AIDS-The Killer Syndrome
HIV or Human Immune deficiency virus is the etiological agent of the widely spreading dangerous
disease called as AIDS or Acquired immune deficiency syndrome. The characteristic feature of this disease is its ability to destroy the immune system of the body such that mild flu can also lead to the death of the patient. The first case was reported in 1981 in young adults who were homosexuals or drug addicts. It is estimated that 3 persons are infected with HIV every minute throughout the world.
HIV is a spherical, enveloped virus about 90-120nm in size. The genome consists of two identical single stranded RNA. When the virus infects a cell, the viral genome transcribes into double stranded DNA
which gets integrated into the host cell chromosome. This is termed provirus.
The genome of HIV contains various structural, non-structural and regulatory genes. The virus is highly mutable. There is a great variability between the virus isolated from two persons and also within a person at different time and sites. It can be inactivated in 10 minutes at 50 degrees C and in seconds at 100degrees.
Pathogenesis or Infection: Infection is transmitted when the virus enters the blood or tissues of host and comes in contact with the T4lymphocytes. Infection is more likely from blood transfusion or sexual contact than from blood products. Once inside the cell the ds DNA of virus integrates into the host genome the virus may divide or remain in a latent state. In an infected individual HIV can be isolated from the blood, lymphocytes, cell free plasma, semen, cervical secretions, saliva, tears, urine and breast milk.
The primary pathogenic mechanism in HIV is the reversal of the T4:T8 (helper: suppressor) ratio. This disrupts the cell mediated immune response and the humoral immunity making the body vulnerable to oppurtunistic pathogens.
Clinical features of HIV infection: AIDS is only the last stage in HIV infection. Within few weeks of infection 10-15% of persons experience fever, malaise, headache and lymphadenopathy, tests for HIV antibody at this time is negative but becomes positive during its course, so this syndrome has been called sero-conversion illness. In the next phase all infected persons test positive but there are no symptoms. In some cases the disease progresses while in others there is no further infection. In the third phase lymph nodes enlarge upto 1.0cm at one or more sites. The fourth phase is the AIDS related complex where the patient shows symptoms such as fatigue, unexplained fever, persistent diarrhea, weight loss of more than 10% of the body weight. Common opportunistic infections are candidiasis, herpes zoster, hairy cell leucoplakia, salmonellosis or tuberculosis. The patients are severely ill and progress to AIDS.
The final stage is the occurrence of full blown AIDS. It is the end stage and severity depends on the type of infection or malignancy present. The most common infection manifestation is with increasing dry cough, dyspnea and fever. Mycobacterium tuberculosis is the most common infecting organism. Mouth is infected with Kaposi’s sarcoma. The Central nervous system infections are the toxoplasmosis and cryptococcosis.
Mucosal and cutaneous tumours and lesions are common. The definition of AIDS has been broadened to include all seropositive persons with CD4 T cell counts of less than 200 per cmm. HIV can cross the blood brain barrier and causes encephalopathy and leads to loss of higher functions, progressing to dementia. Pediatric AIDS is different from adult disease. Nearly half the babies born to infected mothers show the virus. Failure to thrive, chronic diarrhea, lymphadenopathy, tuberculosis and opportunistic bacterial infections are common.Laboratory diagnosis consists of screening and confirmatory tests. The screening test is based on the principle of detecting the presence of antibody produced in the patient in response to the infection. There is a stage called window period where the antibody is not detected. But it is positive after 2-6 months.The test employed is the ELISA (Enzyme Linked Immuno Sorbent assay) and the confirmation test is the Western blot where the presence of atleast 2 HIV gene confirms the infection.
As it is a sexually transmitted disease, the virus present in the semen gains entry through mucosal tears. The best way of preventing this disease is by increasing awareness regarding high risk activities and to an extent the use of condoms.The disease is also transmitted by blood and blood products that is why these days screening of blood donor is mandatory. This restriction is also applicable for the donation of kidney, semen, cornea, bone marrow and other organs as infection may spread with these. The other mode of transmission is through contaminated needle mainly in the drug addicts. The use of unsterile syringes and needleby qualified and unqualifed health worker makes iatrogenic infection likely. Use of disposable syringes and needles should be mandatory.The fifth way of transmission is by needlestick injury or sharp instruments used on sero positive patients by the medical and paramedical staff. Such puncture should be encouraged to bleed and washed. The infection can also transmit from mother to child before, during or after child birth. Infected females should be informed about the risks and advised against pregnancy.
The virus does not transmit by shaking hands, dry kissing, hugging, putting cheeks together, sharing room, bathroom, cooking and eating facilities.Infection does not spread by air, food, water or fomites. Wet kissing is considered risky. There is no cure to this disease.