Ans. (a) Oppounistic infection Natural course of HIV infection can be divided into following stages: HIV infectioh. Seen in 30% of individuals within 3-6 weeks of infection. They present with low grade fever, headache, malaise some time with rash and ahropathy resembling glandular fever. Spontaneous rresolution occurs within weeks. Tests for HIV antibodies are usually negative at the onset of illness but become positive during its course. So this stage is also called as seroconversion illness. `,symptomatic or Latent Infectio. Seen in all patients. This phase which lasts upto several years, patient remain asymptomatic. HIV antibody test is positive in this phase and patients are infectious. This period of clinical latency does not mean viral latency as virus multiplication goes on throughout. "ercictant generalized lvninhadenonathy This stage is defined as presence of enlarged lymphnodes at least 1 cm in diameter in two or more non-contagious extrainguinal sites, that persist for at least three months, in absence of any current illness or medication that may cause lymphadenopathy. AIDS related corn /Ilex. This group include patients with considerable immunodeficiency suffering from various constitutional symptoms or minor oppoinistic infections like oral candidiasis herps zoster, hairy cell leukoplakia. AIDS: This is the endstage representing the irreversible breakdown of immunodefence mechanisms leading to progressive oppounistic infection and malignancies. merr"- During the period of clinical latency 10 billion HIV paicles are produced and destroyed every day. Half life of virus in plasma is about 6 hours. Virus life cycle (from the time of infection of a cell to the production of new progeny that infect the next cell) averages 2.6 days