Final answer:
Broadening the tissue tropism of viruses can decrease their virulence, as seen in attenuated vaccine strains and the emergence of tissue-restricted strains.
Step-by-step explanation:
Yes, there are cases where broadening the tissue tropism decreases the virulence of viruses. One example is the attenuated (weakened) vaccine strains of viruses. These vaccines are created by altering the virus's tissue tropism to make it able to infect a broader range of cells. By doing so, the virus becomes less virulent because it is less able to target and infect the specific cells that cause severe disease. Another example is the emergence of tissue-restricted strains of viruses. For some viruses, broadening their tissue tropism can be disadvantageous for their survival and transmission. They may have evolved to specialize in infecting specific tissues that allow them to replicate and spread more efficiently, and by broadening their tissue tropism, they may lose this advantage and become less virulent. Are there any cases where broadening the tissue tropism decreases the virulence of viruses? Tissue tropism refers to the tendency of most viruses to infect only certain tissue types within a host.
This specificity can sometimes be linked to the severity of the disease caused by the virus. In some instances, when a virus broadens its range of target tissues, it can potentially lead to a decrease in virulence. This could be due to a number of reasons, such as the dilution of the virus across more types of cells, which may reduce its efficacy in any one type of tissue, or it might trigger a more robust immune response from the host, which manages to contain the infection more effectively. An example of a virus that has a broad tropism but generally causes mild disease is the common cold virus. Conversely, viruses like HIV and hepatitis have a narrower tropism, targeting specific cells such as T-helper cells and liver cells, respectively, often resulting in more serious illness. Considering the role of interferons and cytotoxic T cells in the immune response, a virus with a broader tissue tropism might activate multiple immune pathways, promoting more effective clearance of the virus before it causes serious harm. However, it is also possible for a virus with a broader tropism to be more dangerous if it can thereby infect critical tissues or organs whose function is essential for survival.