Circulation of Coxiella burnetii in a Naturally Infected Flock of Dairy Sheep: Shedding Dynamics, Environmental Contamination, and Genotype Diversity

Abstract

Q fever is a worldwide zoonosis caused by Coxiella burnetii. Domestic ruminants are considered to be the main reservoir. Sheep, in particular, may frequently cause outbreaks in humans. Because within-flock circulation data are essential to implementing optimal management strategies, we performed a follow-up study of a naturally infected flock of dairy sheep. We aimed to (i) describe C. burnetii shedding dynamics by sampling vaginal mucus, feces, and milk, (ii) assess circulating strain diversity, and (iii) quantify barn environmental contamination. For 8 months, we sampled vaginal mucus and feces every 3 weeks from aborting and nonaborting ewes (n ‫؍‬ 11 and n ‫؍‬ 26, respectively); for lactating females, milk was obtained as well. We also sampled vaginal mucus from nine ewe lambs. Dust and air samples were collected every 3 and 6 weeks, respectively. All samples were screened using real-time PCR, and strongly positive samples were further analyzed using quantitative PCR. Vaginal and fecal samples with sufficient bacterial burdens were then genotyped by multiple-locus variable-number tandem-repeat analysis (MLVA) using 17 markers. C. burnetii burdens were higher in vaginal mucus and feces than in milk, and they peaked in the first 3 weeks postabortion or postpartum. Primiparous females and aborting females tended to shed C. burnetii longer and have higher bacterial burdens than nonaborting and multiparous females. Six genotype clusters were identified; they were independent of abortion status, and within-individual genotype diversity was observed. C. burnetii was also detected in air and dust samples. Further studies should determine whether the within-flock circulation dynamics observed here are generalizable.Q fever is a widespread zoonosis caused by Coxiella burnetii, a Gram-negative intracellular bacterium that has been reported in a broad range of host species. Livestock, especially small ruminants, are the main sources of human infections (1-3). In domestic ruminants, Q fever's major clinical manifestations are abortions and stillbirths, whose occurrence may translate into significant economic losses (1, 3). In humans, C. burnetii infections range from asymptomatic to severe. Acute forms of the disease may result in high fevers and severe pneumonia or hepatitis, and chronic forms are strongly debilitating and may be fatal when endocarditis develops in patients with underlying heart disease (4-6).Animals and humans become infected essentially through the inhalation of airborne particles contaminated with C. burnetii (3,7,8). Contaminated dust particles may remain infectious for long periods of time due to the capacity of the bacterium to differentiate into highly resistant spore-like forms (9, 10). Consequently, knowledge of C. burnetii's sources and shedding dynamics is essential to assessing the risks of disease transmission and pathogen persistence. On livestock farms, C. burnetii DNA has been found in various environmental matrices, such as dust (11-13) and aerosols (14-16). However, studies that examin...

Swab cloths as a tool for revealing environmental contamination by Q fever in ruminant farms

“…We also found that the Q fever clinical status was related to the probability of detecting a qPCR‐positive dust swab, this probability being higher in herds with series of abortions attributed to Q fever. This result was expected, since C. burnetii shedding is particularly high after an abortion episode (Guatteo, Beaudeau, Joly, & Seegers, ; Joulie et al., ; Rousset, Berri, et al., ). DNA from C. burnetii was nevertheless detected, sometimes with high bacterial loads, in dust swabs sampled from 19 herds not suspected of Q fever.…”

“…Dust samples were screened for the presence of C. burnetii DNA by using a multiplex qPCR method targeting both the IS 1111 gene of C. burnetii and an external control (Joulie et al., ). DNA was extracted with the QIAmp DNA kit.…”

“…Most human cases result from the inhalation of aerosols and dust particles contaminated with the excreta and birth products of infected animals. Within infected ruminant herds, the bacterium is excreted in large quantities in the placenta and foetal membranes by parturient females, whether they have aborted or not; excretion in the vaginal mucus and faeces may last several months, resulting in massive environmental contamination (EFSA, ; Joulie et al., ; Kersh et al., ). As C. burnetii produces highly resistant spore‐like small cell variants, it may persist in the environment for long periods of time.…”

Single Nucleotide Polymorphism Genotyping and Distribution of Coxiella burnetii Strains from Field Samples in Belgium

“…The presence of multiple C. burnetii strains within a farm has been reported by several authors using different genotyping methods (SNP analysis, MLVA) (14,17,27). However, the epidemiological and pathological implications of the circulation of different strains are still unknown.…”

Permissiveness of bovine epithelial cells from lung, intestine, placenta and udder for infection with Coxiella burnetii

“…Feces of aborting ewes contain up to 10 7 GE of Coxiella per gram [37]. Our in vitro study showed that epithelial cells other than mammary gland epithelium also were capable of internalizing C. burnetii but there was little further propagation of bacterial numbers within the cells.…”