What age group of cats is most susceptible to the effects of feline leukemia virus?

Young kittens are the age group most susceptible to the effects of feline leukemia virus (FeLV). This vulnerability is primarily due to their immature immune systems, which are not fully developed and therefore less capable of fighting off infections. Kittens, especially those under six months of age, are at higher risk because they are often in close contact with other cats, which facilitates the transmission of the virus.

In contrast, older cats may have developed some level of immunity through exposure to various pathogens over their lifetime, which can provide them with some protection against FeLV. Middle-aged cats may also be less susceptible if they have been vaccinated against the virus or have had previous exposure that allowed them to build immunity. The statement that all ages are equally affected does not take into account the significant differences in immune response and exposure risk across different life stages in cats. This makes young kittens particularly vulnerable to the effects of FeLV, aligning with the correct choice.