Q fever, a disease caused by Coxiella burnetii bacteria, is typically described as an asymptomatic infection; however, symptoms may arise over time due to an acute self-limiting infection or a chronic and persistent infection with potentially lethal outcomes (1). By persisting inside phagolysosomal cells over time, C. burnetii is associated with vascular injury in cardiac patients (2). Infection primarily occurs as a consequence of contact with an infected animal, inhalation of contaminated aerosols, or, to a lesser degree, consumption of contaminated raw milk, contact with fomites, and tick bites (1). The transmission route and individual susceptibility affect the infectious dose and subsequent disease progression (3).

Domestic ruminants, including goats, sheep, and cattle, have been well established as playing an important role in the C. burnetii zoonotic cycle, primarily due to high levels of human contact compared to other livestock species (4, 5). In addition to ruminants, several other mammalian species, particularly rodents, birds, and reptiles, may act as reservoirs, with natural C. burnetii infections already described in more than 100 wildlife species (6, 7). Although the small sample sizes of such studies strongly limit clinical conclusions, some ruminants and sea lions have presented symptoms of reproductive failure (8).

Q fever remains a globally underestimated disease, particularly in developing countries where surveillance and reporting systems may be limited (9). It is classified as a notifiable disease in many regions, including the EU/EEA and other countries such as Australia, where public health authorities require reporting of confirmed cases (10). However, despite this notifiable status, subnotification is a persistent challenge. Although outbreaks of Q fever are relatively rare, they can occur, especially in areas with high concentrations of livestock, such as farms or rural communities. One of the most significant outbreaks took place in the Netherlands between 2007 and 2010, resulting in over 4,000 human cases (11). Although Q fever is not considered a notifiable disease worldwide (12), information on this disease in Europe can be obtained at the European Center for Disease Control (13). In addition, C. burnetii exposure has been increasingly reported in the Americas, including Brazil, through serological surveys and retrospective hospital studies (1). Brazilian indigenous populations have shown a significantly higher frequency of C. burnetii in communities located in natural forests with hunting practices (14). Interestingly, hunting dogs from Australian Aboriginal villages are more likely to be seropositive than house and shelter dogs (15).

Wildlife is home to countless microorganisms that may evade or overcome the human immune response (16). In addition, the invasion, fragmentation, and deforestation of natural forest areas—aggravated by ecological imbalances and climate change—may lead to increased overlap among humans, livestock, wildlife, and their vectors, thus heightening the likelihood of disease exposure, infection, and transmission (16). Studies have shown exposure to C. burnetii among professionals in direct contact with wildlife, such as wildlife rehabilitators in Australia (17), forestry workers in Poland (18) and Italy (19), and veterinarians worldwide (20–25). Although occupational exposure to C. burnetii has been studied, the zoonotic risk in wildlife environments remains unclear and needs further establishment. Accordingly, the present study aimed to serologically assess professionals with daily contact with free-living and captive wildlife for C. burnetii, along with potential associated risk factors.

Overall, 25 out of 309 (8.09%; 95% confidence interval: 5.54–11.67) wildlife professionals were seropositive for C. burnetii, including 6/54 (11.1%) national and 7/125 (5.6%) state park employees and 6/92 (6.5%) zookeepers and 6/38 (15.8%) animal service workers, with titers ranging from 32 to 128. Two zoo professionals in this study reached titers of 1:128, whereas the other seropositive professionals had titers of 1:64. Variables that were statistically associated with seropositivity included sex, age, job position, forest access, forest access frequency, tick bites, consumption of raw or undercooked meat, and contact with abortion remains (Table 2). However, owing to the low C. burnetii seropositivity and limited statistical power, the associated risk factors could not be thoroughly assessed. No statistically significant associations were found between C. burnetii seropositivity and sex (p = 0.4440), age (p = 0.7636), job position (p = 0.3373), forest access (p = 0.4685), forest access frequency (p = 0.7472), tick bites (p = 0.7106), consumption of raw or undercooked meat (p = 0.1880), or contact with abortion remains (p = 0.9838).

This study presents the first serological investigation of C. burnetii in wildlife professionals in Brazil, including park rangers, zookeepers, and animal service workers. Wildlife may serve as a source of exposure for professionals worldwide, as C. burnetii has been detected in tissue samples of 5.1% of roe deer (Capreolus capreolus), 4.3% of wild boars (Sus scrofa), 9.1% of European hares (Lepus europaeus), 11% of vultures (Gyps fulvus), and 14% of black kites (Milvus migrans) in northern Spain (29). In addition, a study in a Q fever-endemic area of Cyprus detected C. burnetii in mouflons (23/74), foxes (9/32), hares (15/31), and birds (41/131), with 56/195 (28.9%) infected ticks (30) and molecular detection in 12% of rat fleas and 47.6% of fox fleas (31). Although only a few studies of C. burnetii have been conducted in Brazil, molecular detection has been reported in 6/131 (4.6%) wild rodents in southeastern Brazil (32), 4/21 (19.0%) non-hematophagous bats in northeastern Brazil (28), and 9/169 (5.32%) deer in southeastern and central-western Brazil (33).

Studies on C. burnetii exposure among wildlife professionals have been conducted worldwide (17–19, 34). In Australia, 9/147 (6.1%) unvaccinated wildlife rehabilitators were seropositive, and Q fever vaccination was recommended because of its endemicity in this country (17). In Italy, 5/181 (2.8%) forestry rangers with a recent history of tick bites presented antibodies against C. burnetii (19). In Poland, 14/216 (6.4%) employees of National Forests were seropositive, suggesting high contact with C. burnetii-infected ticks in the study area (18). Active forestry workers showed a higher rate of previous exposure to C. burnetii (13/202; 6.4%) compared with that of supervisory forestry staff and muskrat catchers (4/110; 3.6%) in the Netherlands (34). Despite the limited sample size, national park employees (6/54; 11.1%) and animal service workers (6/38; 15.8%) showed higher seropositivity for C. burnetii, which may be associated with spending more time outdoors in wildlife environments and/or direct contact with animals, compared with that of state park employees (7/125; 5.6%) and zookeepers (6/92; 6.5%). Thus, further studies should be conducted with larger sample sizes and different populations of wildlife professionals to fully establish the impact of C. burnetii as an occupational risk associated with wildlife environments worldwide.

Given that human seroprevalence of C. burnetii in most countries has been reported to be low (12), this study revealed a higher overall seropositivity, which may have resulted from contact with wildlife. Nonetheless, the routes of transmission and elimination in wildlife remain unclear, as C. burnetii may behave differently depending on the host animal species, a topic that has not been widely studied to date.

Recent surveys of asymptomatic human populations in Brazil showed seroprevalence rates ranging from 3.2 to 4.5% (1, 35), as well as rates of 1/18 (5.5%) police officers, 8/893 (0.9%) indigenous individuals, and 44/200 (22.0%) quilombola individuals in Paraná State, most of whom live in rural areas near cattle farms (14, 36, 37). Although the relatively high seropositivity observed in the present study suggests that wildlife is an alternative source of human infection, no statistically significant associated risk factors were confirmed, including job position. Given that previous Brazilian studies with higher seropositivity involved individuals at occupational risk, further studies are needed to fully establish the role of wildlife in human infections.

Although this was a prevalence study in asymptomatic human populations, these individuals may develop persistent infections, and C. burnetii can be reactivated under immunosuppressive conditions. Serious complications, such as endocarditis, hepatitis, and meningitis, may occur (2, 38, 39), with one patient with Q fever in Brazil presenting with thrombocytosis and a 40-d fever (40).

Samples from zoo workers were collected at the end of the COVID-19 pandemic using epidemiological questionnaires focused on febrile symptoms. Individuals presenting with flu-like symptoms mostly tested negative for COVID-19. Of the 6/92 (6.5%) C. burnetiid-seropositive individuals, five experienced flu-like symptoms similar to Q fever, and four tested negative for COVID-19. Because such data were not available for other locations, no statistical analysis could be performed.

General preventive measures against C. burnetii infection have mostly focused on animal transmission. These measures include avoiding contact with animals, particularly during delivery and birth, even if the animals appear healthy, and avoiding the consumption of raw milk or raw milk products (41). For individuals in contact with wildlife, the infection risk may be effectively reduced through a set of measures, such as vaccination (which is not currently available in Brazil), proper manure and shearing management, isolation of breeding areas when sick animals are present, proper disposal of risk materials, limiting visitor and unsafe contact, controlling domestic and wild mammal reservoirs, and tick control (42). In addition, effective preventive measures may require continuous passive and active surveillance through a unified and accessible database shared by public health and veterinary services. This should be complemented by environmental and worker health monitoring, along with oversight of wildlife-livestock-periurban interfaces and relevant organizations. Such measures would assist in the prompt identification of this and other reemerging and novel pathogens, aiding in outbreak management, control, and prevention (43).

The present study did not evaluate the serum of both captive and free-living animals, primarily because of the difficulty of establishing specific conjugates for each animal species, as well as the high non-specificity of immunofluorescence conjugates used in wildlife investigations. Thus, currently available serological tests should be optimized and validated for each wildlife species before testing. Additionally, these species require specific handling, restraints, and anesthesia for safe sample collection. Nonetheless, future studies should include testing of these animals, particularly for acute and chronic symptoms, such as reproductive and respiratory disorders, which may be associated with Q fever. Such concurrent serological and molecular surveys involving wildlife professionals and the wildlife species they routinely handle could provide a One Health approach, determining whether exposure occurs and, if so, at what level of job position, location, and wildlife species contact. Finally, wildlife should always be considered as a potential source of C. burnetii transmission to both domestic animals (companion and livestock) and humans, particularly in areas that overlap with or are adjacent to wildlife habitats.

This study is the first serological investigation of C. burnetii in park rangers, zookeepers, and animal service workers in Brazil, with an overall seroprevalence of 8.1% and no associated risk factors for seropositivity. Given that the seroprevalence in this study was higher than that reported in previous surveys of healthy (asymptomatic) human populations, C. burnetii exposure may also represent an occupational risk for wildlife professionals in contact with natural environments in Brazil.