In a span of 45 years, HIV infection and AIDS have attained pandemic proportions. At the time of this writing it was estimated by the World Health Organization (WHO) that approximately 37 million persons are infected worldwide and that approximately 1 million adults in the United States are seropositive for the virus with approximately 40,000 new cases yearly, a number which gas been slowly declining. The CDC furthermore estimates that 18 percent of infections have not been diagnosed. Though the incidence is decreasing, particularly startling are the statistics from sub-Saharan Africa and Southeast Asia, where the WHO estimated that approximately 20,000,000 adults—or almost 9 percent of the adult population—were infected. In some areas of East Africa, 30 percent of adults are infected with the virus.
In the United States, HIV affects mainly homosexual and bisexual males (currently termed “men who sex with men [MSM], comprising two-thirds of all new cases) and male and female drug users (almost one-third of cases). Somewhat less than 2 percent of patients who are at risk are hemophiliacs and others who receive infected blood or blood products, and the disease has occurred in infants born of mothers with HIV. Moreover, the virus may be transmitted by asymptomatic and still immunologically competent mothers to their offspring. Spread of the disease by heterosexual contact accounts for approximately 5 percent of cases, but this number is gradually increasing, partly through the activities of intravenous drug users. By contrast, an estimated 80 percent of African AIDS patients acquire their disease through heterosexual contact.
The related but less common entity of HIV-2 infection causes a generally less severe illness than HIV-1 but may include almost any of the features described below, including dementia. The virus is currently most prolific in Brazil, Cape Verde, and West African countries. The diagnosis is made complicated by the usual findings of a positive ELISA test but a negative or indeterminate Western blot results when conventional methods are used. A specific Western blot test is available for HIV-2.
The inception of highly active anti-retroviral treatment has greatly altered the frequency and presentations of all of the disorders associated with HIV infections, foremost among these, the neurological ones.
Infection with HIV produces a spectrum of disorders, ranging from clinically inevident seroconversion to widespread lymphadenopathy and other systemic manifestations such as diarrhea, malaise, and weight loss, which comprises the direct effects of the virus on all organ systems as well as the complicating effects of a multiplicity of secondary parasitic, fungal, viral, and bacterial infections and a number of neoplasms, all of which require cell-mediated immunity for containment. Until the recent advent of multiple antiviral drug therapy, once the manifestations of AIDS had become established, half of patients died by 1 year and most by 3 years. Neurologic abnormalities had been found in about one-third of untreated patients with HIV but at autopsy the nervous system is affected in nearly all of them. Table 32-2 lists the main infections and neoplastic lesions of the nervous system that complicate AIDS.