Ans: a (Tears) Ref: Harrison, 16th ed, p. 1079; 17th ed, p. 1144HIV is not usually found in tears. It is usually transmitted by semen, cervical secretion and blood.HIVClinical features1. Primary infectionIt is symptomatic in 70-80% of cases and usually occurs 2-4 weeks after exposure. The major clinical manifestations of primary infection are fever. The appearance of specific anti HIV antibodies in serum (Serocinversion) takes place at 3-12 weeks (median 8 weeks)Any HIV infected individual with CD4 T cell count less than 200/cu.mm has AIDS by definition.2. Asymptomatic infectionAsymptomatic infection is a period during which the individual remains well with no evidence of disease except for the possible presence of persistent generalized lymphadenopathy.3. Mildly symptomatic disease.It indicates some impairment of the cellular immune system. These diseases correspond to AIDS related complex conditions, but by definition are not AIDS defining.Acquired Immunodeficiency SyndromeIt is defined by the development of specified opportunistic infections tumors etc. e.g, esophageal candidiasis, cryptococcal meningitis.Correlation between CD 4 count and HIV associated diseases are given below.>500 cells/cu. mm 1. Acute primary infection2. Progressive generalized lymphadenopathy3. Recurrent vaginal candidiasis<200 cells/cu. mm1. Pneumocystis carinii pneumonia2. Mucocutaneous herpes simplex3. Cryptosporidium4. Microsporidium5. Esophageal candidiasis6. Miliary /extra pulmonary tuberculosis7. HIV associated wasting8. Peripheral neuropathy200-500cells/cu. mm1. Pulmonary tuberculosis2. Herpes zoster3. Oropharyngeal candidiasis4. Oral hairy leucoplakia5. Salmonellosis6. Kaposi's sarcoma7. HIV associated idiopathic thrombocytopenia8. Cervical intra epithelial neoplasia 1 and 29. Lymphoid interstitial pneumonitis<100 cells/cu. mm1. Cerebral toxoplasmosis2. Cryptococcal meningitis3. Primary CNS lymphoma4. Non -Hodgkin lymphoma5. HIV-associated dementia6. Progressive multi focal leukoencephalopathy.<50 cells/cu. mm1. CMV Retinitis/gastro intestinal disease2. Disseminated Mycobacterium avium intacellulareGuys, this is a quite exhaustive Table but it is very important for PG entrance examinations. Atleast study the diseases seen when the CD 4 count is less than 100 and less than 50.It is a spherical enveloped virus. Nucleocapsid has icosahedral structure. Virus contain external spikes formed by the 2 major envelop proteins-the external gp 120 and Transmembrane gp 41.Cellular target of HIV* CD4 Helper T cell* Monocyte, macrophage* Dendritic Langerhans cells* Few B cellsGenome is composed of two identical single stranded positive sense RNA copies.Main genes are:gag - determines the core and shell of virusenv - determines the synthesis of envelop glycoproteinPol - polymerase reverse transcriptaseOther genes are-tat, rev, jej, vif, vpu, vpx, vpr, LTR.Replication begins with the high affinity binding of gp 120 with CD 4 cells. After binding with CD 4. gp 120 undergoes conformational changes that facilitates the binding of co receptor. The major co receptor for HIV-1 are CCR-5 and CXCR -4. After fusion, HIV genome RNA is uncoated and internalized into target cell. The reverse transcriptase catalyze the reverse transcription of RNA to DNA. DNA so formed is integrated with host cell chromosome through the action of virus encoded enzyme integrase.There are three groups of HIV-1Group M--most commonGroup OGroup NThere are 9 subtypes of M group. Subtype A is most prevalent worldwide. Subtype C is most prevalent in India and China.Modes of transmissionSexual transmission--Most common mode of transmission worldwide is heterosexual transmission. Chance of infection from male to female is twice as from female to male. Anal intercourse has higher risk of transmission.Transmission by blood and blood productsMaternal -fetal transmission- Risk is 30%. It occurs most commonly in perinatal period.Transmission by other body fluids- Semen, cervical secretions.