Virus

They are the kind of microorganism with the smallest size amongst all those that affect pigs, in fact are so small that most of them can not be seen with an optical microscope. Viruses can only multiply inside the cells of other organisms. Among the main viruses that affect pigs, we find the Influenza virus, herpesvirus (Aujeszky), arterivirus (PRRS), circovirus (PCV2), encephalomyocarditis virus (EMCV), parvovirus, adenovirus, astrovirus, calicivirus, coronavirus, reovirus...

As in the case of bacteria, viruses are able to survive outside the animal for a certain period of time (from days to months or even years), depending on the environmental conditions (cold and humidity normally increase their survival rate), and on the kind of virus.