Epidemiological Analysis of the Acquired Immune Deficiency Syndrome (AIDS)

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Table of Contents

Introduction
Etiology
Epidemiology of AIDS
Epidemiology: The AIDS Pandemic
References

Introduction

The Acquired Immune Deficiency Syndrome (AIDS) is a viral disease of human being caused by the Human Immunodeficiency Virus (HIV). The disease has the sinister effect of severely reducing the immunity of the individual; resulting in an increased susceptibility to potentially fatal opportunistic infections.

The disease was first documented by the center for disease control and prevention in 1981; after the discovery of the causative virus one year before (Gallo, 2006). The scientists had stumbled on a developing pandemic (Kallings, 2008); which as at 2007 had 33.2 million cases on the globe; and has caused the mortality of approximately 2.1 million people [UNAIDS, WHO, 2007].

The origin of the virus (and the disease) has been traced to West-Central Africa through genetic mapping; the disease is thought to have infected the first human in the late 19^th or early 20^th centuries (Gao et al, 1999; Worobey et al, 2008). Currently, the disease has no known cure; and the medications available are antiretroviral drugs that slow down the activities of the HIV virus. While these reduce the mortality and the morbidity, their availability is not reliable especially in countries where the purchasing power of the population is not very strong. The key, therefore, to reducing the prevalence and the incidence of AIDS in the world is through prevention.

Etiology

AIDS results after infection with the Human Immunodeficiency Virus (HIV). The virus is a member of the genus Lentivirus and classified under the family Retroviridae. Members of the genus have a common characteristic of causing chronic diseases and having long incubation periods. Members are single stranded enveloped RNA viruses; after they infect the host cell, the RNA genome is transcribed into double-stranded DNA by an enzyme known as reverse-trancriptase which the virus carries within its structure. The new viral DNA then integrated into the host-cell genome through the action of another enzyme also of viral origin known as integrase. After these events, the cell can take two pathways. On one hand, the infected cell can become latent and continues to perform as normal; on the other hand, the viral DNA in the host cell can go active commanding the cell to generate a large amount of viral RNA copies and release many viral particles that then go ahead to infect new cells and repeat the cycle.

The virus is found in most of the body fluids of the infected person; and this is the main route of infections. These include blood saliva, vaginal secretions and pre-ejaculate. The virus infects cells involved in immunity such as macrophages and helper T cells. The virus has a specific characteristic of infecting and destroying CD4⁺ T cells leading to a severe reduction in the population of these cells in the system.

The virus causes this reduction through three main mechanisms; first, they can infect and kill these cells directly; secondly, the virus increase the rate of apoptosis of these cells (apoptosis is the programmed death of cells which naturally has a low frequency under normal circumstances); and thirdly, through the destructions of cells which the body has detected to be infected with the virus by CD8 cytotoxic lymphocytes.

CD4+ T cells are important for cell-mediated-immunity and a severe reduction result in a breakdown of this mechanism of immunity; this leaves the person extremely susceptible to potentially fatal opportunistic infection.

Two strains of the virus have been recognized; these are HIV-1 and HIV-2. The former was the first to be documented; this has a global distribution and causes most of the disease globally. Additionally, it has a higher virulence and transmissibility than its latter counterpart which is largely confined to West Africa.

Epidemiology of AIDS

Transmission

As mentioned before, the causative virus is found in many of the normal body fluids and secretions; and the movement of these fluids from one individual to another through various mechanisms.

Sexual transmission

Transmission of the virus can occur through various activities that are considered sexual; these include rectal, genital and oral sex; and both in heterosexual and homosexual intercourse. The risk of to the uninfected person varies with these situations; for example the risk is greater in unprotected sex; and is higher for receptive than for insertive acts. The risk is also higher in unprotected anal sex than in both oral and vaginal intercourse. Oral sex, which has had a misconception of being safe is a potential route for infection; and though insertive and receptive acts (Rothenberg et al, 1998; Mastro and de Vincenzi, 1996).

Incidents such as sexual assault carry a disproportionate risk of transmitting HIV; this is because an incident like this is rarely protected; and carries an increased incidence of trauma to the genitalia. Sexually transmitted infections also increase the risk of sexual transmission; this is due to the damage to the epithelium which is usually damaged by the pathogen for example through ulceration; additionally, these diseases cause an immune response causing accumulation of cells in the genitalia that are either susceptible to viral attack or are good sources of the virus; such include macrophages and lymphocytes.

The risk of sexual infection is also lower in a single encounter than in more common long-term sexual relationships that are overlapping; as such a person will have multiple sexual partners with the infection moving rapidly from one relationship to the other.

In the developed world, the risk of sexual transmission of HIV from a woman to a man is 0.04% for each act. The risk of male to female transmission in the same regions is 0.08%. In the third world countries, these rates are four to ten times higher [Morgan et al, 2002]. This has been attributed to various factors; for example, in Africa, heterosexual spread is higher than in many parts of the world; this has been attributed to the high prevalence of schistosomiasis, a condition that damages the vaginal lining [Agnès-Laurence et al].

Blood and Blood products

Contact with blood is generally a risky venture for persons infected with the virus. Epidemiological groups that have been identified to have elevated risk of infections include intravenous drugs users, hemophiliacs, persons receiving blood transfusions, healthcare workers; and people giving and/or receiving tattoos and piercing; and scarifications procedures.

About 30% of all new infections in North America, China and Eastern Europe are attributed to sharing of needles by drug users. Additionally, the world health organization estimates that 2.5% of all new infections in sub-Saharan Africa are caused by injections with infected reused needles in healthcare facilities [WHO, UNAIDS, 2003]. Transmission of HIV by medical professionals has prompted the United Nations General Assembly to advice countries to institute measures to curb this [UNAIDS, 2007]. In addition to this, the WHO also estimates that 5-10% of all new infections on the globe are caused by transfusion of infected blood and its products [WHO, 2001]; while the developed countries have put in place measures to prevent this route of transmission, a huge majority of the global population is still at risk. After recognition of blood as an important route of transmission to and through health-workers, many countries have adopted the Universal precautions that dictate how safely situations where contact with blood and/or body fluids may lead to infection.

Perinatal transmission

The Perinatal period includes the gestation. Parturition and postpartum period; infection can occur in-utero, in the period of birth and via breastfeeding. A pregnancy in an infected mother without any intervention carries about 25% risk of transmission for the infant in the period of pregnancy and birth. Interventions involve a combination of antiretroviral therapy during gestation and delivery via caesarian section; this reduces the risk of transmission by to about 1% (Coovadia, 2004).

In the period after a successful parturition, infection is prevented via complete avoidance of breastfeeding; this has associated side effects of putting the neonate under increased risk of infection due to lack of passive immunity conferred by the mother. Breastfeeding by an infected mother increase the total risk of transmission to the baby by about 4% (Coovadia & Bland, 2007). An alternative to abstinence is breastfeeding combined with prophylactic antiretroviral therapy for the infant [Cochrane Systemic Review].

Other mechanisms

As mentioned before, the virus is found in other body fluids; for example, low concentrations have been shown in saliva, tears and urine. While exchange of these fluids has potential for transmission of the disease, the risk involved is very small (Lifson, 1988).

Epidemiology: The AIDS Pandemic

Since the documentation of AIDS in 1981, over 25 million have been attributed to acquisition of the infection. This make the disease the most destructive epidemic recorded yet. As at 2007, it was estimated that 33.2 million people worldwide were carrying the virus; in the same year, an estimated 2.5 million incidents of infection were recorded [UNAIDS-WHO, 2007].

The pandemic is not homogeneously distributed through out the human population; and some regions have a disproportionately high representation in the load of AIDS on the planet. Additionally, even at the level of a single region or country, the distribution is determined by various factors.

Despite the various steps that have been taken to curb the spread of this disease, the prevalence continues to rise. The region that has heavily suffered from the scourge of this pandemic is sub-Saharan Africa. During the same above period, this region accounted for approximately 68% of all the cases in the world; this amount to about 22.5 million infected people by the end of 2007. The other adversely affected by the disease is Asia; especially the South and South-East portions which accounted for 12% of the global prevalence [UNAIDS-WHO, 2007].

AIDS in the developing world: Sub-Saharan Africa

This is one of the regions that have been worst affected by the AIDS pandemic; and is also the region with the highest incidence rates with the prevalence showing a steady rise year after year despite the various programs that have been put in place to reduce this. The region, which accounts for only about 10% of the human population on the globe, accounts for more than half of the total number of the people infected with the disease. The prevalence rate for HIV in the adult population age between 15 and 49 years for HIV 7.2% (range: 6.6 – 8.0%) with between 20.9 million and 24.3 million cases in this region alone. However, as mentioned before, there are variations in the distributions of the virus from region to region. For example, countries in the southern portion of the continent have among the highest prevalence in the world exceeding 20%; for example, Swaziland has the unenviable prevalence of 30%.

In this region, HIV has a multiple path of spread; these include through sexual transmission, unsafe surgical procedures, transmission by healthcare workers through reuse of medical and surgical instruments and mother to child transmission. Other factors fueling this inferno are poor sex education, cultural practices such as wife inheritance that result in spread of the virus from the widow of a person who died of AIDS.

In this region, the women continue to form a high risk epidemiological group; for every 10 incidences of the virus in men, there are 13 for women. As such a gender gap has developed between the two genders. Additionally, women tend to be infected at a lower age than their male counterparts; as such, the gender gap is most pronounced in the group aged between 15 and 24 years of age whereby there are 36 cases of infection in women for every 10 cases in men.

AIDS in the developed world: United States

The dynamics of HIV/AIDS in the developed world, such as the United States, are quite different from those operating in regions such as Africa. Additionally, the epidemiological risk groups are quite different from those in the other regions. The prevalence of HIV in this country for the adult population is 0.7%; this translates to over 1 million people currently infected.

However, sexual intercourse remains an important route of transmission for the virus; for example, in the US between 2001 and 2005, the highest transmission risk behaviors were intercourse between men accounting for 40 to 49% of incidence and high risk heterosexual intercourse accounting for 2 and 35% incidence [CDC, 2005].

Higher incidence in this region is associated with the African-American population; despite the fact that they make up only about 12% of the total American population, they account for 48% of all the prevalence and about 50% of all the incidences [CDC, 2005]. African-American women in particular are a high risk group as they carry a probability of infection that is nineteen times higher that that of other women [CDC, 2005].

New infections in the United States have also been linked to the use of recreational drugs and in particular, a methamphetamine known as crystal-meth which has been shown to increase the risk of infection among gay men in the US as it reduces the chance of using protection during anal intercourse.

Mortality

Compared to the developing countries, the mortality rate from AIDS has fallen sharply in the developed country; this can be attributed to the widespread use of antiretroviral drugs in the latter (and the widespread unavailability of these medication in the former); and the advanced healthcare that allows for adequate palliative care for person who have developed the disease.

References

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