Coxiella burnetii in the environment: A systematic review and critical appraisal of sampling methods

Global and regional seroprevalence of coxiellosis in small ruminants: A systematic review and meta-analysis

BACKGROUND

Coxiellosis is a neglected zoonosis for occupationally exposed people in many parts of the world. Sheep and goats are two important small ruminants that act as reservoirs for human contamination; however, there is a lack of comprehensive data on the epidemiological aspects of coxiellosis in sheep and goats at regional and global levels. The aim of this study was to systematically review the available articles on seroprevalence of coxiellosis in sheep and goats and estimate the overall seroprevalence in different regions.

METHODS

A systematic search strategy was performed in five electronic repositories for articles published until December 2021. Relevant data were extracted from the selected articles based on the inclusion criteria. A random effect meta-analysis model was used to analyse the data. Results are presented as the prevalence of seropositivity as a percentage and 95% confidence intervals.

RESULTS

The global pooled seroprevalence of coxiellosis in sheep was 17.38% (95% confidence interval [CI]: 15.59%-19.17%). Overall, the regional level pooled prevalence estimates in sheep ranged from 15.04% (95% CI: 7.68%-22.40%) to 19.14% (95% CI: 15.51%-22.77%), depending on region. The global pooled seroprevalence of coxiellosis in goats was 22.60% (95% CI: 19.54%-25.66%). Overall, the regional level pooled prevalence estimates in goats ranged from 6.33% (95% CI: 2.96%-9.71%) to 55.13% (95% CI: 49.61%-60.65%), depending on the region. The prevalence estimates also varied significantly in both sheep and goats depending on age, sex, and rearing systems of the animals (p < 0.001).

CONCLUSION

Seroprevalence of coxiellosis in both sheep and goats is considerable. Routine monitoring of the sheep and goat populations is needed to prevent spillover infection in other livestock and humans.

Coxiella burnetii infection persistence in a goat herd during seven kidding seasons after an outbreak of abortions: the effect of vaccination

Coxiella burnetii infection was monitored during seven kidding seasons (2017-2023) in a dairy goat herd that after an outbreak of Q fever abortions was vaccinated with an inactivated phase I vaccine. Due to the high infection rate just after the outbreak, only the replacement stock was vaccinated during the first three kidding seasons, and when the average herd immunity had decreased (fourth kidding season onwards), the whole herd was vaccinated. Vaginal swabs, feces, and milk were analyzed by PCR to monitor infection, and dust and aerosols were analyzed to measure C. burnetii environmental contamination. One year after the onset of the outbreak, a significant reduction in C. burnetii shedding loads was observed, but the percentage of shedding animals remained high until the third kidding season. By the seventh kidding season, no shedders were detected. The bacterial load excreted was significantly lower in vaccinated compared with unvaccinated animals, and in yearlings compared with multiparous. C. burnetii was detected by PCR in aerosols collected inside the animal premises throughout the study period except in the last season; whereas, aerosols collected outdoors tested negative in the last three kidding seasons. Viable C. burnetii was detectable in environmental dust collected inside the barn until the third kidding season following the outbreak. These results indicate that after an outbreak of Q fever, the risk of infection for humans and susceptible animals can remain high for at least three kidding seasons when the number of C. burnetii animal shedders is still high, even when bacterial excretion is low.

IMPORTANCE

Q fever is a zoonosis distributed worldwide. Ruminants are the main reservoir, and infection can cause high rates of abortion. After entering a farm, Coxiella burnetii infection can persist in the animal population over several lambing/kidding periods. Once infection is established in a herd, vaccination with the inactivated Phase I vaccine significantly reduces bacterial shedding, but although at low levels, excretion may continue to occur for several lambing/kidding seasons. The time that C. burnetii remains viable in the farm environment after an outbreak of Q fever determines the period when risk of infection is high for the people in close contact. This work showed that this period extends at least three kidding seasons after the outbreak. These results provided valuable information on the epidemiology of C. burnetii infection in goat herds and may help to develop guidelines for controlling the disease and reducing infection risk for susceptible people and animals.

Tick-borne pathogens in camels: A systematic review and meta-analysis of the prevalence in dromedaries

Published data on tick-borne pathogens (TBPs) in camels worldwide have been collected to provide an overview of the global prevalence and species diversity of camelid TBPs. Several TBPs have been detected in dromedary camels, raising concerns regarding their role as natural or maintenance hosts for tick-borne pathogens. Insubstantial evidence exists regarding the natural infection of camels with Babesia spp., Theileria spp., Anaplasma spp., and Ehrlichia spp., particularly because most of the camels were considered healthy at the time of sampling. Based on polymerase chain reaction (PCR) testing, a pooled prevalence of 35.3% (95% CI: 22.6-48.1%) was estimated for Anaplasma, which was the most frequently tested TBP in dromedaries, and DNA of Anaplasma marginale, Anaplasma centrale, Anaplasma ovis, Anaplasma platys, and A. platys-like were isolated, of which ruminants and dogs are reservoirs. Similarly, the estimated pooled prevalence for the two piroplasmid genera; Babesia and Theileria was approximately equal (10-12%) regardless of the detection method (microscopy or PCR testing). Nevertheless, Babesia caballi, Theileria equi, and Theileria annulata DNA have frequently been detected in camels but they have not yet been proven to be natural hosts. Scarce data detected Babesia microti, Anaplasma phagocytophilum, and Borrelia burgdorferi sensu lato (s.l.) DNA in blood of dromedaries, although ticks of the genus Ixodes are distributed in limited areas where dromedaries are raised. Interestingly, a pooled seroprevalence of 47.7% (26.3-69.2%) was estimated for Crimean-Congo hemorrhagic fever virus, and viral RNA was detected in dromedary blood; however, their contribution to maintain the viral transmission cycles requires further experimental investigation. The substantially low incidence and scarcity of data on Rickettsia and Ehrlichia species could imply that camels were accidentally infected. In contrast, camels may play a role in the spread of Coxiella burnetii, which is primarily transmitted through the inhalation of aerosols emitted by diseased animals and contaminated environments. Bactrian camels showed no symptoms due to the examined TBPs, meanwhile, clinical disease was seen in alpacas infected with A. phagocytophilum. Similar to dromedaries, accidental tick bites may be the cause of TBP DNA found in the blood of Bactrian camels.

Persistence of obligate intracellular pathogens: alternative strategies to overcome host-specific stresses

In adapting to the intracellular niche, obligate intracellular bacteria usually undergo a reduction of genome size by eliminating genes not needed for intracellular survival. These losses can include, for example, genes involved in nutrient anabolic pathways or in stress response. Living inside a host cell offers a stable environment where intracellular bacteria can limit their exposure to extracellular effectors of the immune system and modulate or outright inhibit intracellular defense mechanisms. However, highlighting an area of vulnerability, these pathogens are dependent on the host cell for nutrients and are very sensitive to conditions that limit nutrient availability. Persistence is a common response shared by evolutionarily divergent bacteria to survive adverse conditions like nutrient deprivation. Development of persistence usually compromises successful antibiotic therapy of bacterial infections and is associated with chronic infections and long-term sequelae for the patients. During persistence, obligate intracellular pathogens are viable but not growing inside their host cell. They can survive for a long period of time such that, when the inducing stress is removed, reactivation of their growth cycles resumes. Given their reduced coding capacity, intracellular bacteria have adapted different response mechanisms. This review gives an overview of the strategies used by the obligate intracellular bacteria, where known, which, unlike model organisms such as E. coli, often lack toxin-antitoxin systems and the stringent response that have been linked to a persister phenotype and amino acid starvation states, respectively.

Tracking the Source of Human Q Fever from a Southern French Village: Sentinel Animals and Environmental Reservoir

Coxiella burnetii, also known as the causal agent of Q fever, is a zoonotic pathogen infecting humans and several animal species. Here, we investigated the epidemiological context of C. burnetii from an area in the Hérault department in southern France, using the One Health paradigm. In total, 13 human cases of Q fever were diagnosed over the last three years in an area comprising four villages. Serological and molecular investigations conducted on the representative animal population, as well as wind data, indicated that some of the recent cases are likely to have originated from a sheepfold, which revealed bacterial contamination and a seroprevalence of 47.6%. However, the clear-cut origin of human cases cannot be ruled out in the absence of molecular data from the patients. Multi-spacer typing based on dual barcoding nanopore sequencing highlighted the occurrence of a new genotype of C. burnetii. In addition, the environmental contamination appeared to be widespread across a perimeter of 6 km due to local wind activity, according to the seroprevalence detected in dogs (12.6%) and horses (8.49%) in the surrounding populations. These findings were helpful in describing the extent of the exposed area and thus supporting the use of dogs and horses as valuable sentinel indicators for monitoring Q fever. The present data clearly highlighted that the epidemiological surveillance of Q fever should be reinforced and improved.

The relevance of the wild reservoir in zoonotic multi-host pathogens: The links between Iberian wild mammals and Coxiella burnetii

Q fever is a worldwide zoonosis caused by an obligate intracellular bacterium, Coxiella burnetii, with only anecdotal reports of human-to-human transmission. The cause of human Q fever infections is the circulation of C. burnetii in animal reservoirs. Infected livestock, particularly goats and sheep, may cause Q fever outbreaks in humans. However, wildlife is the origin of several human Q fever cases. Human impacts on habitats, biodiversity and climate are responsible for changes in the patterns of interaction between domestic animals, wildlife and humans, allowing wild animals to play an increasingly relevant role as Q fever reservoirs. In the Iberian Peninsula, human impacts on the environment combined with a high biodiversity, which could maintain high transmission rates of this multi-host pathogen, make wild reservoirs an important piece in Q fever epidemiology. In this study, we review the reporting of C. burnetii infections and exposure in Iberian wild mammals and analyse the link between the diversity of wild mammals and the frequency of C. burnetii notifications in wildlife. For it, the number of wild mammal species per UTM 10 × 10-km grid in mainland Spain and Portugal was estimated as a potential predictor of C. burnetii transmission. The results of non-linear regression analysis showed a quadratic relationship between the number of wild mammal species per grid and the presence of C. burnetii cases reported in the literature both by serology (R²  = 0.86) and polymerase chain reaction (R²  = 0.83). Increasing wild mammal diversity was linked to increasing C. burnetii transmission until an intermediate level when the relationship was inverted. Thus, at high levels of wild mammal diversity, the risk of C. burnetii transmission was lower. These observations show a role of wild mammal biodiversity in C. burnetii ecology that needs to be further explored to better prevent the negative impact of Q fever in livestock and human health in Iberia.

Performance Evaluation and Validation of Air Samplers To Detect Aerosolized Coxiella burnetii

Coxiella burnetii, the etiological agent of Q fever, is an intracellular zoonotic pathogen transmitted via the respiratory route. Once released from infected animals, C. burnetii can travel long distances through air before infecting another host. As such, the ability to detect the presence of C. burnetii in air is important. In this study, three air samplers, AirPort MD8, BioSampler, and the Coriolis Micro, were assessed against a set of predetermined criteria in the presence of three different aerosolized C. burnetii concentrations. Two liquid collection media, phosphate-buffered saline (PBS) and alkaline polyethylene glycol (Alk PEG), were tested with devices requiring a collection liquid. Samples were tested by quantitative polymerase chain reaction assay (qPCR) targeting the single-copy com1 gene or multicopy insertion element IS1111. All air samplers performed well at detecting airborne C. burnetii across the range of concentrations tested. At high nebulized concentrations, AirPort MD8 showed higher, but variable, recovery probabilities. While the BioSampler and Coriolis Micro recovered C. burnetii at lower concentrations, the replicates were far more repeatable. At low and intermediate nebulized concentrations, results were comparable in the trials between air samplers, although the AirPort MD8 had consistently higher recovery probabilities. In this first study validating air samplers for their ability to detect aerosolized C. burnetii, we found that while all samplers performed well, not all samplers were equal. It is important that these results are further validated under field conditions. These findings will further inform efforts to detect airborne C. burnetii around known point sources of infection. IMPORTANCE Coxiella burnetii causes Q fever in humans and coxiellosis in animals. It is important to know if C. burnetii is present in the air around putative sources as it is transmitted via inhalation. This study assessed air samplers (AirPort MD8, BioSampler, and Coriolis Micro) for their efficacy in detecting C. burnetii. Our results show that all three devices could detect aerosolized bacteria effectively; however, at high concentrations the AirPort performed better than the other two devices, showing higher percent recovery. At intermediate and low concentrations AirPort detected at a level higher than or similar to that of other samplers. Quantification of samples was hindered by the limit of quantitation of the qPCR assay. Compared with the other two devices, the AirPort was easier to handle and clean in the field. Testing air around likely sources (e.g., farms, abattoirs, and livestock saleyards) using validated sampling devices will help better estimate the risk of Q fever to nearby communities.

Analysis of environmental dust in goat and sheep farms to assess Coxiella burnetii infection in a Q fever endemic area: Geographical distribution, relationship with human cases and genotypes

Real-time PCR analysis of environmental samples (dust and aerosols) is an easy tool to investigate the presence of Coxiella burnetii in the farm environment. The aim of this study was to assess the distribution of C. burnetii DNA in dust collected inside animal premises from 272 small ruminant farms in Bizkaia (northern Spain), a region with recent reports of human Q fever cases and outbreaks. Within each farm, 5 samples of dust were collected from difference surfaces, and data on animal census, management procedures, characteristics of the premises and geographic location were collected. Real-time PCR analysis of the dust samples detected presence of C. burnetii DNA in 98 farms (36.0%), flock-prevalence being higher in sheep (38.9%) or mixed ovine-caprine production systems (36.8%), compared to goats (25.0%). Larger bacterial burdens were observed in mixed farms, compared to sheep (p < .05). Single nucleotide polymorphism (SNP) analysis identified 5 different genotypes, with SNP8 being the predominant genotype (73%), followed by SNP6 (11%), SNP2 (9%), SNP4 (5%) and SNP1 (2%). Proportion of farms where C. burnetii DNA was detected differed among the different agricultural counties, and a higher proportion of C. burnetii DNA positive farms was associated with the occurrence of recent human Q fever outbreaks at several geographical locations. Dust sampling in domestic ruminant farms coupled with real-time PCR to screen for the presence of C. burnetii and estimate bacterial load can be a useful tool to identify herds and regions with high prevalence, define priority actions and monitor the effect of control measures. If combined with molecular genotyping and spatial distribution maps, it can help to identify farm contamination sources and trace the origin of human outbreaks.

Geographical Variation in Coxiella burnetii Seroprevalence in Dairy Farms Located in South-Western Ethiopia: Understanding the Broader Community Risk

Q fever is a zoonotic disease that is caused by Coxiella burnetii and leads to abortion and infertility in ruminants and debilitating disease in humans. Jimma zone, including Jimma town, located in the Oromia region of Ethiopia, was affected by an outbreak of abortions in ruminants related to Q fever infection between 2013 and 2015. This study aimed to investigate the geo-clustering of C. burnetii seroprevalence in dairy farms of Jimma town and identify the environmental risk factors associated with seroprevalence distribution. A total of 227 cattle were tested for antibodies against C. burnetii in 25 farms. We explored the clustering of C. burnetii seroprevalence using semivariograms. A geostatistical regression-based model was implemented to quantify the risk factors and to predict the geographical variation in C. burnetii seroprevalence at unsampled locations in Jimma town using OpenBugs. Our results demonstrated that the risk of exposure in dairy cattle varied across the landscape of Jimma town and was associated with environmental risk factors. The predictive map of C. burnetii seroprevalence showed that communities in the eastern part of Jimma town had the highest risk of exposure. Our results can inform community-level investigations of human seroprevalence in the high-risk areas to the east of Jimma.