Land-applied contaminated manure another source of spread of Q fever

Gepubliceerd op
6 mei 2014

A spatial analysis of the Q fever outbreak of 2006-2010 has revealed that new research Q fever outbreaks are often linked with the land application of contaminated manure. Until now it was thought that the contamination came directly from goat farms and therefore it was mainly people living in the vicinity of goat farms who became ill. The research was carried out by Alterra, in cooperation with the Municipal Health Service South Limburg and the University of Maastricht, and was published in the scientific journal PLOS One.

Q fever is a zoonosis, an infectious disease that can be transferred from animals to humans. Previous research had shown that there is a spatial relationship between goat farms that were contaminated with Q fever and the incidence of the illness among humans. As expected more people became ill in the vicinity of contaminated farms that those living at a distance from these farms. “But,” says Alterra researcher Tia Hermans, “we saw that living in the vicinity of goat farms could only explain the Q fever contamination in just over 50% of the cases. So there had to be another factor at play here.”

Research carried out by the Central Veterinary Institute showed that manure from goats can still be contaminated with Q fever up to a maximum of 3 months after lambing. “As a result of this we started to look into it further,” says Tia Hermans. “We looked to see whether there is a relationship in place and time between lambing, the land application of manure and the incidence of the illness in people. Our analyses showed that the lambing peak late in the winter was followed by a peak in land application of manure in the early spring. In May, one month after the land application of manure, the incidence of the illness among humans peaked. The time between the land application of manure and the peak in the number of people ill corresponds with the incubation period of Q fever, the time between the contamination and the first symptoms of the illness.“ 

In a relative sense, the number of people ill in the vicinity of land parcels with contaminated manure was higher than the number of ill people in the vicinity of contaminated goat farms. Also, the incidence around land parcels with contaminated manure was relatively higher than around parcels with non-contaminated manure, and more people were ill around contaminated farms with their own land, than around contaminated farms without their own land (who had to take the manure somewhere else). The land application of contaminated manure therefore plays an important role in the spreading of Q fever.

The results call for a reassessment of the policy measures previously taken to prevent the spread of Q fever. In 2008, a ban on the transport of manure within 90 days after a farm had been declared contaminated was imposed on contaminated farms. This was tightened in 2009 to a ban of 30 days after lambing. Tia Hermans: “Our research shows that most of the transport from contaminated farms takes place within 1 month after lambing. Farmers must be made aware of the consequences of the land application of manure and take effective measures. These measures also apply to the application of manure on the farmer’s own parcels. Our research also shows that in the case of new zoonosis outbreaks, it is necessary to carry out an integrated analysis of animal and human data, on a national scale, and with experts in the area of farm systems, to make sure that such an obvious route for the spread of Q fever is not overlooked again.”