Porcine circovirus type 2 (PCV2) belongs to the viral family Circoviridae and to the genus Circovirus. Circoviruses are small, single-stranded nonenveloped DNA viruses that have an unsegmented circular genome. PCV2 is the primary causative agent of several syndromes collectively known as porcine circovirus-associated disease (PCVAD). Many of the syndromes associated with PCVAD are a result of coinfection with PCV2 virus and other agents such as Mycoplasma and porcine reproductive and respiratory syndrome virus. PCV2 infection is present in every major swine-producing country in the world, and the number of identified cases of PCVAD is rapidly increasing. In the United States, the disease has cost producers an average of 3-4 dollars per pig with peak losses ranging up to 20 dollars per pig. The importance of this disease has stimulated investigations aimed at identifying risk factors associated with infection and minimizing these risks through modified management practices and development of vaccination strategies. This paper provides an overview of current knowledge relating to PCV2 and PCVAD with an emphasis on information relevant to the swine veterinarian.

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Summary A reovirus serotype 3 (Ralph) originally isolated from a 4‐month‐old foal with diarrhea was inoculated into horses and ponies to investigate whether it caused enteric or respiratory disease. The results of these experiments were compared to the results of experimental inoculations of the German strains of reovirus 1 and 3. In the first experiment, four older foals were inoculated per os. In the second experiment four neonatal foals were inoculated by stomach tube. The dams were contact controls. None of the mares or foals became ill, although all the foals shed virus. Seven of eight foals seroconverted. Three of eight contact control mares seroconverted. Six animals were inoculated with Ralph strain virus intranasally and onto the conjunctiva. All the animals exhibited mild signs of upper respiratory disease. All the animals, except one, seroconverted. Virus was reisolated from the feces of all but one animal. Virus was reisolated from nasal or conjunctival swabs from two animals. The German strains of reovirus 1 and 3 each were inoculated into two horses intranasally twice followed by a third intranasal/intravenous inoculation with the heterologous serotype. Mild upper respiratory disease was observed. All four horses seroconverted to both serotypes. Virus was reisolated from nasal swabs from two horses and from one eye swab from a third horse. Reovirus serotype 3 (Ralph isolate) does not appear to cause enteric disease in neonatal or young foals. It did cause a mild upper respiratory disease as did the German strains of reovirus. There was little to no protection against subsequent inoculation afforded by the initial infections. Zusammenfassung Experimentelle Infektion von Pferden und Ponies auf oralem und intranasalem Weg mit dem “New York State” Reovirus Typ 3, dem “deutschen” Reovirus Typ 1 und drei equinen Isolaten Mit dem Reovirus Serotyp 3 (Ralph), ursprünglich isoliert aus einem vier Monate alten Fohlen, wurden Pferde und Ponies infiziert, um zu untersuchen, ob es eine Darmoder respiratorische Krankheit verursacht. Die Ergebnisse dieser Versuche wurden mit den Ergebnissen der experimentellen Infektionen mit dem “deutschen” Reovirus‐Stamm 1 und 3 verglichen. Im ersten Versuch wurden vier ältere Fohlen per os infiziert. Im zweiten Versuch erfolgte die Infektion mittels Magensonde bei vier neugeborenen Fohlen. Die Muttertiere bildeten die Kontaktkontrollen. Keine der Stuten oder Fohlen wurden krank, obwohl alle Fohlen das Virus ausschieden. 7 der 8 Fohlen zeigten eine serologische Reaktion. 3 von 8 Stuten der Kontaktkontrollen hatten eine serologische Reaktion. Sechs Tiere wurden mit dem Virus‐Stamm Ralph intranasal und über die Konjunktiva infiziert. Diese Tiere zeigten alle milde Krankheitssymptome der oberen Atemwege. Alle Tiere außer einem reagierten serologisch. Von allen Tieren, außer einem, wurde das Virus aus dem Kot reisoliert. Von zwei Tieren konnte das Virus aus Nasen‐ oder Konjunktivaltupfer reisoliert werden. Mit jedem der “deutschen” Reovirus‐Stämme 1 und 3 wurden zwei Pferde 2mal intr...

The recent construction of PRRSV infectious cDNA clones affords the opportunity for structural and functional studies of PRRSV genes. However, the inherent instability of the PRRSV genome, the requirement of cell culture propagation, and poor virus recovery have limited the usefulness of the PRRSV reverse genetics system for in vivo studies. Here, we report a unique strategy of infecting pigs by bypassing the traditional in vitro cell culture step required for in vivo studies. We demonstrate that inoculation of RNA transcripts of a PRRSV infectious cDNA clone directly into the lymph nodes and tonsils of pigs produces active PRRSV infection. The information from this study will have significant implications for the study of the molecular mechanism of PRRSV pathogenesis using the reverse genetics system.