CASE 33
He admitted to having unprotected sex with other men. His last encounter was 3 weeks earlier. He denied prior transfusions or intravenous drug use.
LABORATORY STUDIES
Diagnostic Work-Up
Table 33-1 lists the likely causes of the man’s illness (differential diagnosis). A clinical diagnosis of acute human immunodeficiency virus (HIV)-1 infection was considered based on the risk and symptoms. Laboratory-based studies are necessary for confirmation of HIV-1 infection and may include
TABLE 33-1 Differential Diagnosis and Rationale for Inclusion (consideration)
Rationale: Several primary viral infections have similar presentations. Fever, malaise, and lymphadenopathy are common symptoms. CMV is frequently associated with liver involvement. A maculopapular truncal rash can often be seen in primary HIV infection. Oral ulcers are commonly seen with primary HSV infection. Infectious mononucleosis may have associated splenomegaly and, in particular, a severe sore throat. Secondary syphilis is often characterized by a rash that also involves the palms and soles. As seen above, symptoms, signs, and epidemiology (e.g., host risk factors) are helpful in suggesting an infectious etiology, but laboratory investigation is needed for confirmation of the clinical diagnosis.
COURSE
The patient consented to be tested for HIV antibodies, and the result was negative. However, HIV viral RNA level was very high, and a diagnosis of acute HIV infection was made.
MICROBIOLOGIC PROPERTIES
HIV belongs to a subgroup of retroviruses known as lentiviruses (“slow” viruses). The four recognized human retroviruses belong to two distinct groups: the human T lymphotropic viruses, HTLV-1 and HTLV-2, which are transforming retroviruses; and the human immunodeficiency viruses, HIV-1 and HIV-2, which are cytopathic viruses. The course of infection with retroviruses is characterized by a long interval between initial infection and the onset of clinical symptoms. The most common cause of HIV disease in the United States as well as worldwide is HIV-1. The virion structure of HIV-1 consists of a capsid and a surrounding matrix and envelope studded with virus-specific proteins (Fig. 33-1). Embedded in the viral envelope is a transmembrane protein (Env), consisting of a cap made of three molecules called glycoprotein (gp) 120, and a stem of three gp41 molecules that anchor the structure in the viral envelope. The envelope also incorporates a variety of host proteins, including major histocompatibility complex (MHC) class I and II antigens.
FIGURE 33-1 Architecture of HIV-1 virion. Structure of HIV-1, including the outer membrane glycoprotein (gp120) with transmembrane components (gp41) of the envelope, genomic RNA (diploid; 2 copies of identical genome), enzyme reverse transcriptase, p17 inner membrane (matrix), and p24 core protein (capsid).
The bullet-shaped core (capsid) is made of a viral capsid protein, p24. The core surrounds two identical single-stranded RNA copies of the genome, each of which has a copy of the virus’ nine genes, of which six are regulatory. The other three, genes gag, pol, and env, contain information needed to make structural proteins for new virus particles. The core of HIV also includes the HIV nucleocapsid protein and three enzymes that carry out later steps in the life cycle of the virus: reverse transcriptase (RT), integrase, and protease. The HIV inner membrane matrix protein (p17) lies between the viral core and the viral envelope.
EPIDEMIOLOGY
HIV is transmitted by permucosal (sex), parenteral (intravenous drug use), and vertical (in utero to fetus) transmission. HIV infection is currently a major sexually transmitted disease (STD) worldwide. The virus can enter the body through the lining of the vagina, vulva, penis, rectum, or mouth during sex. Having an STD such as syphilis, genital herpes, or chlamydia infection appears to make people more susceptible to acquiring HIV infection during sex with infected partners. This is at least partly due to the presence of genital ulcers. HIV frequently is spread among intravenous drug users by the sharing of needles or syringes contaminated with very small quantities of blood from someone infected with the virus. Women can transmit HIV to their babies during pregnancy or birth.
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