Page 875 - Veterinary Immunology, 10th Edition

by the diversity of these viruses.
VetBooks.ir because the immune system is unable to eliminate them. Diseases of
Even more adapted viruses can result in persistent infection

this type include the lentivirus infections, equine infectious anemia,

and maedi-visna of sheep. Vaccination against these diseases is
essentially unsuccessful. As their adaptation increases, viruses may
cause latent infections and relatively mild, non-lethal disease. Some
herpesvirus infections also fall into this category. The most extreme

examples of virus adaptation are those in which the viral nucleic
acid becomes stably integrated into the host genome. These
endogenous viruses are common in the genomes of domestic
mammals.

In studying the nature of the host responses to viruses, it is
important to recognize that this continuing selective pressure on
both host and virus exists and profoundly influences the outcome
of all viral infections.

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