Porcine epizootic diarrhea
Porcine epizootic diarrhea (PED) or epizootic virus diarrhea (EVD) is a diarrheal disease of pigs caused by coronaviruses that can be associated with a high mortality rate, especially in young piglets. Epidemic incidence of PED has been reported in North America since 2013. In 2014, acute outbreaks were reported in Germany; in Austria, the virus was detected on a farm in fattening pigs of German origin:
Other names for this infectious disease are Epidemic Viral Diarrhea (EVD) and currently in the American literature "Novel Swine Enteric Coronavirus Disease (SEDC). Only pigs are susceptible to this virus; there is no risk of infection to humans or other domestic animals. Infection occurs through virus-containing feces via the so-called faecal-oral route of infection. After experimental infection, the first signs of illness may appear as early as 36 hours. If the pathogen is introduced into a naive herd, the typical signs of disease are visible within 3-5 days.
PED virus was detected for the first time in Austria at the end of 2014. The detection and molecular biological determination of the virus was carried out at the Institute for Veterinary Investigations of the AGES in Mödling. The case report of this first occurrence of PED in Austria was published in the journal BMC Veterinary Research in January 2016 (Steinrigl et al, First detection, clinical presentation and phylogenetic characterization of Porcine epidemic diarrhea virus in Austria, BMC Veterinary Research (2015) 11:310 DOI 10.1186/s12917-015-0624-1).
The diseases on an Austrian farm first appeared shortly after importation in a group of fattening pigs of German origin. The animals showed decreased appetite and had mild diarrhea. The clinical situation had normalized after four weeks; however, by this time the virus had spread to another pen on the same farm: A group of fattening pigs of Austrian origin had the same symptoms, and molecular biology tests showed infection with PEDV here as well. Even several weeks after the disease symptoms had subsided, the virus was still detectable in fecal samples by molecular biology. In the first half of 2015, PEDV was also detected in three other pig farms in Austria. All molecular biological investigations indicate that it is the same pathogen strain that has been causing outbreaks in Western and Central Europe since 2014.
Diarrheal disease similar to PED was first observed in fattening pigs in England in 1971 and subsequently spread to several European countries. Reports are available from Belgium (1978), the Czech Republic (1993), Hungary (1996), and also from Germany, France, Holland, and Switzerland. Thereafter, there have been few - and if any - outbreaks of disease in Europe. In a study conducted in Austria by Möstl et al. (1990), no evidence of the occurrence of PED in the Austrian pig population was found.
In the period 2005 - 2006, infection was detected in 63 herds in Italy. From 2000 and continuing to the present, PED outbreaks have been reported in Korea, China, Thailand, and other Asian countries. Since 2010, outbreaks with high fatality rates in piglets have increased sharply in these countries. In 2013, the first cases of PED occurred in the U.S. states of Iowa and Minnesota. Within a short time, additional outbreaks were recorded throughout the U.S., Canada, Mexico, and Central American states. These outbreaks are associated with major economic losses due to disease and deaths in pigs, but also due to trade restrictions.
Molecular genetic analysis of the virus has detected a new variant of PED virus (PEDV) in the Americas and Asia that appears to be more virulent than the virus originally isolated in Europe in the 1980s. In addition, genetic analyses detected a new coronavirus (deltacoronavirus) that may also be involved in the disease process.
Recently, several acute outbreaks were reported in Germany, first in fattening pigs, but now also in suckling piglets. Mortality was low in fattening pigs, but up to 70% in suckling piglets. All sequencing available to date from the acute cases that occurred in Germany shows a high genetic match to the less pathogenic variant of the strains that occurred in the United States.
The clinical expression of the disease symptoms and their course are strongly dependent on the age of the affected animals and the immunity situation of the herd and are described as follows:
- If the animals of a herd had no contact with the virus until virus introduction (so-called naive or fully susceptible herd), the following symptoms appear in suckling piglets (1-28 days of life): almost 100% of the animals become ill with vomiting; the piglets have acute watery diarrhea. As a result of the severe loss of fluid and the resulting acidosis (hyperacidity of the blood), 50-80% of the piglets may die.
- If the animals are already older, much fewer animals die (1-3 %). Symptoms of diarrhea and loss of appetite can be observed in pigs of all ages, including breeding sows.
- Once the herd has overcome the acute disease event (so-called endemic disease event), the animals' performance returns to approximately normal and diarrhea only occasionally occurs in older or weaned piglets (3rd-6th week of life).
Since the virus is transmitted mainly by infected pigs, feces or objects contaminated with feces (manure, shoes, transport vehicles), attention must be paid to compliance with strict biosecurity or hygiene measures such as cleaning and disinfection of contaminated housing, objects and means of transport. The focus, of course, is on precautionary measures, especially when moving animals from affected stables or regions to unaffected countries and regions. Vaccines are already available in Asia and America, but their effectiveness is controversial.
Based on the clinical symptoms in a foci, only a tentative diagnosis can be made, which must be confirmed by appropriate laboratory testing. Using modern molecular biological methods (PCR), rapid and reliable diagnostics are possible to clarify suspected cases.
The following sample materials are suitable for diagnostics:
- Feces from acutely ill live animals
- intestinal contents and intestinal tissue (small intestine, large intestine) from dead animals
The feces should be chilled (4 °C) and taken within the first 24 h after the onset of diarrhea. Since intestinal tissue becomes autolytic relatively quickly, organ samples or dead animals should be brought or shipped to the laboratory as quickly as possible and refrigerated.
Differential diagnosis should exclude various other diarrheal pathogens:
- Bacterial infections caused by: Escherichia coli, Clostridium perfringens, Salmonella.
- Viral infections caused by: transmissible gastroenteritis virus (TGE), rotavirus, circovirus type 2 (PCV-2), classical swine fever virus (CSF) and African swine fever virus (ASF).
- Parasite infestation: coccidia