education about risk factors for the disease could help to prevent transmission. Taiwan has also recorded a rise in the number of confirmed cases of Q fever since 2005.

 

 

In the Netherlands, education should be part of infection-control efforts that tackle the disease on several fronts, according to Massung. But his outlook for a swift end to the epidemic is bleak. “The severity of the outbreak suggests that it will take several years, at minimum, before the situation can be controlled.”

 

Patients will need to be given proper treatment and monitored for long-term illness and endocarditis — a complication that often follows short bouts of Q fever, which is usually mild. This will take “an unprecedented public health effort”, says Massung.

 

As for the source of bacteria, he believes vaccination and culling of infected animals should eventually cut down on the infection rate in both animals and humans. The vaccine, which can prevent abortions and some infections, was in short supply in 2008 and 2009. But enough doses should be available this year, according to media reports.

 

Horrevorts doubts the effectiveness of animal vaccination, saying it can only reduce the number of bacteria carried by an animal, not prevent infection. He says improving farming procedures can help to reduce disease spread. These range from improved ventilation in potentially contaminated areas to better hygiene when handling manure and helping animals to give birth.

 

Looking years down the line and beyond this outbreak, Massung strikes a note of caution. “A remaining issue is the long-term viability of organisms already in the environment that will likely pose a human infection risk for years to come.”