Keywords: of pev
Description: The Pirbright Institute, Pirbright Laboratory, Ash Road, Pirbright, Woking, Surrey, GU24 0NF, United Kingdom. Teschen disease was first described in Czechoslovakia by Trefny (1930). This severe
The Pirbright Institute, Pirbright Laboratory, Ash Road, Pirbright, Woking, Surrey, GU24 0NF, United Kingdom.
Teschen disease was first described in Czechoslovakia by Trefny (1930). This severe clinical form of pig polioencephalomyelitis, with a mortality of up to 90%, was confined to central Europe until 1952, at which time it was confirmed in Madagascar (Pilet, 1952). In Denmark and England, a disease of pigs characterized by a mild nervous disorder was reported, and the names "poliomyelitis suum" and "Talfan" were used in the respective countries (Bendixen and Sjolte, 1955; Harding et al. 1957). These diseases were mild and there was almost no mortality. However, histological examination of the central nervous tissues revealed changes indistinguishable from those of the more severe Teschen disease. In 1958 it was established by reciprocal cross-neutralization tests in cell culture that Talfan virus was closely related to Teschen disease virus (Chaproniere et al. 1958). It was later shown by immunity tests in pigs that related viruses causing the mild disease can protect pigs against challenge with those viruses causing the severe disease (Huck, 1962; Mayr, 1961).
Porcine enteroviruses (PEV), other than Teschen disease virus, were first described in the late 1950s following the development of tissue culture techniques.
PEVs have been divided into three distinct groups (I, II and III) based on physicochemical properties, type of cytopathic effect (CPE) produced in pig kidney cells and different cell culture host ranges (Zoletto 1965; Zoletto et al. 1974; Knowles et al.. 1979). They are also classified into 11 serologically distinct types (Dunne et al. 1971; Knowles et al.. 1979), groupI consisting of serotypes 17 and 11, group II consisting of serotype 8 and group III consisting of serotypes 9 and 10. Teschen disease virus belongs to serotype 1. Swine vesicular disease (SVD) virus is not included as an additional PEV serotype since it is classified as a porcine variant of the human pathogen coxsackievirus B5 (Knowles et al. 1979).
PEVs are readily cultivated in the laboratory in cell cultures of porcine origin. Primary or secondary cultures of pig kidney or testes are generally used. However, continuous cell lines such as IB-RS-2, PK-15 or MVPK may be also be successfully employed. The type of CPE exhibited in porcine kidney cells can be recognised by experienced workers and used as a preliminary grouping method. The growth of PEV in cells derived from non-porcine sources varies between, and sometimes within, the three PEV groups (Knowles et al. 1979).
Depending on the reason for diagnosis a number of different tissues may be submitted. PEVs have been associated with nervous, respiratory, reproductive and digestive disorders. They are commonly found in faeces of both normal and sick pigs and isolation rates may be high (Knowles, 1983; Honda et al. 1990c). PEVs may also be isolated as incidental findings during the diagnosis of other diseases of pigs such as SVD or foot-and-mouth disease (FMD). In these cases, a test capable of differential diagnosis may be of vital importance to facilitate the rapid reporting of results (Knowles, 1988).
The ultimate typing test is still virus neutralization since the presence of multiple serotypes may be detected, however, where many tests are to be performed complement fixation is recommended (Knowles and Buckley, 1980; Knowles, 1983; Caracappa et al. 1985; Shin et al. 1987). Other techniques such as immunofluorescence (Watanabe, 1971), immunodiffusion (Sulochana and Derbyshire, 1978a), immunoperoxidase (Sulochana and Derbyshire, 1978b; Honda et al. 1990a) have been developed, however, none of these techniques have been employed for serotyping principally due to a lack of specificity. An enzyme-linked immunosorbent assay (ELISA) for PEV typing is currently being developed at Pirbright employing rabbit and guinea pig antisera raised against purified, inactivated viruses.