The Biology of the Goat

Introduction to the CAE virus

Viruses are very small, simple organisms that have only one goal in life -- to make more of themselves. They are so small they can carry only a small number of genes plus a few important molecules all wrapped up in a protein coat. For this reason, viruses need to invade a cell and exploit the machinery of that cell to replicate. Viruses are completely dependent on the genetics and function of the cell that plays host to them.

The virus that causes inflammation of the brain (encephalitis) in young goats and degenerative arthritis and mastitis in adult goats is a member of the retrovirus family of viruses. These viruses carry their genes in the form of RNA instead of DNA. While there are other types of RNA viruses, retroviruses are unique in that the RNA is converted into double-strand DNA shortly after the virus enters the cell. This DNA is then inserted into the genome of the living cell to become a permanent gene within the chromosome of the host cell.

The CAE virus is classified as belonging to a subgroups of retroviruses called lentiviridae. Lenti is the latin word for slow describing the long disease process which can sometimes takes years to develop. Another virus that is very similar to the CAE virus is the Maedi-visna virus (MVV). MVV, the first lentivirus to be discovered in 1954 in Icelandic sheep causes inflammation of the lungs and wasting of the spinal cord and brain. In the US the disease is called ovine progressive pneumonia (OPP) The CAE and Maedi-visna viruses are so similar and since recent evidence shows that both viruses can cross-infect both sheep and goats, CAEV and MVV are now more often referred to as Small Ruminant Lentiviruses (SRLVs).

The CAE virus is most commonly passed through milk and especially colostrum from an infected dam to her kids. This is called vertical transmission. The virus can also be passed, but only rarely from one goat to another which is called horizontal transmission. In sheep, horizontal transmission of MVV appears to be an more important source of infection.

Next: The structure of the CAE virus