Serological, pathological and polymerase chain reaction studies on Mycoplasma hyopneumoniae infection in the wild boar

Mycoplasma hyopneumoniae in free-living wild boars in Paraná, Brazil

This is the first study conducted in Paraná, Brazil, to investigate Mycoplasma hyopneumoniae (Mhyo) infection in free-living wild boars. Eighty-eight wild boars were managed by authorized controllers between 2017 and 2019 in the state of Paraná in southern Brazil. Management georeferencing, sex, and weight were recorded for each animal. The presence of Mhyo antibodies in wild boar serum samples was evaluated using a commercial indirect ELISA kit. The presence of enzootic pneumonia-like gross lesions was evaluated, and the observed macroscopic lesions were subjected to immunohistochemistry (IHC). The Chi-square test and the intensity of the association with the odds ratio and 95% confidence interval were used to evaluate the differences in the qualitative variables between groups (sex and municipality). Juvenile wild boars exhibited a higher seroprevalence than older ones (p = 0.005). The Teixeira Soares municipality differed in Mhyo seroprevalence in comparison with Castro (p < 0.001), Ponta Grossa (p = 0.004), and Carambeí (p < 0.001). Females were 6.79 times more likely to present consolidation lesions than males (p = 0.004). Among the evaluated lung samples with injuries, 57.1% (8/14) and 53.8% (7/13) were Mhyo positive by IHC in Castro and Ponta Grossa, respectively, confirming that the identified macroscopic lesions were caused by Mhyo. This study demonstrates the circulation of Mhyo in free-living wild boars, which raises concerns regarding the epidemiological role of this animal species for the spread of the pathogen.

Health profile of free-range wild boar (Sus scrofa) subpopulations hunted in Santa Catarina State, Brazil

Wild boars represent a potential dissemination source of important pathogens to public and animal health, since they can host several pathogens. This study aimed to evaluate the health profile of wild boars hunted for population control in the state of Santa Catarina (SC), south of Brazil. For this study, tissue and blood samples were collected from 61 wild boars hunted from October 2017 to November 2018. All 61 serum samples were screened for antibodies by different assays, presenting the following seroprevalence: 52.4% for porcine circovirus type 2 (PCV2); 21.3% for Leptospira spp.; 19.7% for Mycoplasma hyopneumoniae; 13.1% for hepatitis E virus (HEV); and 9.8% for influenza A virus (IAV). No seroreaction was observed for Brucella spp. and classical swine fever virus (CSFV). At necropsy, the main lesions observed were evidence of pulmonary metastrongylid parasites, haemorrhagic lymph nodes and white-spotted liver. Histopathological analyses mainly showed interstitial pneumonia, bronchopneumonia and bronchi-associated lymphoid tissue (BALT) hyperplasia. There was a significant association between metastrongylid parasitism and BALT hyperplasia in lungs. Pathological findings of wild boars indicate that the assessed individuals were not exposed to notifiable diseases, such as CSFV, African swine fever virus and foot-and-mouth disease, which cause economic damage by non-tariff trade barriers. However, the detection of antibodies against PCV2 and M. hyopneumoniae, pathogens that impact commercial production, indicates the circulation of these agents, with frequency variation in wild populations. This shows the potential risk of pathogen transmission among domestic swine populations and free-living ones. The detection of antibodies against zoonotic agents such as HEV, IAV and Leptospira spp., other than characterizing the pathogens' circulation in these populations, suggests a potential risk to public health and pig farming, depending on the interactions established with the environment, humans and domestic swine.

Suidae and Tayassuidae

The Suidae and Tayassuidae live on all continents except Antarctica. True wild boars were indigenous to Europe and Asia and are the ancestors to the domestic pig; with whom they share the same scientific name Sus scrofa. Wild boars have been introduced to the Americas and many islands. Because of the close genetic relationship, in many areas they have interbred with domestic pigs and formed considerable populations of feral suids that represent wild boar and feral pig crosses. Wild suid populations are relatively hardy and most disease research has been focused on their potential as a reservoir for diseases of concern for commercial pig production. The Togian Island babirusa, pygmy hog, Visayan warty pig, Javan warty pig, and Chacoan peccary are endangered. For all species, hunting, habitat loss, and hybridization are important threats to conservation.

Update on Mycoplasma hyopneumoniae infections in pigs: Knowledge gaps for improved disease control

Mycoplasma hyopneumoniae (M. hyopneumoniae) is the primary pathogen of enzootic pneumonia, a chronic respiratory disease in pigs. Infections occur worldwide and cause major economic losses to the pig industry. The present paper reviews the current knowledge on M. hyopneumoniae infections, with emphasis on identification and analysis of knowledge gaps for optimizing control of the disease. Close contact between infected and susceptible pigs is the main route of M. hyopneumoniae transmission. Management and housing conditions predisposing for infection or disease are known, but further research is needed to better understand M. hyopneumoniae transmission patterns in modern pig production systems, and to assess the importance of the breeding population for downstream disease control. The organism is primarily found on the mucosal surface of the trachea, bronchi and bronchioles. Different adhesins and lipoproteins are involved in the adherence process. However, a clear picture of the virulence and pathogenicity of M. hyopneumoniae is still missing. The role of glycerol metabolism, myoinositol metabolism and the Mycoplasma Ig binding protein-Mycoplasma Ig protease system should be further investigated for their contribution to virulence. The destruction of the mucociliary apparatus, together with modulating the immune response, enhances the susceptibility of infected pigs to secondary pathogens. Clinical signs and severity of lesions depend on different factors, such as management, environmental conditions and likely also M. hyopneumoniae strain. The potential impact of strain variability on disease severity is not well defined. Diagnostics could be improved by developing tests that may detect virulent strains, by improving sampling in live animals and by designing ELISAs allowing discrimination between infected and vaccinated pigs. The currently available vaccines are often cost-efficient, but the ongoing research on developing new vaccines that confer protective immunity and reduce transmission should be continued, as well as optimization of protocols to eliminate M. hyopneumoniae from pig herds.

Detection and phylogenetic analysis of Mycoplasma hyopneumoniae from Tibetan pigs in western China

Enzootic pneumonia (EP), often caused by Mycoplasma hyopneumoniae, occurs in Tibetan pigs between October and December in Western China. The aim of this study was to determine the prevalence of M. hyopneumoniae in Tibetan pig herds and also the prevalence of infection. M. hyopneumoniae was detected using enzyme-linked immunosorbent assay, polymerase chain reaction (PCR), and 16S rRNA sequencing. Twenty-nine inflammatory gross-lesions were observed in 155 lungs of slaughtered pigs. Invasion of focal lymphocytes was confirmed by paraffin sectioning and hematoxylin-eosin staining of lung sections. Bronchoalveolar lavage fluid (BALF) from slaughtered Tibetan pigs and nasal swabs from others were assayed using PCR. The prevalence of M. hyopneumoniae in Tibetan pig herds (via ELISA) was 20.48% (93/454) in 3 provinces (Sichuan, Tibet autonomous region, and Qinghai) between October and December of 2014. The difference in prevalence among animals in six different growing stages was statistically significant (P < 0.05). Anti-M. hyopneumoniae antibody was detected in breeding sows (45.83%; 22/48) and piglets (50%; 3/6). PCR and gel electrophoresis of BALF showed that 6.45% (10/155) of pigs were positive for M. hyopneumoniae. The presence of M. hyopneumoniae in serum was higher in piglets and breeding sows than in any other group. In conclusion, the results of this study showed that M. hyopneumoniae is prevalent among Tibetan pigs between October and December in Western China. To the authors' knowledge, this is the first investigation of M. hyopneumoniae prevalence in Tibetan pigs of Western China using serological tests, PCR, and 16S rRNA sequencing.

Modelling the within-herd transmission of Mycoplasma hyopneumoniae in closed pig herds

Background

A discrete time, stochastic, compartmental model simulating the spread of Mycoplasma hyopneumoniae within a batch of industrially raised pigs was developed to understand infection dynamics and to assess the impact of a range of husbandry practices. A ‘disease severity’ index was calculated based on the ratio between the cumulative numbers of acutely and chronically diseased and infectious pigs per day in each age category, divided by the length of time that pigs spent in this age category. This is equal to the number of pigs per day, either acutely or chronically infectious and diseased, divided by the number of all pigs per all days in the model. The impact of risk and protective factors at batch level was examined by adjusting ‘acclimatisation of gilts’, ‘length of suckling period’, ‘vaccination of suckling pigs against M. hyopneumoniae’, ‘contact between fattening pigs of different age during restocking of compartments’ and ‘co-infections in fattening pigs’.

Results

The highest ‘disease severity’ was predicted, when gilts do not have contact with live animals during their acclimatisation, suckling period is 28 days, no vaccine is applied, fatteners have contact with pigs of other ages and are suffering from co-infections. Pigs in this scenario become diseased/infectious for 26.1 % of their lifetime. Logistic regression showed that vaccination of suckling pigs was influential for ‘disease severity’ in growers and finishers, but not in suckling and nursery pigs. Lack of contact between gilts and other live pigs during the acclimatisation significantly influenced the ‘disease severity’ in suckling pigs but had less impact in growing and finishing pigs. The length of the suckling period equally affected the severity of the disease in all age groups with the strongest association in nursery pigs. The contact between fatteners of different groups influenced the course of infection among finishers, but not among other pigs. Finally, presence of co-infections was relevant in growers and finishers, but not in younger pigs.

Conclusion

The developed model allows comparison of different prevention programmes and strategies for controlling transmission of M. hyopneumoniae.

Electronic supplementary material

The online version of this article (doi:10.1186/s40813-016-0026-1) contains supplementary material, which is available to authorized users.

Increased Mycoplasma hyopneumoniae Disease Prevalence in Domestic Hybrids Among Free-Living Wild Boar

Wildlife immune genes are subject to natural selection exerted by pathogens. In contrast, domestic immune genes are largely protected from pathogen selection by veterinary care. Introgression of domestic alleles into the wild could lead to increased disease susceptibility, but observations are scarce due to low introgression rates, low disease prevalence and reduced survival of domestic hybrids. Here we report the first observation of a deleterious effect of domestic introgression on disease prevalence in a free-living large mammal. A fraction of 462 randomly sampled free-living European wild boar (Sus scrofa) was genetically identified as recent wild boar-domestic pig hybrids based on 351 SNP data. Analysis of antibody prevalence against the bacterial pathogen Mycoplasma hyopneumoniae (Mhyo) showed an increased Mhyo prevalence in wild-domestic hybrids. We argue that the most likely mechanism explaining the observed association between domestic hybrid status and Mhyo antibody prevalence would be introgression of deleterious domestic alleles. We hypothesise that large-scale use of antibiotics in the swine breeding sector may have played a role in shaping the relatively deleterious properties of domestic swine immune genes and that domestic introgression may also lead to increased wildlife disease susceptibility in the case of other species.

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.

Prevalence of and risk factors associated with viral and bacterial pathogens in farmed European wild boar

The aim of this study was to estimate in farmed European wild boars the prevalence of and risk factors associated with a range of common porcine viral and bacterial infections, namely, porcine parvovirus (PPV), porcine circovirus type 2 (PCV2), swine influenza virus (SIV), Aujeszky’s disease virus (ADV), classical swine fever virus (CSFV), swine vesicular disease virus (SVDV), coronavirus causing transmissible gastroenteritis (TGEV), porcine reproductive and respiratory syndrome virus (PRRSV), Mycoplasma hyopneumoniae, Lawsonia intracellularis, Brucella spp., and Leptospira spp. A sampling frame was compiled based on a national record of wild boar farmers, and 32 farms were surveyed.

Serological screening was carried out on 303 samples from animals slaughtered between 2005 and 2008, and random-effect logistic regression models were developed for pathogens with a ‘non-zero’ prevalence. The apparent animal prevalence for PPV, PCV2, and L. intracellularis was 46.5% (95% confidence interval [CI] 41–52%), 51.1% (95% CI 45–57%) and 59.2% (95% CI 54–65%), respectively. Apparent farm seroprevalence rates for PPV, PCV2 and Lawsonia intracellularis were 56.3% (95% CI, 39–73%), 21.9% (95% CI, 8–36%) and 78.1% (95% CI, 64–92%), respectively. No antibodies were detected against SIV, ADV, CSFV, SVDV, TGEV, PRSSV, Leptospira spp., Brucella spp., or M. hyopneumoniae. Increasing herd size, proximity to dense populations of domestic swine and later sampling times within the survey period were found to be risk factors. Overall, the seroprevalence of these pathogens in farmed wild boar was similar to that in the farmed domestic pig population in Finland. However, it is possible that the rearing of wild boars in fenced estates may predispose them to particular infections, as reflected in higher antibody titres.

A survey of the transmission of infectious diseases/infections between wild and domestic ungulates in Europe

The domestic animals/wildlife interface is becoming a global issue of growing interest. However, despite studies on wildlife diseases being in expansion, the epidemiological role of wild animals in the transmission of infectious diseases remains unclear most of the time. Multiple diseases affecting livestock have already been identified in wildlife, especially in wild ungulates. The first objective of this paper was to establish a list of infections already reported in European wild ungulates. For each disease/infection, three additional materials develop examples already published, specifying the epidemiological role of the species as assigned by the authors. Furthermore, risk factors associated with interactions between wild and domestic animals and regarding emerging infectious diseases are summarized. Finally, the wildlife surveillance measures implemented in different European countries are presented. New research areas are proposed in order to provide efficient tools to prevent the transmission of diseases between wild ungulates and livestock.

Transmission of swine pathogens: different means, different needs

There seems to be two main types of pathogens that cause diseases in swine: those that are mainly introduced through direct pig contacts, and those that are often, and in some situations mainly introduced by indirect transmission means. In this review, the mange mite (Sarcoptes scabiei), toxigenic Pasteurella multocida and Brachyspira hyodysenteriae will be used as examples of the first type, and foot and mouth disease virus, Mycoplasma hyopneumoniae and porcine reproductive and respiratory syndrome (PRRS) virus as examples of the second. It is now clear from various epidemiological studies as well as experimental and field data that aerosol transmission of some swine pathogens plays an important role in their epidemiology. As previous biosecurity programs did not take this factor into consideration, it can at least partially explain why many of these programs suffered frequent failures and why air filtration is now becoming increasingly popular in North America. Identifying and quantifying transmission means should be a priority for every important infectious disease for which it has not been done.