Wild boar populations are increasing across Brazil, raising concerns that these animals may pose risks beyond agricultural damage. A new study from Goiás State has found that commercially raised wild boars carry high levels of antibiotic-resistant bacteria, highlighting a potential public health concern.
Scientists have long suspected that farmed wild boars could serve as reservoirs for antimicrobial-resistant microbes. However, evidence from Brazilian commercial farms has been limited, leaving uncertainty about the extent of the problem.
How the study was conducted
Researchers collected rectal swab samples from 100 apparently healthy European wild boars raised on two commercial farms in central Brazil.
The samples were tested for Salmonella and Escherichia coli (E. coli) and evaluated against a panel of commonly used antibiotics to determine resistance patterns.
The researchers also screened the bacteria for virulence genes—genetic traits that help bacteria attach to host tissues, survive within the body and cause disease. Their aim was to assess not only antimicrobial resistance but also the bacteria’s potential to cause infections.
Multidrug-resistant E. coli was widespread
Only one animal tested positive for Salmonella, suggesting that this pathogen posed a relatively low immediate risk within the study population.
The findings for E. coli, however, were markedly different. The bacterium was isolated from 56 of the 100 wild boars.
Among those isolates, 55 met the definition of multidrug resistance, meaning they were resistant to antibiotics belonging to multiple drug classes.
The highest levels of resistance were observed for sulfonamides, tetracycline, amoxicillin, ampicillin and doxycycline, antibiotics that are widely used in both veterinary and human medicine.
Most bacterial isolates remained susceptible to ceftriaxone, an important antibiotic frequently reserved for serious human infections. Nevertheless, the researchers caution that even limited resistance to critically important antibiotics warrants ongoing surveillance.
Disease-causing genes raise additional concerns
The team also searched for genes associated with bacterial virulence.
Nearly 30 percent of the E. coli isolates carried the tsh gene, which helps bacteria adhere to host tissues.
Smaller numbers of isolates contained the papC and iss genes, which are associated with urinary tract colonization and survival within the bloodstream.
Several bacterial strains carried more than one virulence gene, suggesting they may have an increased capacity to cause disease under favorable conditions.
Where the resistance may originate
According to farm managers, antibiotics were not routinely administered to the animals.
This suggests that the observed resistance may have developed through environmental exposure rather than direct antibiotic use on the farms.
Antibiotic residues and resistance genes can persist in soil and water for extended periods, where they continue circulating among environmental bacteria.
Bacteria can also exchange resistance genes through mobile genetic elements, allowing antimicrobial resistance to spread rapidly between different bacterial species.
Because wild boars move freely between forests, farmland and areas influenced by human activity, they regularly encounter livestock, wildlife and contaminated environments, creating numerous opportunities for resistant bacteria to spread between ecosystems.
One Health implications
The findings support the importance of the One Health approach, which recognizes that human, animal and environmental health are closely interconnected.
Rather than viewing antimicrobial resistance solely as a medical problem, One Health emphasizes monitoring how resistant bacteria and resistance genes circulate among animals, humans and the environment.
As commercial wild boar farming expands and escaped animals contribute to growing feral populations, these animals may become increasingly important reservoirs of antimicrobial-resistant bacteria.
The researchers argue that captive wild boars should be incorporated into Brazil’s national antimicrobial resistance surveillance programs.
European wild boars are not native to South America. They were introduced primarily for hunting during the early twentieth century and have since hybridized with domestic pigs while spreading across much of Brazil. Forest fragments provide shelter, while nearby agricultural fields, including corn and sugarcane plantations, offer abundant food resources.
The study analyzed samples collected between 2014 and 2017 and has several limitations, including the small number of farms and reliance on farm managers’ reports regarding antibiotic use. Nevertheless, it provides some of the first detailed evidence of antimicrobial resistance patterns in Brazil’s commercial wild boar industry and highlights that addressing antimicrobial resistance requires surveillance well beyond hospitals and healthcare settings.
