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

Abstract

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.

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

“…23,000 km 2 ), of which a large part reaches altitudes above the timber line, and iv) the part of Ticino located south from the Alps (approx. 2,812 km 2 ); (4) covering most of the Swiss border to France, Germany and Italy; and (5) complementing former studies on wild boar pathogens in Switzerland [ 77 , 78 ]. Contacts are possible among wild boar in the study units A-D (i.e., northern population) whereas wild boar in study unit E (Ticino, i.e., southern population) are separated from the northern population by the Alps and can only interact with Italian wild boar populations.…”

“…Calculation of the target sample size per hunting season and study unit was derived from the regional hunting bags and performed with the WinEpiscope 2.0 software package. Since 2011 samples sizes have been calculated with the aim of estimating prevalence and assuming a prevalence of 50 %, with a confidence level of 95 % and an accepted absolute error of 5 % [ 78 ]. Efforts were made towards an even age and sex distribution among units.…”

Abattoir-Based Measures to Assess Swine Welfare: Analysis of the Methods Adopted in European Slaughterhouses

“…EP-like lesions normally appear as a purple or gray area of pulmonary consolidation of the cranioventral lobes [ 58 ]. The appearance of the lesions depends on the stage of the disease: damaged lobes are swollen in the acute stage of the disease, while in the chronic phase, interlobular scarring tissue is typically present [ 59 ].…”

Animal Welfare and Production Challenges Associated with Pasture Pig Systems: A Review

“…These animals have been identified as potential sources of African swine fever virus [56,73,84], Aujeszky's disease [78,79], brucellosis [78,79,82], Campylobacter [80], classical swine fever [85], giardiasis [80], salmonellosis [81], Streptococcus suis [77], toxoplasmosis [81,82], trichinellosis [61,82], tuberculosis [86,87], and yersiniosis [81] in domestic animals, and leptospirosis, tuberculosis, hepatitis E, brucellosis, and trichinellosis in humans [56,78,83]. Conversely, Batista Linhares et al indicated greater probability of contagion of enzootic pneumonia caused by Mycoplasma hyopneumoniae from domestic pigs to wild boars [88]. Pathogens can also be transmitted through consumption of contaminated meat, as in the case of bacteria such as Escherichia coli, Listeria monocytogenes, and Campylobacter [80,81] or viruses such as African swine fever [73] and classic swine fever [85].…”