A Look at the Pseudorabies Virus

Many people may think that Pseudorabies and Rabies are the same thing. Well, they are very similar but Pseudorabies is different. It is an acute, typically fatal disease with a worldwide distribution that primarily affects pigs. It will affect domestic and other wild animals incidentally. The Pseudorabies virus rose as a significant pathogen in the United States ever since the 1960's. This is most likely due to the fact that there has been a large increase in swine confinement or that more virulent strains have emerged. To identify the virus, symptoms are very similar to Rabies, which is why it gets the nickname "Mad Itch". Pseudorabies has been successfully eradicated from the vast majority of the United States.

The virus is transmitted nose-to-nose or fecal-oral contact. Indirect transmission occurs via inhalation of the virus. Clinical signs really depend on the age of the infected animal. Younger swine are at higher risk than older. The primary sites of viral replication occur in the nasal, pharyngeal, or tonsillar region. The virus will spread via the lymphatic system on to the regional lymph nodes, where the replication of the virus continues. The virus also spreads to the brain where it further replicates. In addition to the gross and microscopic lesions present, there are other diagnostic means for confirming infection such as isolation of the virus, fluorescent antibody testing, and serologic testing. The primary sites for virus isolation are the brain, spleen, and the lung.There is no treatment for acute pseudorabies infection, however, there is vaccination available that can alleviate the clinical signs of infection in pigs of specific ages. There have been numerous programs developed to eradicate the pseudorabies virus. This includes whole-herd depoplulation and offspring segregation. Usually, problems other than the virus itself need to be resolved before the whole-herd depopulation is deemed cost effective. In the offspring segregation program, young piglets are taken from vaccinated sows and are raised at another site into adulthood. If enough are raised in this manner, the original breeding population may be depopulated and the new herd can repopulate the breeding herd. In this case, all of the offspring must be tested individually and have negative results before being sold to someone. When it comes down to eradicating the virus through breeding, it is all through genetics and passing on genes that are not infected so that the repopulated herd becomes un-infected. The pseudorabies virus is very harmful to a farmers herd and can cost a farmer hundreds of thousands of dollars if not identified and eradicated early on.

Resources:

The Merck Veterinary Manual;http://www.merckvetmanual.com/mvm/index.jsp?cfile=htm/bc/102200.htm