Identification of Brucella spp. in feral swine (Sus scrofa) at abattoirs in Texas, USA

Disease Progression and Serological Assay Performance in Heritage Breed Pigs following Brucella suis Experimental Challenge as a Model for Naturally Infected Feral Swine

Invasive feral swine (Sus scrofa) are one of the most important wildlife species for disease surveillance in the United States, serving as a reservoir for various diseases of concern for the health of humans and domestic animals. Brucella suis, the causative agent of swine brucellosis, is one such pathogen carried and transmitted by feral swine. Serology assays are the preferred field diagnostic for B. suis infection, as whole blood can be readily collected and antibodies are highly stable. However, serological assays frequently have lower sensitivity and specificity, and few studies have validated serological assays for B. suis in feral swine. We conducted an experimental infection of Ossabaw Island Hogs (a breed re-domesticated from feral animals) as a disease-free proxy for feral swine to (1) improve understanding of bacterial dissemination and antibody response following B. suis infection and (2) evaluate potential changes in the performance of serological diagnostic assays over the course of infection. Animals were inoculated with B. suis and serially euthanized across a 16-week period, with samples collected at the time of euthanasia. The 8% card agglutination test performed best, whereas the fluorescence polarization assay demonstrated no capacity to differentiate true positive from true negative animals. From a disease surveillance perspective, using the 8% card agglutination test in parallel with either the buffered acidified plate antigen test or the Brucella abortus/suis complement fixation test provided the best performance with the highest probability of a positive assay result. Application of these combinations of diagnostic assays for B. suis surveillance among feral swine would improve understanding of spillover risks at the national level.

Integrated Bioinformatics-Based Subtractive Genomics Approach to Decipher the Therapeutic Drug Target and Its Possible Intervention against Brucellosis

Brucella suis, one of the causative agents of brucellosis, is Gram-negative intracellular bacteria that may be found all over the globe and it is a significant facultative zoonotic pathogen found in livestock. It may adapt to a phagocytic environment, reproduce, and develop resistance to harmful environments inside host cells, which is a crucial part of the Brucella life cycle making it a worldwide menace. The molecular underpinnings of Brucella pathogenicity have been substantially elucidated due to comprehensive methods such as proteomics. Therefore, we aim to explore the complete Brucella suis proteome to prioritize the novel proteins as drug targets via subtractive proteo-genomics analysis, an effort to conjecture the existence of distinct pathways in the development of brucellosis. Consequently, 38 unique metabolic pathways having 503 proteins were observed while among these 503 proteins, the non-homologs (n = 421), essential (n = 350), drug-like (n = 114), virulence (n = 45), resistance (n = 42), and unique to pathogen proteins were retrieved from Brucella suis. The applied subsequent hierarchical shortlisting resulted in a protein, i.e., isocitrate lyase, that may act as potential drug target, which was finalized after the extensive literature survey. The interacting partners for these shortlisted drug targets were identified through the STRING database. Moreover, structure-based studies were also performed on isocitrate lyase to further analyze its function. For that purpose, ~18,000 ZINC compounds were screened to identify new potent drug candidates against isocitrate lyase for brucellosis. It resulted in the shortlisting of six compounds, i.e., ZINC95543764, ZINC02688148, ZINC20115475, ZINC04232055, ZINC04231816, and ZINC04259566 that potentially inhibit isocitrate lyase. However, the ADMET profiling showed that all compounds fulfill ADMET properties except for ZINC20115475 showing positive Ames activity; whereas, ZINC02688148, ZINC04259566, ZINC04232055, and ZINC04231816 showed hepatoxicity while all compounds were observed to have no skin sensitization. In light of these parameters, we recommend ZINC95543764 compound for further experimental studies. According to the present research, which uses subtractive genomics, proteins that might serve as therapeutic targets and potential lead options for eradicating brucellosis have been narrowed down.

Transmission of antibiotic resistance at the wildlife-livestock interface

Antibiotic-resistant microorganisms (ARMs) are widespread in natural environments, animals (wildlife and livestock), and humans, which has reduced our capacity to control life threatening infectious disease. Yet, little is known about their transmission pathways, especially at the wildlife-livestock interface. This study investigated the potential transmission of ARMs and antibiotic resistance genes (ARGs) between cattle and wildlife by comparing gut microbiota and ARG profiles of feral swine (Sus scrofa), coyotes (Canis latrans), cattle (Bos taurus), and environmental microbiota. Unexpectedly, wild animals harbored more abundant ARMs and ARGs compared to grazing cattle. Gut microbiota of cattle was significantly more similar to that of feral swine captured within the cattle grazing area where the home range of both species overlapped substantially. In addition, ARMs against medically important antibiotics were more prevalent in wildlife than grazing cattle, suggesting that wildlife could be a source of ARMs colonization in livestock.

Analysis of microbiome data from feral swine, coyotes, domesticated cattle, and the surrounding environment reveals that wild animals harbor more abundant antibiotic-resistant organisms than livestock, and might act as a source of antibiotic-resistant microbes in outbreaks.

Brucella suis and farm biosecurity: assessing risk in pigs raised outdoors in New York State

OBJECTIVE

To evaluate the Brucella suis exposure status of pigs raised with outdoor access on farms in New York State and assess biosecurity and management practices of those farms.

ANIMALS

250 pigs that were raised for commercial purposes, had access to the outdoors, and were > 4 months of age on 24 farms in New York State.

PROCEDURES

Farms were randomly selected from a sampling frame generated for the study and contacted to recruit them to participate. Participating farms were provided a questionnaire to complete. Up to 30 pigs per farm were tested for serum anti-Brucella antibodies.

RESULTS

Farm were classified as seasonal and year round. Seasonal farms raised pigs for slaughter, and year-round farms bred pigs, raised them for slaughter, and sold live pigs to others to raise. None of the 250 pigs had antibodies to Brucella spp. Nevertheless, the biosecurity assessment revealed a need for enhanced practices in procurement and management of swine in a wide range of areas.

CLINICAL RELEVANCE

There was no evidence for ongoing B suis infection on these swine farms in New York State, but biosecurity and preventive practices at these facilities could be improved to prevent the introduction and spread of B suis and other pathogens.

Dispersal and Land Cover Contribute to Pseudorabies Virus Exposure in Invasive Wild Pigs

We investigated the landscape epidemiology of a globally distributed mammal, the wild pig (Sus scrofa), in Florida (U.S.), where it is considered an invasive species and reservoir to pathogens that impact the health of people, domestic animals, and wildlife. Specifically, we tested the hypothesis that two commonly cited factors in disease transmission, connectivity among populations and abundant resources, would increase the likelihood of exposure to both pseudorabies virus (PrV) and Brucella spp. (bacterial agent of brucellosis) in wild pigs across the Kissimmee Valley of Florida. Using DNA from 348 wild pigs and sera from 320 individuals at 24 sites, we employed population genetic techniques to infer individual dispersal, and an Akaike information criterion framework to compare candidate logistic regression models that incorporated both dispersal and land cover composition. Our findings suggested that recent dispersal conferred higher odds of exposure to PrV, but not Brucella spp., among wild pigs throughout the Kissimmee Valley region. Odds of exposure also increased in association with agriculture and open canopy pine, prairie, and scrub habitats, likely because of highly localized resources within those land cover types. Because the effect of open canopy on PrV exposure reversed when agricultural cover was available, we suggest that small-scale resource distribution may be more important than overall resource abundance. Our results underscore the importance of studying and managing disease dynamics through multiple processes and spatial scales, particularly for non-native pathogens that threaten wildlife conservation, economy, and public health.

Loci Associated With Antibody Response in Feral Swine (Sus scrofa) Infected With Brucella suis

Feral swine (Sus scrofa) are a destructive invasive species widespread throughout the United States that disrupt ecosystems, damage crops, and carry pathogens of concern for the health of domestic stock and humans including Brucella suis-the causative organism for swine brucellosis. In domestic swine, brucellosis results in reproductive failure due to abortions and infertility. Contact with infected feral swine poses spillover risks to domestic pigs as well as humans, companion animals, wildlife, and other livestock. Genetic factors influence the outcome of infectious diseases; therefore, genome wide association studies (GWAS) of differential immune responses among feral swine can provide an understanding of disease dynamics and inform management to prevent the spillover of brucellosis from feral swine to domestic pigs. We sought to identify loci associated with differential antibody responses among feral swine naturally infected with B. suis using a case-control GWAS. Tissue, serum, and genotype data (68,516 bi-allelic single nucleotide polymorphisms) collected from 47 feral swine were analyzed in this study. The 47 feral swine were culture positive for Brucella spp. Of these 47, 16 were antibody positive (cases) whereas 31 were antibody negative (controls). Single-locus GWAS were performed using efficient mixed-model association eXpedited (EMMAX) methodology with three genetic models: additive, dominant, and recessive. Eight loci associated with seroconversion were identified on chromosome 4, 8, 9, 10, 12, and 18. Subsequent bioinformatic analyses revealed nine putative candidate genes related to immune function, most notably phagocytosis and induction of an inflammatory response. Identified loci and putative candidate genes may play an important role in host immune responses to B. suis infection, characterized by a detectable bacterial presence yet a differential antibody response. Given that antibody tests are used to evaluate brucellosis infection in domestic pigs and for disease surveillance in invasive feral swine, additional studies are needed to fully understand the genetic component of the response to B. suis infection and to more effectively translate estimates of Brucella spp. antibody prevalence among feral swine to disease control management action.

Influence of species of negative control sera on results of a brucellosis fluorescence polarization assay

We evaluated serologic responses of cattle, bison, elk, and swine representing negative control, early vaccination (4-8 wk), late vaccination (21-28 wk) or booster vaccination, early after-experimental challenge (2-4 wk), and late after-experimental challenge (8-21 wk), in a brucellosis fluorescence polarization assay (FPA; n = 10 sera per species per treatment) using negative control sera from cattle, bison, elk, and swine (n = 5 per species). Sera from cattle shedding Brucella abortus strain RB51 in milk were also evaluated against the 20 negative control sera. The species of negative control sera used in the FPA could increase (p < 0.05) delta millipolarization (mP; delta mP = sample mP - negative control mP) results. In general, the species of negative control sera did not alter the interpretation of FPA results in control, vaccinated, or infected animals. Even after repeated RB51 vaccinations in bison, cattle, or elk, or in cattle shedding RB51 in milk, serologic results from the FPA remained negative. Species differences in FPA results were noted; elk developed robust humoral responses very quickly after infection that resulted in strong positive FPA results. In cattle and bison, humoral responses appeared to develop over a longer period of time, and greater delta mP values were detected at later times after infection. Sensitivity of the FPA for detecting infected animals was greatest for elk in early challenge samples and bison in late challenge samples. Our data suggest that species of origin of negative control sera does not influence interpretation of the FPA in natural hosts of Brucella abortus.

Framework for assessing vertebrate invasive species damage: the case of feral swine in the United States

The aim of this study is to provide a general overview of the economic impacts associated with vertebrate invasive species (VIS) in the United States and suggests a methodology for differentiating types of damage. We identify a general framework for categorizing VIS damage that separates this damage into three main categories: destruction, depredation, and disease. We then examine how this framework fits into current published estimates of damage and management costs. Economic impacts associated with feral swine damage and management are plentiful enough to warrant separate treatment from other VIS and are observed in all three categories. For all VIS examined in this study, damage estimates associated with destruction provide the most evaluations of VIS impacts, especially destruction of crops. Evaluations of the losses associated with depredation are largely absent from the literature. We find that while published studies have estimated substantial economic impact associated with VIS, the current state of the literature focusing on VIS frequently fails to address all of the categories of damage, is difficult to compare or replicate, and is unsuited for extrapolation to nation-wide estimates of damage.

Vaccine safety studies of Brucella abortus S19 and S19ΔvjbR in pregnant swine

Brucellosis in swine is caused by Brucella suis, a bacterial infection of nearly worldwide distribution. Brucella suis is also transmissible to humans, dogs and cattle and is considered a reemerging disease of public health concern. To date, there is no effective vaccine for swine. This prompted us to investigate the potential use of the commercially available vaccine for cattle or the live attenuated vaccine candidate S19ΔvjbR. As the first step, we sought to study the safety of the vaccine candidates when administered in pregnant sows, since one of the major drawbacks associated with vaccination using Live Attenuated Vaccines (LAV) is the induction of abortions when administered in pregnant animals. Fifteen pregnant gilts at mid-gestation were divided into four groups and subsequently vaccinated subcutaneously using different formulations containing 2.0 ± 0.508 × 109 CFU of either S19 or S19ΔvjbR. Vaccination in pregnant animals with the vaccine candidates did not induce abortion, stillbirths or a reduction in litter size. Multiple tissues in the gilts and piglets were examined at the time of delivery to assess bacterial colonization and histopathological changes. There was no evidence of vaccine persistence in the gilts or bacterial colonization in the fetuses. Altogether, these data suggest that both vaccine candidates are safe for use in pregnant swine. Analysis of the humoral responses, specifically anti-Brucella IgG levels measured in serum, demonstrated a robust response induced by either vaccine, but of shorter duration (4-6 weeks post-inoculation) compared to that observed in cattle or experimentally infected mice. Such a transient humoral response may prove to be beneficial in cases where the vaccine is used in eradication campaigns and in the differentiation of vaccinated from infected animals. This study provides evidence to support future efficacy studies of both vaccine candidates in swine.

A case of Brucella aortitis associated with development of thoracic aortic aneurysm and aortobronchial fistula

OBJECTIVES

The purpose of this case report is to document the occurrence of granulomatous aortitis complicated by formation of a saccular aneurysm and aortobronchial fistula due to Brucella infection.

METHODS

A 65-year-old man with a history of feral swine hunting presented with hemoptysis and was found to have a saccular thoracic aortic aneurysm and associated aortobronchial fistula. The aneurysm underwent operative repair with closure of the aortobronchial fistula.

RESULTS

Histopathological examination of the aneurysm wall revealed evidence of granulomatous aortitis. Cultures of the blood and aortic wall tissue were positive for Brucella suis.

CONCLUSIONS

Although rare, Brucella infection should be considered in the differential diagnosis of aortic aneurysm with granulomatous aortitis.

Wild Boar: A Reservoir of Foodborne Zoonoses

Wild boar populations around the world have increased dramatically over past decades. Climate change, generating milder winters with less snow, may affect their spread into northern regions. Wild boars can serve as reservoirs for a number of bacteria, viruses, and parasites, which are transmissible to humans and domestic animals through direct interaction with wild boars, through contaminated food or indirectly through contaminated environment. Disease transmission between wild boars, domestic animals, and humans is an increasing threat to human and animal health, especially in areas with high wild boar densities. This article reviews important foodborne zoonoses, including bacterial diseases (brucellosis, salmonellosis, tuberculosis, and yersiniosis), parasitic diseases (toxoplasmosis and trichinellosis), and the viral hepatitis E. The focus is on the prevalence of these diseases and the causative microbes in wild boars. The role of wild boars in transmitting these pathogens to humans and livestock is also briefly discussed.

Field evaluation of low-dose warfarin baits to control wild pigs (Sus scrofa) in North Texas

Wild pigs (Sus scrofa) are a highly detrimental invasive species that occupy a rapidly expanding range within the United States. In Australia, field trials evaluating baits containing 0.09% warfarin resulted in wild pig population reduction >95%. The objective of this study was to conduct an EPA-approved field trial to evaluate the use of bait containing low-dose warfarin (0.01% and 0.005%) in reducing wild pig numbers in Texas. An 8-week field test was conducted in the panhandle ~100 km southeast of Amarillo. Two ~8 km² treatment plots were selected and each presented with either 0.01% or 0.005% warfarin baits. One control plot (~8 km²) was presented placebo. The baits were delivered using 30 species-specific feeders per plot (n = 90) that kept wildlife from accessing the toxicant. Pig movements and feed consumption were monitored during pre-treatment, treatment, and post-treatment periods. All pigs with VHF transmitters within the 0.005% warfarin-treated plot (n = 14) succumbed to the warfarin (100% mortality). Overall, 35 wild pigs were found dead from warfarin toxicosis, within both treatment plots. Total feed consumption by wild pigs was reduced by ~97.8% and ~96.2% for the 0.005% and 0.01% warfarin baited plots, respectively, indicating the absence of pigs was a result of toxic bait consumption. Results of 97 systematic searches of the treatment plots indicated no warfarin-induced non-target wildlife fatalities. Warfarin residues in wild pig livers averaged 3.69 mg/kg (n = 13) and 2.89 mg/kg (n = 9) for pigs recovered within the 0.005% plot and 0.01% warfarin plot, respectively. This study is the first efficacy field evaluation of a wild pig toxicant conducted in the US. The results suggest low-dose warfarin bait, presented in species-specific feeders, can effectively reduce wild pig numbers and pose minimal risk to non-target wildlife and domestic animals. A product containing warfarin may provide another management tool in reducing wild pig problems.

Infectious agents in feral swine in Ohio, USA (2009-2015): A low but evolving risk to agriculture and public health

As highly mobile and prolific animals, feral swine threaten public and livestock health. To quantify these threats, we analyzed disease surveillance samples to estimate the prevalence of key pathogens and parasites in feral swine captured in Ohio. Between 2009 and 2015, samples from 205 feral swine were tested for up to 13 pathogens. Methicillin susceptible Staphylococcus aureus was cultured from 29 of 138 (21%) individuals and antibodies to Leptospira spp. (16/69; 23%), Toxoplasma gondii (11/76; 15%), Trichinella spiralis (4/69; 6%), hepatitis E virus (1/32; 3%), Brucella spp. (2/138; 1%), and influenza A virus (2/176; 1%) were also detected. Lungworms (Metastrongylus spp.) were frequently identified (46/55; 84%). Evidence of infection or exposure was not detected to Mycobacterium bovis, classical swine fever, pseudorabies, and porcine reproductive and respiratory syndrome. All positive Brucella and hepatitis E virus samples and 63% (10/16) of the positive Leptospira spp. samples came from individuals identified as illegal out-of-state feral swine introductions. Results indicated an overall low prevalence of pathogens in feral swine in Ohio; however, the importation of live feral swine from other states remained an important concern for pathogen introduction and spread.

Antibodies to Various Zoonotic Pathogens Detected in Feral Swine (Sus scrofa) at Abattoirs in Texas, USA

The zoonotic risk posed to employees by slaughtering feral swine (Sus scrofa) at two abattoirs in Texas was assessed by testing feral swine serum samples for exposure to influenza A virus, Leptospira, Trichinella spiralis, and Toxoplasma gondii. Blood was collected from a total of 376 feral swine between the two facilities during six separate collection periods in 2015. Antibodies to one or more serovars of Leptospira were identified in 48.9% of feral swine tested, with Bratislava and Pomona as the most commonly detected serovars, and antibodies to influenza A virus were detected in 14.1% of feral swine. Antibodies to T. gondii and T. spiralis were identified in 9.0 and 3.5%, respectively, of feral swine tested. Our results suggest that abattoir employees should be aware of the potential for exposure to various zoonotic pathogens when slaughtering feral swine, wear appropriate personal protective equipment, and participate in medical monitoring programs to ensure detection and prompt treatment. In addition, consumers of feral swine should cook the meat to the appropriate temperature and wash hands and kitchen surfaces thoroughly after preparing meat.