Short communication
The prevalence of porcine teschovirus in the pig population in northeast of China

https://doi.org/10.1016/j.jviromet.2013.06.005Get rights and content

Highlights

  • Porcine teschovirus (PTV) is widespread and increasing in swine herds in northeast of China.

  • Four serotypes (PTV-2, -4, -6, and -8) were detected.

  • Recombination among PTV serotypes has occurred evidently in the field.

  • PTV commonly occurs with other viruses of swine.

  • The relationship between PTV and disease is unclear.

Abstract

The prevalence of porcine teschovirus (PTV) in swine herds in northeast China was investigated. In 2008–2009, 1384 samples of pig sera were collected from 42 farms in Shandong, Hebei, Heilongjiang, and Jilin provinces and in Tianjin City and were tested for specific antibody against PTV-8 by immunofluorescence assay. All 42 pig herds were positive for antibodies against PTV-8, and 61.3% of the serum samples were PTV-8 positive. During the survey, one PTV strain was isolated and named Fuyu/2009; phylogenetic analysis showed that the PTV Fuyu/2009 belongs to the PTV-8 serotype. The serological results indicate that most if not all pig herds in northeast of China have been exposed to PTV. RT-PCR performed on 114 clinical samples indicated a possible association between PTV and disease. According to genotyping based on partial VP1 sequences, four serotypes (PTV-2, -4, -6, and -8) were identified in northeast of China; sequence data also provided evidence of natural recombination between PTV serotypes and indicated that homologous recombination may be a driving force in PTV evolution. The role of PTV in disease remains inconclusive. The current results together with published results indicate that the prevalence of PTV is increasing among swine herds in northeast of China.

Introduction

Porcine teschovirus (PTV) belongs to the family Picornaviridae and the genus Teschovirus. Two PTV strains (the Teschen and Talfan strains) were first isolated during outbreaks of polioencephalomyelitis in Europe in 1929 and 1957, respectively (Trefny, 1930, Harding et al., 1957). PTV was classified previously within the genus Enterovirus and was known as porcine enterovirus (PEV) but has been reclassified as PTV with 13 subtypes (PTV-1 to PTV-13) based on detailed genetic analyses (Zell et al., 2001).

As categorized by the Office International Epizooties, PTV is now a List B Pathogen and is now recognized as a worldwide pathogen of pigs. Among domestic animals, the pig is considered the most infected commonly and severely by PTVs. PTV causes various clinical symptoms such as neurological disorders (e.g., polioencephalomyelitis), reproductive disorders (Dunne et al., 1965), diarrhea (Izawa et al., 1962), and pneumonia (Meyer et al., 1966). Because PTV is persistent, it can survive on pig farms for a long time, and this persistence increases the probability of mixed infections with other pathogens such as PRRSV and CSFV. Mixed infections could lead to more serious diseases of pigs and greater economic loss than single infections. In 2007, RT-PCR had been used to detect PTV infection in numerous fever cases among swine in the Jiangsu region of China (Zhu, 2008); the PTV-positive rate was 47.5%, indicating that PTV infection is widespread among pigs in that region of China.

Because of a lack of serological data, the occurrence of PTV in pigs in China is difficult to assess. The current study had the following aims: to assess the occurrence of PTV in pigs in China based on the routine diagnosis and molecular epidemiology; A variety of assays were used. An indirect immunofluorescence assay was used to detect PTV-specific antibody. A multiplex RT-PCR (mRT-PCR) assay was used for simultaneous detection of multiple detect multiple viral infections of swine including those caused by PTV. A real-time reverse transcription polymerase chain reaction (RT-PCR) assay based on TaqMan probes was used to detect all types of PTVs.

Section snippets

Survey

From September 2008 to September 2009, a total of 1384 sera samples were collected from 42 swine herds in northern China. Each sample was from one pig (age 20 days to 6 months), and from 4 to 200 samples were obtained from each herd (Table 1). The herds were located in four provinces (Shandong, Hebei, Heilongjiang, and Jilin) and also in Tianjin City. The pigs were selected randomly for sampling. The collected sera were stored at −20 °C in the laboratory.

A total of 205 clinical samples including

Serological survey

Among the 1384 sera samples, 849 (61.3%) reacted with PTV-8 in the IFA (1:20). All 42 swine herds were PTV-seropositive. The percentage of PTV-seropositive animals in the herds ranged from 23.3% to 95.0% (Table 1) and was greater than 40% in most herds (Fig. 1).

In one herd, sera samples were collected from the same 10 piglets at age 4, 8, 12, and 16 weeks. The percentage of pigs in which PTV was detected by IFA was 40% when the pigs were 4 weeks old and 100% when the pigs were 16 weeks old (

Discussion

PTV virus was first detected in Europe, has been enzootic in Europe and other regions, and is currently one of the major infectious pathogens of swine worldwide (Teschovirus Encephalomyelitis, 2008). Several regions around China have reported PTV. PTV strains were isolated from diseased swine in Japan and found to be pathogenic to swine (Yamada et al., 2004). The PTV isolation rate was 20% in swine herds in Taiwan, where all PTV subtypes except PTV-5 were isolated PTV-1 was isolated in mainland

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  • Cited by (14)

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      However, the numbers of F-RNA coliphages excreted by swine are relatively low at levels ranging from 2.0 to 5.5 log plaque forming units (PFU)/g (Havelaar et al., 1990; Jones and Johns, 2012), posing difficulties for detection and quantification by molecular based assays at the lower limits. Porcine teschovirus (PTV), a picornavirus, has also been identified as a potential indicator of fecal contamination by swine in water, it is cultivable and is excreted abundantly (Jiménez-Clavero et al., 2003; Jones et al., 2014; Qiu et al., 2013). PTVs are usually nonpathogenic although some pathogenic strains, Teschen and Talfan, have been associated with encephalomyelitis, a serious neurological disorder, that led to significant economic losses in swine herds (Doherty et al., 1999; Harding et al., 1957).

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