Final answer:
The incidence of retrovirus infections in cats, such as those caused by FeLV and FIV, is variable and dependent on regional factors. Viral genetic information that does not replicate the virus can be maintained by the host if it does not negatively impact the host or provides an evolutionary advantage.
Step-by-step explanation:
Regarding the question, 'What can be said about the incidence of retrovirus infections in cats over the years?' the correct answer is that it varies depending on the region. The incidence of retroviruses like feline leukemia virus (FeLV) and feline immunodeficiency virus (FIV) can differ based on factors such as the prevalence of the virus in the local feline population, the effectiveness of vaccination programs, and local awareness and management of the disease by pet owners and veterinarians.
Explaining in terms of selection how viral genetic information that no longer replicates the virus is maintained by the host: certain viral genetic elements may be conserved within a host's genome because they do not impose a significant negative impact on the host, or they may offer some evolutionary advantage to the host organism. This genetic material can sometimes provide benefits such as resistance to other infections or a selective advantage under particular environmental conditions, prompting its retention in the host genome through natural selection.