HIV (Human Immunodeficiency Virus) is a unique virus known as a retrovirus. Its primary target is the T-helper cells, specifically the CD4 cells, which are crucial components of the host’s immune system and defense mechanisms.

AIDS (Acquired Immunodeficiency Syndrome) is a condition affecting the human immune system. It is caused by infection with the human immunodeficiency virus. In children, the acquisition of HIV is most often through perinatal transmission, also known as vertical or maternal-infant transmission, occurring from mother to child. Essentially, HIV is the causative agent of AIDS.

Introduction to HIV & AIDS in Children.

While significant strides have been made in the effort to eliminate human immunodeficiency virus (HIV) among children, the worldwide impact of pediatric HIV and the resulting acquired immune deficiency syndrome (AIDS) remains a significant concern for healthcare professionals globally, particularly in resource-limited regions.

Epidemiology

Each day, approximately 1500 children under the age of 15 become infected with HIV. A large majority, estimated at 90%, reside in sub-Saharan Africa. In 2005, there were an estimated 2.3 million (ranging from 1.7 to 3.5 million) children worldwide living with HIV. The primary route of infection for these children was transmission during pregnancy (in utero), during the birthing process, or through breastfeeding – all avenues where transmission can be prevented with appropriate interventions. The prognosis for many children infected with HIV is unfortunately poor. Globally, AIDS is responsible for 3% of all deaths in children under the age of five. This number escalates to 6% in sub-Saharan Africa, making AIDS a leading cause of mortality among young children in that region. Alarmingly, one in seven individuals globally who die from HIV-related illnesses is a child under the age of 15. This high rate is largely attributed to the insufficient implementation of programs aimed at preventing mother-to-child transmission of HIV on a widespread scale. Without access to HIV care, including antiretroviral therapy, the progression of HIV infection in children tends to be particularly rapid. In 2005, it was estimated that 380,000 (with a range of 290,000 to 500,000) children died from causes related to HIV. Tragically, it is estimated that half of these children did not survive beyond their second birthday.

Mode of Transmission

There are several ways HIV can be transmitted to children:

Mother to child transmission: This is the predominant mode of HIV acquisition in children, accounting for over 95% of infections in infants in Africa. Transmission can occur during pregnancy, at the time of delivery, or potentially through breastfeeding. Without intervention, between 30% and 40% of HIV-positive women who breastfeed will transmit the virus to their newborns.

Sexual transmission among adolescents: As adolescents become sexually active, unprotected sexual contact with an HIV-infected individual can lead to transmission.

Sexual abuse of children: Unfortunately, sexual abuse is a potential route of HIV transmission in children.

Transfusion of infected blood or blood products: While less common in settings with robust blood screening procedures, the transfusion of blood or blood products contaminated with HIV can transmit the virus.

Unsterile injection procedures, and scarification: The reuse of needles or other sharp instruments without proper sterilization for injections or traditional practices like scarification can transmit HIV if the instruments are contaminated with the virus.

Risk factors for mother to child HIV-transmission

Several factors can increase the likelihood of HIV transmission from a mother to her child:

Maternal factors

Women with high viral load are more likely to transmit HIV to their newborns: A higher amount of the virus circulating in the mother’s blood increases the probability of transmission.

Women with severe immunosuppression (CD4 count below 200) and those with advanced disease: Mothers with weakened immune systems or more advanced HIV infection have a higher risk of transmitting the virus.

Maternal micronutrient deficiencies increase the risk of MTCT of HIV significantly: Poor nutritional status in the mother can elevate the risk of transmission.

Prolonged rupture of membranes, chorioamnionitis, and STIs: Conditions during pregnancy and delivery, such as the amniotic sac breaking for an extended period, infection of the amniotic sac and its fluid (chorioamnionitis), and the presence of sexually transmitted infections, can increase transmission risk.

During breastfeeding, cracked nipples and breast abscesses: Breastfeeding when the mother has open sores or infections on the nipples can facilitate viral transmission.

HIV-1 is more readily transmitted from an HIV-infected woman to her infant than is HIV-2: HIV exists in different strains, and HIV-1 is generally more easily transmitted vertically than HIV-2.

Infant factors

Prematurity: Babies born prematurely may have less developed immune systems, potentially increasing their susceptibility to infection.

Breastfeeding: While breastfeeding provides crucial nutrients, it also presents a risk of HIV transmission if the mother is infected.

Oral thrush and oral ulcers: The presence of fungal infections (thrush) or open sores in the infant’s mouth can increase the likelihood of HIV transmission during breastfeeding.

Invasive fetal monitoring: Procedures that break the baby’s skin during labor can potentially increase the risk of exposure to maternal blood and subsequent transmission.

Birth order (first twin) in twin pregnancy: In twin pregnancies where the mother is HIV-positive, the first twin born may have a slightly higher risk of exposure to maternal blood and secretions during delivery.

Pathogenesis

The human body is composed of numerous different types of cells. These cells regularly create new cellular components to maintain their function and to reproduce.

Viruses operate by inserting their own genetic material into the host’s cells. Consequently, when the body’s cells attempt to produce new components, they inadvertently produce new virus particles as well.

HIV primarily targets the cells of the immune system.

Although HIV can infect various cell types, its primary target is the T4-lymphocyte, also known as the CD4 cell. This type of white blood cell plays a critical role in alerting the immune system to the presence of foreign invaders or disease within the body.

Once HIV attaches to a structure on the CD4 cell, it introduces its genetic material inside. This effectively transforms the CD4 cell into a factory for producing more HIV.

HIV enters the CD4 cell through a process involving a viral protein called GP120, which facilitates fusion and entry into the cell.

Next, HIV needs to reach the cell’s nucleus. To do this, it undergoes important changes in its structure so it is not recognized and destroyed by the cell. HIV utilizes a special process called reverse transcription to achieve this.

The genetic material of HIV is now present within the cell’s nucleus, but in a modified form after reverse transcription. It then undergoes integration into the host genome, becoming a permanent part of the cell’s genetic code.

The cell’s machinery then begins to produce new components of HIV instead of its normal cellular components. This involves transcription (copying the viral DNA into RNA) and translation (using the RNA to build viral proteins).

Before the newly formed HIV particles can leave the cell, they need to be assembled. This is similar to how parts of a car are put together in a factory. HIV uses a specific protein to facilitate this assembly process, called budding, allowing the new virus particles to be released from the cell.

HIV continues to attack many CD4 cells. The infected CD4 cells initially produce many new copies of the virus and then die. These new copies of HIV then infect other CD4 cells, which also produce more virus and subsequently die. This destructive cycle continues, leading to the destruction of more and more CD4 cells, the production of ever-increasing amounts of HIV, and the infection of previously healthy CD4 cells.

Steps / Phases in HIV entry

The entry of HIV into a cell requires both CD4 and chemokine receptors on the cell surface. The process involves the following phases:

1. Viral Entry: The process begins with the binding of the viral protein gp120 to the CD4 receptor and a chemokine receptor on the surface of the target cell. This interaction causes a conformational change in another viral protein, gp41, leading to the fusion of the viral envelope with the cell surface membrane. As a result, strands of viral RNA are released into the cell cytoplasm.

2. Reverse Transcription: Typically, in nature, DNA serves as the template for producing RNA. However, retroviruses like HIV possess the unique ability to convert their single-stranded RNA into double-stranded DNA. This crucial step is facilitated by a viral enzyme called reverse transcriptase.

3. Integration: The newly synthesized viral DNA then enters the cell’s nucleus and integrates itself into the host cell’s chromosomal DNA. Once integrated, the viral DNA is referred to as a provirus.

4. Transcription: Going back to RNA. When the infected lymphocytes are activated, the viral DNA undergoes transcription, resulting in the production of multiple copies of viral RNA. The HIV RNA contains 9 genes that provide the instructions for producing structural proteins, such as those forming the viral envelope and core. It also codes for essential viral enzymes like reverse transcriptase, integrase, and protease.

5. Translation: The viral RNA then serves as a blueprint for the synthesis of viral proteins, a process known as translation.

6. Viral protease: A viral enzyme called protease plays a critical role by cleaving (cutting) long chains of viral proteins (polypeptides) into smaller, functional enzyme components. These components include integrase and reverse transcriptase, which are essential for the production of new virus particles (virions).

7. Assembly and budding: Finally, the newly synthesized viral RNA and proteins are packaged together and released from the surface of the lymphocyte, a process known as budding. These newly formed virions are then able to infect other cells.

How HIV attacks the body.

Think of the CD4 cell (a type of white blood cell) as a friend that protects the body. When problems like coughs or diarrhea try to attack the body, the CD4 cells fight them off, defending their friend.

Now, imagine HIV entering the body and starting to attack these CD4 cells. The CD4 cells realize they cannot defend themselves against HIV. Gradually, the CD4 cells lose their battle against HIV. The body is left without its main defense system.

Being without defense is like being alone and vulnerable. All sorts of problems, like coughs and diarrhea, can now take advantage and start attacking the body. Eventually, the body becomes so weak that all kinds of diseases can attack without much resistance.