by Joanna Hay

Created on: June 26, 2009   Last Updated: June 27, 2009

Although it has been mostly eradicated from the US, pseudorabies virus remains a constant threat to hog producers throughout the world. The virus results in various manifestations of disease depending on age and species, but death rates and economic losses can be astronomical. Pigs are the species most commonly affected, but many others can also become infected with up to 100% mortality.

Pseudorabies is caused by a herpes virus. The symptoms resulting from infection were first described in 1813 in cattle that were housed with pigs. A Hungarian scientist named Aladar Aujeszky was the first person to isolate the causative agent and identify it as a virus. As a result, his name is often associated with the disease in hogs. In 1909 a scientist named Weiss discovered that pigs are the definitive host of the virus. This means that although others species can become infected and transmit the disease at a low level, only pigs survive infection long enough for the virus to complete its life style and multiply.

Once the virus has multiplied in its host, it can be transmitted in nasal secretions or feces. Coughing and sneezing aerosolizes viral particles and results in infective droplets that can remain suspended for up to seven hours. The disease can be transmitted from pig to pig by these droplets or by fecal contamination of feed bunks. The disease can also move from farm to farm via infective droplets on the wind, transport of infected animals, or transport of feces on vehicles and other equipment.

The clinical appearance of pseudorabies infections in pigs depends on the age of the pig at the time of infection. Pigs less than seven days old are the most susceptible. They show a rapid onset of neurologic abnormalities including seizures and circling. The animal quickly becomes comatose and almost 100% die. Weaned piglets between three and six months of age show similar neurologic signs as well as respiratory disease including coughing, sneezing, and copious nasal discharge. The disease is fatal for about 50% of pigs in this age range. Once pigs reach the five to nine week old range they begin to develop some resistance to the disease. Similar signs will be seen to those in younger pigs, but only 10% mortality is present. The biggest problem during this time frame is loss of growth, which has serious economic repercussions. If pigs are infected between nine weeks of age and adulthood, the virus does not result in mortality but does severely compromise the immune

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