Essex was one of the first to link animal and human retroviruses to immunosuppressive disease, to suspect that a retrovirus was the cause of AIDS, and to determine that HIV could be transmitted through blood and blood products to hemophiliacs and recipients of blood transfusions.
Essex was at the forefront in identifying the link between animal and human retroviruses and immunosuppressive disease, suspecting a retrovirus as the cause of AIDS, and demonstrating that HIV could be transmitted through blood and blood products to individuals with hemophilia and those receiving blood transfusions.