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.

Luc Belloy,Isabel Lechner,Helmut Segner,Michael Lierz,Francesco C. Origgi,Marie-Pierre Ryser-Degiorgis,Mainity Batista Linhares

doi:10.1371/journal.pone.0119060

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.

Highlights

Enzootic pneumonia (EP) is one of the most important sources of disease-associated losses in swine production [1,2,3]
While 25 animals tested PCR-positive with bronchial but negative with nasal swabs, the contrary occurred for six animals, and the obtained kappa-value of 0.39 suggested a low agreement between the results generated with these two sampling materials
This study compared the diagnostic performance of nasal and bronchial swabs for detection of Mycoplasma hyopneumoniae (Mhyop) in wild boar, documented the occurrence and typical features of both macroscopic and histologic lung lesions associated with infection, estimated the prevalence of Mhyop in freeranging wild boar from different geographical regions, and identified risk factors for infection

Summary

Introduction

Enzootic pneumonia (EP) is one of the most important sources of disease-associated losses in swine production [1,2,3]. This lung disease is caused by Mycoplasma hyopneumoniae (Mhyop). Enzootic pneumonia mainly affects mid- to late finishing pigs, though infection can be traced back to birth. The main infection route is direct contact with infected swine (sow and pen mates). Infections in previously EP-free herds can often be traced back to the introduction of subclinically infected animals into the herd [4,6,7]. Viable Mhyop have been detected up to 9.2 km from an infected herd [7,8,9]

Objectives

Methods

Results

Discussion

Conclusion