Final answer:
Individuals with T-cell deficiencies are prone to infections caused by bacteria, viruses, fungi, and protozoa, as T-cells are essential for a strong immune response to these pathogens.
Step-by-step explanation:
Individuals with T-cell deficiencies are vulnerable to a wide array of infections because T-cells are a crucial part of the immune system responsible for fighting off pathogens. These organisms can include bacteria, such as Treponema pallidum, which causes syphilis; viruses, like Varicella-zoster virus (human herpesvirus 3) which causes chickenpox and shingles, Hepatitis B virus, a type of hepadnavirus that leads to hepatitis, Parvovirus B19 which can cause anemia, and various retroviruses.
Individuals with a T-cell deficiency are also susceptible to protozoan infections such as Toxoplasma gondii, which can lead to toxoplasmosis, especially in the immunocompromised. Infections can also be caused by fungi, including opportunistic fungi such as Aspergillus, Candida, and Pneumocystis, which can lead to serious conditions in those with weakened immune systems. A deficiency in T-cells can be caused by various conditions, including HIV/AIDS, which is the most common cause of immunodeficiency due to its destruction of helper T cells.