Page 679 - Veterinary Immunology, 10th Edition

VetBooks.ir The Virome

The viral component of the microbiota is called the virome—the
collection of all viruses found within an animal. They include not

only the viruses of eukaryotic cells that cause infection and disease
but also the endogenous viruses that are integrated into and form a
significant component of mammalian genomes. This virome differs
greatly between individuals and may be even more diverse than the
bacterial microflora. It has been estimated that the number of

distinct viruses in human stool samples can range from 50 to almost
3000. In addition to mammalian viruses, the virome contains huge
numbers of bacteriophages, perhaps as many as 100 phages for

every bacterium. These phages prey on the bacteria and may play a
role in transmitting genes between bacteria. When alterations in
diet change the composition of the bacterial microflora, they also
alter the composition of the phage population.
Certain enteric viruses such as the noroviruses can influence the

development of the enteric immune system. Thus they can restore
intestinal morphology and lymphocyte function in germ-free mice.
Conversely, the ability of noroviruses to persistently infect animals

depends on the microbiota. Antibiotics prevent persistent norovirus
infections by changing the composition of the microbiota. Removal
of the virome with antiviral drugs can result in enteritis.

679