Introduction to Week 6

During the previous weeks we have seen different groups of viruses that affect animals, organized according to the mechanism they use for transmission. This knowledge has allowed us to understand better the difficulties raised by diagnosis and the control measures more appropriate to avoid their transmission. To finish the course, we will complete the general overview of animal viruses by studying two families that produce chronic infections,

which may persist during long periods in the host: retroviruses and herpesviruses. What a big problem, right? Animals are infected but they do not show anything wrong. But at any given time, the clinical signs can re-emerge. Herpesvirus and retroviruses are able to hide in different types of cells, barely showing. This allows them to escape the control of the immune system. This situation, called latency, hinders the diagnosis and the control measures designed to avoid the spread of the disease. Retroviruses, the family to which human immunodeficiency virus belongs, also produce slow and progressive diseases in animals, such as feline leukemia and immunodeficiency.

They can do this because they are able to integrate in the genome of the host cell, behaving as Mendelian genes, i.e., when the cell is divided, the progeny cell also is infected by the viruses. The big family of the herpesviruses, which includes well-known viruses, such as those which produce cold sores in people, encompasses many viruses causing diseases of different type in animals such as cows, pigs, poultry, carp or even oysters. They do this because they are able to remain non-integrated in the cell, as episomes.

Knowing the characteristics of these families of viruses and of the diseases that they produce will help us to assess their importance in husbandry and in pets, and also to analyze the threat they may represent for certain animal species.