Enteral coronaviruses of swine - Literature review

SUMMARY Enteric diseases induced by viruses are highly prevalent and have great economic importance in the swine industry. From the many viruses, which can be found in the background of watery diarrhoea the coronaviruses were chosen to be reviewed in this paper. One of the first enteric diseases of swine discovered was transmissible gastroenteritis (TGE), which became endemic in Europe, as later on its deletion mutant, the porcine respiratory coronavirus (PRCV) spread worldwide. Porcine epidemic diarrhoea (PED), recognized later, is also caused by a coronavirus and it can be only differentiated from TGE by laboratory diagnostic methods, as their clinical and pathological appearance is quite similar. Recently, PED appeared in the previously porcine epidemic diarrhoea virus (PEDV) free North America, and spread rapidly causing great economic losses. These out-breaks attracted the attention to the renewed investigation of PED in European countries as well, which resulted in founding different contemporary viruses in several countries, including Hungary. Several years ago, a novel coronavirus, porcine deltacoronavirus (PDCoV) was discovered in China, then appeared as an enteropathogen in the United States (US), and spread also to other Asian countries, but has not been reported in Europe yet. Based on the currently available field observations from the US and Asia, the clinical disease caused by PDCoV seems to be milder with lower mortality compared to PED. On the other hand, it causes a differential diagnostic challenge, which is made even more difficult by the fact that porcine coronaviruses can occur in the same animal at the same time. At the moment, vaccines are available only for the prevention of TGE and PED, but not for PDCoV, and research is still in progress to make them more effective by reducing virus shedding and inducing proper local immunity on the mucous membrane of the small intestine