Dairy Sheep Played a Minor Role in the 2005-2010 Human Q Fever Outbreak in The Netherlands Compared to Dairy Goats

Abstract

Q fever is an almost ubiquitous zoonosis caused by Coxiella burnetii. This organism infects several animal species, as well as humans, and domestic ruminants like cattle, sheep and goats are an important animal reservoir of C. burnetii. In 2007, a sudden rise in notified human Q fever cases occurred in The Netherlands, and by the end of 2009, more than 3500 human Q fever patients had been notified. Dairy sheep and dairy goats were suspected to play a causal role in this human Q fever outbreak, and several measures were taken, aiming at a reduction of C. burnetii shedding by infected small ruminants, in order to reduce environmental contamination and thus human exposure. One of the first measures was compulsory notification of more than five percent abortion within thirty days for dairy sheep and dairy goat farms, starting 12 June 2008. After notification, an official farm inspection took place, and laboratory investigations were performed aiming at ruling out or demonstrating a causal role of C. burnetii. These measures were effective, and the number of human Q fever cases decreased; levels are currently the same as they were prior to 2007. The effect of these measures was monitored using a bulk tank milk (BTM) PCR and an antibody ELISA. The percentage PCR positive dairy herds and flocks decreased over time, and dairy sheep flocks tested PCR positive significantly less often and became PCR negative earlier compared to dairy goat herds. Although there was no difference in the percentage of dairy goat and dairy sheep farms with a C. burnetii abortion outbreak, the total number of shedding dairy sheep was much lower than the number of shedding dairy goats. Combined with the fact that Q fever patients lived mainly in the proximity of infected dairy goat farms and that no Q fever patients could be linked directly to dairy sheep farms, although this may have happened in individual cases, we conclude that dairy sheep did not play a major role in the Dutch Q fever outbreak. BTM monitoring using both a PCR and an ELISA is essential to determine a potential C. burnetii risk, not only for The Netherlands but for other countries with small ruminant dairy industries.

Keywords: Coxiella burnetii; ELISA; PCR; caprine; goat; monitoring; sheep; surveillance.

Figure 1

Number of small ruminant holdings in The Netherlands, percentages of flocks and herds containing sheep (63% only sheep, 14% sheep and goats), goats (23% only goats, 14% goats and sheep), or both species (14% both sheep and goats), and percentages of small scale and professional holdings per animal species.

Figure 2

Densities of dairy goat herds (left; above in 2020 and below in 2010) and dairy sheep flocks (middle; above in 2020 and below in 2010). The right map shows the number of Q fever patients with confirmed status reported to the municipal health service from 1 January 2007 to 31 December 2010 per 100,000 population. All maps based on two digit postal code areas in The Netherlands.

Figure 3

The percentage of Coxiella burnetii PCR-positive dairy goat herds (total population in 2020 n = 400) and dairy sheep flocks (total population in 2020 n = 35) in The Netherlands based on the bulk tank milk monitoring program between 2009 and 2020.

Figure 4

The median and interquartile range (IQR) of the SP% of Coxiella burnetii BTM samples of all dairy goat herds (n = 400) and dairy sheep flocks (n = 35) in The Netherlands between 2009 and 2020.