Towards harmonised procedures in wildlife epidemiological investigations: A serosurvey of infection with Mycobacterium bovis and closely related agents in wild boar (Sus scrofa) in Switzerland

Bovine Tuberculosis in Wild Boar (Sus scrofa) in Slovenia

Mycobacteria of the Mycobacterium tuberculosis complex (MTC) are capable of infecting a wide variety of animals. Wild boar (Sus scrofa) has been recognized as an important wildlife reservoir for bovine tuberculosis. We screened wild boar in Slovenia for the presence of (1) Mycobacterium bovis in tissues and (2) antibodies to M. bovis in blood samples. In 2016 and 2017, 1284 tissue samples from 676 wild boar were subjected to cultivation. In 2018 and 2019, blood samples from 132 wild boar were examined using an ELISA kit. None of the MTC species were isolated from the tissue samples, and no antibodies to M. bovis were detected in the blood samples. Several nontuberculous mycobacteria (NTM), identified by 16S rRNA sequencing and/or matrix-assisted laser desorption ionization time-of-flight mass spectrometry, were found in the tissues of 9.8% of the wild boar: Mycobacterium nonchromogenicum, Mycobacterium peregrinum/Mycobacterium septicum, Mycobacterium avium, Mycobacterium engbaekii, Mycobacterium arupense, Mycobacterium algericum, Mycobacterium bohemicum, Mycobacterium confluentis, Mycobacterium flavescens, Mycobacterium fortuitum, Mycobacterium thermoresistibile, and Mycobacterium vaccae. Species-level identification was not possible for 21.2% of the isolates. At the time of the study, wild boar in Slovenia were not at risk from bTB; the significance of the presence of NTM in wild boar remains to be clarified and evaluated from a One Health perspective.

Worldwide Swine Tuberculosis-Positive Rate and Associated Risk Factors, 1966-2020: A Systematic Review and Meta-Analysis

Background: Tuberculosis (TB) is a chronic, zoonotic infectious disease caused by Mycobacterium tuberculosis that infects not only humans but also animals such as pigs, cows, buffaloes, sheep, and goats. Among them, pigs are one of the main food animals in the world. If pigs are infected with M. tuberculosis, meat products will be negatively affected, causing economic losses to the livestock industry. There is currently no systematic epidemiological assessment of swine TB in the world, so it is important to know the prevalence of swine, and these data are currently lacking, so we performed a statistical analysis. Results: We searched 6791 articles and finally included data from 35,303 pigs from 15 countries or territories, showing a combined prevalence of TB in pigs of 12.1% (95% confidence interval [CI]: 9.2 to 15.9). Among them, the prevalence rate of swine TB in Europe was 15.2% (95% CI: 11.1 to 20.7, 2491/25,050), which was higher compared with other continents, and the difference was significant; the positive rate of PCR method was higher in the detection method subgroup, which was 15.7% (95% CI: 8.0 to 31.0, 376/2261); Mycobacterium bovis was detected in pigs in the M. tuberculosis typing group (9.5%, 95% CI: 6.7 to 13.5, 1364/21,430). The positive rate is higher compared with Mycobacterium capris. Conclusion: This systematic review and meta-analysis is the first to determine the global prevalence of TB in swine herds. Although the seroprevalence of swine TB in this article is very low, the harm of TB cannot be ignored. It is important to take effective control and preventive measures to stop the spread of TB to reduce the impact of diseased pigs on animal husbandry and human health.

Presence of Foodborne Bacteria in Wild Boar and Wild Boar Meat-A Literature Survey for the Period 2012-2022

The wild boar is an abundant game species with high reproduction rates. The management of the wild boar population by hunting contributes to the meat supply and can help to avoid a spillover of transmissible animal diseases to domestic pigs, thus compromising food security. By the same token, wild boar can carry foodborne zoonotic pathogens, impacting food safety. We reviewed literature from 2012-2022 on biological hazards, which are considered in European Union legislation and in international standards on animal health. We identified 15 viral, 10 bacterial, and 5 parasitic agents and selected those nine bacteria that are zoonotic and can be transmitted to humans via food. The prevalence of Campylobacter, Listeria monocytogenes, Salmonella, Shiga toxin-producing E. coli, and Yersinia enterocolitica on muscle surfaces or in muscle tissues of wild boar varied from 0 to ca. 70%. One experimental study reported the transmission and survival of Mycobacterium on wild boar meat. Brucella, Coxiella burnetii, Listeria monocytogenes, and Mycobacteria have been isolated from the liver and spleen. For Brucella, studies stressed the occupational exposure risk, but no indication of meat-borne transmission was evident. Furthermore, the transmission of C. burnetii is most likely via vectors (i.e., ticks). In the absence of more detailed data for the European Union, it is advisable to focus on the efficacy of current game meat inspection and food safety management systems.

Development and evaluation of a multi-antigen serological assay for the intra-vitam diagnosis of Tuberculosis caused by Mycobacterium bovis in pigs

Bovine Tuberculosis (bTB) is a chronic disease caused by Mycobacterium bovis, affecting cattle and other mammalian species, such as pigs. In the present work, we developed a novel multi-antigen assay (The TB-Luminex multiplex test) to diagnose bTB in pig sera. Moreover, we investigated the seroreactivity to the different antigens employed (MPB83, MPB70, CFP10 and ESAT6) and the possible correlation with bTB lesions distribution in the positive pigs. The serum samples were collected from 59 bTB positive pigs and 186 pigs reared in an officially Tuberculosis free area. Sera were processed according to an optimized protocol for the detection of antibodies by a multiantigen assay using Luminex technology. The positive group showed visible lesions with localized (54.2%) or generalized (45.8%) distribution. Culture confirmed the infection in 62.7% of the cases, and histopathology and intra-vitam assays were used as additional confirmatory tests. Within the set of antigens tested, the immunodominant was MPB83 (positive in 94.9% of the affected pigs), followed by CFP10, MPB70 and ESAT6 (positivity shown in 81.3%, 67.8% and 25.4% of the positive pigs tested, respectively). The best antigens combination was MPB83/CFP10, with a 96.6% sensitivity and 96.8% specificity. Overall, the test showed high sensitivity (98.3% and 86.4%) and specificity (96.2% and 97.8%), if sera were considered positive according to the positivity to a single antigen or at least two antigens, respectively. The TB-Luminex multiplex test results did not give significantly different outcomes according to lesions distribution. Given the present study results, the TB-Luminex multiplex test is a reliable test capable of detecting bTB in most infected pigs with good Se and Sp, regardless of the stage of the disease. In conclusion, multi-antigen tests can be used as individual tests and screening tools for domestic and wild suids within bTB eradication programs.

Risk factors associated to a high Mycobacterium tuberculosis complex seroprevalence in wild boar (Sus scrofa) from a low bovine tuberculosis prevalence area

Animal tuberculosis is a worldwide zoonotic disease caused principally by Mycobacterium bovis, a member of the Mycobacterium tuberculosis complex (MTC). In southern Iberian Peninsula, wild reservoirs such as the wild boar, among other factors, have prevented the eradication of bovine tuberculosis. However, most of the studies have been focused on south-central Spain, where the prevalence of tuberculosis is high among wild ungulates and cattle herds. In northern regions, where wild boar density and bovine tuberculosis prevalence are lower, fewer studies have been carried out and the role of this species is still under debate. The aim of this study was to describe the temporal and spatial distribution of antibodies against MTC in wild boar from the Basque Country, northern Spain. Sera from 1902 animals were collected between 2010 and 2016. The seroprevalence was determined with an in house enzyme-linked immunosorbent assay and the search of risk factors was assessed by Generalized Linear Models. Overall, 17% of wild boars (326/1902; 95%CI, [15.5%–18.9%]) showed antibodies against MTC. Risk factors associated with seropositivity were the year and location of sampling, the number of MTC positive cattle, the distance to positive farms and the percentage of shrub cover. Younger age classes were associated with increased antibody titres among seropositive individuals. The seroprevalence detected was higher than those previously reported in neighbouring regions. Hence, further studies are needed to better understand the role of wild boar in the epidemiology of tuberculosis in low tuberculosis prevalence areas and consequently, its relevance when developing control strategies.

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.

A picture of trends in Aujeszky's disease virus exposure in wild boar in the Swiss and European contexts

BACKGROUND

In parallel to the increase of wild boar abundance in the past decades, an increase of exposure to the Aujeszky's disease virus (ADV) has been reported in wild boar in several parts of Europe. Since high animal densities have been proposed to be one of the major factors influencing ADV seroprevalence in wild boar populations and wild boar abundance has increased in Switzerland, too, a re-evaluation of the ADV status was required in wild boar in Switzerland. We tested wild boar sera collected from 2008-2013 with a commercial ELISA for antibodies against ADV. To set our data in the European context, we reviewed scientific publications on ADV serosurveys in Europe for two time periods (1995-2007 and 2008-2014).

RESULTS

Seven out of 1,228 wild boar sera were positive for antibodies against ADV, resulting in an estimated seroprevalence of 0.57% (95% confidence interval CI: 0.32-0.96%). This is significantly lower than the prevalence of a previous survey in 2004-2005. The literature review revealed that high to very high ADV seroprevalences are reported from Mediterranean and Central-eastern countries. By contrast, an "island" of low to medium seroprevalences is observed in the centre of Europe with few isolated foci of high seroprevalences. We were unable to identify a general temporal trend of ADV seroprevalence at European scale.

CONCLUSIONS

The seroprevalence of ADV in wild boar in Switzerland belongs among the lowest documented in Europe. Considering the disparity of seroprevalences in wild boar in Europe, the fact that seroprevalences in Switzerland and other countries have decreased despite increasing wild boar densities and the knowledge that stress leads to the reactivation of latent ADV with subsequent excretion and transmission, we hypothesize that not only animal density but a range of factors leading to stress - such as management - might play a crucial role in the dynamics of ADV infections.

Serological Follow-up of Tuberculosis in a Wild Boar Population in Contact with Infected Cattle

There is an increasing concern in several European countries over the role that tuberculosis (TB)-infected wild boar may play in the progress of bovine TB eradication campaigns. In 2004, as a consequence of the detection of a TB focus in wild boar from a National Game Reserve (NGR) located in southern Catalonia, a surveillance programme based on post-mortem inspection for detection of macroscopic TB-like lesions (TBLL) was initiated in the affected area. The source of infection for wild boar was linked to a tuberculous cattle herd located in the same area. Besides, the results of the surveillance programme in wild boar were used for the validation of an indirect enzyme-linked immunosorbent assay (ELISA) specific for Mycobacterium tuberculosis complex (MTBC) IgG antibodies. Using this ELISA, a seven-year serological study of MTBC in wild boar from the NGR was conducted in 173 animals (93 adults, 44 juveniles-yearlings and 36 piglets) culled between 2004 and 2010. ELISA results and presence of TBLL showed excellent agreement for adult and juvenile wild boar (Kappa index = 0.85; 95% CI: 0.76-0.95). Of the thirty-eight adults, yearlings and juveniles classified as positives by the ELISA, 34 (89%) showed TBLL at necropsy. In contrast, none of the ELISA-positive wild boar piglets (n = 20) showed TBLL, suggesting the detection of early antibody responses to the infection. Overall, this study contributes to the knowledge of wild boar humoral responses to MTBC. The results also highlight the usefulness of this serological test for wild boar TB surveillance.

Investigating the role of free-ranging wild boar (Sus scrofa) in the re-emergence of enzootic pneumonia in domestic pig herds: a pathological, prevalence and risk-factor study

Enzootic pneumonia (EP) caused by Mycoplasma hyopneumoniae has a significant economic impact on domestic pig production. A control program carried out from 1999 to 2003 successfully reduced disease occurrence in domestic pigs in Switzerland, but recurrent outbreaks suggested a potential role of free-ranging wild boar (Sus scrofa) as a source of re-infection. Since little is known on the epidemiology of EP in wild boar populations, our aims were: (1) to estimate the prevalence of M. hyopneumoniae infections in wild boar in Switzerland; (2) to identify risk factors for infection in wild boar; and (3) to assess whether infection in wild boar is associated with the same gross and microscopic lesions typical of EP in domestic pigs. Nasal swabs, bronchial swabs and lung samples were collected from 978 wild boar from five study areas in Switzerland between October 2011 and May 2013. Swabs were analyzed by qualitative real time PCR and a histopathological study was conducted on lung tissues. Risk factor analysis was performed using multivariable logistic regression modeling. Overall prevalence in nasal swabs was 26.2% (95% CI 23.3–29.3%) but significant geographical differences were observed. Wild boar density, occurrence of EP outbreaks in domestic pigs and young age were identified as risk factors for infection. There was a significant association between infection and lesions consistent with EP in domestic pigs. We have concluded that M. hyopneumoniae is widespread in the Swiss wild boar population, that the same risk factors for infection of domestic pigs also act as risk factors for infection of wild boar, and that infected wild boar develop lesions similar to those found in domestic pigs. However, based on our data and the outbreak pattern in domestic pigs, we propose that spillover from domestic pigs to wild boar is more likely than transmission from wild boar to pigs.