Human Immunodeficiency Virus (HIV) Infection

Overview

Plain-Language Overview

Human Immunodeficiency Virus (HIV) Infection is a condition caused by a virus that attacks the body's immune system, specifically the cells that help fight infections. This virus mainly targets CD4+ T cells, which are crucial for protecting the body against illnesses. As the infection progresses, the number of these immune cells decreases, making it harder for the body to defend itself. This leads to increased vulnerability to infections and certain types of cancers. The virus is transmitted through bodily fluids such as blood, semen, vaginal fluids, and breast milk. Without treatment, HIV can progress to Acquired Immunodeficiency Syndrome (AIDS), a severe stage where the immune system is critically weakened.

Clinical Definition

Human Immunodeficiency Virus (HIV) Infection is a chronic viral infection caused by the retrovirus HIV, which primarily targets and depletes CD4+ T lymphocytes, leading to progressive immunodeficiency. The virus integrates into host DNA via the enzyme reverse transcriptase, establishing a persistent infection. The hallmark of HIV infection is the gradual decline in CD4+ T cell count, resulting in impaired cell-mediated immunity. This immunosuppression predisposes patients to opportunistic infections, malignancies such as Kaposi sarcoma, and neurologic complications. Transmission occurs through exposure to infected bodily fluids, including sexual contact, blood transfusion, and vertical transmission from mother to child. The clinical significance lies in the risk of progression to Acquired Immunodeficiency Syndrome (AIDS), defined by severe immunodeficiency and life-threatening opportunistic diseases.

Inciting Event

Exposure to infected bodily fluids such as blood, semen, vaginal secretions, or breast milk initiates infection.
Transmission occurs through mucosal surfaces or direct bloodstream entry.
Initial infection often follows a high-risk sexual encounter or needle sharing event.
Vertical transmission occurs during intrapartum or postpartum exposure to maternal fluids.

Latency Period

The acute retroviral syndrome occurs 2-4 weeks after exposure with nonspecific symptoms.
Clinical latency can last from several years to over a decade without symptoms.
During latency, viral replication continues at low levels despite lack of symptoms.
Progressive CD4+ T cell decline eventually leads to symptomatic AIDS.

Diagnostic Delay

Early symptoms are often nonspecific and flu-like, leading to misdiagnosis.
Lack of routine HIV screening in asymptomatic individuals delays diagnosis.
Stigma and fear may prevent patients from seeking timely testing.
Misattribution of symptoms to other infections or conditions delays recognition.

Patient Population

Sexually active adults aged 15-49 years represent the majority of new infections.
Men who have sex with men (MSM) have a higher prevalence of HIV infection.
Intravenous drug users are a high-risk group due to needle sharing.
Newborns and infants born to HIV-positive mothers are at risk of vertical transmission.
Certain regions such as sub-Saharan Africa have higher HIV prevalence.

Risk Factors

Unprotected sexual contact with an infected partner is the most common transmission route.
Sharing contaminated needles among intravenous drug users increases risk.
Receiving unscreened blood transfusions or organ transplants can transmit HIV.
Mother-to-child transmission during pregnancy, delivery, or breastfeeding is a significant risk.
Presence of other sexually transmitted infections enhances susceptibility to HIV.

Clinical Presentation

Signs & Symptoms

Fever, night sweats, and weight loss are common systemic symptoms.
Chronic diarrhea may occur due to opportunistic infections or HIV enteropathy.
Oral thrush and mucosal ulcers reflect immunosuppression.
Neurologic symptoms including cognitive decline, peripheral neuropathy, or meningitis.
Recurrent infections such as pneumonia, tuberculosis, or herpes zoster.

History of Present Illness

Initial presentation may include fever, lymphadenopathy, rash, and pharyngitis during acute infection.
Patients often experience a prolonged asymptomatic period with gradual weight loss and fatigue.
Progression to AIDS is marked by opportunistic infections, chronic diarrhea, and neurological symptoms.
Recurrent infections such as oral candidiasis and Pneumocystis pneumonia are common in advanced disease.

Past Medical History

History of sexually transmitted infections increases suspicion for HIV.
Previous intravenous drug use is a significant risk factor.
Prior blood transfusions before routine HIV screening implementation are relevant.
Use of pre-exposure prophylaxis (PrEP) or antiretroviral therapy affects disease course.

Family History

No direct hereditary pattern, but family members may share risk behaviors increasing exposure.
Vertical transmission risk is higher if the mother is HIV-positive and untreated.
Genetic factors such as CCR5 delta-32 mutation can confer resistance but are rare.
Family history of immunodeficiency syndromes may complicate diagnosis but is distinct.

Physical Exam Findings

Generalized lymphadenopathy is common in early and chronic HIV infection.
Oral candidiasis and oral hairy leukoplakia indicate immunosuppression.
Kaposi sarcoma lesions appear as violaceous plaques or nodules on skin or mucosa.
Cachexia and wasting syndrome may be evident in advanced disease.
Neurologic deficits such as distal sensory polyneuropathy or cognitive impairment may be present.

Physical Exam Maneuvers

Lymph node examination to assess for persistent, painless lymphadenopathy.
Neurologic screening including mental status and peripheral nerve function to detect HIV-associated neurocognitive disorders.
Skin inspection for Kaposi sarcoma or other opportunistic infections.
Oral examination to identify candidiasis or hairy leukoplakia.
Pulmonary auscultation to evaluate for opportunistic pneumonias.

Common Comorbidities

Tuberculosis is a frequent co-infection in HIV patients worldwide.
Hepatitis B and C virus infections commonly co-occur due to shared transmission routes.
Human papillomavirus (HPV) infection increases risk of anogenital cancers.
Depression and other psychiatric disorders are prevalent in HIV-infected individuals.
Cardiovascular disease risk is elevated due to chronic inflammation and antiretroviral therapy.

Diagnostic Workup

Diagnostic Criteria

Diagnosis of HIV infection is established by detecting HIV antibodies and/or HIV RNA in blood. Initial screening is performed using a fourth-generation antigen/antibody combination immunoassay that detects both HIV-1/2 antibodies and p24 antigen. Positive screening tests require confirmation with an HIV-1/HIV-2 antibody differentiation assay. If results are indeterminate or discordant, HIV RNA PCR testing is used to confirm infection. A confirmed diagnosis requires reactive screening and confirmatory tests demonstrating the presence of HIV infection.

Pathophysiology

Key Mechanisms

HIV infects and depletes CD4+ T cells, leading to progressive immunodeficiency.
Reverse transcriptase converts viral RNA into DNA, enabling integration into host genome.
Viral integration into host DNA causes persistent infection and latency.
Chronic immune activation and inflammation contribute to immune system exhaustion.
Loss of cell-mediated immunity predisposes to opportunistic infections and malignancies.

Involvement	Details
Organs	Lymph nodes are key organs where HIV replicates and causes immune system damage.
	Brain can be affected by HIV leading to neurocognitive disorders due to viral invasion and inflammation.
	Bone marrow may be involved in HIV-associated cytopenias and impaired hematopoiesis.
Tissues	Lymphoid tissue is a major site of HIV replication and CD4+ T cell depletion.
Tissues	Gut-associated lymphoid tissue (GALT) is an early and significant site of CD4+ T cell loss in HIV infection.
Cells	CD4+ T cells are the primary target of HIV infection and their depletion leads to immunodeficiency.
	Macrophages serve as reservoirs for HIV and contribute to viral persistence and dissemination.
	Dendritic cells capture HIV and facilitate its transmission to CD4+ T cells.
Chemical Mediators	Cytokines such as IL-1, IL-6, and TNF-alpha are elevated during HIV infection and contribute to immune activation and inflammation.
	Reverse transcriptase is the viral enzyme targeted by multiple antiretroviral drugs to inhibit HIV replication.
	Integrase is a viral enzyme essential for integration of HIV DNA into the host genome.

Treatments

Pharmacological Treatments

Nucleoside Reverse Transcriptase Inhibitors (NRTIs)
- Mechanism:
  - Inhibit HIV reverse transcriptase by acting as nucleoside analogs causing chain termination during viral DNA synthesis.
- Side effects:
  - Lactic acidosis
  - Hepatotoxicity
  - Bone marrow suppression
- Clinical role:
  - First-line
Non-Nucleoside Reverse Transcriptase Inhibitors (NNRTIs)
- Mechanism:
  - Bind directly to HIV reverse transcriptase causing allosteric inhibition of viral DNA synthesis.
- Side effects:
  - Rash
  - Hepatotoxicity
  - Neuropsychiatric symptoms
- Clinical role:
  - First-line
Protease Inhibitors (PIs)
- Mechanism:
  - Inhibit HIV protease, preventing cleavage of viral polyproteins and maturation of infectious virions.
- Side effects:
  - Hyperlipidemia
  - Insulin resistance
  - Lipodystrophy
- Clinical role:
  - First-line
Integrase Strand Transfer Inhibitors (INSTIs)
- Mechanism:
  - Block HIV integrase enzyme, preventing integration of viral DNA into host genome.
- Side effects:
  - Insomnia
  - Headache
  - Elevated creatine kinase
- Clinical role:
  - First-line
Entry Inhibitors (e.g., Maraviroc)
- Mechanism:
  - Block CCR5 co-receptor on host cells, preventing HIV entry.
- Side effects:
  - Hepatotoxicity
  - Cough
  - Dizziness
- Clinical role:
  - Second-line
Fusion Inhibitors (e.g., Enfuvirtide)
- Mechanism:
  - Prevent fusion of HIV envelope with host cell membrane by binding gp41.
- Side effects:
  - Injection site reactions
  - Increased risk of bacterial pneumonia
- Clinical role:
  - Second-line

Non-pharmacological Treatments

Consistent use of condoms and safe sex practices to prevent HIV transmission.
Regular monitoring of CD4 count and viral load to guide therapy and detect treatment failure.
Nutritional support and management of opportunistic infections to improve immune function.
Counseling and support for adherence to antiretroviral therapy to prevent resistance.

Prevention

Pharmacological Prevention

Pre-exposure prophylaxis (PrEP) with tenofovir/emtricitabine reduces HIV acquisition risk.
Post-exposure prophylaxis (PEP) initiated within 72 hours after exposure to prevent infection.
Antiretroviral therapy (ART) to suppress viral replication and prevent disease progression.
Prophylaxis against opportunistic infections such as trimethoprim-sulfamethoxazole for Pneumocystis jirovecii pneumonia.
Vaccination against preventable infections like pneumococcus and influenza.

Non-pharmacological Prevention

Consistent condom use reduces sexual transmission of HIV.
Needle exchange programs decrease transmission among intravenous drug users.
Routine HIV screening in high-risk populations enables early diagnosis and treatment.
Safe blood transfusion practices prevent transmission via contaminated blood products.
Counseling and education on risk reduction and adherence to therapy.

Outcome & Complications

Complications

Opportunistic infections such as Pneumocystis jirovecii pneumonia and cryptococcal meningitis.
AIDS-defining malignancies including Kaposi sarcoma, non-Hodgkin lymphoma, and invasive cervical cancer.
HIV-associated neurocognitive disorders ranging from mild impairment to dementia.
Immune reconstitution inflammatory syndrome (IRIS) after initiation of antiretroviral therapy.
Progressive immunodeficiency leading to AIDS and death if untreated.

Short-term Sequelae	Long-term Sequelae
Acute retroviral syndrome presenting with flu-like symptoms shortly after infection. Transient lymphadenopathy and rash during seroconversion. Opportunistic infections emerging as CD4 count declines below critical thresholds. Drug-related adverse effects from initiation of antiretroviral therapy. Immune reconstitution inflammatory syndrome (IRIS) causing paradoxical worsening of infections.	Chronic immunosuppression leading to recurrent infections and malignancies. HIV-associated neurocognitive decline progressing to dementia in some patients. Cardiovascular disease due to chronic inflammation and metabolic effects of therapy. Chronic kidney disease from HIV-associated nephropathy or drug toxicity. Lipodystrophy and metabolic syndrome related to long-term antiretroviral use.

Short-term Sequelae

Long-term Sequelae

Acute retroviral syndrome presenting with flu-like symptoms shortly after infection.
Transient lymphadenopathy and rash during seroconversion.
Opportunistic infections emerging as CD4 count declines below critical thresholds.
Drug-related adverse effects from initiation of antiretroviral therapy.
Immune reconstitution inflammatory syndrome (IRIS) causing paradoxical worsening of infections.

Chronic immunosuppression leading to recurrent infections and malignancies.
HIV-associated neurocognitive decline progressing to dementia in some patients.
Cardiovascular disease due to chronic inflammation and metabolic effects of therapy.
Chronic kidney disease from HIV-associated nephropathy or drug toxicity.
Lipodystrophy and metabolic syndrome related to long-term antiretroviral use.

Differential Diagnoses

Human Immunodeficiency Virus (HIV) Infection versus Acute Infectious Mononucleosis

Human Immunodeficiency Virus (HIV) Infection	Acute Infectious Mononucleosis
Risk factors include unprotected sexual contact, intravenous drug use, or blood transfusion	Recent close contact with individuals having sore throat and fever, often adolescents or young adults
Progressive depletion of CD4+ T cells with inversion of CD4:CD8 ratio	Elevated atypical lymphocytes predominantly CD8+ T cells reactive to Epstein-Barr virus
Positive HIV-1/2 antigen/antibody combination immunoassay and confirmatory HIV RNA PCR	Positive heterophile antibody (Monospot) test

Human Immunodeficiency Virus (HIV) Infection versus Cytomegalovirus (CMV) Infection

Human Immunodeficiency Virus (HIV) Infection	Cytomegalovirus (CMV) Infection
Infection caused by Human Immunodeficiency Virus, a retrovirus	Infection caused by Cytomegalovirus, a herpesvirus
Chronic progressive immunodeficiency leading to opportunistic infections and AIDS-defining illnesses	Often causes mononucleosis-like syndrome in immunocompetent hosts or severe organ-specific disease in immunocompromised
Positive HIV antigen/antibody test and HIV RNA viral load	Positive CMV PCR or pp65 antigenemia assay

Human Immunodeficiency Virus (HIV) Infection versus Primary Immunodeficiency Disorders (e.g., Severe Combined Immunodeficiency)

Human Immunodeficiency Virus (HIV) Infection	Primary Immunodeficiency Disorders (e.g., Severe Combined Immunodeficiency)
Typically presents in adolescence or adulthood after initial asymptomatic period	Presents in infancy or early childhood with severe recurrent infections
Selective depletion of CD4+ T cells due to viral destruction	Profound lymphopenia affecting both T and B cells due to genetic defects
Positive HIV serology and viral RNA detection	Genetic testing revealing mutations in genes like IL2RG or ADA

Human Immunodeficiency Virus (HIV) Infection versus Tuberculosis (Disseminated)

Human Immunodeficiency Virus (HIV) Infection	Tuberculosis (Disseminated)
Exposure related to high-risk behaviors for HIV transmission	Exposure to individuals with active pulmonary tuberculosis or residence in endemic areas
Chest imaging may show bilateral interstitial infiltrates typical of Pneumocystis pneumonia	Chest imaging shows upper lobe cavitary lesions or miliary pattern
Positive HIV antigen/antibody test and HIV RNA PCR	Positive acid-fast bacilli smear or culture, or positive nucleic acid amplification test for Mycobacterium tuberculosis

Human Immunodeficiency Virus (HIV) Infection versus Chronic Hepatitis B Virus (HBV) Infection

Human Immunodeficiency Virus (HIV) Infection	Chronic Hepatitis B Virus (HBV) Infection
Infection caused by Human Immunodeficiency Virus, a retrovirus targeting immune cells	Infection caused by Hepatitis B virus, a DNA virus affecting liver
CD4+ T cell count decline with positive HIV antigen/antibody and RNA tests	Elevated liver enzymes with positive HBsAg and HBV DNA
Progressive immunodeficiency with opportunistic infections and AIDS-related malignancies	Chronic liver disease with risk of cirrhosis and hepatocellular carcinoma