• HIV mutates rapidly
• HIV is not expressed in many cells that are infected
• HIV is not completely cleared by the host immune response after primary infection.
• HIV isolates show a marked variation, especially in the envelope antigens-variability that probably promotes the emergence of neutralization-resistant mutants
• Lack of an appropriate animal model for HIV.
• Chimpanzees are the only animals that are susceptible to HIV.

Novel methods are under investigation:

• Soluble form of CD4 has been made by recombinant DNA techniques and is being studied as a viral blocking agent. As CD4 is the HIV receptor on cells, soluble CD4 may inhibit HIV from infecting cells; may block gp120-mediated events, such as cell fusions and may serve as a targeting signal to direct cytotoxic agents to HIV-infected cells.
• Gene therapy approach are being developed that are designed to achieve "intracellular immunization," ie., genetically alter target cells to make them resistant to HIV.

Control measures:

To avoid epidemic spread of HIV it is important to educate the people about eliminating the high risk factors.

• All blood donors should be tested for HIV antibody
• Myths to be dispelled about HIV

HIV is not spread by

• Sharing meals with an HIV +ve patient
• Exposures to sneezing, coughing, or other casual contacts.