Veterinary aspects of a Q fever outbreak in the Netherlands between 2005 and 2012

Abstract

In a six week period from May 2007 onwards, almost one hundred patients from Herpen, a small village in the province of Noord-Brabant, were diagnosed with a lower respiratory tract infection, and ultimately, Coxiella burnetii was found to be the causal agent. This finding made up the start of a large Q fever outbreak.The aim of this thesis is to describe veterinary aspects of this outbreak in the Netherlands between 2005 and 2012 to be able to improve control and preventive measures aiming at reducing the shedding of C. burnetii and thus environmental contamination, in order to reduce human exposure. As no recent information was available on professionally exposed persons, the research described in this thesis additionally aims to determine consequences of exposure for livestock veterinarians.

After a description of the outbreak in 2007 and 2008, a seroprevalence study was performed and pregnant and periparturient dairy goats in the south-eastern part of the Netherlands were demonstrated to have the highest seroprevalence. Bulk tank milk (BTM) testing, using a real-time (RT) PCR and ELISA, showed that in the same region a significantly larger proportion of BTM samples was PCR and ELISA positive compared to the rest of the Netherlands.

Initially, the aim of the BTM surveillance program, a sensible method to detect shedding of C. burnetii, was to declare dairy goat herds C. burnetii free. However, from December 2009 onwards farms were declared infected based on positive results, and on those farms all pregnant dairy goats were culled and the remaining goats got a lifetime breeding ban.

On one of those farms where all animals had been vaccinated since 2008 and all pregnant goats had been culled, we demonstrated that individual testing and culling of positive animals did result in a negative BTM PCR which remained negative, until, the end of the observation period.

In several outbreaks, manure was identified as the most probable source of a Q fever outbreak. In our study, we found no association between the incidence of human Q fever and the dispersal of goat manure originating from farms with confirmed abortion storms in 2008 and 2009.This lack of association is supported by our temperature measurements in dunghills on two farms with C. burnetii shedding dairy goats.

Under field conditions, we studied the effect of vaccination with phase one vaccine Coxevac® (CEVA, Santé Animale) on bacterial shedding. We demonstrated that in samples of uterine fluid, vaginal mucus, and milk from 957 pregnant animals in 13 herds prevalence and bacterial load were reduced in vaccinated animals compared with unvaccinated animals. These effects were most pronounced in animals during their first pregnancy.

In Dutch livestock veterinarians, antibodies against C. burnetii were demonstrated in 123 (65.1%) out of 189 veterinarians, and number of hours with animal contact per week, number of years graduated as veterinarian, rural or sub urban living area, being a practicing veterinarian, and occupational contact with swine were associated with seropositivity.